Released with permission of Exxon-Mobil Corporation, 2002


(As Developed in the Petroleum Industry)









(i) Collecting of rock samples

(a) Surface samples

(b) Subsurface samples

(ii) Processing of samples

(iii) Examination and identification of microfaunas

(iv) Filing of records and samples

(v) Summarization of sample records


(i) The establishment of local biostratigraphical columns

(a) Studies based on surface samples

(b) Studies based on subsurface samples

(ii) Integration of local biostratigraphical columns

(iii) Dating the units of a regional stratigraphical column in terms of the standard geological time scale

(a) The non-absolute aspect of the geological time scale

(b) The unfortunate choice of some type stages

(c) Lingering errors

(d) Failure to distinguish between ecological and temporal factor

iv) Palaeo-ecological studies and palaeogeographical reconstruction

(a) Implications of lateral changes

(b) Palaeo-ecological deductions

(c) Tests of rationality

(d) Presentation of palaeogeographical data


EXAMPLE 1    A basinal flank which subsided at a rate equal to the rate of accumulation of sediments, so that sea-floor conditions remained stable. (Based on the Naparima Basin of Trinidad)

EXAMPLE 2    A basinal flank on which the rate of accumulation of sediments differed from the rate of subsidence. (Based on the Borbón Basin of northwest Ecuador)

EXAMPLE 2-A Lateral equivalence of two dissimilar formations inferred and later demonstrated. (Based on the Angostura and Viche formations of Ecuador.)

EXAMPLE 3    Cyclical repetition of facies (Based on Miocene deltaic sediments in Trinidad.)

EXAMPLE 4    Facies-pattern over a buried ridge (Based on examples in the Talara area of Peru)

EXAMPLE 5    A piedmont facies (Based on the Danian Mal Paso formation of Peru)

EXAMPLE 6    Effect of regional subsidence on different facies-provinces (Based on the Pliocene sediments of Egypt)

EXAMPLE 7    Organic reefs (bioherms)





Figure  Page

Flow-sheet of laboratory treatment of field-samples

Figure 1(A): Spot-map as submitted by the field-geologist

Figure 1(B): Corresponding palaeontological spot-map, using symbols as defined below

Figure 1(C): Stratigraphic column derived from field geology and washed residue studies

Figure 2(A): Unmodified form of distribution chart

Figure 2(B): Species-grouped according to their zonal ranges on the original chart (Figure 2(A))

Figure 2(C): Distribution chart representing the data of Figure 2(A) modified to emphasize the faunae assemblage of each zone

Figure 3: Illustrating the integration of local stratigraphic columns

Figure 4(A): Correlation and classification of sediments in the Naparima Basin of Trinidad

Figure 4(B): Correlation and classification of sediments in the Naparima Basin of Trinidad

Table 1: Ranges of some planktonic foraminifera in the Naparima Basin

Figure 5(A): Initial interpretation based on reconnaissance study of outcrops and fossils

Figure 5(B): Revised interpretation incorporating zonation based on planktonic foraminifera

Figure 5(C): Interpretation based on extended field studies, well evidence, and detailed micropalaeontology

Figure 6: Cyclical repetition of facies in the Miocene of Trinidad

Figure 7: Facies-pattern over a buried ridge. (Based on the Talara formation of Peru.)

Figure 8: The depositional distory of the Mal Paso formation in N. W. Peru

Range chart of genera of planktonic foraminifera

Figure 9(A): Frequency ratios of selected ecologically restricted species

Figure 9(B): Hypothetical dip-section showing the levels at which different faunules are dominant

Figure 10: Species-concept diagrams


The science of palaeontology is largely academic in its scope. Though fascinating to the layman as much as to the expert scientist, the reconstruction of ancient creatures and their environment is seldom applicable to material problems of human welfare. The location of aquifers, of structurally sound or unsound bases for large structures, of beds of coal, and similar problems of structural geology may be simplified by attention to the fossils present in neighbouring rock exposures, but usually the solution can be found without their aid.

In sharp contrast to the general case, palaeontology is applied extensively and indispensably in solving the structural problems associated with the discovery of petroleum. The need arose for a method of subdividing great thicknesses of lithologically uniform beds and of distinguishing between similar sediments known to lie both above and below certain oil sands. Palaeontology has filled this need, since the vertical ranges of fossils are limited and a given assemblage of forms can only occur within a fixed zone. A drawback to the practical use of most fossils lies in their limited availability: surface mapping is commonly necessary in areas of thick alluvial cover or deeply weathered sediments, and subsurface samples consist of the bit-cuttings and occasional cores, only a few inches in diameter, collected in the course of drilling a well. Under these conditions the finding of normal-sized molluscs, echinoids and other familiar megafossils becomes a matter of chance. Recourse must therefore be made to microscopic fossils so small that a representative suite may reasonably be expected in a few ounces of rock from a given formation, whether the sample be from an outcrop, a test-pit, an auger hole or a deep well.

Following up the promising results of a few pioneer students[1], several oil companies in the United States began to experiment with micropalaeontological correlation in the second decade of this century. The value of the results proved so high that by now the absence of a micropalaeontological laboratory within the geological department of an oil company is unusual. A voluminous literature now exists, devoted exclusively to the  classification and distribution of fossil Foraminifera, ostracods, conodonts, and minute members of other phyla.

The expanding role of applied micropalaeontology may be followed in a series of presidential addresses[2] to the American geological institutions, since every few years the president has chosen to review the current state of petroleum geology and ancillary sciences. At first the new tool was regarded with hope tempered with misgiving. The similarity of many Recent and Tertiary microfaunas was held by some to nullify the value of microfossils in zonation, but experience proved these pessimists wrong. Micropalaeontology thus became an accepted branch of petroleum geology, ranking equally with field geology, geophysical prospecting, and electric well logging in its contributions to the solution of structural and stratigraphical problems encountered in the search for oil.

For many years zonation and correlation were the only goals sought by practising micropalaeontologists, and their work was considered adequate if they could recognize the “Marginulina zone”, the “Heterostegina zone” and similar units. A more recent development has been the application of micropalaeontology to regional palaeogeography, a line of research which naturally followed the trend of search for oil in stratigraphical traps. The great East Texas field[3], in particular, showed that faulted and anticlinal structures were not necessary for major accumulations of oil. The isolation of porous beds could be due to depositional factors such as differential current-sorting, offshore gradation of sands into clays, reef developments or unconformable capping of porous by non-porous beds. Areas in which these conditions may be expected at depth can be deduced only from palaeogeographical studies which reveal the ancient shorelines and axes of intermittent uplift, the trends along which most interfingering of different types of sediment may be expected below the surface.

The necessity for palaeogeographical research in the location of new petroliferous territory has been mentioned, and the application of micropalaeontology suggested as a more accurate control than the lithological basis of most existing palaeogeographical studies, in the more recent surveys of the status of petroleum geology. Microfaunal assemblages are closely controlled by ecological factors. Slight changes in temperature, depth, salinity, and bottom conditions may cause a complete change of a marine microfauna, though insufficient to alter the megascopic aspect of the sea-floor sediments. Published data on the ecological distribution of Recent microorganisms are limited, though growing rapidly, but are already adequate for tolerably accurate reconstruction of the life-environment of most microfossil assemblages. The typical features are known of the living assemblages characteristic of fresh-water, brackish, littoral, neritic, and abyssal facies in different regions of the earth and by a process of extrapolation the ecological significance of extinct forms may be deduced. Published literature on the application of micropalaeontology to palaeogeography is still in its infancy, though significant reports exist in the confidential files of the major oil companies.

The purpose of the present paper is to discuss the methods by which the results of micropalaeontological studies may be used to the best effect in complementing petroleum geology as a whole. Laboratory technique and micropalaeontological zonation are treated more briefly than the application of micropalaeontology to palaeogeography, since the two former topics have already been treated extensively in the literature.

To maintain continuity of the text all references are given separately in an annotated bibliography at the end of the paper.


The four main steps in accumulating micropalaeontological data are as follows:

(i) collecting of rock samples
(ii) processing of rock samples
(iii) examination and identification of the microfaunas encountered
(iv) classification and interpretation of the results obtained

As has been stated, the main theme of this paper is the final item, but inasmuch as valid interpretation requires reliable groundwork it is necessary to include a brief discussion of the manipulative techniques in relation to the final quality of the interpretive results.[4]

(i) Collecting of rock samples

In general, surface samples are collected by the field geologists and subsurface samples by the well geologists, but the palaeontologist should make himself familiar with the techniques in force and should be prepared to suggest modifications which may improve his own final results.

(a) Surface samples[5]

Surface samples are collected from natural exposures such as sea-cliffs and stream banks, from artificial exposures such as road-beds and foundations for new buildings, from test-pits and from auger-holes. Samples of these different types are variably affected by weathering and surface contamination, and the palaeontologist should ascertain that the samples submitted to him suffer as little as possible in these respects.

Optimum size of samples is a matter of opinion, but in general they should be as large as is reasonably possible. The writer favours between one and two pounds from each locality. Exceptionally, and only in areas where the zonal succession of microfaunas is so well known as to be routinised on a semi-statistical basis, much smaller samples of uniform bulk are used.

The spacing of collecting localities is a matter of economic significance. Over-wide spacing may fail to reveal an important zone or zonule, whereas over-close spacing may lead to the same interpretation as sampling on a broader grid, thus wasting time, money and effort. The palaeontologist should be alert to detect fault in either of these respects, basing his recommendations on the complexity of structure and facies-variation apparent from preliminary and progressive studies of an area.

As soon as the broad outlines of structure and stratigraphy have become apparent the palaeontologist should choose control sections for the collection of very closely spaced samples on which to base his faunal distribution charts. As far as possible these control sections should be aligned on simple structures and should give over-lapping coverage of the whole stratigraphical column locally exposed, including lateral variants of the different formations.

(b) Subsurface samples[6]

Subsurface samples are obtained from exploitation and exploration wells. Drill samples from seismograph shot-holes are a special case. The most satisfactory samples for palaeontological research are cores because they are free from contamination and give an accurate record of the sediments at depth. However, extensive coring is costly and for this reason the bit-cuttings are commonly used for routine micropalaeontological studies of well sections. The main drawback to bit-cuttings is that as a rotary well is drilled steadily deeper there is inevitably much mixing of freshly drilled rock chips with material caving from higher up the hole or lagging in the mud-stream. There is similar, but far less severe, contamination of cuttings in cable-tool (percussion) wells. The resulting heterogeneity introduces an element of doubt into any conclusions based on the micropalaeontology of cuttings.

For simple correlation of neighbouring wells, when once a standard zonation has been established by coring or extrapolation from surface samples, cuttings are entirely satisfactory for recognizing the tops of the successive zones penetrated by a well. In routine work of this type the spacing routine varies, but one sample from each twenty to thirty feet of hole is adequate for most normal purposes. Usually within a single oil-pool there is a constant relationship between changes in lithology, microfauna and electric parameters. The microfaunas are useful in checking the normality or abnormality of a well section while drilling is actually in progress, but for final precise correlation the electric (Schlumberger) log is often more satisfactory.

The palaeontologist concerned should pay special attention to exploratory (‘wildcat’) wells drilled outside the limits of proven structure and stratigraphical sequence. A coring programme should be prepared, designed in the first instance to demonstrate the anticipated zonal succession but subject to adjustment as the well is drilled. In the early exploration of an area strategically taken cores are invaluable and the full exploitation of numerous pools has been retarded by failure to recognize this fact.

Control sections are as important in the subsurface as at the surface, especially in the deeper beds which do not crop out in the vicinity. Adequate sample coverage, preferably by continuous coring, should be organized in favorably placed wells.

(ii) Processing of samples

For microscopical study it is necessary to reduce the rock samples to fine residues or, in the case of limestones and hard sandstones, to prepare thin or polished sections. The preparation of rock sections is a standard laboratory routine which needs no further comment here but some remarks are made below on the preparation of washed residues.

The preparation of fine residues from the softer sediments—mostly clays, shales, silts and unconsolidated sands—requires the two stages of disintegration and sieving (or decantation). Disintegration may be accomplished by mere soaking in water, as with the colloidal clays, or it may call for lengthy manual processes in the cases of indurated or non-porous rocks. Faintly argillaceous samples react gradually to plain water or a weak electrolyte such as sodium carbonate solution. Porous but non-argillaceous samples may be disrupted by alternate freezing and thawing after soaking in water, or by the crystallization of sodium thiosulphate after soaking in a strong solution of this salt. The disintegration of non-porous, non-argillaceous rocks cannot always be achieved satisfactorily for the purpose of extracting microfossils, and recourse to sectioning may be required. Exceptionally, in a brittle rock in which they are not too tightly bound to the matrix, the microfossils may be freed by careful crushing with pestle and mortar, by using light vertical blows with avoidance of rotary grinding. Various mechanical aids to disintegration are available, such as ball-mills, pressure bombs and supersonic vibrators[7].

After disintegration of a sample, its microfossils are concentrated from the raw residue by decantation or by washing through sieves with a stream of water. The objective is to remove both the finer colloidal and silty matter and the coarser rock particles. The grades of sieves used vary with the type of fauna under study but most foraminifera and ostracods pass a 30-mesh sieve and are retained by a 100-mesh sieve. The action of a jet of water may be destructive of fragile faunas and in such cases the slower process of decantation is recommended. An alternative is to place the raw residue in a bag of suitably fine cloth and tie it over the orifice of a slowly running water faucet. The wet residue obtained by one or other of these processes is spread on a dish and dried by gentle heating.

A branch of micropalaeontology of rising importance is the study of fossil plant spores. The specialized technique used in their extraction utilizes the fact that these minute fossils are remarkably inert and remain unaffected by chemical processes which completely digest the inorganic matter in which they are embedded. Hydrofluoric acid is the reagent most used in the preparation of spore concentrates.

Siliceous microfossils may be extracted from calcareous matrices by treatment with dilute acid. Best results are obtained by the slow application of very weak acid, since violent effervescence is destructive of such delicate organisms as radiolaria.

(iii) Examination and identification of microfaunas[8]

The most important phase of micropalaeontological technique is the scrutiny and analysis of the residues and sections prepared from the rock samples received at the laboratory. Points to record are: the type of microfaunal assemblage; the presence of microfossils of zonal value; the micro-lithology of the sample. A flexible system of filing and recording samples and data must be established and its efficiency will have a marked effect on the final interpretive results obtained.

As received from the processing department, washed residues consist of finely divided rock matter which usually contains microscopic fossils. The micropalaeontologist should examine both the rock matter and the fossil content but commercial practice varies as to the details of presentation of samples. In some cases the palaeontologist studies the washed residues and either merely makes written records or himself picks out a representative microfossil assemblage, placing the pickings in suitable slides. In other laboratories junior assistants pick the fauna and pass their slides on to the palaeontologist along with glass vials containing cuts of the residues. In some well routinised laboratories only the slides picked by the junior assistants are examined. When practicable the middle method is recommended, since it frees the micropalaeontologist from much purely manipulative work and gives him correspondingly more time for interpretive research. The tedium of picking microfaunas out of washed residues may be reduced, under suitable conditions of preservation, by a process of flotation in some medium such as carbon tetrachloride.

The closeness of scrutiny given to individual prepared residues depends on the problem in hand and the phase of development reached in the study of the area concerned. In the case of a well drilled to exploit a structure already intensively drilled and studied, the palaeontologist does little more than check the expected appearance of changes in microfauna and microlithology, but in the initial exploration of an area greater detail is required. Until analytical study has established which microfossils are most significant in correlation, it is requisite to make a detailed faunal list for each sample and to note any lithological features which may assist in defining stratigraphical subdivisions. After the establishment of faunal zones and zonules, the first objective of exploratory studies, the same records will be used in palaeogeographical research and for this reason notes should be made on the grade and degree of sorting of sands, presence of two-phase sediments, occurrence of glauconite, and all similar minor clues to depositional history.

The preparation of faunal lists for all samples taken in exploratory surveys has been recommended above, but the question might be raised of correct identification and nomenclature of microfossils in a previously unstudied area. The difficulty is dealt with simply, by grouping the organisms encountered under appropriate generic names and referring to their different species by numbers. This local classification is controlled by a collection of type-slides housing chosen specimens of all the species, each labelled with genus-name, species-number and sample-number. Genus names[9] are best used in the simplest sense possible without leading to an unwieldy number of species referred to any one of them: as instances it may be adequate to classify the ostracods encountered simply as Ostracod 1, Ostracod 2, et seq. without referring to actual genera, or to include several verneuilinid genera of foraminifera under the working name Gaudryina. This simplification is considered to be advisable for its expediency, its reduction of the chance of introducing synonyms, and its reduction of personal factors in a laboratory employing several palaeontologists. If material from several disconnected areas is under study it may prove convenient to prepare separate type-collections, in which case prefix letters are used to avoid confusion between species from different areas. The identification of microfossils in a correct, academic sense is of no benefit during the exploratory phase of micropalaeontological studies. It does become important in a later phase of research when regional correlation and palaeo-ecology are under study, and at this stage a cross-index may be prepared showing that Marginulina A-4 and Vaginulina C-6 are both actually Dentalina nonexistens Fulano, and so forth.

The value of the type-collection is increased by maintaining a card-index to record the stratigraphical and geographical ranges of all the species. Whenever a species is found higher or lower than it was previously known, or when a new area is studied and yields species already in the type-collection, corresponding entries are made in the card-index, which thus becomes a useful supplement to formal distribution charts.

In recording microfaunal lists a note should be made of the relative frequency of different species. There are two reasons for this. One is that certain assemblages sometimes persist through a great thickness of uniform strata with no marked change in their constituent species but a variation in the particular species dominant at different levels. In such cases zonation is based on faunal statistics rather than on the actual ranges of the different species encountered. The second reason for recording frequency is that palaeo-ecological deductions are based on the species dominant in microfossil assemblages much more than on the scarce, sporadically-appearing forms. For instance a few Globigerinas are a normal constituent of any marine microfauna, not excluding beach sands and lagoonal deposits, but a flood of Globigerinas is strongly suggestive of a rather deep open sea environment. The symbols —(flood), • (abundant), O(common) and X (scarce) are used in many laboratories and are more distinctive than the initials F, A, C, and S sometimes used.

(iv) Filing of records and samples

A major commercial laboratory may receive samples at a rate of several hundred daily. These must be processed, examined, recorded, and stored in an orderly manner or confusion will result. Use of a continuous series of ‘laboratory numbers’ for the identification of samples (in the order of receipt) is recommended as requiring a minimum amount of clerical work and hence giving minimum scope for errors in copying sample data. The flow-sheet below shows the essential steps involved in handling the samples for which washed residues are to be prepared: with slight modification it is applicable for special samples requiring thin-section preparation, heavy residue study, chemical analysis, megafossil extraction, and so forth.

Flow-sheet of laboratory treatment of field-samples

Received at Laboratory

Field Sample

Tag with field number, locality details, etc.







Preliminary Recording

Field Sample, Placed in a metal bowl and examined

Tag. Lab. Number entered, brief lithological description written on back. (Code letters may be used to indicate process needed—WR, washed residue; TS, thin-section; M, megafossils, etc.


Control-book. Lists lab. nos. in numerical order with corresponding sample data, a card-index is maintained, based on control-book, to give cross-reference between field and lab. numbers.


to processing room



Actual Processing

Field sample (WR) soaked in water

Tag clipped to side of bowl


Half sample may be stored for future reference, filed in order of lab. numbers if this routine is followed.







Washed residue prepared from field sample

Tag used to identify residue while drying


Original tag to files (check on labelling errors)






Record Stage of Recording

Dried residue placed in envelope or other container marked with lab. number

Sample card prepared showing field and lab. Numbers and lithological description as on the tag, with blank spaces for further data







Microscopic Study

Residue examined by palaeontologist. Slide picked if required

Sample card used for entry of the microscopic data


Sample cards to files









Residues and slides to storage cabinets


The flow-sheet is recommended for a busy laboratory handling many samples from numerous sources. It may be unnecessarily complex for a small laboratory. Furthermore, this system is primarily designed for use with extensive field surveys, to avoid the tedium and fruitful source of error inherent in repeated copying of the field geologists’ sample numbers and topographical data. In a laboratory primarily concerned with well samples, a ready-made basis for orderly filing and recording exists in the fact that wells are usually numbered consecutively and samples from each well are received in order of regularly increasing depth. Nevertheless, the use of laboratory numbers for well samples has some advantages such as a greater ease of labelling slides and small vials. Printed tag-labels and sample cards and uniform sizes of residue containers and microfossil slides are recommended for ease of operation. Description of gross lithology by the palaeontologist concerned is not strictly necessary but is recommended to improve liaison between field and laboratory: washed residues may give a false impression of their source, especially if appreciable amounts of colloidal clay were originally present.

Instead of cards for recording the details of well samples a strip-log may be used. The term is almost self-explanatory and applies to a strip of paper marked with a central half-inch column. Conventional symbols are used for plotting the microlithology of the samples in the column and written annotations on fauna and lithology are entered on the wide margins. Strip-logs on a scale of 1:5000 or 1:2500 are much more convenient for the comparison of well sections than sheafs of written notes.


      Field Geologist: H. R. Gotham                                          Area: upper Hamster River

Field No.                                                                                                                      Lab. No.

HRG-81    Microlithology:       grey glauconitic micaceous shale                                19157

                  Microfauna:            Rotalia B-3 (0), Buliminidae (X),
ostracods (X), echinoid fragments (X)

                  Determination:       Rosetta formation, Rotalia B-3 zone

HRG-82                                                                                                                      19158

                  etc., etc.

o r

      WELL No. DP-18                                                              SAMPLE RANGE:

                                                                                                                Cores: ------
                                                                                                            Cuttings: 1080-1460’

1080-1170’   Microlithology:          bluish calcareous clay

                     Microfauna:               very rich and diversified;
Gastropod 18 (O)

                     Determination:          Concourse formation, probably lower part

1170-1320’   Microlithology:          coarse heterogeneous sand (plus cavings)

                     Microfauna:               weak as above, probably all cavings

                     Determination:          Vanguard sand


                     etc., etc.

