BULLETIN OF THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS
VOL. 48 NO. 11 (NOVEMBER. 1964). PP. 1847-1850
R. M. STAINFORTH[2]
Caracas, Venezuela
A recent paper in this Bulletin by Orville L. Bandy (1963-a) is important in demonstrating
the validity of Cenozoic planktonic foraminiferal zonation in yet another major
area, namely, the Philippine Islands. The relation of the zones to regional
stratigraphy and paleoenvironmental trends is well presented and the author is
to be congratulated.
Nevertheless, issue is taken with
an aspect of Bandy’s paper epitomized by the following remark in his discussion
of the ages of the zones (p. 1740).
“The Burdigalian Stage is
considered to be Middle Miocene because the two most significant foraminiferal
changes in the Miocene serve to subdivide it reasonably into three parts. These
changes occur at the Aquitanian-Burdigalian boundary and at the
Burdigalian-Vindobonian boundary.”
In my opinion the division of the Miocene into Lower, Middle, and Upper is firmly established by international usage, and any casual attempt to change the scheme will only cause confusion. The accepted subdivisions are: Lower Miocene equals Aquitanian-Burdigalian; Middle Miocene equals Helvetian-Tortonian, jointly known as Vindobonian; and Upper Miocene equals Sarmatian-Pontian. This division of the Miocene is to be found in such major compilations as Cooke et al. (1943), Gignoux (1950), Eames et al. (1962) and innumerable major and minor works. Gignoux
differs in placing the Aquitanian in the Oligocene, but is otherwise in
agreement.
A second cogent reason exists for
not separating the Aquitanian and Burdigalian into Lower and Middle Miocene
respectively. This is the body of stratigraphic researches made in Aquitaine during
the last decade by members of the geological faculty of the University of
Bordeaux. As long ago as 1954 (Vigneaux et al.) it was recognized that the classic Aquitanian and
Burdigalian “stages” represent facies of a single coastal deposit and are not
truly a pair of sequential time-stratigraphic units. In the subsurface of
Aquitaine they pass laterally into a sequence of rather deep-water shales,
bounded sharply below and above by shallow marine beds of Oligocene and
Helvetian age. This shale unit was designated the Girondian Stage, a valuable
term which unfortunately has received little mention or acceptance in the
stratigraphic literature.
Studies by the Bordeaux group have
continued, and a more recent compilation concludes with the following paragraph,
literally translated from the French (Caralp and Vigneaux, 1961):
“In conclusion, it appears that
the Burdigalian and Aquitanian possess no chronostratigraphic value. Their
superposition, when it exists, can take place at no matter what moment within the
interval considered. For future purposes they constitute simply temporal
lateral facics, paleo-geographically localized, of a single stage, the
Girondian.” Bandy’s proposed revision would make half the Girondian Stage Lower
Miocene and half Middle Miocene, an unnatural procedure in its type region and
therefore undesirable in worldwide stratigraphy.
Drooger (1958, p. 175) has argued that the new unit, Girondian, is unnecessary, as it merely represents a lithostratigraphic equivalent of the combined Aquitanian and Burdigalian, and its erection does not resolve the difficulties of distinguishing these two stages. I hold the contrary opinion that the term Girondian is potentially very useful. Its type development is an open marine deposit which can be correlated directly, by planktonic foraminiferal zonation, with the Lower Miocene of the rest of the world. This is not true of the type Aquitanian and Burdigalian, quite apart from their dubious status as time-stratigraphic units. The short word “Girondian” is more convenient than the cumbersome compound “Aquitanian-Burdigalian,” just as “Vindobonian” is preferable to “Helvetian-Tortonian.”