The routine outlined in the foregoing pages for treating, studying and recording microfaunal material embodies the essential requirements for a full interpretive analysis of the material. Every laboratory has its own problems of climate, availability of equipment and man power, dominant rock type in the samples received, and so on. The flow-sheet of basic routine varies correspondingly from laboratory to laboratory as modifications are introduced to allow for these local factors. No attempt is made here to go into details of these useful modifications, but it is stressed that the test of efficient routine lies in the three points:

Prompt availability of micropalaeontological analyses of all samples received at the laboratory.  

Ready availability of old sample records (largely governed by an efficient filing system).

Completeness of records, so that no further reference to stored samples and slides is normally necessary when queries are received.

(v) Summarization of sample records

Up to this point the routine of preparing and recording individual samples achieved by issuing two types of sample reports, Routine and Non-routine.

A routine typescript report is made for each batch of samples received from a given source—field geologist or well—the contents being copied directly from sample cards. Copies are issued to all interested parties and one is kept in the laboratory files. Typical forms of layout are shown below.

Non-routine reports include progress and final reports on research projects, notes on the implications of new discoveries, desirable revisions of stratigraphical columns, and so forth. Also falling in this category are the summary reports made on completion of wells and field surveys; according to circumstances these may contain much or little interpretive reasoning.


In the application of micropalaeontology to geological problems, the validity and completeness of interpretive analysis depends on making the most efficient use of the


Optional but recommended

Washed residue (or rock section) of each sample

A portion of each sample, for future comparisons and checks

Sample card showing source and analytical data for each sample

Microfossil slide(s) for each sample

Type-collection(s) of microfossil species

File of routine and non-routine reports as under (v) above

Cross-index between source of samples and storage system

Card-index showing ranges of all microfossil species


Figure 1(A): Spot-map as submitted by the field-geologist


Figure 1(B): Corresponding palaeontological spot-map, using symbols as defined below

Figure 1(C): Stratigraphic column derived from field geology and washed residue studies

samples on which studies are based. For this reason some space has been devoted above to outlining a routine appropriate for a laboratory engaged in micropalaeontological research as well as workaday correlation. Modification of this routine may be desirable for special local conditions, but the final effect should be completeness and ready availability of the following items:

These are the basic tools of research; the products of interpretive research—distribution charts, spot-maps, palaeogeographical maps and textual matter—will be filed alongside them.

Any scientific research is a controlled advance from the known to the unknown, an elucidation of successively farther reaching relationships. The normal pattern of progress in micropalaeontological research is:

(i) establishment of local biostratigraphical columns for each of several small areas,

(ii) integration of the initial results to give a biostratigraphical column of regional application,

(iii) dating the units of the column in terms of the standard geological time scale,

(iv) palaeo-ecological studies leading to palaeogeographical reconstruction.

Analytical methods applied in the separate phases of research are discussed below.  

(i) The establishment of local biostratigraphical columns

(a) Studies based on surface samples

On completion of a field survey the palaeontologist possesses a set of analytical records of the samples sent in for study. He has probably noticed that they fall within a limited number of groups with distinguishing characteristics but he does not know the significance of this variation. The clue to the relationship of faunal and lithological changes lies in the preparation of a spot-map.

The draughting of a spot-map begins with a blank topographical map submitted by the field geologist and marked with all sample localities and major structural features. The palaeontologist marks his data for the individual samples against their positions as spotted on the map. A system of symbols or code letters is used to distinguish between the different faunal groups already noted, with written annotations for minor variations of possible significance. More often than not, the resulting picture shows a pattern of relationship between microfaunal groups and structural position of the samples. From this relationship the local biostratigraphical column may be deduced: this process is illustrated on Figure 1 by a simple hypothetical spot-map and the basic zonation derived from it.

It is now possible to arrange the samples in their correct stratigraphical order and to prepare a distribution-chart of the vertical ranges of microfossil species. The function of this chart is to reveal greater detail of the faunal characteristics of the zones already

Figure 2(A): Unmodified form of distribution chart

recognized and also to establish further zonal subdivisions for use in detailed correlation with neighbouring areas. The significance and validity of a distribution-chart are directly proportional to the closeness of spacing of the samples entered on it, for which reason the spot-map should be examined critically before deciding which lines of samples to use. The possible desirability of first collecting some additional samples to fill in gaps on the map should be considered. It is preferable to avoid great lateral spread of the samples plotted, in case of facies change or unsuspected local structures: as a safeguard, distribution charts may be made for several parallel lines of samples and may be unified later if they show no discrepancies.

The construction of a distribution-chart is purely mechanical. Squared paper is used with two axes marked at right-angles. Along one axis sample-numbers are written in stratigraphical order and along the other the names of all microfossil species listed in the microfaunas of the selected samples. On a large chart ease of plotting is increased by first making out the species list in alphabetical order. The sample-cards are taken in order and their microfaunal records entered in the appropriate column of the chart,










Anomalina 1, 4, 5
Bolivina 1, 2
Bulimina 1, 2
Cibicides 1
Uvigerina 1
Vaginulina 1, 2







Bulimina 7
Uvigerina 2

Ammobolculites 2
Ammodiscus 3
Anomalina 6
Bathysiphon 2
Bulimina 6
Textularia 2
Trochammina 1
Verneuilina 1







Ammobolculites 1
Ammodiscus 2
Bathysiphon 1
Bulimina 5
Textularia 2
Vaginulina 3

Allomorphina 1







Bulimina 3

Bolivina 4





Ammodiscus 1



Bolivina 3
Cibicides 3
Siphogenerina 1, 2



Bulimina 4




Anomalina 2, 3
Cibicides 2
Siphogenerina 3, 4
Uvigerina 5
Virgulina 1

Uvigerina 3, 4

Figure 2(B): Species-grouped according to their zonal ranges on the original chart (Figure 2(A))

using a frequency symbol, as recorded, opposite the name of each species listed. The first draught of the chart is of the form shown on Figure 2(A), a hypothetical example.

A chart of the type described contains all the information required but can be used more readily if the species are arranged in a stratigraphical order, thus emphasizing the assemblages characteristic of successive layers. Before attempting this, the chart should be checked for levels of marked faunal change (other than those derived from the spot-map). A simple method is to put symbols or coloured marks against the highest and lowest occurrences of all the species on the chart: some zonal significance may then be attached to any level at which a concentration of such marks is seen.  After recognition of the zonal divisions a second simple process gives the species list in order of stratigraphical significance: a square grid is prepared as depicted on Figure 2(B) and each species is marked in the square appropriate to its recorded range. A revised distribution chart may now be plotted with the species listed in order from top to bottom of successive columns of the grid just described. For convenient reference an alphabetical key may be provided on the opposite side of the chart, the final version thus having the form shown in Figure 2(C). It is usual to use the name of a characteristic fossil rather than a number designating each zone. Referring again to Figure 2(C), Zone 1 might be named the “Bolivina 1” zone. Zone 2 the “Bulimina 6” zone, and so on.

(b) Studies based on subsurface samples

In principle the erection of a microfaunal zonation is the same for a set of well samples as for surface samples, but in practice some allowance must be made for the difference in source.

The fact that well samples are labelled with the depth from which they were collected obviates the need for any equivalent of a spot-map. A distribution chart may be prepared by plotting faunal records against a depth scale, and it will give a zonation valid for a single well. However, the results will be more acceptable if based on the joint evidence of several neighbouring wells and, according to local conditions, discrepancies may or may not be apparent when the faunal zonations of these separate wells are laid side by side. If there should be signs of structural elimination or repetition of section, unconformity, or lateral change of facies the probable cause should be ascertained by use of electric logs, drillers’ logs, rate-of-penetration charts and other records. A composite chart may then be compiled to show the entire zonal scheme applicable to the subsurface beds of the area considered.

Due allowance must be made, in plotting subsurface distribution charts, for the type of samples used. The ideal case is based on continuous cores, since no question of contamination then arises, provided that drilling mud was carefully removed before the samples were processed. More often the bulk of the section is represented by bit-cuttings and in this case contamination may give rise to serious error. In general, the abrupt appearance of a species in fair abundance in the residues of the cuttings is a reliable indication of the top of its range, but if its frequency dwindles downwards this may signify passage below the base of its range or may represent the actual distribution of the species. The significance of sporadic microfossils in bit-cuttings varies with local conditions, most of all with the degree to which the formations penetrated tend to cave into the hole. It may be noted that if and as caving continues the volume of contaminatory rock matter increases rapidly with each unit increase in hole diameter. Wells in Trinidad frequently pass through beds of mudflow, a highly colloidal, hydrophilic clay full of heterogeneous microfossils, and in such cases contamination is so severe as almost to obliterate the autochthonous faunas in cuttings for several hundred feet below the mudflow band: yet other cases could be cited in which contamination due to caving is negligible. There is, in fact, no valid generalisation covering the problem of contamination of well cuttings; it is a local problem to be

Figure 2(C): Distribution chart representing the data of Figure 2(A) modified to emphasize the faunae assemblage of each zone

solved by accumulated experience qualified by information gained from cores and extrapolations to surface sections.

(ii) Integration of local biostratigraphical columns

Micropalaeontological studies in a region are first applied in a detailed manner in some limited area chosen arbitrarily for its ease of accessibility, discovery of oil nearby, excellence of surface exposures, or some comparable reason. As geological exploration proceeds parallel studies are made on related, but possibly disconnected, areas and it becomes desirable to erect a master zonation which will indicate the units of regional extent, those which are localised, and what relationship exists between synchronous local variants.

Superficially there might appear to be little difficulty in compressing several detailed distribution charts into a single one which will retain the major features common to all. Actually there exist major difficulties and sources of error which need to be recognized and assessed. The prime source of error is failure to distinguish between time-controlled and facies-controlled changes in microfauna. A living community of micro-organisms exists in a state of delicate ecological balance with its environment. Any slight change in temperature, salinity, turbidity, turbulence, or other factor included in the collective term facies must cause slight modification of the fauna: a major ecological change may cause almost complete reconstitution of the assemblage. In contrast to this intimate relationship between facies and faunal constitution, time-controlled changes in microfaunas are slight in relation to the fine subdivisions used in local zonation. Evolutionary trends are evident in certain phyla but in application are better suited to the identification of epochs or stages than of minor zones. Exceptionally the time of blending of two previously isolated faunal provinces may be marked by an abrupt appearance of foreign forms [10] without any general change in facies-type.

Since facies-variation affects microfaunas much more intimately and more profoundly than any non-ecological progressive time effect, it follows that all local changes of fossil microfaunas, in the vertical as well as the lateral sense, are best treated as symptoms of ecological change with no intrinsic time significance. They only acquire age-determinative value when the facies-pattern of the sediments has been established and has been tied in to a time-grid based on non-ecological factors. In order to illustrate the term facies-pattern the flank of any normal marine basin may be considered: at a given instant a sequence of distinct but laterally intergradational facies must exist, representative of deep offshore, shallow offshore, inshore, littoral, and brackish to terrestrial milieux. As long as sea-floor depths remain unchanged the gradational boundaries between facies-provinces remain fixed and the corresponding sediments show consistent lateral change but little vertical change. More usually, the flank of the basin is subsiding or emerging and there is a corresponding lateral shift of facies provinces: over a period of time the different facies-provinces overstep one another’s initial boundaries to extents and in directions governed by the diastrophic and depositional history of the basin. The resulting complex of interfingering and overlapping sediments differing in lithology and fauna is the facies-pattern of the region. It is a four-dimensional continuum in which the time dimension bears a determinable, but not necessarily simple, relationship to the spatial configuration. The smaller the area under study, the less error is made in assuming coincidence between time planes and lithologically defined horizons: the greater the area, the less desirable is this assumption.

The spatial relationships of different facies within a block of sediments are more readily apparent than temporal factors, for the former are indicated by gross physical features of rock type and bulk fauna whereas the latter must be determined by reference to specialised fossil groups, not necessarily conspicuous, or to mineral analyses. Consequently in first attempts to compile a regional stratigraphical chart it is recommended that lithological correlation be used in establishing a framework. A broad correspondence is to be expected between major faunal variants and major lithological units, though more variability is to be expected in the microfaunas because in life they were sensitive to ecological changes too slight to affect the processes of sedimentation. On its completion, the regional chart should be checked for homogeneity: lateral and vertical gradations are to be expected but should show parallelism between lithological and faunal trends. Of special importance are the mixed facies gradation between two or more ‘pure’ facies: the original evidence may indicate lateral equivalence of a richly fossiliferous clay in one sector with a barren sand in another, but the correlation remains inferential unless physical interfingering or gradation through weakly fossiliferous silts can be demonstrated in the intervening area.

In order to establish the temporal setting of a regional facies-pattern, attention must be paid to non-ecological variables in the sediments. Of greatest importance from the micropalaeontological point of view are minute remains of floating organisms (immune from sea-floor facies effects) and of free-swimming organisms (which could avoid hostile environments). The floating organisms which occur most frequently as microfossils are the planktonic (pelagic) foraminifera and radiolaria: less frequent and rarely used in commercial work are coccoliths and other flagellates, diatoms and Calpeonellidae. Swimming organisms include ostracods and fish (as teeth, scales and otoliths, possibly also as conodonts and scolecodonts), certain crinoids (as dissociated ossicles) and possibly other obscure phyla. Pollen and spores from terrestrial plants have been used successfully in establishing zonation of continental beds and in inter-correlation of marine and continental beds. It may be noted that planktonic forms such as the graptolites, cephalopods, and stalkless crinoids are the basis of the most reliable long-range megafossil correlations, whereas correlations based on benthonic megafossils may be in error, reflecting only a similarity of facies.

(Complementary to palaeontological variables which are independent of local facies and therefore suitable as time-indicators, the variations of the mineral content of sediments reflect changes in the type of source-rock supplying detritus. Such changes are induced by progressive erosion or by igneous activity and metamorphism associated with orogeny. The usual method of studying mineral variation is based on the ‘heavy minerals’ which do not float in bromoform. Counts are made of the grains of different constituents in the heavy residues and, after analysis of the results, consistent fluctuations of mineral frequency provide datum-points on a time scale. Rittenhouse recently introduced the concept of hydraulic value to account for the different lateral spread of mineral grains derived from a single source but differing in size, shape and specific gravity. [11] In the past, failure to allow for this factor has been comparable to confusing ecological and temporal factors in microfaunas, but recent work incorporating the concept of hydraulic value has given valuable results. Although

Figure 3: Illustrating the integration of local stratigraphic columns

 (1) Correlation of Four Columns on the Basis of Thickness, Lithology arid Facies-Faunas of the Beds


(2) Correlation as Above with Superimposed Zones Based on Planktonic Microfossils, Evolutionary Sequences, Heavy Minerals, and Other Facies-Free Indices


(3) Data as Above Plotted Against a Scale of Time-Units Based on the Zones.

few micropalaeontologists have time to spare for the tedious routine of quantitative heavy-residue analysis, they should be familiar with the type of results obtainable, because in barren sands fringing marine deposits it may be very helpful to extrapolate microfossil zones parallel to the mineral zones.)

To determine the time dimension applicable to a chart of regional zonation is tantamount to preparing a distribution chart of the facies-free microfossils and using it as an overlay on the chart based on benthonic facies faunas. The necessary data are available on the local distribution charts discussed above under III-(i). In the writer’s experience planktonic foraminifera, radiolaria, and ostracods are the most reliable time-markers, in the order stated, for Tertiary and Cretaceous studies. In older rocks planktonic foraminifera are absent and emphasis has been placed on the ostracods. The time-grid based on floating and free-swimming forms may be supplemented by the evidence of evolutionary trends in the benthonic genera. [12] The larger foraminifera (Orbitoididae, Discocyclinidae, Fusulinidae, etc.) show regular trends of development in their embryonic chambers and general form and in regional correlation possess a great value limited only by their restriction to near-shore facies. Certain smaller foraminifera show evolutionary trends proved empirically to be valid in age-determination over great distances. Still other smaller foraminifera may show a provincialised evolutionary trend, such as a tendency of rebuilds to develop aberrant evolute forms at certain levels.

By attention to the microfossil groups emphasized above a sequence of time-significant subdivisions may be recognized in each area of the original study. These new zones may be superimposed on the regional chart as first draughted and they provide the time dimension inherent in the regional facies-pattern. If they indicate parallelism between facies units and time units stable deposition, with sedimentary infill compensated by general subsidence, is indicated. If there is obliquity or transection of time-planes relative to layers of uniform facies regression or transgression is indicated. Absence of any time-significant zone must indicate a diastem or unconformity, unless its absence draws attention to some previously unsuspected structural anomaly.

Figure 3 illustrates the preceding remarks on the basis of a hypothetical example.

(iii) Dating the units of a regional stratigraphical column in terms of the standard geological time scale

In the course of geological studies extending back for more than a century, various phyla, genera, and species of fossils have been shown to be restricted to short intervals within the geological column. In studies of a new region special search is made for marker fossils of this type and, when found, they provide the basis for dating the units of the local succession. In general, the older the rocks, the more reliable are long-range correlations based on index fossils. The principle of such correlation is sound but there are sources of error to be known and avoided; viz.:

(a) The non-absolute aspect of the geological time scale

Time, “like an ever-rolling stream”, is the axis against which the history of the earth is measured. The standard geological time scale is a form of calendar, now established on a quantitative basis as a result of studies of radioactive minerals. [13] This time scale is an objective reality but is almost always used subjectively. The more precise are attempts to delimit minor time subdivisions, the greater is the disagreement among stratigraphers, simply because no man can be omniprescient and each individual stresses the branch of knowledge in which he specializes. The indices for subdivision of the geological time scale are almost always fossils and the intention has been to make the major breaks in the time scale correspond to major breaks in faunal trends. However, it does not follow that an abrupt change of terrestrial life must coincide with a change in the deep marine fauna, nor that such a change in one hemisphere should be equally pronounced in the other. Consequently such questions as the correct designation of correlatives of the Maestrichtian, Danian, and Montian stages or the exact correlation of the North American and Russian Permian stages remain unsettled, controversial issues.

A secondary means of correlation is the study of cycles of sedimentation and diastrophism. [14] Certain clearly marked events such as the Laramide orogeny and the Jacksonian transgression left their imprint in the sediments over vast regions of the earth. Correlation on this basis must be applied with discretion as the basal beds of an unconformable sequence may vary in age owing to slow encroachment over a land mass. Errors may result (as in Peru and Ecuador) from attempting to correlate unconformities in a mobile geosyncline with those of an adjacent taphrogenic province. [15] Some authors support the theory of eustatic changes of sea level as the underlying cause of major marine transgressions and regressions, but there are few cases in which the physical evidence conforms completely with this hypothesis. [16]

(b) The unfortunate choice of some type stages

The concept of a stage as the smallest regionally recognizable time-stratigraphical unit dates back to a time when very little attention was paid to facies-control, of faunas. There was a strong tendency to assume different ages for different faunas and as a result some of the stage names now in use include overlapping units partly based on synchronous but environmentally different faunas. A desideratum is an agreed series of multiple type units designed to exemplify the variation of faunas in accepted stages under different environmental and climatic conditions. The following quotations illustrate modern views on the subjects of the preceding paragraphs.

Kleinpell 1938      “The synchronization of stratal units as small as stages in areas as geographically remote as Europe and California may well be considered extremely hazardous in the light of present knowledge. Similarly synchronization between either of these areas and the intermediate Caribbean area is also hardly to be considered reliable within the limits of a stage or zone.” [17]

Arkell 1933           “…few of the geologists working in other countries at first adopted d’Orbigny’s stages, for with their more detailed local knowledge they were unable to recognize any such ten divisions which might have been ‘delineated by nature with bold strokes across the whole earth’…” [18]

Davies 1934        “While Eras, Periods and Epochs can be recognized over most of the world (allowing some elasticity in correlation for epochs) correlation of Ages (sic) over wide areas is dangerous at present. To write of ‘Bartonian’ or ‘Burdigalian’ as if they could be confidently identified in lands far away from their type locality is inadvisable.“ [19]

Schenck 1935      “(in Europe)…only in local areas is there an appreciable faunal break between the Eocene and Oligocene. The species from the Upper Eocene Barton clay of England are closely related to the lower Tongrian ones from Belgium, The ‘great faunal break’ at the close of the Oligocene is a myth, both in Europe and America. The difficulty, moreover, of separating the Cretaceous from the Tertiary is classic. How to distinguish the Miocene from the Pliocene or how to divide the Pliocene from the Pleistocene have never been stated to universal satisfaction.” [20]

Hedberg 1937     “Terms of the standard time-scale (Oligocene, early Eocene, etc.) are convenient as a means of expressing opinions on the approximate or relative geological age of sediments. Their value lies particularly in the fact that they are in use throughout the whole world. However, since there is much difference as to their scope even in the region where most of them originated (Western Europe) it is impossible that they should have any very exact significance in northern South America.” [21]

(c) Lingering errors

An erroneous age-determination, once published, is never completely eradicated from the literature. Kugler gives a good example in reference to the Palaeocene (midway) Soldado formation [22] exposed on Soldado Rock near Trinidad. In 1912 Maury described the fauna and recognized its affinities to the Midway assemblages of the southeastern United States. In 1928 Liddle, owing to his mistranslation of an intervening paper in German by Kugler, confused Palaeocene and Upper Eocene beds on the islet. In 1929 Maury corrected Liddle’s error but nevertheless in 1934 Shimer quoted the faulty passage of Liddle. In 1935 Maury corrected Shimer but in the same year Schuchert drew on Liddle’s erroneous version for one of his famous treatises on palaeogeography. Kugler’s paper of 1938, dedicated to the memory of the lately deceased Carlotta J. Maury, reiterated her correct initial statement and pointed out the series of erroneous references, but with the error already appearing in well-known compilations there is little doubt that future authors will perpetuate it.

Schuchert (1935) [23] accepted determinations of the Oceanic formation of Barbados as Miocene, overlooking the more up-to-date demonstrations of its Middle Eocene to Middle Oligocene age: likewise he treated the San Fernando formation of Trinidad as Oligocene despite long-standing recognition of its Eocene age. These errors are incorporated in his treatment of the diastrophic history of the Antillean region and are likely to be disseminated by subsequent authors,

The moral to be drawn from such examples is that an age-determination based on fossils should only be made or accepted after checking the validity of age-assessment of the fauna used as a standard. Circular reasoning is to be avoided—of the type: “fauna (a) from country A is questionably Miocene: fauna (b) from country B  is the same as fauna (a): faunas (c) and (d) from countries C and D are almost identical with (b) so must be Miocene: fauna (a) is typically Miocene by comparison with (b), (c) and (d)”. Spread over several publications issued at leisurely intervals the argument is not readily recognized as specious and examples of this type do exist. [24] The molluscan faunas of Panama have long been an accepted standard for the younger Tertiary of the Caribbean region, but current studies are revealing long-concealed errors in their age-assessments. [25]

(d) Failure to distinguish between ecological and temporal factor [26]

Although not so sensitive as micro-organisms, the larger marine invertebrates are limited as to habitat and, in part, are structurally specialized for life in certain environments—robust or sessile in areas of heavy wave action, discoidal in areas of rapid sedimentation, and so on. A megafauna specialized for life in a certain habitat might persist with little change for a considerable period: in the fossil state it would be erroneous to consider all occurrences of such a fauna synchronous.

A case in point is the so-called Hannatoma fauna of mid-Tertiary molluscs in northern South America. [27] In its first published description it was referred to the Middle Oligocene of Peru and Ecuador. [28] Subsequent discoveries of the same basic fauna in Colombia and Ecuador were at first regarded as synchronous since they were found in thick otherwise almost barren, brackish-water sediments and no reason was seen to doubt their synchroneity with the southerly examples. Then, as local studies were incorporated into regional compilations, an anomaly arose in that beds with the Hannatoma fauna fell in an interval which on grounds of marine faunas and regional history must be regarded as Upper Eocene. In a symposium on this anomaly the joint opinion of the contributors is that the principal species of the Hannatoma fauna were long-ranging forms specialized for life in a brackish-water habitat and are not suitable fossils for long-range correlation.

A comparable case has arisen from the failure of some authors to recognize that on account of uniform facies, the foraminiferal faunas (mid-Tertiary) of the continental shelf of northern South America include many persistent forms. A clearly defined zonation based on planktonic species is applicable over this whole region, but several authors have published erroneous correlations based on unreliable, long-ranging benthonic species.

iv) Palaeo-ecological studies and palaeogeographical reconstruction

The methods discussed up to this point have been almost mechanical, largely capable of application by an intelligent person with little geological knowledge, The recognition of age-significant fossils and their application to dating a succession certainly do call for palaeontological knowledge, both of the literature and of fossil assemblages.  However, palaeontologists have been split into the ‘palaeo-biologists’ and the ‘biostratigraphers’ and those of the former group, more concerned with the morphology, phylogeny and classification of fossils than with their status as symptoms of earth history, possess the knowledge requisite for the type of correlation so far discussed. [29]

To progress beyond correlation into the realm of palaeogeography the ‘biostratigraphical-altitude must be adopted. Constant attention must be given to the problem of how fossils may best be applied to interpreting the earth’s history with its complex cycles of subsidence and emergence, its changing climates and its shifting continental margins. The problem passes from static analysis of a three-dimensional space continuum to dynamic analysis of a four-dimensional space-time continuum, and coincident with this development it becomes less easy to lay down set rules of procedure in reaching the desired result. An analogy with modern detective fiction is tempting: Father Brown, Dr. Thorndyke, Mr. Nero Wolfe, M. Poirot, and their many fictional colleagues can step beyond the stolid police routine of classifying clues, and the successful palaeogeographer must likewise develop some degree of intuition in picking on the key to a complex problem. A less fanciful indication is given by the term introduced by Cram—“controlled imagination”. [30]

The first clue to the palaeogeography of a region is given by charts of the type shown on Figure 3. From these can be seen certain trends of transgression, stability or regression. There is, however, a random factor in the data because of the arbitrary choice of the areas selected for detailed study. The section may, by chance, be representative for the region but equally it may chance to be atypical and to omit or overemphasize certain features. It is at least a starting point for interpretive studies.

The main lines of approach in applying micropalaeontology to palaeogeography are:

(a) implications of lateral changes

(b) palaeo-ecological deductions

(c) tests of rationality

(d) preparation of palaeogeographical maps

Discussion of these four topics follows.

(a) Implications of lateral changes [31]

Stratigraphical correlations prepared for application to structural problems are based on the recognition of identical or closely similar sequences of rock types and fossil faunas at several suitably spaced localities. The literature dealing with local problems, such as the structure and stratigraphy of a single oilfield or pool, is far more voluminous than that covering the depositional histories of regional tracts. In consequence, there exists something of a cult for establishing ‘marker-beds’ and emphasizing their continuity.

In palaeogeographical research the emphasis is placed differently, since lateral discontinuities and gradations often provide the key to understanding some phase of depositional history. A widespread and uniform bed may on occasion indicate an event of regional significance, yet examples will be cited below which show such an interpretation to be false and misleading.

In the world as we know it today lateral change from one environment to another is a normal effect of physiographic and climatic variation. Davies (1934) recognizes some eighteen marine provinces and six terrestrial provinces characterised by distinctive faunal associations. Each of these major provinces could be broken into innumerable sub-provinces governed by the accident of local ecological conditions. An obvious example is any coast line where different types of rock have been exposed to marine erosion. The harder rocks form cliffs and headlands with boulder beaches at their base; the softer rocks are eroded into bays and inlets with sand or mud-flat beaches. Islets, sand bars and spits, dunes, lagoons, coral reefs, mangrove swamps and other similar features may be present. Where streams and rivers reach the sea the coast is modified into estuaries or deltas. Viewed ecologically a varied coast line such as this presents a series of intergradational facies units. Focal points could be chosen where peculiarities of environment have induced the co-existence of specialized organisms, such as robust sessile forms on an exposed rocky shore or burrowers and mud-ingesters on mudflats. In between these foci of pure facies type the lateral merging of different physical extremes is matched by a gradation of one faunule into another.

At right angles to the coastline there is a gradation from the landward facies to the deep oceanic environment. The main stages are:

Terrestrial and fresh-water facies
Brackish facies
            Eulittoral (intertidal) facies
                        Sublittoral facies
                                    Deep sea (archibenthic, abyssal) facies

The physical processes normally active in these different environments vary from one to another, causing variation in sedimentary type. The eulittoral, intertidal facies, for example, is characteristically very heterogeneous in rock-type, whereas the deep sea facies is typically fine textured and homogeneous over vast areas. Local sedimentary type is largely a function of erosion and of transport of particles as governed by Stokes’ law, so that physiography, marine currents and availability of mineral matter are controlling factors, modified by such effects as electrolytic flocculation of colloids at river mouths, bio-chemical precipitation and growth of organic reefs. Marine life is affected directly by these physico-chemical factors and also by variations of temperature, salinity, stagnancy, turbidity, aeration and similar effects which are not reflected in the inorganic sediments. Most of these ecological variants are direct functions of sea depth, which is therefore commonly used as a reference datum in comparing different facies. Although each main depth zone differs from the others in conspicuous aspects of sedimentary type and faunal community, no sharp boundaries usually separate them: there are intermediate transitional zones in which intermingling and gradation of characters are observable.

The rocks which form the basis for micropalaeontological research were formed under similar conditions to the sediments of Recent sea floors. That some rocks were laid down in deep water, others in shallow water, is reflected in their lithology and fossil content, and lateral gradation from one fossil facies to another is normal, as in Recent marine sediments.

(b) Palaeo-ecological deductions

Palaeo-ecology is the study of fossil communities in relation to their environment. It is the branch of palaeogeography in which lateral and vertical changes among different types of animal and plant assemblages are used to establish ancient climatic changes, drainage patterns, emergences and subsidences of sea floors, and related palaeogeographical subjects which are reflected more clearly in their effects on fossil organisms than in their influence on the mechanics of sedimentation.

The prime axiom of palaeo-ecology is that specialization of a fossil fauna indicates the same environmental control as would lead to the development of a similarly specialized unit among Recent faunas. A frequently cited example is that coral reefs in the modern seas only flourish in warm, clear water of normal salinity, and it is assumed that fossil coral reefs are an index of similar marine conditions. A fossil fauna which lived in fresh water may be identified by its specialization along the same trends as a Recent fresh-water fauna, e.g. molluscs thin-shelled and smooth, charophytes present, admixture of terrestrial matter, especially plant spores in abundance. A means of direct check on the temperatures of ancient environments is being developed by Urey, the basic method being to determine the carbon-isotope ratios in the calcium carbonate of fossils and from these figures to deduce the original temperature at which the shell was formed. [32]

Organisms vary in their degree of tolerance of environmental changes. The prefixes ‘eury’ and ‘steno’, implying respectively broad and slight tolerance, are used in descriptive terms such as eurybathic, euryhaline, stenohygric, stenothermal. In palaeo-ecology the most significant fossils are those of stenobathic, stenothermal and stenohaline organisms, since they can be used as indices of former conditions of sea-depth, water temperature, and salinity.

Our knowledge of the ecology of living marine micro-organisms, applicable to palaeo-ecology is drawn from the results of oceanographical research. Since the cruise of the British research ship H. M. S. “Challenger” in 1873-1876, many vessels of various nationalities have made cruises, either world wide in scope or limited to some special region such as the polar seas, with the purpose of collecting organic material and physico-chemical data for the advance of oceanographical research  Some of the better known research ships have been the “Dana” (Denmark), “Meteor” (Germany), “Discovery” (Great Britain), “Willebrord Snellius” (Holland), “Maud” and “Fram” (Norway), “Albatross”, “Carnegie”, “Catalyst” and “E. W. Scripps” (U.S.A.). [33] The knowledge of life in the open oceans provided by these ships has been supplemented by studies of the faunas of coastal waters made by various shore-based institutions. [34] Up to the present, the sea floor at the outer edge of the continental shelf and the upper edge of the continental slope has not been investigated as thoroughly as the shallower and deeper regions which flank this province.

The ecology of terrestrial organisms can be studied without the elaborate preparations necessary for an oceanographical cruise, but palaeo-ecology is so largely concerned with marine sediments that knowledge of Recent terrestrial life is seldom significant. An exception lies in the use of plant spores as indicators of climate. Between the poles and the equator there is a well marked floral zonation: among trees in the northern hemisphere the birch, the conifers, the oaks, the palms and the mango typify provinces successively farther from the pole. During the Pleistocene epoch advances and retreats of the polar ice-cap caused parallel movements of the plant communities  Evidence of this is to be found in the spore content of the glacial and interglacial sediments. It may be noted that the results of such studies match the palaeo-ecological evidence of foraminifera in cores from the Atlantic ocean floor, and jointly they add greatly to the preciseness of our knowledge of correlation of the interglacial periods formerly based on gross physical features such as leached surfaces in glacial tills and changes of provenance of erratic boulders. [35]

An aspect of marine life which militates against positive palaeo-ecological deductions is the tendency of specialization among all animal phyla for life in all variants of the marine environment. (Plants are more limited because photosynthesis is only operative down to the maximum depth of penetration of sunlight.) Consequently it is exceptional for any major phylum of animals to be restricted to a particular environment: it is usually necessary to descend to the level of genus, or even species, in designating index-forms of special habitats.

This adaptiveness of marine animals reduces the number of broad generalisations which can be made on the palaeo-ecological significance of fossils. In bio-stratigraphy the significance of fossils can be expressed by many generalisations of the type, “The graptolites and trilobites are index fossils for the Palaeozoic, ” but few of these dicta have palaeo-ecological counterparts. Of relatively few orders is it even true to say that they are exclusively marine, since specialization has permitted entry into brackish and fresh-water environments. Among the larger organisms, this difficulty can partly be overcome by considering morphological specialization rather than systematic classification of the animals in a given community, since the larger marine invertebrates frequently show a mechanistic adaptation of their body-form to fit them for a certain environment. The corals in areas of heavy surf are compact sphaeroidal forms but their close relatives in quiet water develop delicate ramose and flabelliform shapes. The decapod crustaceans include armadillo-like forms (Emerita) which can withstand the buffeting of waves on  sandy beaches, compressed forms (Petrolisthes) which can elude enemies by backing into crevices among rocks, small planktonic forms (Lucifer), free-swimming forms with oar-like limbs (Portunus), deep-water species with long slender limbs and appendages (Nematocarcinus, Aristaeus), and the amphibious hermit crabs (Eupagurus) which use acquired gastropod shells instead of having chitinous armour of their own. (Even the sessile barnacles are not distant relatives of the mobile decapods, and their resemblance to the molluscan limpets is a typical case of homoeomorphy due to environmental specialization.) Similar examples of wide adaptation to specialized conditions could be cited for the molluscs, the echinoids, the worms or the fishes. Hence an assemblage of marine megafossils may reveal its ecological status merely by the morphological features of the organisms present. An abundance of thick-shelled calcareous fossils, regardless of individual orders, genera, and species, is a fairly sure sign of deposition in a warm shallow sea—shallow because of the high concentration of sunlight necessary for photo-synthetic production of a high carbonate-ion concentration, warm because the rate of the reaction of lime precipitation is very slow in cool water.

Micro-organisms, among which a linear dimension of half an inch is exceptional, rarely show any mechanistic adaptation of their hard parts appropriate to their chosen milieu. The foraminifera of tropical coastal waters are often dominated by discoidal genera such as Amphisorus, Amphistegina. Peneroplis, etc., the shape of which doubtless prevents the burial which would befall spherical forms of the same mass; but other externally similar discoidal forms such as Cyclammina and Robulus, are typical of rather deep offshore water. The planktonic Globigerinidae have very thin inflated tests, yet so do many non-planktonic foraminifera. The Upper Cretaceous Gümbelinas were evidently planktonic but only differ superficially from the benthonic Bolivinas. Among Recent foraminifera there are many baffling instances of species closely similar in size, appearance and relationship but demonstrably different in their optimum habitats. For example, the genus Elphidium is commonly regarded as an index of warm coastal waters, yet the species E. incertum is restricted to a subarctic habitat: the genus Nonion includes species restricted to inshore waters, such as N. scapha, and others typical of ocean-floor faunas, such as N. pompilioides. Uvigerina peregrina, only known from cool water, differs only in detail from other Uvigerinas which live in warm water. As a basis for ecological deduction it is therefore preferable to emphasize the over-all aspect of a microfauna rather than the presence of any particular species.

Among the assemblages of micro-organisms which typify special environments are the following:


Chara is an algal genus of fresh-water habit, characterised by an ability to secrete lime in its tissues. An abundance of its oögonia, ellipsoidal spore-cases with spiral ridges encircling them, is a clue to fresh-water sediments.

The calcareous algae are usually recognized as megafossils, and under optimum conditions they may be a main component of organic limestones. However, under less favorable conditions they may be present only as a minor element in a fossil community, not readily recognizable except in washed residues. They are symptomatic of warm shallow sea water.

The spores of terrestrial plants are liable to occur in abundance in continental deposits. In lesser quantities they may occur in marine sediments, since they were subject to aeolian distribution. They are of value as climatological indices, at least within the geological range of Recent floras.


The radiolaria are exclusively marine. Because the radiolarian oozes of the Recent oceans are of abyssal origin their fossil counterparts have often been claimed as deep-sea sediments. More recently authors have tended to challenge this belief, and the term ‘pseudabyssal’ has been applied to radiolarites of shallow origin. In western North America a relationship has been claimed between vulcanism, an excess of silica in the neighbouring sea, and a rich Tertiary radiolarian fauna. In western South America Tertiary sediments with a microfauna consisting almost entirely of radiolaria have been claimed to mark the paths of cold marine currents. [36]


Literature on the ecology of ostracods is scanty, but it is a matter of observation that the more ornate species with angular and sculptured tests are marine, whereas the fresh-water types are simple bean-shaped forms with no pronounced irregularities of shape and only a low degree of surface ornamentation. Ostracods are not usually present in deep sea sediments. [37]


More detailed studies have been made of the ecology of foraminifera than of any other order of micro-organisms, and some consistent relationships have been indicated between the presence of certain forms and the prevailing ecological conditions,  Some of the assemblages most useful in palaeo-ecology are described below.

An association with abundant discoidal calcareous foraminifera of large size is typical of shallow near-shore waters in tropical and subtropical latitudes. In Recent examples the most typical families are the Camerinidae, Peneroplidae, Alveolineliidae, Amphisteginidae, Calcarinidae, Cymbaloporidae and Planorbulinidae. Extinct families which appear to have lived under similar conditions include the Orbitoididae, Discocyclinidae and Miogypsinidae. To some extent the depth-control within this group  is due to commensality with algae.

An assemblage similar to the last often typifies offshore reefs, the main difference being a greater diversity of fauna, in particular a greater abundance of planktonic and benthonic smaller foraminifera of open sea character and often an admixture of sessile micro-organisms such as the foraminifera Carpenteria and Rupertia and the bryozoan Cupularia.

In general a microfauna with a small number of foraminiferal species, thirty or less is representative of a shallow environment, regardless of its richness in individuals  The shallower inshore waters are more subject to annual and diurnal changes of temperature, reduction of salinity by river discharge, physical effects of storm currents and tides than the waters of the open sea. The majority of foraminiferal species cannot tolerate such a wide range of conditions. In warm shallow waters such as the coasts of the Caribbean Sea, the western Atlantic and the southern Mediterranean a profusion of Elphidium spp. and Streblus (‘Rotalia’. auct.) beccarii is usual. In cooler waters, such as the west coast of America excepting the Panamic province, the Discorbinae and Buliminidae of the genera Bolivina, Bulimina and Uvigerina dominate the micro-faunas. The Miliolidae and certain species of Nonion and Nonionella also tend to occur in abundance in the shallow coastal environment.

Streblus beccarii, in particular, and many species of Elphidium are notably euryhaline. As well as in coastal waters of normal salinity they can thrive in a subsaline environment such as Lake Maracaibo [38] or in the supersaline waters such as Lago Enriquillo [39] in Hispaniola.

A distinctive assemblage known from numerous fossil occurrences, though apparently not recorded among Recent faunules, consists almost exclusively of large simple arenaceous foraminifera of the genera Bathysiphon, Hormosina, Cyclammina, Haplophragmoides, Trochammina, Gaudryina s. l., Clavulina s. l., Verneuilina, Valvulina, and others. Development of such a fauna seems to be closely related to turbidity of sea water, since the examples known represent a piedmont facies (Chaudiere and Nariva formations of Trinidad, Capiricual member of Santa Inés formation of Venezuela, Mal Paso formation of Peru, and the alpine Flysch), deposition at the mouth of a large delta (Cruse formation of Trinidad) or re-deposition of mudflow exudations and slumped clays (Ste. Croix formation, in part, of Trinidad, Socorro formation, in part, of Ecuador). [40] It is feasible that the excessive turbidity of these environments inhibits photosynthesis and thus leads to too low a concentration of carbonate ion for the viability of calcareous organisms. It is also possible that in the presence of a surplus of clay colloids base-exchange reactions reduce the available calcium ion.

Another assemblage dominated by arenaceous foraminifera exists under stagnant, usually brackish conditions. In this instance the species are small, usually with flimsily constructed tests. Ammobaculites, Trochammina, and Haplophragmoides are genera of wide distribution represented in this environment by diminutive species, and there are other genera which seem to be restricted to a brackish habitat, such as Leptodermella, Lagunculina, Ammoastuta, and Trochamminita. Such a fauna is known from bayous and salt marshes in the Mississippi delta, from Miocene deltaic sediments and from a Recent salt marsh in Trinidad, and also in the Mississippi area in shallow marine facies under stagnant, poorly oxidised conditions.

Sometimes associated with tiny arenaceous foraminifera in the brackish facies is a suite of small calcareous forms with the genera Buliminella, Nonion, and Nonionella dominant. A peculiarity in several instances is a yellowish to russet orange coloration which suggests that an appreciable content of ferric salts is present in the shell material. This calcareous faunule has been noted in the Recent Mississippi delta [41] , Pliocene estuarine beds in the Nile valley, and Miocene deltaic beds in Venezuela and Trinidad. [42]

In tropical America some Upper Oligocene and Lower Miocene microfaunas are dominated by costate Siphogenerinas of the S. transversa species-group. These assemblages appear to represent deposition in warm shallow water. In Ecuador the greatest concentration of these Oligo-Miocene Siphogenerinas seems to be at the intergradation between deposits of the continental shelf and the outer edge of an advancing fan of terrigenous sediments. In Recent faunas species of the same group have been recorded off various Pacific and West Indian islands, partly at depths as shallow as ten meters.

An abundance of Lagenidae and Buliminidae, both represented by numerous genera and species, is a sign of rather deep water. This is especially the case if they are accompanied by species of Gyroidina, Epistomina, Cassidulina, Laticarinina, Lagena and other genera more typical of deep than of shallow water. Under certain conditions, not yet fully understood, the buliminid genera Bolivina (B. costata, B. floridana, etc.) and Uvigerina (U. pygmaea, etc.), and the lagenid genus Robulus (R. calcar, etc.) may dominate an inshore faunule.

The planktonic foraminifera (sometimes less accurately called the pelagic foraminifera) live in the surface layers of the oceans and are dispersed by currents, only sinking to the sea floor at death. Consequently they are not valid as indicators of sea floor conditions. In the modern oceans ‘Globigerina oozes’, almost entirely composed of the tests of foraminifera, are typical of abyssal depths, but it is fallacious to deduce from this that any sediment of like composition must be of deep water origin. At any place where strong surface current sets towards an island or continental coast an abundance of    planktonic foraminifera will be found in the littoral deposits: this is exemplified by shallow-water Globigerina limestones in some of the Pacific islands. [43] In an area where warm and cold currents intermingle the death rate of the planktonic foraminifera may be high: this appears to explain an abundance of Globigerinoides sacculifer, etc., in sub-littoral Miocene beds of northwest Ecuador, where the ancestral Humboldt current met the warmer waters of the Caribbean province. The two cases cited are exceptions, however, and if a gradient can be demonstrated along which increasing abundance of planktonic foraminifera corresponds to increasing distance from a coastline, then increasing sea depth may be assumed: the Eo-Oligocene Naparima Basin of Trinidad provides a good example.