A revision is conceivable of the accepted definitions of Lower, Middle, and Upper Miocene, but it should be formulated by some internationally recognized authority such as a commission of the International Geological Congress. The measurement of geological time is based on many indirect techniques, which include: biostratigraphy (the life-ranges and evolution of fossils-plants, vertebrate and invertebrate animals, and their multiple phyla); lithostratigraphy (the physical evidence of diastrophic and depositional cycles); geochemistry (radio-isotopic dating); and combinations of paleogeographic scope. Planktonic foraminiferal zonation, while admittedly important, is only one of these many techniques. Key levels in the geologic time scale must be based on the integrated evidence of all available techniques without undue emphasis on any single one.
In the case of the Lower Miocene
the paleogeographic evidence presents the accepted interval
(Aquitanian-Burdigalian or Girondian) as a natural unit based on a simple cycle
of marine transgression, subsidence, and regression. The three phases
correspond reasonably closely with the zones of G. dissimilis, G. insueta, and G.
fohsi. This statement refers to the type
region (Aquitaine) but is also applicable to the South American-Caribbean
region, where transgressive unconformity is commonplace at the base of the G.
dissimilis Zone and where open marine
conditions are widely reduced at the end of the G. fohsi Zone. In the paper under discussion the same pattern is
discernible in the Philippines, especially in the Central Valley of Luzon
(Bandy, 1963-a, p. 1739), The “Orbulina datum” falls indefinitely within the cycle and, in the paleogeographic sense, would be an unnatural level for separation of such important units as the Lower and the Middle Miocene.
Although I deprecate Bandy’s application of two “significant
foraminiferal changes” to a revised formal subdivision of the Miocene, I
heartily agree with him on their great value in regional correlation (see
Stainforth, 1960). A third datum of worldwide significance is the level of
abrupt and plentiful appearance of Globigerinoides triloba-group, which elsewhere Bandy (1963–b, -c) has himself
termed “the Globigerinoides triloba
datum at the base of the Aquitanian” or “at the Oligocene-Miocene boundary.” It
was surprising to see no mention of Globigerinoides in the paper on the Philippines, even though the zonal
sequence is amply defined by the other planktonic forms listed.
Bandy, O. L., 1963-a, Cenozoic planktonic foraminiferal zonatIon and basmal development in the Philippines: Am. Assoc. Petroleum Geologists Bull., v. 47, no. 9, p. 1733-1745.
— 1963-b, Cenozoic planktonic forarniniferal zonation (abs.): Am. Assoc. Petroleum Geologists Bull., v.47, no. 2, p. 1768.
— 1963-c, Aquitanian planktonic 6 raminifera from Erben Guyot: Science, v. 140,1). 1402-1403.
Caralp, Ch. J., and Vigneaux, M., 1960, Considérations sur le Miocène inférieur aquitain: Geol. Gesell. Wien Mitteil., v. 52 (1959), p. 49-66.
— and — 1961, Nouvelle interprétation des “étages” du Miocène infèrieur en Aquitaine: Soc. Géo1. France, C.R.S., no. 5, séance du 15 mai, 1961.
Cooke, C. W., Gardner, J., and Woodring, W. P., 1943, Correlation of the Cenozoic formations of the Atlantic and Gulf Coastal Plain and the Caribbean Region: Geol. Soc. America Bull., v. 54, p. 1713-1723.
Drooger, C. W., 1958, Foraminifères importants pour les subdivisions et limites du Miocène inférieur-moyen: 83me. Congrés des Sociétés Savantes, Section des Sciences, p. 171-179.
Eames, F. E., Banner, F. T., Blow, W. H., and Clarke, W. J., 1962, Fundamentals of mid-Tertiary stratigraphical correlation: Cambridge Univ. Press.
Gignoux, M., 1950, Géologie stratigraphique (4me. ed.): Masson et Cie., Paris.
Stainforth, R. M., 1960, Current status of transatlantic Oligo-Miocene correlation by means of planktonic foraminifera: Rev. Micropaléontologie, v. 2, no. 4, p. 219-230.