The presence of a rich planktonic microfauna in a sediment in the absence of any benthonic fauna commonly signifies a euxinic facies [44] (Pons Euxinus = the Black Sea). This usually implies the presence of a silled basin in which the bottom water layers stagnated and became charged with toxic hydrogen sulphide. Normal benthonic life was thus inhibited, though the nekton and plankton were unaffected. In the Caucasus Lower Tertiary marls with a fauna of Globigerinas, Gümbelinas, Globorotalias, and Hantkeninas are interbedded with marls carrying a rich benthonic fauna in addition to these planktonic genera. This appears to be an example of euxinic conditions, as do the Cretaceous Globigerina and Gümbelina limestones of the Andean geosyncline, Mexico, and elsewhere. Modern examples are the Black Sea itself and some of the Norwegian fjords.

In general the planktonic foraminifera thrive-best in warm waters. Globorotalia menardii is considered an exceptionally strong index for warm conditions. Globigerina pachyderma, however, is an exception indicative of cool to cold water. Frequency ratios of these and other species have been used to establish temperature fluctuations in the late Quaternary, based on submarine cores from the floor of the north Atlantic Ocean. [45]


Dwarfing is commonly related to abnormal salinity. High salinity, such as results from solar evaporation of an isolated lagoon, may cause the effect, or it may result from low salinity in an area of strong fluvial discharge. [46]


Sedimentary samples may be barren of fossils for the primary reason of representing a sterile environment or the secondary reason of non-preservation. Secondary barrenness is suspected in the presence of abundant products of chemical weathering (gypsum, selenite, limonite, laterite, jarosite, etc.). If there is no such evidence, and especially if similar sediments nearby do carry a fauna, some life-inhibiting ecological factor must be suspected. Possibilities to be assessed in individual cases include physical effects such as abnormally high or low temperatures; chemical effects such as abnormal concentrations of chloride, sulphide, or carbonate ion; and mechanical effects such as turbulence, scouring, or dumping of sediments. A wide range of diurnal or annual fluctuation of ecological factors is also highly inimical to micro-organic life.


Several authors have shown by localised examples that comminuted fragments of megafossils can be identified as to genus and even species. If a particular megafossil has known ecological significance its recognition from fragments in washed residues may be used to supplement other palaeo-ecological data.


The mode of life of some extinct organisms has been found by experience to match the generalisations applicable to their living descendents. For instance an abundance of plant spores has been typical of continental deposits since the dawn of plant life; ornate ostracods have occurred in marine but not in fresh-water facies at least since the Cretaceous.

In the case of foraminifera it has been mentioned above that closely similar species may pertain to entirely different environments, hence reliable deductions cannot be drawn from superficial resemblance between a certain fossil species and a Recent form of limited habitat. More reliable is the process of identifying facies-provinces from the areal distribution of different types of microfaunal assemblage and then deducing the palaeo-ecological status of individual species. The two species Hantkenina alabamensis Cushman and Uvigerina (Uvigerinella) carapitana Hedberg may be cited as representative examples. [47] The former has a world-wide range in Upper Eocene sediments and occurs in a variety of marine facies. It might, therefore, be taken as either a eurybathic benthonic species or as a planktonic form. The question is decided by considering the euxinic-facies marls in the Upper Eocene of the Caucasus, where this species occurs in association with a purely planktonic assemblage of Globigerinidae and Globorotaliidae and hence must itself be assumed to have been planktonic in habit. Uvigerina carapitana is an Upper Oligocene species recorded in several countries of South America and the Antilles. Along with many other Buliminidae of the same age it is restricted to the sublittoral (neritic) facies, not appearing in the shallower littoral facies nor in the deeper archibenthic Globigerina marls. Furthermore, in Ecuador U. carapitana is not a common species except at the inner margin of the neritic facies, just beyond the outer margin of a sheet of encroaching littoral sediments which gradually filled in the basin of deposition. This extinct species has thus been established by inferential reasoning as a significant palaeo-ecological index.

In other cases it becomes apparent that certain microfossils were subject to ecological control of their distribution but the controlling factor is not readily apparent. The Upper Cretaceous genus Siphogenerinoides may occur as one element in a richly diversified neritic-facies microfauna, as in the Pazul Basin of northwest Peru, yet in adjacent beds of similar lithology this genus may be abundant to the exclusion of almost all other foraminifera. Evidently Siphogenerinoides could endure an extreme of some ecological factor, such as stagnancy, which left no tangible record in the sediments. The genus Epistomina shows a similar uneven distribution in the Jurassic and Lower Cretaceous of northern Germany. [48]


Palaeo-ecological deductions regarding a fossil microfauna are based on recognition of specialization corresponding to that of a Recent fauna of known environment. If the degree of specialization is high, reliable conclusions may be drawn from a single sample. In general it is more satisfactory to study a group of related samples, to ensure that their apparent environmental features blend into a rational facies-pattern. Some examples from the literature are mentioned in the bibliography. [49]

(c) Tests of rationality

No version of the depositional history of a region is acceptable if it contains irrational elements. To take a simple example, if the Upper Eocene should be construed as an emergent phase represented by continental and marginal marine facies, it would be irrational to postulate a small centrally placed abyssal facies of the same age. The evidence leading to such a conclusion would need to be re-assessed to determine the cause of discordancy. Faulty age determination, incorrect structural interpretation, reworking of faunas, confusion of sample data, or some comparable reason usually comes to light when such cases are investigated.

A palaeogeographical reconstruction is considered rational if it postulates only the normal processes of sedimentation and if their products show a normal intergradation. In a given region during any geological epoch there tended to be some fundamental pattern underlying the detailed sequence of events: such patterns included periodic isostatic adjustments during a mountain-building phase, block-fault foundering, and slow epeirogenic uplift or subsidence. A palaeogeographical reconstruction which conforms to such a pattern is rational but one which claims an implausible mixture or alternation of such basic features is irrational.

In northwest Ecuador, in thick jungle almost inaccessible except along the main rivers, sections on several parallel streams indicated a monocline in Lower Oligocene shales. Microfaunas indicated a semi-barren, euxinic facies. On one river an algal limestone was mapped, dipping concordantly with the shales, and on field evidence it was taken as an interbedded lens. However, in palaeogeographical terms such a relationship, with no signs of intergradation, appears irrational and requires checking. In this particular case the limestone was later proved to be Upper Oligocene in age, a relic of a landslip which had fortuitously left a large block inclined at the same angle as the monoclinal Lower Oligocene shales.

In northern Peru, isopach studies appeared to indicate transgression of a certain formation over a sculptured erosional surface of older rocks. The geomorphology of the reconstructed surface seemed logical, hard sandstones forming fault-scarp ridges and soft shales marking depressions. The deeper-water facies in the transgressive formation were confined to its thickest parts, its thinner parts carrying only shallow-water facies-faunas. The palaeogeographical picture was rational except for one point, namely the very high vertical relief postulated on an erosional surface which would more naturally be a peneplane. Recognition of this irrationality led to a critical review, whereby it was established that block-faulting along the lines of the pre-existing pattern had been renewed during the deposition of the transgressive formation. This explained not only the mechanistic irrationality, but also an abnormally abrupt change from a shallow-water to a deep-water facies, the apparent development of some orbitoidal reefs in deep water, and other palaeo-ecological peculiarities of the transgressive formation.

In Barbados the Eocene and Oligocene sediments show a succession upwards of poorly sorted piedmont-facies sediments, radiolaria beds, Globigerina marls, and neritic-facies clays. [50] On the assumption that the radiolaria beds represent an abyssal facies it has been claimed that during the Eocene epoch the sea-floor underwent rapid downbuckling from a shallow level to depths of 5000 to 6000 meters and then rose again. On mechanical grounds such profound and rapid movement appears implausible (though one may not deny it dogmatically until island arcs are more fully understood) [51] . The apparent irrationality may be removed by claiming that radiolaria beds are not necessarily evidence of abyssal deposition.

Usually palaeogeographic deductions which might be termed freakish, requiring the supposition of a special set of conditions, are suspect in a check of rationality. Nevertheless local peculiarities do now exist (as in the Sargasso Sea, the Bay of Fundy and the Baltic Sea) and they must have existed in the course of geological time. In Trinidad the Oligocene Ste. Croix beds are closely similar in lithology and fauna to the Brasso formation (Esmeralda member). The main difference is that the Brasso is a peripheral formation of the Naparima Basin, representing the sublittoral facies and grading offshore into the deep-water Cipero marls, whereas the Ste. Croix beds are lenses of  shallow-water sediments situated out in the basin and completely enveloped by the Cipero marls (see Figure 4(A)). The explanation of this phenomenon must rank

Figure 4(A): Correlation and classification of sediments in the Naparima Basin of Trinidad

as freakish, yet it seems well authenticated. It is that anticlinal ridges were pushed up from the floor of the basin and provided platforms on which colonies of shallow-facies organisms could settle. Such a process conforms with the basic pattern in Trinidad (lateral compaction due to gravity collapse on the sloping Guiana shield) and it is worthy of note that sand lenses in the Ste. Croix beds are lag sediments, of which the only likely source is submarine extrusion of mudflow. [52]

A different type of irrationality arises from the uncritical assumption that because some particular sector has been studied in more detail than others it is necessarily typical of the region as a whole. Examples are cited from Trinidad and Ecuador. In the former case the large Fyzabad oil field was taken as a standard of reference when various outlying smaller pools were developed. It so happens that the Miocene Cruse formation at Fyzabad shows only one cycle of deltaic deposition, whereas in some of the newer pools the main cycle is broken into three sub-cycles. Solely because of the preconception based on Fyzabad, the cyclical repetition of lithology and faunules was for some time taken to indicate overthrusting and an entirely erroneous concept was formed of the geological conditions. In the Manta area of Ecuador outcrops are limited by a thick mantle of Pleistocene Tablazo beds, and consequently the coastal cliffs have been over-emphasized as the key to subsurface geology inland. This led to a faulty interpretation of structure and stratigraphy which was only dispelled by the drilling of a deep well. In both examples incorrect assessment of structure and stratigraphy caused incorrect interpretation of palaeogeography, and the basic reason was unjustified extrapolation from a known to an unknown sector.

(d) Presentation of palaeogeographical data [53]

The aim of palaeogeographical studies is to discern how, in the course of geological time, the outlines and physiography of lands and seas have been changed by the effects of orogeny, epeirogeny, and taphrogeny and by the constant processes of weathering, erosion and sedimentation. The ideal basis for such studies is an area with abundant outcrops and closely spaced, carefully sampled wells, simple structure, a stratigraphical succession readily subdivisible in terms of facies and age, and evidence as to the nature of any beds removed by erosion. With such a groundwork it is possible to follow the broad pattern of sedimentary cycles and orogenic phases and the fine pattern of their effects at different localities. In practice the ideal is never attained and some degree of extrapolation becomes necessary to cover gaps due to erosion, inaccessibility or alteration of beds, lack of index criteria, or undecipherable structure.

Supposing that the available evidence has been sifted and analysed and the palaeogeographer has formed definite ideas on the sequence of geological events, the problem which next arises is to present his conclusions in a graphic form readily assimilable by other geologists. This is by no means a simple matter since the palaeogeographical concept is a four-dimensional continuum of space relationships varying in respect to a time axis. To register the space relationships at any chosen instant in geological time requires some form of perspective drawing (block-diagram, fence-diagram or serial sections) or contour drawing as a base, with superimposed colours or symbols to denote different faunal or lithological facies. Any attempt to indicate the course of changing events, of which the phase represented is only an arbitrary choice, is likely to result in a diagram so complicated as to be unintelligible. Consequently it is usual to employ a serial technique in graphic representation of palaeogeographical conclusions. Points in time are selected, either as representing extreme fluctuations in the trend of geological events or as being accurately determinable on faunal grounds at widespread sections, and a facies diagram is prepared corresponding to each of these time points. When viewed in order these serial diagrams indicate the trends of geographical change in geological time.

An alternative method, applicable to the simpler palaeogeographical processes such as infill of an embayment, is to mark successive positions of facies-province boundaries on a single map. Boundary lines corresponding to three or four phases of the process may be indicated, each line being numbered to indicate which phase it represents. Bands of colour along the boundaries give a key to the expansion and shrinkage of different facies-provinces, and arrows may be used to emphasize the direction of shift.

Comprehension of a complex chain of palaeogeographical events may be ensured by preparing a simplified perspective drawing to emphasize the main trends, after which local anomalies and peculiarities may be depicted on the appropriate serial diagrams. In general, it seems more acceptable to present palaeogeographical diagrams in a simple but lucid form than to lose clarity in an attempt to present complex details which might better be discussed textually. Various types of graphic representation are used in illustration of other sections of this paper.


In the following pages some examples are given to demonstrate the palaeo-geographical significance of fossil microfaunas. They are all, except the last, based on first-hand studies by the writer while employed by various oil companies. The purpose of these examples is to illustrate methods of analysis and interpretation rather than to publicise local data, hence the writer has felt free to ignore details of local importance but irrelevant to the main theme. This attitude is further justified by the fact that much of the basic information used must, while it remains unpublished, be regarded as the confidential property of the oil companies concerned.

EXAMPLE 1       A basinal flank which subsided at a rate equal to the rate of accumulation of sediments, so that sea-floor conditions remained stable.
(Based on the Naparima Basin of Trinidad)

The area considered shows three parallel belts, each typified by a distinctive rock-type. The northernmost consists of clastic sediments grading irregularly upwards from conglomeratic basal beds, through grits and sandstones, to muddy, sandy shales. These comprise the Nariva formation and its various members. The middle strip is dominated by clay-shales but the lithology is variable, locally including limestones, conglomerates, glauconitic beds, orbitoidal sandstones, and both calcareous and non-calcareous clays and shales. The older, more variable, parts comprise the San Fernando formation and the younger, more uniformly shaly, parts belong to the Brasso formation. These two strips are peripheral to a large central area occupied by highly calcareous marls of the Cipero formation and other subdivisions of the Naparima marl group.

Megafossil evidence indicates that each of the three lithologically distinct groups has an age range from Upper Eocene to Upper Oligocene. Hence clearly, since their deposition was synchronous, their differences must be due to environmental factors. The Nariva formation is practically barren but its physical characteristics, such as coarse average grade, conglomeratic layers and ripple marks, denote a littoral environment. The San Fernando fauna includes large orbitoids, irregular echinoids, various molluscs, crustaceans, calcareous algae, and other fossils which jointly suggest a sub-littoral environment. The Brasso likewise contains molluscs of inshore type. The Naparima marls contain very few megafossils but the molluscs Thyasira and Pleurophopsis in the Cipero formation indicate a cold, therefore in tropical latitudes presumably a deep, environment.

Figure 4(B) is a correlation table of the Naparima Basin sediments based on field geology and megafossils. The evidence cited is imperfect because of lack of fossils in the Nariva and the lower parts of the Naparima marls. Even if structural conditions were less complex in the Naparima Basin it would be difficult to make a more closely knit interpretation of stratigraphical relationships because of the great vertical thicknesses of uniform lithology and the abrupt lateral changes of rock-type. The published literature on the basin proves the difficulty of making an exact interpretation on a basis of field geology and megapalaeontology. Perusal of the studies of Wall and Sawkins (1860),

B) Distribution of Age-Significant Megafossils and Larger Foraminifera:
Note the much more precise correlation in Diagram A) based on microfossils.

1. Derived megafossils as young as Paleocene in boulders.

2. Upper Eocene molluscs, echinoids, larger foraminifera, etc.

3. Middle Oligocene molluscs and larger foraminifera.

4. Upper and late Middle Oligocene megafossils and larger foraminifera

5. Upper Oligocene and Miocene molluscs.

6. Upper Oligocene molluscs of deep-water type.

Figure 4(B): Correlation and classification of sediments in the Naparima Basin of Trinidad

Guppy (1866-1893), Waring (1926), Illing (1928), Liddle (1923), Lehner (1936) and Kugler (1936) shows the gradual realization of lateral equivalence, but it was not until Renz (1942) utilised the results of intensified microfaunal research that a coherent and detailed interpretation began to emerge. [54]

The fossil microfaunas of the Naparima Basin provide additional stratigraphical information of three categories, viz., zonation based on planktonic species, palaeo-ecology based on the lateral variation of the assemblages, and positive evidence of lateral transition shown by intermingling of facies-controlled faunas.

Zonation [55]

The Naparima marls contain exceedingly abundant planktonic foraminifera. Most of the species had a limited life range and are therefore applicable to a zonal scheme, as tabulated below. The oldest marls (Lizard Springs and Navet formations) contain in their faunas certain planktonic foraminifera (Globorotalia velascoensis, Hantkenina mexicana, H. aragonensis, and others) indicative of an age range from Upper Cretaceous to Middle Eocene. Of more immediate interest are the younger beds (Hospital Hill and Cipero marls, Lengua calcareous clay) in which six zones are clearly defined by the ranges of Hantkenina primitiva, Globigerina concinna, G. dissimilis, Globigerinatella insueta, Globorotalia fohsi, and G. menardii. These species appeared and vanished in succession with only slight overlap in their ranges. Usually one or the other of them is present in a representative sample, but in their absence numerous other planktonic species are valid as zonal indicators.

Table 1: Ranges of some planktonic foraminifera in the Naparima Basin












Hantkenina primitiva








Globorotalia cerroazulensis








Globigerina dissimilis








Globigerina insueta








Globigerinatella insueta








Globigerinoides sacculiferus








Globigerinoides conglobatus








Globorotalia mayeri








Globigerina grimsdalei








Globigerinoides rubrus








Globorotalia praemenardii








Globorotalia fohsi








Candorbulina universa








Globorotalia menardii








Sphaeroidinella dehiscens








Globigerinita naparimensis








Variations of average frequency are not shown. The larger symbols (XXX) indicate the name-species of the six zones.

The same zones are demonstrable by changes in the benthonic microfaunas of the marls, but in attempting to establish correlation between the deep-water marls and the sublittoral deposits the benthonic forms are of little value. This is because ecological differences led to the development of such entirely different benthonic assemblages that, while it may be difficult to distinguish Upper Eocene and Middle Oligocene faunas within  the San Fernando formation, it requires almost an act of faith to believe that Lower Oligocene assemblages from the San Fernando and Cipero formations actually lived in synchronous and contiguous deposits. However, attention to the planktonic foraminifera shows the same distribution of species in the sublittoral facies as in the marls. In the San Fernando formation the zones of Hantkenina primitiva and Globigerina concinna are easily recognizable and in the Brasso the characteristic species of the younger zones appear.

In the littoral-facies Nariva formation, sensu stricto, microfaunas are sparse and consist largely of arenaceous benthonic foraminifera. However, the succession of sandy beds is locally broken by thin marly beds with weak, but zonally determinable, faunas of San Fernando type. Along the line of the main change of facies it is locally possible to observe physical intergradation of the Nariva into an offshore facies of determinable zone. At Bon Accord the basal Nariva conglomerate has a shaly matrix in which Hantkenina primitiva has been noted.


The Naparima marls are fossil versions of the Globigerina-oozes of the modern ocean floors. The Cipero formation has been discussed in detail in the literature and shown to match the definition of a Globigerina-ooze as a sediment consisting, to at least 25 percent of its dried weight, of unbroken foraminifera with a ratio of more than 25 to 1 of planktonic to benthonic specimens. In the Cipero faunas the frequency ratios of species and specimens referrable to different benthonic families of foraminifera match most closely the figures for Recent faunas living below 300 meters, as recorded on sea-floor profiles off California and in the Gulf of Mexico. The uniform composition of the Naparima marl microfaunas over wide areas and through great thicknesses indicates long-standing ecological stability, a criterion of deep rather than shallow marine conditions. [56]

The microfaunas of the San Fernando formation confirm the evidence of variable lithology and of megafossils as to its moderately shallow-water environment. The type of microfauna varies considerably in adjacent beds and planktonic foraminifera are not as conspicuous as in the Naparima marls. The ‘larger foraminifera’, species of Operculinoides, Lepidocyclina and Asterocyclina, are well represented in the faunas, locally in rock-forming abundance. The Brasso formation also contains orbitoidal layers near its base, but the strongest indication of its shallow-water origin is an abundance of costate Siphogenerinas in its microfaunas.

The Nariva facies-province was largely a sterile environment, but in the muddy shales of the upper Nariva a microfauna of large simple arenaceous foraminifera (Eggerella, Bathysiphon, etc.) is present. As noted earlier, such assemblages are taken to indicate a marine environment in which turbidity is the dominant ecological factor.

Positive evidence of lateral transition

On a large-scale map the concentric facies-provinces of the Naparima marls, San Fernando/Brasso and Nariva formations stand out clearly, but the local details of lateral transition are less easy to discern. Natural outcrops are rare. Deep weathering and tropical vegetation prevent access and force the field geologist to rely on auger surveys supplemented by test pits. The resulting lithological map is not a reliable record of changes of facies. In one sector it may clearly show a facies change, e. g. from Nariva sand to Brasso calcareous clay, but in another it may show only uniform marly clay where actually the Cipero and San Fernando formations interfinger.  

Washed residue studies provide a means of precise detection of changing facies  In each of the three main provinces the micro-faunas contain certain ‘facies-markers’, foraminiferal species which persisted throughout the deposition of that facies but were ecologically inhibited from migrating laterally out of their own province. In the Nariva Eggerella sp. is the main facies marker, supplemented by short-ranging foraminifera and ostracods at certain levels. In the San Fernando and Brasso formations the facies markers include Vaginulina elegans mexicana, Pseudoglandulina conica, Uvigerina curta-group, Plectofrondicularia miocenica-group, Frondicularia tenuissima, Siphogenerina transversa, Ceratobulimina evoluta, Cibicides trinitatensis, Lingulina grimsdalei and many others. A few of the many facies markers typical of the Cipero and older Naparima marls are Ammolagena clavata, Bolivinopsis (? Spiroplectammina) clotho/cubensis, Cibicides cicatricosa, Dentalina havanensis, a group of the Ellipsoidinidae, Karreriella subcylindrica, and Planulina illingi.

Examination of washed residues from a line of auger samples taken in the strike across a facies boundary usually shows a lateral change of microfauna as in the example below.

NORTH                                                                                                                              SOUTH

Brasso formation                                     Transition beds                                      Cipero formation

Pure Brasso microfauna

Brasso assemblages with sprinkling of Cipero facies markers

Cipero assemblages with sprinkling of Brasso facies markers

Pure Cipero fauna

Occasionally the transitional beds show faunal features other than simple admixture. A case in point is provided by beds in lateral transition between the Nariva and Cipero formations. These beds tend to contain a fauna composed only of indeterminate arenaceous foraminifera and Nodosaria spp., although Nodosaria is never a dominant genus in either of the parent facies. (Direct lateral passage from the Nariva to the marl facies without intervention of the San Fernando/Brasso facies is a feature only locally demonstrable but of general significance. It implies that the Nariva facies was controlled by some factor independent of sea depth, a condition satisfied by treating it as a turbid-water province.)


By study of their microfaunas, individual samples of the sediments of the Naparima Basin can usually be diagnosed as to zonal position and palaeo-ecological status. The microfaunal zonation gives an accurate key to the complex structures of the basin, and when the structure is understood its effects may be eliminated before the palaeo-ecological data are applied to palaeogeographical reconstruction. Figure 4(A) shows such a reconstruction, in which microfaunal details have been used to supplement the megascopical data on which Figure 4-B was based.

In descriptive terms, littoral, sublittoral, and archibenthic facies-provinces have existed side by side through the Upper Eocene and Oligocene. The positions of the three provinces remained stable, with only minor encroachment of one over another: this indicates steady subsidence of the basin at a rate equal to the rate of accumulation of sediments. A marginal turbid-water facies, attributed to rapid erosion and re-deposition of the Central Range landmass, at times overstepped the sublittoral facies and merged laterally into the archibenthic facies.  

Supplementary note. The Ste. Croix beds are shown on the diagrams, but they are not mentioned in the text because they are peculiar to the Naparima Basin and have no bearing on the general theme of this example. They are lenses of shallow-water sediments enclosed in the deep-water Cipero marls and they owe their existence to local upwarping of the floor of the basin. [57]

EXAMPLE 2       A basinal flank on which the rate of accumulation of sediments differed from the rate of subsidence.
(Based on the Borbón Basin of northwest Ecuador)

Present understanding of the palaeogeography of the Borbón Basin was achieved in three stages. Reconnaissance field geology supported by megafaunal evidence appeared to indicate widespread unconformity at a mid-Oligocene level. Then zonation by planktonic foraminifera showed that over much of the area time planes transect the ‘unconformity’, which is in fact a surface of abrupt facies change. Finally the samples from more detailed field surveys and test wells were analysed and gave a fairly exact understanding of the depositional history. [58]

The region is difficult of access, being covered by tropical forest, and the initial reconnaissance survey was limited to the courses of the main-rivers. By extrapolating across the unsurveyed areas a map was prepared which seemed to show an Oligo-Miocene group of sands, silts and orbitoidal limestones resting unconformably on an Eo-Oligocene group of marine shales. Around the margin of the basin angular unconformity was demonstrable and in central portions the projected plane of unconformity matched a sharp change from shales to coarse sands. The basic relationship then assumed is shown on Figure 5(A).


Figure 5(A): Initial interpretation based on reconnaissance study of outcrops and fossils

Preliminary examination of the microfaunas of samples collected on the reconnaissance survey appeared to confirm this interpretation, as the assemblages in the marine shales (Zapallo, Pambil and Viche formations) differed in kind and in preservational aspect from the faunas of the overlying Angostura and Onzole formations. A routine analysis of the faunas was made with a view to establishing microfaunal zones. To assist in regional correlation special attention was paid to the planktonic foraminifera and it was found that the sequence of Zapallo, Pambil, and Viche shales corresponded closely to the zones of Hantkenina primitiva, Globigerina concinna, G. dissimilis, Globigerinatella insueta, and Globorotalia fohsi as defined in Trinidad. Attention was next paid to the presumed transgressive formations and the surprising discovery came to light that these    sediments also fell within the zones of Globigerinatella insueta and Globorotalia fohsi. This could only mean that the Angostura sands and Viche shales were synchronous but environmentally different deposits. The sharp lithological break between them was not a plane of unconformity but merely the physical expression of gradual encroachment of a littoral over a sublittoral facies. Figure 5-B depicts the revised concept of age relationships between the various formations.

Figure 5(B): Revised interpretation incorporating zonation based on planktonic foraminifera

The reconnaissance survey was followed by more detailed mapping  Special efforts were made to obtain samples along the Angostura/Viche and Onzole/Viche contacts. Test wells provided subsurface material. Microfaunal analysis of the new material showed many details, minor in themselves but of cogent value in interpretation of the facies pattern. Points of this type were: observation of the restriction of gerinella carapitana and Trifarina sp. to beds transitional between the Viche and the Onzole; development of a zonule rich in Amphistegina lessoni at the outer fringe of the Angostura province; abundance of Siphogenerina transversa group in the Viche only near its transitional contact with the Angostura. Beds of the Globigerina concinna and Globigerinatella insueta zones are in unconformable contact around the edges of the basin; towards the centre of the basin highly foraminiferal shales of the two zones are separated by a band of ashy shales with a meagre fauna of long ranging (tolerant) forms; still farther out the two zones become part of a sequence of marine shales with no marked break in lithology or in benthonic microfauna. Collation of all these palaeo-ecological data against a time grid based on the foraminiferal zonation led to a detailed reconstruction of the facies pattern, depicted on Figure 5(C).

Expressed in terms of depositional history. Figure 5(C) indicates the following sequence of events:

(1) A normal sedimentary basin existed in Upper Eocene and Lower Oligocene time  It is mostly represented by marine shales (Zapallo and Pambil) but marginal conditions are shown by orbitoidal reefs in the Playa Rica sands.

(2) At mid-Oligocene time an orogenic spasm raised and tilted the margin of the basin. Volcanic activity at this time seems to be indicated by offshore deposition of ashy shales and by temporary disappearance of the rich sublittoral microfauna.

(3) General subsidence led to development of a marginal littoral facies (Angostura) transgressive over eroded Lower Oligocene and older rocks. Meanwhile normal sublittoral conditions were restored in the off shore areas, as shown by the deposition of the Viche formation, ecologically similar to the Zapallo and Pambil shales.

Figure 5(C): Interpretation based on extended field studies, well evidence, and detailed micropalaeontology

(4) Locally the rate of subsidence exceeded the rate of sedimentation, with the result that the sublittoral facies encroached over the littoral facies.

(5) As the rate of subsidence dwindled the process was reversed. A marginal facies consisting of foreset beds (Angostura) and topset beds (Onzole) advanced steadily into the basin. By Lower Miocene time subsidence had ceased and infill of the basin was completed by sediments of the Onzole type.

EXAMPLE 2-A   Lateral equivalence of two dissimilar formations inferred and later demonstrated.
(Based on the Angostura and Viche formations of Ecuador.)

As a digression from the generalized study of the Borbón Basin a very clearcut case of lateral equivalence of dissimilar formations is here extracted.

The Angostura formation consists largely of coarse sand characterized by an abundance of euhedral grains of various volcanic minerals. Local variants are conglomerates and cream algal limestones. Shell beds occur at certain levels. The micro-fauna consists of white foraminifera, among which the most conspicuous are species of Valvulineria, Bolivina, Robulus, and Cibicides.

The Viche formation consists of massive uniform clay-shales with few megafossils. The microfauna consists largely of cream to brown foraminifera among which species of Cassidulina, Gyroidina, Epistomina, and the nodosarian genera are conspicuous along with many others which barely appear in the Angostura assemblages.

Superficially these two formations have almost no features in common, yet a detailed study has shown them to be intimate lateral equivalents representing the littoral and sublittoral facies in a single sedimentary basin. The first clue to their possible equivalence was field evidence that they both lay between the Pambil and Onzole formations (see Figure 5). Confirmation was given by their content of planktonic foraminifera, both of them proving to include the zones of Globigerinatella insueta and Globorotalia fohsi. Direct evidence was later obtained by demonstration of a facies boundary marked by intermingling of faunas and by development of specialised faunules, such as the Siphogenerina transversa, Uvigerinella carapitana, and Amphistegina lessoni assemblages, not known elsewhere in the basin.

EXAMPLE 3       Cyclical repetition of facies
(Based on Miocene deltaic sediments in Trinidad.)

Probably the finest example of rhythmical or cyclical repetition of a sequence of different facies is provided by the Pennsylvanian cyclothems of Illinois, but their existence is demonstrated with little recourse to micropalaeontology. [59] The Miocene deltaic sediments of southern Trinidad present a less impressive example, but it is of some interest here because microfaunal studies aid in understanding its lithological expression.

In the Naparima Basin the Oligocene Cipero marls were followed by the Lower Miocene Lengua calcareous clay. The Lengua was, in essence, a transitional unit which heralded and finally merged into a massive fan of deltaic sediments advancing from the Orinoco drainage system. These deltaic beds, the Cruse and Forest formations of current stratigraphy, eventually filled and obliterated the Naparima Basin and were succeeded by brackish- and fresh-water beds of the Morne l’Enfer and La Brea formations.

Superimposed on the main marine-to-nonmarine cycle is a series of sub-cycles, not equally developed in all areas. In the Fyzabad sector only one subcycle is readily recognizable within the Cruse formation but in other oil pools the same formation shows a triple subdivision. Figure 6 shows at the left (schematically and not to scale) the

Figure 6: Cyclical repetition of facies in the Miocene of Trinidad

lithological and electrical logs of a well drilled through the Lower Forest, Cruse and Lengua formations in a pool where the subcycles are well defined. The thrice repeated sequence of colloidal clay, silt and porous sand is clearly marked in the Cruse. The Lower Forest shows the basal clay followed by the silt of a fourth subcycle but the pattern peters out in the Upper Forest. Microfaunal analysis of cores from the Cruse and Lower Forest shows three foraminiferal assemblages, each of which is practically confined to one of the three types of sediment. The colloidal clays carry a rich fauna composed almost exclusively of large robust species of the arenaceous genera Bathysiphon, Hormosina, Valvulina, Cyclammina, Haplophragmoides, etc. The silts are largely barren but occasional layers are rich in tiny flimsy-tested arenaceous species of Haplophragmoides, Ammobaculites, Trochammina, Textularia, Valvulina, etc. The sands also tend to be barren but if a fauna is present it consists of small calcareous species of Uvigerina, Buliminella, Nonion, Nonionella, Robulus, etc. The writer made some computations of relative frequency of these three faunules at different levels, averaged over a group of neighbouring wells, and found a definite relationship between faunal statistics and position in a subcycle. This is shown graphically on the right of Figure 6.

A local, non-regional cause for the repetition of facies seems to be indicated by the consistency of each of the three faunules and by the lateral variability of the cyclical pattern. The problem has not yet been fully analysed but it appears probable that the colloidal clays represent periodic isostatic adjustment in the form of subsidence balanced by extensive extrusion of mudflow from the core of the Southern Range anticlinorium. On this basis the silts, become foreset beds and the sands topset beds of fans of deltaic sediments advancing after each subsidence. The incompetent Naparima marls typically deform in a plastic manner under sedimentary or gravitational load. [60] In the literature on the Mississippi delta, built out over a more competent substratum, no clear parallel has been found to the Miocene subcycles of Trinidad.

There is practical value in recognition that the repetition of facies is a palaeo-ecological effect. For instance it prevents faulty interpretation in which nonexistent faulting might be introduced and it facilitates correlation between pools which differ in details of subsurface lithology.

EXAMPLE 4       Facies-pattern over a buried ridge
(Based on examples in the Talara area of Peru)

In general the existence of a buried ridge is most simply shown by isopach studies. In the example chosen, complex block-faulting has reduced the value of uncompensated isopach studies, but microfaunal variations within the overlapping sediments show a direct relationship to the original buried topography.

During a mid-Eocene interval there was a phase of uplift, block-faulting and strong erosion. The general effect was peneplanation but the hard Pariñas sandstone, interbedded between thick shale formations, resisted erosion and gave rise to numerous ridges. When subsidence led to marine transgression by the Talara formation these ridges in the sea floor caused development of a distinctive facies-pattern. [61]

Figure 7 is a schematic representation of the distribution of facies in the Talara formation. Transgression is first indicated by the appearance of conglomeratic sands with an orbitoidal fauna (Discocyclina, Amphistegina). These beds give place to shallow-water silts with a fauna rich in small foraminifera but limited as to species: only the five species “Trochamminasamanica, Hopkinsina talarana, Buliminella quemadana, Cassidulina cladra and Valvulineria perversa occur consistently and in abundance. Both units thin towards the ridge, the silts usually overstepping the sands but often failing to cover the crestal strip. The silts are followed by marine shales which are appreciably thinner over the crest of the buried ridge than on its flanks. The thinner, frequently sandy, shales

Figure 7: Facies-pattern over a buried ridge. (Based on the Talara formation of Peru.)

over the crest carry a shallow-facies fauna consisting of a flood of the single species Valvulineria duboisi with sparse specimens of Lepidocyclina and Operculinoides. In their thicker outlying parts the shales carry an entirely different fauna, a rich highly diversified foraminiferal assemblage including large species of Robulus, Globigerina, Nodosaria, Pseudoglandulina, Bulimina, etc., indicative of rather deep water. Faunal gradation is demonstrable between the two extremes, the elements suggestive of deep water becoming scarcer towards the ridge and the shallow water indices disappearing from the faunas in the reverse direction. The deep-water assemblage grades upwards as well as laterally, into a faunule of intermediate type indicative of shallowing by sedimentary infill, a process which culminated with deposition of flaggy sandstones conformably above the shales.

Recognition of the basic facies-pattern is of practical importance in detecting subsurface faults. Two oil wells may both pass directly from Talara shale down into Pariñas sandstone. In one of them the crestal facies is well developed, hence a normal unconformable contact may be assumed. In the other the deep-water facies is present but neither of the basal transgressive facies appears below it, hence elimination by faulting of part of the section appears probable.

EXAMPLE 5       A piedmont facies
(Based on the Danian Mal Paso formation of Peru)

A piedmont facies, also known as a flysch or dump-deposit facies, is developed where large-scale structural activity has caused products of erosion of an uplifted landmass to be deposited in concentrated fashion in a neighbouring sea. The mountain-building phase of geosynclinal activity is marked by piedmont facies such as the alpine Flysch or the Nariva and Chaudiere formations of Trinidad. Piedmont facies may also develop in grabens and half-grabens formed during taphrogeny, if erosion of the up-faulted blocks is rapid; examples are the Mal Paso formation of Peru and the Socorro formation of Ecuador. As an example for discussion the Mal Paso formation has been chosen because micropalaeontology has played an essential role in demonstrating its depositional history. [62]

The depositional environment of the Mal Paso formation is indicated by four inter-linked peculiarities, viz.:

(i)    The formation is covered by Tertiary rocks. Well evidence near Negritos shows an almost rectilinear boundary between two provinces, in one of which the Mal Paso thickness is of the order of 5000 to 8000 feet but in the other seldom exceeds 500 feet  This condition is suggestive of a buried fault. On physical evidence alone the faulting might have ante-dated completion of Mal Paso deposition or it might have post-dated it with heavy pre-Tertiary erosion on the upthrown side. Examination of microfaunas indicates a zonule, rich in Eponides huaynai and Robulus rotulatus, which only occurs at the top of the Mal Paso and is uniformly developed on both sides of the fault. This is clear evidence that faulting occurred either before or during Mal Paso deposition, not later.

(ii)   In the downfaulted, but not in the upfaulted, province the base of the Mal Paso contains a thick poorly sorted, heterogeneous conglomerate. This rests on Upper Cretaceous shales of the Redondo formation. The Redondo is complete and not appreciably eroded, since the same sequence of four foraminiferal zones based on an evolutionary set of Siphogenerinoides spp. is present below the Mal Paso as at the type locality some twenty miles away. Yet a plentiful component in the basal Mal Paso conglomerate consists of angular pebbles of soft shale, clearly not far travelled and shown by their microfauna to come from all levels within the Redondo formation. The seeming paradox is most simply explained by assuming that the conglomerate is derived from erosion of the upthrown scarp. This assumption is supported by conditions on the upthrown side of the fault, where the upper Mal Paso rests unconformably on deeply eroded Redondo shale or on still older rocks, fragments of which also occur in the conglomerate.

(iii) At its type locality (Pazul) the Redondo shale passes transitionally upwards into the sandy Monte Grande formation. The latter carries an impoverished microfauna but significant in it are the planktonic foraminifera Globigerina rugosa and Gümbelina globulosa. In the Mal Paso these two species are present only in the shales just above the basal conglomerate. Hence in a time sense the basal Mal Paso conglomerate, lying between the zones of Siphogenerinoides parva and Globigerina rugosa, corresponds merely to an ephemeral transition. This evidence accords better with a concept of abrupt graben-faulting and rapid erosion than with the more usual explanation of a massive conglomerate as a sign of erosion during a lengthy period of emergence.

(iv) Except for foraminifera the Mal Paso is practically barren of any fossils. Foraminifera are abundant, but the fauna is of a restricted type completely dominated by large arenaceous species of the genera Bathysiphon, Pelosina, Haplophragmoides, Cyclammina, Spiroplectammina, Trochammina, etc. Such calcareous species as are present are very scarce except in the Eponides huaynai-Robulus rotulatus zonule at the top of the formation.

       A controlling factor in the development of microfaunas consisting dominantly of large arenaceous foraminifera, as inferred from numerous fossil examples, is turbidity of the water in their domain. The mechanism may simply be that turbidity inhibits photosynthesis, lack of photosynthesis precludes growth of calcareous organisms, and absence of competitive calcareous foraminifera stimulates the growth of the arenaceous genera. In the case of the Mal Paso, dominance of the arenaceous genera corresponded to the phase of active erosion and rapid deposition, concomitant with highly turbid water; the calcareous forms only became common in the final phase when erosion on one side and sedimentary infill on the other had reduced the topographic gradient across the fault and had converted the graben into a normal marine basin.

Figure 8 depicts stages in the depositional history of the Mal Paso sediments, based on the foregoing discussion.

EXAMPLE 6       Effect of regional subsidence on different facies-provinces
(Based on the Pliocene sediments of Egypt)

Structural movements on a regional scale are reflected in all the facies-provinces of a region. Epeirogenic uplift is marked by a general shallowing of facies-type, subsidence by a deepening. Tilting may cause both effects simultaneously. A point to stress is that vertical changes of microfauna induced by the local effects of movement are liable to vary considerably from place to place. Lack of index-species may prevent a bio-stratigraphical approach, but the palaeo-ecological evidence of movement at numerous localities provides a basis for correlation.

In Egypt three isolated sections reveal evidence of post-Miocene subsidence. They are separated by wide areas denuded of Pliocene sediments by subsequent erosion, so that direct correlation is not possible. The three sections are entirely distinct, lithologically and faunally, but on palaeogeographical grounds there seems to be no reasonable doubt as to their correlation. [63]

Figure 8: The depositional distory of the Mal Paso formation in N. W. Peru

In the Western Desert and Libya the Miocene sediments are fringing limestones with a shallow marine microfauna of Elphidium, Rotalia and Discorbis and in the higher layers the semi-littoral Borelis melo. Locally there are remnants of overlying beds, finer-textured sediments with a much more diversified microfauna, indicative of definitely deeper water.

Some 500 miles to the east, in the Nile valley at Cairo and farther upstream, an incised valley in Eocene limestone is filled by Pliocene beds. The microfauna is an assemblage of tiny ferruginous Buliminellas, Nonions, Nonionellas, etc. strongly suggestive of estuarine conditions. Drowning of the pre-Nile valley is indicated.

The Gulf of Suez is a deep narrow rift filled with Lower Miocene marine sediments followed by Middle Miocene evaporites. Some 250 miles southeast of Cairo, in the southerly part of the Gulf, marine sediments are known above the evaporites. They contain a microfauna which includes genera and species-groups conspicuously different from any known in the Miocene of the Gulf or in the Mio-Pliocene of the Mediterranean coast. It is tentatively assumed that in post-Miocene subsidence a portal was opened corresponding to the present Red Sea, and that the unfamiliar species are migrants by this route from the Indian Ocean.

To reiterate, viewed factually the three sections have almost nothing in common, but viewed palaeogeographically they provide evidence of a widespread post-Miocene subsidence.

EXAMPLE 7       Organic reefs (bioherms)

Fringing and barrier reefs, built up by colonial organisms such as corals, algae or rudistids, have tended to form in shallow water peripheral to large marine basins. If oil should be generated within the basinal sediments it would tend to migrate updip towards the porous reefal mass. Consequently, it is not surprising that some of the world’s most prolific oilfields, such as the Middle East fields and more recent discoveries in Canada and Texas, should be fossil reefs. [64]

In North America the discoveries in Alberta have led to vigorous investigation into the oil possibilities of other neglected or undiscovered reefal trends. Interesting new methods are being developed for making palaeogeographical maps which will reveal trends favourable to the growth of bioherms. However, since most of this research is concerned with Palaeozoic rocks micropalaeontology finds little application. In the Middle East, in contrast, the reefs are of Upper Cretaceous and Tertiary age and a study of microfaunal facies-variation has given the key to exact understanding of the depositional history of the reefs. As the rocks involved are mostly limestones, a technique has been developed for the recognition of facies-types from their characteristics in thin section.

F. R. S. Henson, the protagonist of these studies in the Middle East, has shown that, by noting the direction of interdigitation and overlap of different facies, the status of a reef may be determined relative to cycles of regression and transgression. [65] Henson recognizes the co-existence of five principal facies during the growth of a reef. In order of encounter along a traverse from land to sea they are:

         Facies                             Type of microfauna

Littoral clastic facies:       variable, not genetically related to the reef.

Back-reef facies:            an assemblage of Miliolidae, Peneroplidae and Alveonellidae is typical; also some Planorbulinidae, Rotaliidae, Amphisteginidae and Orbitolinidae may be present.

Reef-core facies:            dominantly reef-building organisms (corals, algae, bryozoa, rudistids); foraminifera rare, mostly sessile forms such as Rupertia and Homotrema, with thick-shelled Amphistegina and Rotalia.

Fore-reef facies:             foraminifera large, robust and abundant; include (according to age) Nummulitidae, Orbitoididae, Miogypsinidae, Peneroplidae, Alveolinidae, Rotaliidae, Orbitolinidae and Lituolidae. Echinoid fragments are also plentiful.

Basinal facies:                a normal marine assemblage of Globigerinidae and small benthonic foraminifera.


Possibly many genera of foraminifera are planktonic in the early stages of the microspheric generation, but there are very few which complete their life-cycle in the surface waters of the oceans. Despite the small number of genera and species, the planktonic foraminifera are conspicuous in both Recent and fossil sediments by reason of the countless millions of individuals co-existent under favourable conditions. The Cipero marl of Trinidad is a fossil Globigerina-ooze in which the tests of planktonic foraminifera constitute from a third to a quarter of the total bulk of sediment.

In the course of Cretaceous and Tertiary time there was a steady advent and extinction of different planktonic species. Their mode of life resulted in almost worldwide distribution in every type of marine facies. Several genera, such as Gümbelina, Globotruncana, Globorotalia and Hantkenina, followed evolutionary trends in the development of species. These factors render the group of the utmost importance as precise indices of geological age. [66] This fact has been utilised in local studies, where

Range chart of genera of planktonic foraminifera

complexity or monotony of facies has hindered zonation on the basis of benthonic species, and it has been applied in regional correlation in the mid-American countries and in direct correlation of the mid-American and Middle East Tertiaries. There is scope for a concerted effort by micropalaeontologists towards establishment of world-wide correlations, but progress towards this end has been slow.

The chart indicates the geological ranges of genera known or suspected to be planktonic in habit. As is evident from the chart, certain generic combinations suffice to determine the age of an assemblage of planktonic foraminifera: a Gümbelina-Globotruncana fauna is diagnostic for Upper Cretaceous age, for instance, whereas an Orbulina-Globigerinoides fauna denotes the Upper Tertiary or younger. By attention to species a still finer time-grid may be established, as is indicated in the discussion of different genera which follows.

Globigerina [67]

In the literature the speciation of Globigerina is in such a confused state that in recent years the authors of many faunal papers have merely recorded the presence of the genus and have not figured nor attempted to determine the different species present. The late renowned J. A. Cushman, whose work was a stimulus to all students of foraminifera, usually followed this practice, which is unfortunate for its retardation of knowledge of the geographical and geological ranges of the various species.

Most of the species of Globigerina have certain conspicuous features in common, such as a globose test, inflated chambers and large ventral apertures into an open umbilicus, and they are therefore less easy to separate than the diversified species of benthonic genera such as Bulimina or Cibicides. Nevertheless close scrutiny will show that a normal post-Cretaceous microfauna of deep marine facies contains five or six species of Globigerina, each of which is consistent in its special characteristics. The chamber arrangement of Globigerina is a trochoid spiral and a basic feature of each species is the form into which this spire has been modified. In plan view it may be trigonal, quadrate, pentagonal, or polygonal.

      TRIGONAL                            QUADRATE                                                               PENTAGONAL HEPTAGONAL

(G. canariensis)                  (G. venezuelana)        (G. triloculinoides)               (G. altispira)               (G. cretacea var. eggeri)

In side view the spire may be flattened, moderately high, or lofty, viz.:

                                           DEPRESSED                                     LOW                                                  LOFTY

                                          (G. compressa)                           (G. concinna)                                     (G. bradyi)

In each species the individual chambers possess the same shape—globular, reniform, appressed or digitate, as the case may be—and they are arranged in a regular manner. The rate of increase of chamber size is a very constant feature of each species and according as it is low, as in G. venezuelana, or high, as in G. triloculinoides, two species with a basically similar spire may look entirely different. Certain species show individual peculiarities such as a supplementary chamber bridging the apertures in G. dissimilis, the presence of extra chamberlets in G. venezuelana and the bizarre adult chambers of G. fistulosa and G. digitata. It has been claimed that each species is consistent in the surface density of pores visible in the shell under high magnification, and that differentiation of species can be made on this basis alone. [68]

The various features which distinguish one species of Globigerina from another only become marked in the adult test. Juvenile specimens are much less easy to distinguish and may readily be confused with related genera such as Globigerinoides and the orbulines unless growth-series are carefully picked out.

The sequence of species of Globigerina in the geological column shows few evolutionary features. This may indicate diffusion from various centres of the species which successively, and usually abruptly, became dominant in the planktonic faunas. Differential migration has certainly affected the geographical spread of the genus, as is shown by examples such as the extinction of G. concinna in the mid-Oligocene of the Caribbean region but persistence of the same species into the Miocene of the Mediterranean region.

Because of the lack of marked evolutionary trends the establishment of life-ranges of the Globigerinas must be studied empirically. Foraminifera have been referred to the genus from rocks as old as the Pennsylvanian (G. seminolensis) [69] , Permian (G. permica) [70] and Jurassic (G. lobata) [71] but it is only in the Lower Cretaceous that forms are found which may fairly be considered planktonic on morphological and palaeo-ecological grounds. These Cretaceous species are almost all low spires of globular chambers, five to seven per whorl. Only in the late Cretaceous are more globose forms seen, such as G. mckannai [72] foreshadowing the dominance of this group in the Tertiary assemblages. In the Eocene many species have a hispid or pustulose shell surface, a character of scarce development in the post-Eocene Globigerinas. A finely cancellate shell surface is an almost invariable feature of the Tertiary species and is related to an array of fine radiating spines; whether this specialization was an evolutionary development during the Eocene, or whether the habitually poorer preservation of Cretaceous faunas has prevented its observation, is a subject not yet clarified.

Globigerinoides [73]

This genus differs from Globigerina in the presence of supplementary apertures on the dorsal side of the adult test, in addition to the normal ventrally-placed globigerinid apertures. The genus was only separated from Globigerina by Cushman in 1927, by which time most of the known species had already been listed under Globigerina. The type description employs the phrase “numerous large supplementary apertures”, and in stratigraphical studies the word “large” should be stressed because, although Globigerinas with loosely attached chambers have been recorded in the Eocene, true Globigerinoides with large lunate dorsal apertures do not appear until later in the Tertiary. There is an abrupt and explosive development of such species, coincident with the first appearance of orbuline genera, in the mid-Tertiary of regions as widely separated as the mid-Americas, the Middle East and the Far East. In the geological time-scale as locally applied the “Orbulina-surface” (LeRoy, 1948) [74] has been variously classified as from mid-Oligocene to mid-Miocene in age, but it appears reasonable to claim that this faunal datum is a valid index of contemporaneity and that the discrepancies arise from former acceptance of less reliable indices.

The ancestral form of Globigerinoides is probably G. trilobus [75] , from which arose the involute G. conglobatus [76] , the lofty-spired G. rubrus [77] , the deformed G. sacculiferus [78] and other basically similar species, most of which have persisted through the Tertiary into Recent faunas.

Orbuline genera

A spherical test covered by radiating spines is ideally suited to a micro-organism of planktonic habit. Many of the radiolaria are so constructed. In the mid-Tertiary spherical Globigerinidae appeared in which the main apertures were suppressed and a globular adult chamber almost completely enveloped the trochoid embryo. Orbulina universa and Candorbulina universa [79] (usually separated by systematists, though possibly synonymous) rapidly achieved world-wide distribution and have persisted unchanged from the Upper Oligocene to the Recent. A more complex genus (Globigerinatella) [80] with sinuous chamberlets covering the sutures appeared in the Caribbean region just before Orbulina but was short-lived, as was the similar Lower Miocene genus Globigerinita [81] . Still earlier, in the Upper Eocene, a species developed in which eleven or twelve chambers are visible externally, arranged in a regular trochoid manner but so shaped that they conform with the spherical contours of the test; this is Globigerina mexicana [82] , recorded from Mexico, the West Indies, Spain, Switzerland and the Middle East.

Nautiliform genera (Globigerinella, etc.)

Certain globigerinid species show development from a compressed trochoid initial stage to a bisymmetrical nautiloid coil of adult chambers. Species of this type appeared as early as the Lower Cretaceous (Globigerinella cushmani) [83] . In the Upper Cretaceous of Arkansas Biglobigerinella [84] is recorded, a genus in which the adult chambers tend to split into symmetrically placed pairs. The genus Globigerinelloides [85] is another Upper Cretaceous variant typified by semi-evolute coiling. In the Middle Eocene of Peru and Ecuador simple globose species of Globigerinella made a short-lived appearance. From late Oligocene to Recent G. aequilateralis [86] has been widely distributed. Lack of any records of nautiliform species in the Lower Eocene and Lower Oligocene suggests repeated evolution from trochoid stock rather than persistence of an unbroken line of them since the Cretaceous. On the basis of type figures Hastigerina [87] , Thomson 1876, may be a prior synonym of Globigerinella, Cushman 1927 [88] , but the possibility needs to be checked by a comparison of types.


This is a planktonic genus which may be considered a derivative from Globigerinella by elongation of the adult chambers into club-shaped and finger-shaped forms. This development started with some small Cretaceous species (H. subcretacea [89] , H. simplex [90] ) and gave rise to a group of Eocene species which are among the largest planktonic foraminifera. In Peru and Ecuador an evolutionary series of species runs through the Middle and Upper Eocene and Lower Oligocene but available data do not suffice to establish the regional scale of the evolutionary pattern. In washed residues specimens of Hastigerinella are usually found broken into individual chambers.


The basic form of this genus is a compressed nautiliform coil of four to six chambers, each of which is prolonged radially or carries a prominent radial spine. In the oldest species (subgenus Aragonella) the chambers are apiculate. These are followed by species (subgenus Applinella) in which a stout spine is present, centrally placed in the juvenile chambers but tending to move nearer the anterior suture in adult chambers. In the next youngest subgenus (Hantkenina s. s.) the spines are more distinct, no longer related to radial prolongation of the chambers, and are close to or enveloped by the anterior suture. End-forms are the subgenera Hantkeninella. which shows ontogenetic recapitulation of the Applinella-Hantkenina s. s. evolution, and Cribrohantkenina, an inflated form with a subglobular final chamber. The apertures of successive subgenera show evolutionary development from a simple arched slit through a tripartite slit with projecting lips to a complex aperture of large subcircular pores.

The rapid evolution of Hantkenina, its demonstrably planktonic mode of life, and its world-wide distribution make its subgenera valuable age-indicators. The oldest species are Lower Eocene and the youngest are Upper Eocene. [91] The abrupt extinction of the genus shortly after the appearance of the highly specialized forms H. bermudezi and H. supersuturalis suggests phylogerontism. [92] Records exist of the usually Upper Eocene H. alabamensis in the basal Oligocene of the Gulf Coast, but competent authorities have asserted that the specimens are allochthonous. [93]

Globorotaliidae (Globotruncana, Globorotalia, etc.)

This family appears to have developed from Globigerina by the appearance of two peripheral keels (Globotruncana). The primitive Globorotalias evolved from Globotruncana by suppression of one keel and they gave rise in their turn to more advanced forms, at first with an acute periphery but later with no relic of their keeled ancestry.

Globotruncana has been divided into an evolutionary sequence of species which in the successive stages of the Cretaceous show an increasingly lofty spire and the development of the double keel to maximum prominence in the lower Senonian, then reduction of this feature in the upper Senonian. No Danian species are known. [94]

The evolutionary pattern in Globorotalia is not so clear-cut, though several lines of development may be recognized and are partly segregated under the names Turborotalia, Truncorotalia [95] , Globorotalites, Rotalipora [96] , Thalmanninella [97] and Cribrogloborotalia [98] . During the long life-range of Globorotalia s. l. there has been an oscillation in the dominant type. Non-umbilicate, ventrally conical forms, for instance, are normal in Upper Eocene and Plio-Pleistocene faunas but seldom occur in Oligo-Miocene faunas. Tumid forms with an open pit between ventral projections of the chambers are characteristic of the late Cretaceous and Palaeocene. Species with a hispid, spinose or papillate shell do not appear in the post-Eocene faunas. [99]


In the Upper Cretaceous of many parts of the world species of the hetero-helicid genus Gümbelina are found in great numbers. Their mode of occurrence is the same as Globotruncana and the genus appears to have been planktonic in habit. [100]

The basic form of Gümbelina is a simple biserial set of globular chambers. Smooth simple forms persisted during the Lower and Middle Cretaceous but in the Santonian they began to show specialization. During the Campanian and Maestrichtian highly specialized forms became conspicuous, some possessing heavily striate or costate tests, others developing an angular, quadrate cross section. Still others, by the growth of additional adult chambers, led to the appearance of the multiserial genera Ventilabrella, Pseudotextularia and Planoglobulina. The specialized species and genera died out abruptly at the end of the Maestrichtian and in Danian and younger faunas only small, simple Gümbelinas are found, never in abundance. [101]


This genus is distinguished from other Globigerinidae by the non-cancellate, almost porcellanous, shell of its adult chambers. The chambers follow a quadrate coil, non-umbilicate and strongly inflated ventrally. The adult chambers tend to encroach successively farther over the flattened dorsal surface. Usually the genus is regarded as monotypic, based on P. obliquiloculata (Parker and Jones, 1865) but study of the literature [102] suggests that Globigerina inflata is synonymous and hence that the genotype should be designated P. inflata (d’Orbigny, 1839) [103] . It is a geologically young genus, first appearing in the late Miocene and persisting into present day faunas.


This is an involute development from Globigerina in which the later chambers envelop the earlier ones. Externally three chambers are usually visible in a trochoid coil so modified that the test has a smooth ovoid outline. The aperture is a broad slit corresponding to the umbilicus of Globigerina. The shell surface is cancellate in the juvenile stage but tends to become vitreous in mature individuals. The genus is found in Recent faunas and dates back to the Lower Miocene. [104]


Statistical analysis of microfaunas has found three main applications in micropalaeontology, viz.:

(1) Determination of palaeo-ecological status of fossil faunas by study of the frequency-ratios of species and genera.

(2) Study of statistical variations of fauna in relation to stratigraphic level.

(3) Checking the validity of species.

(1) Frequency-ratios of species and genera in relation to their environment

Analysis of Recent marine microfaunas has shown a definite variation in the dominance of different foraminiferal families in samples from different habitats. Tentative assumption that similar variations in fossil microfaunas implied similar facies-control resulted in plausible palaeogeographical reconstructions in accord with other evidence. Consequently the statistical approach has become a recognized means of palaeo-ecological determination.

The simplest method is to make a systematic analysis of a chosen micro-fauna and then to express the number of species per family as a percentage of the total number of foraminiferal species recorded. A comparison of the figures with those recorded among Recent faunas gives an indication of the depth and temperature favoured by such an assemblage.

The method above is simple but it gives a distorted impression of any fauna containing floods of certain facies-controlled species. In the Cipero marl of Trinidad, for instance, the Lagenidae provide one-fifth of the number of foraminiferal species and the Globigerinidae only one-twentieth, but by number of individual specimens the Lagenidae form less than one-thousandth of the fauna whereas the Globigerinidae form over nine-tenths. To allow for such factors it is desirable to make counts or computations from which the frequency-ratios of specimens, rather than species, per family may be assessed.

In a mixture of components of which the true mean proportions vary between 95 percent and .0001 percent of the whole it is difficult to obtain reliable figures for the minor ingredients on a basis of actual counts. If c samples are counted and P1, P2, P3,…Pc are the individual percentages recorded for a certain component, then the standard error of Pm, the arithmetic mean percentage, is:

If small samples are counted and Pm is low, then the probable error is too high to be acceptable. If large samples are counted the probable error is reduced but the process becomes very lengthy. The writer therefore prefers a simple system of computation in which the samples are analysed, each species is marked by a symbol as being scarce, common or abundant. Values of 1, 10 and 100 are ascribed to these symbols and the frequency ratios of different families are based on summation of the figures allotted to their species. Intermediate values such as ‘fairly common’ (5) and ‘almost abundant’ (50) may be introduced. The method is subjective but gives consistent results when applied by an experienced worker. It is advisable to check by some actual counts the ratios which correspond to one’s own personal assessment of the relative abundance of different species: modifications such as 1:4:8:40:100 or 1:6:20:100:150 may be found more accurate than the scale of 1:5:10:50:100 used as an example.

The probable environment of a fossil microfauna is determined by comparing its statistical composition with those of Recent assemblages (Lowman, Natland, Norton, Parker, Phleger, etc.; see bibliography). [105] A sequence of samples may be used to show a trend of changing facies.

(2) Statistical variations related to stratigraphical level

Gradual vertical changes in a fossil fauna may have been caused by a slow palaeo-ecological change or by evolutionary change of its components. An ecological cause may be demonstrable by detailed statistical analysis of a set of samples, as outlined in the foregoing section. A simpler method is to use the “oscillation chart” of Israelsky. [106] The basis of this approach is selection of a few microfossil species which are common in one but scarce in others of a series of intergradational facies-variants. Israelsky used a

Figure 9(A): Frequency ratios of selected ecologically restricted species.

well in Louisiana as an example and chose five groups of calcareous foraminifera as indices, including:

Group I (brackish water)

Rotaliabeccarii; Elphidium spp.

Group II (shallow marine)

Quinqueloculina spp.; Virgulinella spp.

Nonion scapha-group; Nonionella spp.

Buliminella curta; Reussella spinulosa

Group III (intermediate)

Discorbis spp.; Eponides antillarum

Cibicides concentricus

Group IV (intermediate)

Robulus spp.; Amphistegina lessoni

Cibicides carsteni

Group V (fairly deep marine)

Cancris sagra; Lagena spp.

Siphonina sp.; Casidulinidae

Gyroidina soldani-group

For analytical purposes a unit volume of sediment is taken from each of a set of equally spaced samples. After processing, the number of specimens of each index species in each sample is counted, all other species being ignored. The figures are totalled for each of the five groups, expressed as percentages and plotted against a depth scale.

Fig 9(A) (after Israelsky) gives the idealized form of an oscillation chart showing a point of maximum subsidence between two emergent phases. Fig. 6, used earlier to demonstrate cyclical repetition of facies in Trinidad, is another example. Use of these charts is clearly valid for correlation of dissimilar well sections by assuming that points of maximum subsidence or of corresponding cyclical position lie on a time-plane—see Fig. 9-B (also after Israelsky). They might also be applied to recognition of unconformities or faults in cases of faunal discontinuity, such as Group-I and Group-V faunas in contiguous layers.

Figure 9(B): Hypothetical dip-section showing the levels at which different faunules are dominant.

The heavy dashed line joins points of deepest facies in-.the wells and is valid for time correlation. The more obvious correlation along the oblique bands of uniform facies is not valid in a chronologic sense. (adapted after Israelsky 1949: American Association of Petroleum Geologists, Bulletin Bull., XXXIII, pp. 95, 98).

Frequency-ratios may be applied to the zonation of thick uniform sections. The Miocene Globigerina-marls of the Gulf of Suez are a case in point, only divisible into two somewhat arbitrary zones on the basis of species-ranges. Tromp has shown a trend of change in the frequency-ratios of different globigerinid genera, Globigerina becoming commoner while Globigerinella and Globigerinoides become scarce in the younger beds. [107] The figures are tabulated below:

Proportion per genus of total globigerinid fauna

                                     Lower                    Middle                    Upper                    Basal

                                   Miocene                 Miocene                 Miocene                 Pliocene

Globigerina                 43 ± 2%                75 ± 15%               80 ± 17%                  91%

Globigerinella              24 ± 5%                11 ±  9%                10 ± 8%                    1%

Globigerinoides          33 ± 7%                 15 ± 7%                 10 ± 5%                    7%

Orbulina                        <2%                      <2%                 mainly<2%                  1%

The method has been successfully applied in well correlations but its value in routine studies is offset by the laborious process of counting: Tromp mentions a count of 1,492,416 Globigerinidae in a single 100-gram sample.

The evolutionary change of a species may be discernible without recourse to detailed measurement. An example is the change from the thickset Bulimina jacksonensis to the slender B. sculptilis at the Eocene/Oligocene boundary in the Caribbean region. However, measurements of specimens from successively higher layers may reveal an almost imperceptible change in the mean form and thus provide a method of fine zonation. The diagram below shows the variations in length of Bolivina marginata and B. m. multicostata in successive zones of the Miocene of Florida. [108] Mean, minimum and

Length in millimeters

                            BOLIVINA MARGINATA                                                     BOLIVINA MARGINATA MULTICOSTATA

maximum lengths all show a tendency to reduce with decreasing age. (These particular data are open to criticism because of the small number of specimens counted and failure to separate microspheric and megalospheric individuals, but they serve for an example.)

Hofker has used a statistical approach to evolutionary subdivision of the family Globigerinidae. He states: “A very reliable and, within a given species, very constant character is the porosity of the test. Not only is the nature of the pores very constant within a given species but also, in a successive series, the pores are often much finer in the geologically older forms than in the more recent ones. In order to have a clear and accurate way of expressing the nature of the porosity in different species I have invented the ‘pore-index’. A drawing, as accurate as possible, is made of the surface of the test of some of the last-formed chambers, viewed in a clarifier (rhicinus oil) under a magnification of about 500x. A one-centimetre square opening is cut in a thick piece of paper, and this square is superimposed on the drawing at several places in order to obtain an average count of the pores found within this area. The average number of pores is recorded and their average diameter is added to the expression. The nature of the porosity is indicated in the following manner: 15-2, 500´. The first figure represents the average number of pores per sq. cm.; the second gives the average diameter of the pores in mm., both at a magnification of 500x.” [109] No comments by other students on the validity of Hofker’s pore-index have yet been noted, but it appears to offer a statistical basis for classification of the stratigraphically important but systematically difficult family Globigerinidae.

Bolli has shown a relationship between stratigraphical level and the ratio of dextrally coiled to sinistrally coiled individuals of certain foraminifera. [110] In general he notes that in the oldest assemblages the two forms are present in equal amounts, but each species tends to select either dextral or sinistral coiling so that in the younger assemblages only a few individuals differ from the rest. He also notes cases of abrupt change in the dominant direction of coiling, a curious phenomenon which, though difficult to explain, can be applied in zonal studies.

Carter, working on foraminiferal faunas in the English Pliocene, has shown that the bulk-distribution of foraminifera shows the same pattern of frequency-fluctuation as is shown by sieve-analysis statistics of the inorganic sediments. [111] The implication of this parallelism is that the bulk of the microfauna is exogenous. However, certain individual species of foraminifera show an independent frequency-pattern and these are presumed to be indigenous elements of the fauna. [112]

(3) Statistical checks on the validity of species

The concept of a fossil species dates back through the centuries to a time when fossils were regarded as individual curiosities, variously held to be relics of the Flood or the Creation or mere tricks of Nature. [113] As palaeontology became a systematic study the status of fossils as the remains of once-living organisms was established and eventually a belief in their evolutionary development became general. Nevertheless, fossil species continued to be defined in morphological terms and specimens were identified on a subjective basis of idiomorphy with designated types. [114]

Only in recent years has the subjective approach to speciation been challenged  The basis for the challenge is the zoological definition of a living species as an interbreeding natural population. A natural population is not a suite of living idiomorphs: the adult individuals vary in size and shape and the individuals of different growth-stages vary markedly in form. The human male gives a sufficient example, the height of adults varying about a mean of five to six feet between gerontic extremes near three and nine feet, while the head-to-body ratio of the infant is much higher than that of the adult. A population can be defined in statistical terms based on the mean dimensions and the degree of variability of the component parts of its individuals. Small samples may be compared statistically and the probability of their derivation from the same species (population) may be assessed objectively. The methods and formulas are those normal in the study of random samples, but care must be taken to study different growth-stages and sexual variants separately.

Figure 10: Species-concept diagrams

It is reasonable to claim that an objective definition of a fossil species is preferable to the subjective method of comparison of specimens but in practice certain difficulties arise. One is that it cannot be established that certain fossils were actually or potentially, interbreeding; another is that non-preservation, current sorting, palaeo-ecological factors or incomplete collecting may render statistical analysis of a collection non-representative of the original population. A more philosophical difficulty is that a species must be regarded as a unit in the stream of life. A population is a temporary cross-section of this continuum and the neo-zoologists are, in a sense, fortunate in having only one cross-section to consider. The problem of the palaeontologist is expressed graphically on Fig. 10 where populations of an evolving species are indicated at hemeras T1, T2, T3, etc., in geological time. The T1- and T8-populations are completely distinct and would be determined by subjective comparison as different palaeontological species, whereas the T4- and T5-groups scarcely differ. The basic problem is subdivision (classification) of a continuum into discrete portions: the process is unnatural but it is a human failing that tabulated facts and figures are more readily comprehensible and transmissible than abstruse and nebulous descriptions. All that need be stated here is that a quantitative statistical method is better justified than the usual qualitative subjective approach to the definition of fossil species.

The foregoing remarks apply to fossils in general. As applied to micro-fossils in particular, one point which stands out clearly is that this group is ideally suited to statistical analysis. Rich populations need no special search and it is a simple matter to obtain a sequence of them in known stratigraphical order. There are, however, very few papers extant in which a correct statistical approach has been made to speciation of microfossils. In classifying the Fusulinidae various dimensions and ratios have been used but multivariate analysis of the apparently different species Triticites collus and T. caccus has indicated that they do not differ significantly: this seems to imply over-fine splitting of species within the family. Study of ostracods has given statistical confirmation of the assumption that a discontinuous series of size variants represents successive moult-stages in a single species. Scatter diagrams have been used to show different species of a foraminiferal genus within a fauna (though the possibility of dimorphism does not appear to be eliminated in some of the examples seen). A detailed attempt was made to employ statistics in defining several species of Elphidium from Pacific Coast faunas, but the conclusions have since been declared invalid because of faulty mathematical technique. [115]

Negative evidence of the importance of statistical control of the designation of species lies in the over-elaborate subdivision of most foraminiferal genera. Nonion, for instance, is a simple nautiloid genus of which the species vary mainly in the ratio of maximum to minimum diameters, the ratio of axial thickness to mean diameter, the number of chambers and the bluntness of sharpness of the periphery. If the species of Nonion are treated as mere geometrical variations about a mean form some fifty forms may be visualized, but at least a hundred and fifty have been described in the literature. Similarly with Quinqueloculina a generous estimate of eighty variants can be visualized, based on length-to-breadth ratio, cross-sectional outline and size, but some two hundred smooth species have been described: as late as in 1949 seven species were described as new from a single Eocene fauna in Louisiana. [116]

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In this section references to the literature are given in an order corresponding to the arrangement of the preceding text. [Ed: In this text digitized in 2003, notes below relate to endnote numbers in the text. The original, typewritten text provided only page references in the bibliography. We have retained relevant notes and made reference to particular text; any inaccuracy is ours. Please inform us.] The list is not exhaustive but it includes the source-references of specific points cited and representative general references many of which include bibliographies. Most of the papers cited are American, a fact partly due to the writer’s limited library facilities in Peru but nevertheless indicative of the great volume of micropalaeontological literature sponsored, directly or indirectly, by the American oil industry.

     Ref: no objection to use, Wallie Rasmussen, Exxon-Mobil legal department, 23 Nov 2002.

[1]      R. D. Reed, American Association of Petroleum Geologists, Bulletin vol. 15, pp. 731-754. 1931.
C. Croneis, American Association of Petroleum Geologists, Bulletin vol. 25, pp. 1219-1225. 1941.

[2]      1928: J. J. Galloway, Journal of Paleontology vol. 2, pp. 225-227.
1932: F. Lahee, Geological Society of America, Bulletin vol. 43, p. 960.
1933: R. S. Bassler, Geological Society of America, Bulletin, vol. 44, pp. 269, 279, 284.
1938: J. A. Cushman, Geological Society of America, Bulletin vol. 49, pp. 363-365.
1941: C. Croneis, American Association of Petroleum Geologists, Bulletin vol. 25, pp. 1243-1250.
1946: J. R. Sandidge, American Association of Petroleum Geologists, Bulletin vol. 30, pp. 1088-1094.
1946: C. Stock, Geological Society of America, Bulletin vol. 57, pp. 320-322.
1947: H. V. Howe, American Association of Petroleum Geologists, Bulletin vol. 31, pp. 713-730.

[3]      H. E. Minor and M. A. Hanna in “Stratigraphic type oilfields”, published by American Association of Petroleum Geologists, 1941. pp. 600-640.

[4]      H. G. Schenck and B. C. Adams, Journal of Paleontology vol. 17, pp. 554-5. 1943.
M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, pp. 35-51, 1945.
L. W. LeRoy and H. M. Crain, “Subsurface Geologic Methods” by L. W. LeRoy and H. M. Grain, Colorado School of Mines, 1st Edition.,  pp. 85, 86, 1949.

[5]      F. H. Lahee, “Field Geology”, 4th ed., chapter 14. McGraw-Hill Co., Inc., New York. 1941.

[6]      L. W. LeRoy and H. M. Crain, “Subsurface Geologic Methods” by L. W. LeRoy and H. M. Grain, Colorado School of Mines, 1st Edition.,  pp. 296-298. 1949

[7]      W. Wetzel, Erdöl und Kohle, vol. 3, no. 5, pp. 212-214. Hamburg; 1950.

[8]      K. Zittel, ed. C. R. Eastman, “Text-book of Palaeontology”, Macmillan & Co., London 1927.
M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, pp. 8-31. 1945.
L. W. LeRoy and H. M. Grain, “Subsurface Geologic Methods” by L. W. LeRoy and H. M. Grain, Colorado School of Mines, 1st Edition.,  pp. 58-84, 1949.

[9]      Calcareous algae:
J. H. Johnson, Journal of Paleontology vol. 19, pp. 350-354. 1945.
G. Colom, Sociedad Española de Historia Natural, Boletín, tomo 34, pp. 379-388. Madrid, 1934.
R. E. Peck, Journal of Paleontology vol. 8, pp. 83-119: 1934.
J. A. Cushman, “Foraminifera: their classification and economic use”, 4th ed., Harvard University Press, 1948.
B. F. Ellis and A. R. Messina, “Catalogue of Foraminifera”, American Museum of Natural History, New York 1940
et seq.
J. J. Galloway, “A manual of foraminifera”, Bloomington, Ind., 1933.
M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, pp. 55-93. 1945.
Megafossil fragments:
H. L. Geis, Journal of Paleontology vol. 10, pp. 427-448. 1936.
J. S. Smiser, Journal of Paleontology vol. 5, pp. 293-295. 1931.
                        Journal of Paleontology vol. 7, pp. 123-163. 1933.
C. L. Cooper, Journal of Paleontology vol. 16, pp. 764-776. 1942.
R. B. Campbell, Journal of Paleontology vol. 3, pp. 254-279. 1929.
E. Aberdeen, Journal of Paleontology vol. 14, pp. 127-139. 1940.

[10]     An example is the presumed appearance of Indian Ocean elements in a microfauna of Mediterranean stock in the Pliocene of Egypt. See R. M. Stainforth, Journal of Paleontology vol. 23, pp. 420,421. 1949.

[11]     G. Rittenhouse, Geological Society of America, Bulletin vol. 54, pp. 1725-1780. 1943.

[12]     Orbitoidal foraminifera:
J. J. Galloway, Journal of Paleontology vol. 2, pp. 45-69, 1928.
(This paper is at fault in not making due allowance for known age-ranges. For example the Cretaceous
Lepidorbitoides and Pseudorbitoides are classed as descendents of the Eocene Helicolepidina.)
R. W. Barker anti T. F. Grimsdale, Journal of Paleontology vol. 10, pp. 231-247. 1936.
W. á Wengen, Hendelingen van het vierde Nederlandsch-Indisch Natuurwetenschappelijk Congres, pp. 448-466. Java, 1926.
Bulimina spp.
B. C. Adams, 6th Pacific Science Congress, Proceedings vol. 2, pp. 665-670. University of California Press, 1940.
Planktonic foraminifera:
See under Section V below. [
Ed: notes 67 et seq.]

[13]     C. S. Piggott and W. D. Urry, Geological Society of America, Bulletin vol. 53, pp. 1187-1210. 1942.

[14]     Symposium, International Geological Congress, Report of 18th Session, part 12. London, 1950.

[15]     F. G. Snyder and H. E. Wheeler, Journal of Geology vol. 55, pp. 146-159. 1947.
M. Gignoux, “Géologie stratigraphique”, pp. 25, 502, 530. Masson et Cie., Paris, 1950.
A. A. Olsson, Bulletins of American Paleontology, vol. 17, no. 62, p. 11 etc. 1930.
(Olsson wrongly correlates the basal Talara unconformity—Middle Eocene—of the taphrogenic province of western Peru with the Jacksonian transgression—Upper Eocene—of the Andean geosyncline.)

[16]     P. H. Kuenen, “Marine Geology”, pp. 532-551. Wiley & Sons, New York, 1950.

[17]     R. M. Kleinpell, “Miocene Stratigraphy of California”, p. 98. Published by Amer. Ass. Petr. Geol., 1938

[18]     W. J. Arkell, “The Jurassic system in Great Britain”. Oxford University Press, 1933.

[19]     A. M. Davies, “Tertiary faunas”, vol. 2, p. 159. Murby &c Sons, London, 1934.

[20]     H. G. Schenck, American Association of Petroleum Geologists, Bulletin vol. 19, p. 529. 1935.

[21]     H. D. Hedberg, Geological Society of America, Bulletin vol. 48, p. 1976. 1937.
(A pertinent statement, too lengthy to quote in full, is made by M. Kay, American Association of Petroleum Geologists, Bulletin vol. 31, pp. 163-166. 1946.)

[22]     1912. C. J. Maury, Acad. Nat. Sci. Philadelphia, Jour. vol. 15, pp. 28-31.
1928. R. A. Liddle, “The geology of Venezuela and Trinidad”, pp. 223-225. Fort Worth, Texas.
1929. C. J. Maury, Journal of Geology vol. 37, p. 177.
1934. H. W. Shimer, Geological Society of America, Bulletin vol. 35, p. 909.
1935. C. J. Maury, Science, vol. 82, no. 2122, p. 192.
1935. C. Schuchert, “Historical geology of the Antillean-Caribbean region”, p. 701. Wiley & Sons, New York
1938. H. G. Kugler, Ministerio de Fomento, Boletín de geología y minería, tomo 2, nos. 2-4, English ed., pp. 204-224. Caracas, Venezuela.

[23]     C. Schuchert, 1935, as above.

[24]     F. A. Schilder, Schweizerischen Päleontologischen Gesellschaft, Abhandlungen, Band 62. 1939.
(An attempt to recognize evolutionary trends in the cypraeid molluscs, at fault due to earlier confusion of Oligocene and Miocene limestones in Trinidad.)

[25]     W. P. Woodring and T. F. Thompson, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 223-247. 1949.

[26]     J. E. Eaton, American Association of Petroleum Geologists, Bulletin vol. 15, pp. 367-384. 1931.

[27]     Symposium, Journal of Paleontology vol. 23, pp. 145-160. 1933.

[28]     J. B. Dorr, Journal of Paleontology vol. 7, pp. 432-438. 1949.
E. S. Franklin, Journal of Paleontology vol. 18, pp. 301-319. 1944.
(For comments on these papers see H. H. Renz, Geological Society of America, Memoir 32, pp. 86, 87, 1948 and R. M. Stainforth, Journal of Paleontology vol. 22, pp. 144, 145. 1948.)

[29]     J. M. Weller et al. Journal of Paleontology vol. 21, pp. 570-575. 1947.
                        vol. 22, pp. 264-269. 1948.
                        vol. 23, pp. 677-679. 1949.

[30]     I. H. Cram, American Association of Petroleum Geologists, Bulletin vol. 29, p. 861. 1945.

[31]     A. M. Davies, “Tertiary faunas”, vol. 2, map (frontispiece) and chapter 1. Murby & Sons, London, 1934
Symposium, “Sedimentary facies in geologic history”, Geological Society of America, Memoir 39. 1949.
L. W. LeRoy and H. M. Crain, “Subsurface Geologic Methods” by L. W. LeRoy and H. M. Grain, Colorado School of Mines, 1st Edition., pp. 28-40. 1949.
W. H. Twenhofel, Journal of Paleontology vol. 8, pp. 456-468. 1934.
T. L. Bailey, Geological Society of America, Bulletin vol. 46, pp. 489-502. 1935.
R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, pp. 1313-1318. 1948.
A. C. Ellisor, American Association of Petroleum Geologists, Bulletin vol. 24,. pp. 435-475. 1940.
S. W. Lowman, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 1944-1947. 1949.

[32]     H. C. Urey et al., Geological Society of America, Bulletin vol. 62, pp. 399-416. 1951.

[33]     “Albatross” (U. S. A.)
J. M. Flint, U. S. National Museum, Report for 1897, pp. 249-349. 1899.
J. A. Cushman, idem, Bulletin 161, parts 1-3. 1942.

       “Challenger” (Great Britain)
Report on the scientific results of the voyage of H. M. S. “Challenger” during the years 1873-76. H. M. Stationery Office, London, 1884.
(separate volumes for each phylum)

       “Meteor” (Germany)
Deutschen Atlantischen Expedition aud dem Forsungs- und Vermessungsschiff “Meteor”, 1925-27; Wissenschaftliche Ergebnisse. Berlin and Leipzig.

[34]     Belgium:
J. A. Cushman, Institut Royal des Sciences Naturelles de Belgique, Mémoire 111. 1949.
E. Heron-Allen and A. Earland, Royal Microscopical Society, Journal for 1911, pp. 436-448. 1911.
(a summary of several earlier papers)
E. Heron-Allen and A. Earland, Linnéan Society, Transactions, 2nd series. Zoology, vol. 2, part 13, pp. 197-300. 1916.
North Atlantic:
F. B. Phleger, Geological Society of America, Bulletin vol. 50, pp. 1395-1422. 1939
                        Geological Society of America, Bulletin vol. 53, pp. 1073-1098. 1942
West Atlantic:
F L Parker, Museum of Comparative Zoology, Bulletin, vol. 100, no. 2, pp. 213-241. Cambridge, Mass., 1948.
Antillean-Caribbean region:
R. D. Norton, Scripps Institute of Oceanography Bulletin, Technical series, vol.  2, no. 9. 1930.
S. W. Lowman, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 1950-1963. 1949.
P. J. Bermudez, Sociedad Cubana de Historia Natural, Memorias, vol. 19, no. 3. 1949.
P. Bronnimann, Naturforschungs Gesellschaft, Verhandlungen. Band 60, pp. 180-185. Basel, 1949.
East Pacific:
M. L. Natland, Scripps Institute of Oceanography, Bulletin, technical series, vol. 3, no. 10. 1933.
J. A. Cushman,
op. cit., vol. 1, no. 10. 1927.
North Pacific:
J A. Cushman, U. S. National Museum, Bulletin 71, parts 1-6. 1910-1917.
F. W. Millett, Royal Microscopical Society, Journal, numerous short papers. 1898-1904.
W. J. Parr, Royal Society of Victoria, Proceedings, vol. 44, pp. 1-14, 218-234. Melbourne, 1932.
East Africa:
E. Heron-Allen and A. Earland, Zoological Society, Transactions, vol. 20, part 12, pp. 363-383; part 17, pp. 543-794. London, 1914-1915.
Mediterranean Sea:
H. Sidebottom, Manchester Literary and Philosophical Society, Memoirs and Proceedings, vols. 48-54, many short papers. 1904-1910.
South Atlantic:
E. Heron-Allen and A. Earland, Royal Microscopical Society, Journal, series 3, vol. 49, pp. 102-108, 324-334; vol. 50, pp. 38-45; vol. 52, pp. 253-261. London, 1929-1932.
F. Chapman, W. J. Parr, et al, Australasian Antarctic Expedition 1911-1914, Scientific Reports, Series C, Zoology and Botany. Sydney 1937.
W. J. Parr, B. A. N. Z. Antarctic Research Expedition, 1929-1931: Reports, series B, vol. 5, pt. 6, pp. 233-392. 1950.
Brackish-water provinces:
H. D. Hedberg, Journal of Paleontology vol. 8, pp. 469-476, 1934.
H. Hiltermann, Erdöl und Kohle, vol. 2, pp. 4-8. Hamburg, 1949.

[35]     F. B. Phleger and W. A. Hamilton, Geological Society of America, Bulletin, vol. 57, pp. 961-963. 1946.
E. S. Deevey, American Journal of Science, vol. 237, pp. 691-724. 1939.
L. L. Ray, Geological Society of America, Bulletin vol. 51, pp. 1851-1918. 1940.

[36]     [Ed: see also general references given under notes 8 and 9.] W. G. Woolnough, American Association of Petroleum Geologists, Bulletin vol. 26, pp. 765-792. 1942.
D. Andrusov, Práce Státneho Geologického Ustavu sosit 25, pp. 132-135. Bratislava, 1950.

[37]     [Ed: see also general references given under notes 8 and 9.] H. B. Ward and G. C. Whipple, “Fresh-water biology” , chapter 24, Wiley &: Sons, New-York, 1945.

[38]     [Ed: see also general references given under notes 8 and 9.] H. D. Hedberg, Journal of Paleontology vol. 8, pp. 469-476. 1934.

[39]     [Ed: see also general references given under notes 8 and 9.] P. J. Bermudez, Sociedad Cubana de Historia Natural, Memorias, vol. 19, no. 3, p. 315. 1950.

[40]     [Ed: see also general references given under notes 8 and 9.] H. H. Renz, 8th American Scientific Congress, Proceedings, Geological Sciences, General geology, pp. 528, 529. University of California Press, 1942.
H D Hedberg and A. Pyre, American Association of Petroleum Geologists, Bulletin vol. 28, pp. 20-24. 1944.
D. L. Frizzell, Journal of Paleontology vol. 17, pp. 331-353. 1943.
T. Lipparini, Servicio Geologico d’ltalia, Bolletino, vol. 71 (1947, ‘48 & ‘49), nota 11, pp. 5, 6. Rome, 1951.
R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, pp. 1308, 1317. 1948.
R. Grill, 18th International Geological Congress, Report, part 15, pp. 51 (abstract), 59. London, 1950.

[41]     [Ed: see also general references given under notes 8 and 9.] S. W. Lowman, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 1950-1963. 1949.

[42]     [Ed: see also general references given under notes 8 and 9.] J. A. Cushman and P. Bronnimann, Cushman Laboratory for Foraminiferal Research, Contributions vol. 24, pp. 15-21; 37-42. 1948.

[43]     [Ed: see also general references given under notes 8 and 9.] G. W. Crickmay, H. S. Ladd and J. E. Hoffmeister, Geological Society of America, Bulletin vol. 52, pp. 79-106. 1941.

[44]     [Ed: see also general references given under notes 8 and 9.] M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, pp. 193, 194. 1945.

[45]     [Ed: see also general references given under notes 8 and 9.] F. B. Phleger, Geological Society of America, Bulletin vol. 50, pp. 1395-142Z. 1939.
                        Geological Society of America, Bulletin vol. 52, pp. 1073-1098. 1942.
F. B. Phleger and W. A. Hamilton, Geological Society of America, Bulletin vol. 57, pp. 951-966. 1946.

[46]     [Ed: see also general references given under notes 8 and 9.] Symposium, Journal of Paleontology vol. 18, pp. 51-70. 1944.

[47]     [Ed: see also general references given under notes 8 and 9.] M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, p. 193. 1945.
P. Bronnimann, Journal of Paleontology vol. 24, p. 397. 1950.

[48]     [Ed: see also general references given under notes 8 and 9.] M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, p. 185. 1945.

[49]     Examples of palaeo-ecological reconstruction
A. Examples not based primarily on microfossils:
Diatomites and fish-beds, Algeria:
R. V. Anderson, Journal of Geology vol. 41, pp. 673-698. 1933.
Pennsylvanian of Missouri
W. F. Bailey, Journal of Paleontology vol. 9, pp. 482-602. 1935.
Gulf Coast Tertiary:
M. Bornhauser, American Association of Petroleum Geologists, Bulletin vol. 31, pp. 698-712. 1947.
The Permian:
C.C. Dunbar, Geological Society of America, Bulletin vol. 52, pp. 313-332. 1941.
Miocene of California:
J E Eaton, U. S. Grant and H. B. Allen, American Association of Petroleum Geologists, Bulletin vol. 25, pp. 193-262. 1941.
Silurian reef, Illinois:
H. A. Lowenstam, “Structure of typical American ‘ Oilfields”, pp. 153-158. Published by Amer. Ass. Petr. Geol., 1948.
Gulf Coast Tertiary:
W. G. Meyer, American Association of Petroleum Geologists, Bulletin vol. 23, pp. 197-209. 1939.
Permian of Arizona:
D. Nicol. Journal of Paleontology vol. 18, pp. 553-557. 1944.
Crinoidal limestone:
T. G. Payne, American Association of Petroleum Geologists, Bulletin vol. 26, pp. 1697-1770. 1942.
Cretaceous ammonites:
G. Scott, Journal of Paleontology vol. 14, pp. 299-323. 1940.
L. W. Stach, Journal of Geology vol. 44, pp. 60-65. 1936.
East Indies:
J. F. H. Umbgrove, American Association of Petroleum Geologists, Bulletin vol. 22, pp. 1-78. 1938.
Barred basins, pseudabyssal sediments:
W G Woolnough, American Association of Petroleum Geologists, Bulletin vol. 21, pp. 1101-1157. 1937.
                        American Association of Petroleum Geologists, Bulletin vol. 26, pp. 765-792. 1942.
Series: “Report of the committee on marine ecology Issued annually by the National Research Council, Washington, D. C., 1941-1951.
Symposium, Journal of Paleontology vol. 9, pp. 63-81 92-147,72-283. 1935.
H. G. Schenck, Journal of Paleontology vol. 2 pp. 158-165 1928.
T. W. Vaughan, Geological Society of America, Bulletin vol. 51, pp. 433-4o8. 1940.
B. Examples based on microfaunas:
Liassic foraminifera, England:
T. Barnard, 18th International Geological Congress, Report, part 15, pp. 39-41. London, 1950.
Eocene foraminifera, Washington State:
R. S. Beck, Journal of Paleontology vol. 17, pp. 584-614. 1943.
Fossil pollen:
W. S. Cooper, Journal of Geology vol. 50, pp. 981-994. 1942.
Submarine Tertiary off New England:
J. A. Cushman, Geological Society of America, Bulletin vol. 47, pp. 413-440. 1936.
Orbitoidal foraminifera, India:
L. M. Davies, 6th Pacific Science Congress, Proceedings, vol. 2, pp. 483-501. University of California Press, 1940.
Oligo-Miocene foraminifera, California:
R. M. Kleinpell, “Miocene stratigraphy of California”, pp. 11-19, 79-87. Published by Amer. Ass. Petr. Geol., 1938.
Tertiary and Recent microfaunas, Gulf Coast:
S. W. Lowman, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 1971-1983. 1949.
Tertiary foraminifera, Washington State:
W. W. Rau, Journal of Paleontology vol. 22, pp. 153-155. 1948.
Oligo-Miocene foraminifera, Venezuela:
H. H. Renz, Geological Society of America, Memoir 32, p. 40 et seq. 1948.
Tertiary microfaunas, Barbados:
A. Senn, Eclogae Geologicae Helveticae, vol. 40, pp. 200-222. 1948.
Tertiary microfaunas of Ecuador:
R. M. Stainforth, Journal of Paleontology vol. 22, pp. 135-139. 1948.
Radiolarites, Turkey:
S. W. Tromp, Journal of Geology vol. 56, pp. 492-494. 1948.
Gault foraminifera, England:
M. H. Khan, Geological Magazine, vol. 87, pp. 175-180, London, 1950.
(NOTE: additional references in which a quantitative approach is used are given under section VI below.
[Ed: see notes 105 et seq.])

[50]     A. Senn, Eclogae Geologicae Helveticae, vol. 40, no. 2, pp. 199-222. 1948.

[51]     H. H. Hess, American Philosophical Society, Proceedings, vol. 79. 1938.
J. L. Rich, Geological Society of America, Bulletin vol. 62, pp. 1193-1196. 1951.

[52]     C. C. Wilson, American Association of Petroleum Geologists, Bulletin vol. 24, pp. 2102-2125. 1940.

[53]     L. W. LeRoy and H. M. Crain, “Subsurface Geologic Methods” by L. W. LeRoy and H. M. Grain, Colorado School of Mines, 1st Edition., pp. 595-681. 1949.
T. H. Bower, American Association of Petroleum Geologists, Bulletin vol. 31, pp. 340-349. 1947.
T. B. Haites. idem, pp. 777-778.
Representative examples of serial maps are to be found in Schuchert’s well-known treatises, Weeks’ “Palaeogeography of South America” (American Association of Petroleum Geologists, Bulletin, vol. 31, pp. 1194-1229) and other readily accessible papers.

[54]     1860 G. P. Wall and J. G. Sawkins, “Report on the geology of Trinidad”, H. M. Stationery Office, London.
1866-99 R. J. L. Guppy, Quart. Jour. Geol. Soc., vol. 22, pp. 570-590; vol. 48, pp. 519-541, and other papers, many of them first printed in ephemeral local publications but later reprinted by G. D. Harris in Bulletins of American Paleontology, vol. 8, no. 35. 1921.
1928 V. C. Illing, Quart. Jour. Geol. Soc., vol. 84, pp. 1-56.
1928 R. A. Liddle, “The geology of Venezuela and Trinidad”. Fort Worth, Texas.
1935 E. Lehner, Annales de l’Office Nationale des Combustibles Liquides, no. 4, pp. 691-730. Paris.
1936 H. G. Kugler, American Association of Petroleum Geologists, Bulletin vol. 20, pp. 1439-1453.
1942 H. H. Renz, 8th American Science Congress, Proceedings, vol. 4, p. 540 et seq. University of California Press
1948 R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, pp. 1306-1308, 1313-1319.

[55]     Renz 1942 and Stainforth 1948 as above.
J. A. Cushman and R. M. Stainforth, Cushman Laboratory for Foraminiferal Research, Special Papers 14, pp. 3-12.
J. A. Cushman and H. H. Renz, Cushman Laboratory for Foraminiferal Research, Special Papers 22, pp. 1-3. 1947.
P. Bronnimann, Cushman Foundation for Foraminiferal Research, Contributions vol. 1, pp. 80-82, 1950; vol. 2, pp. 16-18, 1951
                        Journal of Paleontology vol. 24, pp. 397-420. 1950.
H. Bolli, Cushman Foundation for Foraminiferal Research, Contributions vol. 1, pp. 82-89. 1950.

[56]     R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, pp. 1319-13Z7. 1948.

[57]     Stainforth 1948, as above, pp. 1318-1319.

[58]     R. M. Stainforth, Journal of Paleontology vol. 22, pp. 140-144. 1948.

[59]     H. R. Wanless and F. P. Shepard, Geological Society of America, Bulletin vol. 47, pp. 1177-1206. 1936. (Includes an extensive bibliography on cyclical sedimentation.)

[60]     C. C. Wilson, American Association of Petroleum Geologists, Bulletin vol. 24, pp. 2115-2121, etc. 1940.
R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, p. 1319. 1948.

[61]     B. Stone, Cushman Foundation for Foraminiferal Research, Contributions, ? 1952 (in press).

[62]     D. L. Frizzell, Journal of Paleontology vol. 17, pp. 331-353. 1943.

[63]     R. M. Stainforth, Journal of Paleontology vol. 23, pp. 420, 421. 1949.

[64]     Symposium (including Henson 1950 as below), American Association of Petroleum Geologists, Bulletin vol. 34, pp. 181-312. 1950.
“Bibliography of organic reefs, bioherms and biostromes”, issued gratis by the Seismograph Service Corporation, Tulsa, Okla., 1950.

[65]     F. R. S. Henson, American Association of Petroleum Geologists, Bulletin vol. 34, pp. 215-238. 1950.

[66]     T. F. Grimsdale, Third World Petroleum Congress, Proceedings, vol. 1. Leyden, 1951.
R. M. Stainforth Journal of Paleontology vol. 22, pp. 114-125. 1948.
L. W. LeRoy, Journal of Paleontology vol. 22, pp. 500, 501. 1948.

[67]     Globigerina
G. canariensis
A. d’Orbigny in “Histoire Naturelle des Iles Canaries by P Barker-Webb and S. Bérthelot, tome 2, part 2, p. 133, pl. 2, figs. 10-12. Paris, 1839.
G. venezuelana
D. Hedberg, Journal of Paleontology vol. 11, p. 681, pl. 92, fig. 7. 1937.
G. altispira
J. A. Cushman and P. W. Jarvis, Cushman Laboratory for Foraminiferal Research, Contributions, vol. 12, p. 5, pl. 1, figs. 13, 14. 1936.
G. triloculinoides
H. J. Plummer, Texas Univ. Bulletin, Bureau of Economic Geology, no. 2644, p. 134, pl. 8, fig. 10. 1926.
G. cretacea var. eggeri
E. Heron-Allen and A. Earland, British Antarctic (“Terra Nova”) Expedition 1910, Natural History Report, Zoology, vol. 6, no. 2, p. 188, pl. 7, figs. 6-8. British Museum (N. H.), 1922.
(this name is an invalid synonym of
G. eggeri Rhumbler)
G. compressa
H J. Plummer, as for G. triloculinoides above, p. 135, pl. 8, fig. 11. 1926.
G. concinna
A. E. Reuss, Kaiserlichen Akadamie der Wissenschaften, Mathematisch-Naturwissenschaftliche Classe, Denkschriften, Bd. 1, p. 373, pl. 47, fig. 8. Vienna, 1850.
G. bradyi
H Wiesner in E. von Drygalski, Deutsche Süd-Polar Expedition, 1901-1903, Bd. 20, p. 133. Berlin and Leipzig, 1931.
G. dissimilis
J A. Cushman and P. J. Bermudez, Cushman Laboratory for Foraminiferal Research, Contributions vol. 13, p. 25, pl. 3, figs. 4-6, 1937.
G. fistulosa
R J Schubert, Geologische Reichsanst., Verhandlungen, p. 323, tf. 2, p. 324. Vienna, 1910.
G. digitata
H. B. Brady, Quarterly Journal of Microscopical Science, vol. 19 (n. s.), p. 286. London, 1879.

[68]     J. Hofker, The Micropaleontologist, vol. 4, pp. 16, 17, American Museum of Natural History, 1950.

[69]     B. H. Harlton, Journal of Paleontology vol. 1, p. 24, pl. 5, fig. 7. 1927.

[70]     A. de Gregorio, Annales Géologiques de le Paléontologie, livre 52, p. 48, pl. 20, figs. 1, 2. Palermo, 1930.

[71]     O. Terquem, “Cinquiéme mémoire sur les foraminifères du systéme Oölithique de la zone á Ammonites parkinsoni de Fontoy (Moselle)” p. 364, pl. 41, figs. 6-9. Metz, France, 1883.

[72]     M. P. White, Journal of Paleontology vol. 2, p. 194, pl. 27, fig. 16. 1928.

[73]     J. A. Cushman, Cushman Laboratory for Foraminiferal Research, Contributions vol. 3, p. 87. 1927.

[74]     L. W. LeRoy, Journal of Paleontology vol. 22, pp. 500-508. 1948.

[75]     A. E. Reuss, Kaiserliche Akademie der Wissenschaften, Mathematisch-Naturgewissenschaftliche Classe, Denkschriften, Bd. 1, p. 374, pl. 47, fig. 11. Vienna, 1850.

[76]     H. B. Brady, Quarterly Journal of Microscopical Science, vol. 19 (n. s.), p. 286. London, 1879.

[77]     A. d’Orbigny, in Ramon de la Sagra, “Histoire physique et naturelle de l’Ile de Cuba” p. 82, pl. 4, figs. 12-14. Paris, 1839.

[78]     H. B. Brady, The Geological Magazine, vol. 4 (n. s.), decade 2, p. 535. London, 1877.

[79]     J. A. Cushman and A. L. Dorsey, Cushman Laboratory for Foraminiferal Research, Contributions vol. 16, pp. 40-42. 1940.
L. W. LeRoy, Journal of Paleontology vol. 22, pp. 500-508. 1948.

[80]     J. A. Cushman and R. M. Stainforth, Cushman Laboratory for Foraminiferal Research, Special Papers 14, pp. 68, 69, pl. 13, figs. 7-9. 1945.
P. Bronnimann, CFC vol. 1, pp. 80-82. 1950.

[81]     P. Bronnimann, CFC vol. 2, pp. 16-18. 1951.

[82]     J. A. Cushman, Cushman Laboratory for Foraminiferal Research, Contributions vol. 1, p. 6, pl. 1, fig. 8. 1925.
T. F. Grimsdale, Third World Petroleum Congress, Proceedings, vol. 1. Leyden, 1951.
M. R. de Gaona and G. Colom, Estudios Geologicos, no. 12, p. 379, etc., Instituto de Investigaciones Geologicos “Lucas Mallada”, Madrid, 1950.
P. J. Bermudez, Cushman Laboratory for Foraminiferal Research, Special Papers 25, p. 279. 1949.
H. Bolli, Eclogae Geologicae Helveticae, vol. 43, no. 2, p. 113, 1951.

[83]     H. Tappan, Journal of Paleontology vol. 17, p. 513, pl. 83, fig. 5, 1943.

[84]     C. G. Lalicker, Journal of Paleontology vol. 22, p. 624, pl. 92, figs. 1-3. 1948.

[85]     J. A. Cushman and A. ten Dam, Cushman Laboratory for Foraminiferal Research, Contributions vol. 24, p. 42, pl. 8, figs. 4-6. 1948.

[86]     H. B. Brady, Quarterly Journal of Microscopical Science, vol. 19 (n. s.), p. 285, London, 1879.

[87]     W. Thomson (in J. Murray), Royal Society, Proceedings, vol. 24, p. 534. London, 1876.

[88]     J. A. Cushman, Cushman Laboratory for Foraminiferal Research, Contributions vol. 3, p. 87. 1927.

[89]     H. Tappan, Journal of Paleontology vol. 17, p. 513, pl. 83, fig. 4. 1943.

[90]     A. L. Morrow, Journal of Paleontology vol. 8, p. 198, pl. 30, fig. 6. 1934.

[91]     H. E. Thalmann, Eclogae Geologicae Helveticae, vol. 25, pp. 287-292. 1932
Stanford University Publications, University series, geological science, vol. 3, no. 1, pp. 1-24. 1942.
American Journal of Science, vol. 240, pp. 802-820. 1942.
Geological Society of America, Bulletin vol. 57, pp. 1236, 1237. 1946.
P. Bronnimann, Journal of Paleontology vol. 24, pp. 397-420. 1950.
T. F. Grimsdale, Annals and Magazine of Natural History, ser. 12, vol. 4, pp. 292-294. 1951.

[92]     P. Bronnimann, as above.

[93]     H. alabamensis, disputed records in the basal Oligocene:
H. V. Howe, Journal of Paleontology vol. 2, pp. 173-176. 1928.
B. Stone, Journal of Paleontology vol. 23, p. 157. 1949.

[94]     O. Renz, Eclogae Geologicae Helveticae, vol. 29, pp. 1-149. 1936.
H. Bolli, Journal of Paleontology vol. 25, pp. 187-199. 1951.

[95]     Globorotalia s. s.; Turborotalia; Truncorotalia
J. A. Cushman and P. J. Bermudez, Cushman Laboratory for Foraminiferal Research, Contributions vol. 25, pp. 26-45, pl. 5-8. 1949.

[96]     F. Brotzen, Sveriges Geologiska Undersökning, Avhandlingar, ser. C. no. 451 (årsb. 36, no. 8), pp. 31, 32. Stockholm, 1942.

[97]     J. Sigal, Institut Français de Pétrole, Revue, vol. 3, No. 4, p. 101. Paris, 1948.

[98]     J. A. Cushman and P. J. Bermudez, Cushman Laboratory for Foraminiferal Research, Contributions vol. 12, p. 36. 1936

[99]     Critique of the subgenera: T. F. Grimsdale, Third World Petroleum Congress, proceedings, vol. 1, Leyden, 1951.

[100]    M. F. Glaessner, “Principles of Micropalaeontology” by M. F. Glaessner, Melbourne University Press, p. 193, 1945.

[101]    N. L. Thomas and E. M. Rice, Journal of Paleontology vol. 1, pp. 141-144. 1927.
J. A. Cushman, U. S. Geological Survey, Professional Paper 206, pp. 12, 103-109, pl. 44-46. 1946.

[102]    J. A. Cushman, Cushman Laboratory for Foraminiferal Research, Contributions vol. 3, p. 90. 1927.

[103]    A. d’Orbigny in “Histoire Naturelle des Iles Canaries” by P Barker-Webb and S. Bérthelot, tome 2, pt. 2, Zoology, p. 134, pl. 2, figs. 7-9. Paris, 1839.

[104]    J. A. Cushman, Cushman Laboratory for Foraminiferal Research, Contributions vol. 3, p. 90. 1927.

[105]    a) In Recent microfaunas from various environments:
The Skagerak

H. Höglund, Zoologiska Bidrag fran Uppsala, Bd. Z6. 1947.
Gulf of Mexico
S. W. Lowman, American Association of Petroleum Geologists, Bulletin vol. 33, pp. 1950-1963. 1949.
Florida, Bahamas
M. L. Natland, Scripps Institute of Oceanography, Bulletins, Technical series, vol. 3, no. 10, pp. 225-230. 1933.
R. D. Norton, op. cit., vol. 2, no. .9, pp. 331-388. 1930.
Eastern seaboard of the United States
F. L. Parker, Museum of Comparative Zoology, Bulletin, vol. 100, no. 2, pp. 213-241. Cambridge, Mass., 1948.
Plankton of deep-sea cores
F. B. Phleger, Geological Society of America, Bulletin vol. 50, pp. 1395-1422. 1939;
vol. 53, pp. 1073-1098. 1942;
vol. 57, pp. 951-966. 1946.
Marsh Bay, Massachusetts
F B. Phleger and W. R. Walton, American Journal of Science, vol. 248, pp. 274-294. 1950.
Red Sea
R. Said, CFC vol. 1, pp. 9-29. 1950.
Equatorial Atlantic Ocean
W. Schott, Deutsche Atlantische Expedition “Meteor”, 1925-27, Wissenschaftliche Ergebnisse, Bd. 3, Teil 3. Berlin and Leipzig, 1935.
(b) In fossil microfaunas, with deductions as to environment:
Eocene of Washington State
R. S. Beck, Journal of Paleontology vol. 17, pp. 587-590. 1943.
Oligocene and Pleistocene of Italy
C. Emiliani, Journal of Paleontology vol. 24. pp. 485-491. 1950.
Oligo-Miocene of California
R. M. Kleinpell, “Miocene stratigraphy of California”, fig. 5. Published by Amer. Ass. Petr. Geol., 1938.
Miocene of Jamaica
D K. Palmer, Bulletins of American Paleontology, vol. 29, no. 115, pp. 11-15. 1945.
Pleistocene of Atlantic sea-floor.
F. B. Phleger, as under (a) above.
Eo-Oligocene of Washington State
W. W. Rau, Journal of Paleontology vol. 22, pp. 153-155. 1948.
Oligocene and Miocene of Venezuela
H. H. Renz, Geological Society of America, Memoir 32, pp. 40-76. 1948.
Oligocene of Trinidad
R. M. Stainforth, American Association of Petroleum Geologists, Bulletin vol. 32, pp. 1319-1327., 1948.

[106]    M. Israelsky, American Association of Petroleum Geologists, Bulletin vol. 33, p. 92-98. 1949.

[107]    S. W. Tromp, Journal of Paleontology vol. 23, pp. 223-224; 673-676. 1949.

[108]    J. A. Cushman and R. Todd, Cushman Laboratory for Foraminiferal Research, Contributions vol. 17, pp. 29-31. 1941

[109]    J. Hofker, The Micropaleontologist, vol. 4, pp. 16-17. American Museum of Natural History, 1950.

[110]    H. Bolli, CFC vol. 1, pp. 82-89. 1950.

[111]    D. J. Carter, Geological Magazine, vol. 88, no. 4, pp. 236-248. 1951.

[112]    Not cited in the text:
Morphological evolution of Globorotalia
K. Schmid, Eclogae Geologicae Helveticae, vol. 27, pp. 45-143. 1934.
J. A. Cushman and R. W. Harris, Cushman Laboratory for Foraminiferal Research, Contributions vol. 2, pp. 92-94. 1927.
Morphological evolution of Bolivinoides
H. Hiltermann and W. Koch, Geologische Jahrbuch, Bd. 64, pp. 595-632. Hannover/Celle, 1950.
C. Emiliani, Rivista Italiana di paleontologia e Stratigrafia. Anno 15, fasc. 1, pp. 1-15. Milan 1949.
Pliocene foraminifera, Japan
Y. Takayanagi, Tohoku University, Institute of Geology and Paleontology, Short Papers, no. 2, pp. 23-26. 1950

[113]    B. L. Clark, Journal of Paleontology vol. 19, pp. 158-172. 1945.
N. D. Newell, Journal of Paleontology vol. 22, pp. 225-232. 1948.

[114]    B. Burma, Journal of Paleontology vol. 22, pp. 725-761. 1948.
Journal of Paleontology vol. 23, pp. 95-103. 1949.
C. Emiliani, Journal of Paleontology vol. 24, pp. 485-491. 1950.

[115]    Burma 1948, 1949 and Emiliani 1950 as above.
C. L. Cooper, Journal of Paleontology vol. 19, pp. 368-375. 1945.
M. G. Rutten, Journal of Paleontology vol. 9, pp. 527-545. 1935.
D. Nicol, Journal of Paleontology vol. 18, pp. 172-185. 1944. (criticized by Burma - 1948, pp. 737-741 - and Emiliani - 1950, pp. 488, 489).

[116]    K. M. Hussey, Journal of Paleontology vol. 23, pp. 120, 121. 1949.