Vigneaux, M., Magné, A., Veillon, M., and Moyes, J., 1954, Aquitanien et Burdigalien: Acad. des Sciences, C. R., t. 239, séance du 4 oct., 1954, p.818-820. Paris.
ORVILLE L. BANDY[4]
Los Angeles, California
A
study of planktonic foraminiferal zonation in the Philippines (Bandy, 1963a)
provided criteria for defining stages of the Tertiary in much the same way and
on the same general basis as that used by Blow (1959), Bolli (1957, 1959), and
others for a number of tropical areas of the world. Two significant faunal
changes in the Miocene sections were defined as the appearance of orbulinids at
or near the base of the Burdigalian (Orbulina datum) and the appearance of keeled species of the Globorotalia
menardii group at the top of the
Burdigalian (Globorotalia menardii
datum). In this Philippine study, it was suggested that three divisions of the
Miocene should be: Lower Miocene equals the Aquitanian, Middle Miocene equals
the Burdigalian, and Upper Miocene equals the Vindobonian and Sahelian. The
faunal changes are discussed at some length in a more complete study of
Cenozoic planktonic foraminiferal zonation (1964).
R. M. Stainforth has taken exception to the usage of Lower, Middle, and Upper Miocene in connection with the Philippine study. He recommends adherence to the usage: Lower Miocene equals Aquitanian-Burdigalian; Middle Miocene equals Helvetian-Tortonian (Vindobonian); and Upper Miocene equals Sarmatian-Pontian (Sahelian). His views are supported by an imposing list of references in the literature. Is this well established international usage? Gignoux (1950), Grill (1963), and many others prefer to include the Aquitanian within the Oligocene, making the Aquitanian-Burdigalian boundary a subdivision between epochs. At the top of the Miocene the entire Sarmatian and Pontian (Sahelian in its entirety) is included within the Pliocene by still others (Durham, Jahns, and Savage, 1954). As an extreme case, perhaps, it would thus be possible to envisage a Miocene Epoch made up of Burdigalian and Vindobonian stages only. In this case one might prefer Upper and Lower Miocene subdivisions with no Middle Miocene. It would seem that international usage is not especially well established in some circles.
As cited in the preceding companion discussion by Stainforth,
the classic Aquitanian and Burdigalian stages may represent facies of a single
coastal deposit (Vigneaux et al. 1954); however, Blow (1959), Bolli (1959), Stainforth (1960), Eames ci al. (1962), and others have used both of these stages in conjunction with planktonic foraminiferal zonation. It is becoming evident to increasing numbers of paleontologists that planktonic foraminifera demonstrate a remarkable and dependable zonation in marine deeper-water facies of tropical areas of the world. Thus, a series of stage names is needed for the planktonic sequence and the tendency has been to relate the standard European stage names to the planktonic sequence in order to preserve many of these original early terms. The Girondian (Caralp and Vigneaux, 1961) can not be accepted as equivalent to the Aquitanian-Burdigalian in terms of the current planktonic zonation assigned to these stages; this would mean that a single stage would embrace one of the most dramatic faunal changes in the Middle Tertiary!
Stainforth recommends, in his
penultimate paragraph, the employment of paleogeography in establishing stages.
The basic tenet of determining evolutionary changes in geologic time may have
little direct correlation with paleogeographic conditions of shallow-water
environments, especially if one utilizes criteria based on open sea planktonic
foraminiferal groups recorded in deeper-water facies. It is desirable to
determine changes in fossils in geologic time, interrelating this work with
that in progress on absolute chronology, as a basis for establishing valid
time-stratigraphic units. The urgent need is for better and more precise
methods of evaluating the chronology of geologic phenomena (including
paleogeographic features).
Regarding the lack of mention of
the Globigerinoides triloba datum at
the base of the Aquitanian (Bandy, 1963b, 1963c, 1964) in the Philippine paper
(1963a), the datum concept was developed following the completion of the
Philippine paper but unfortunately appeared in print before the earlier work on
the Philippines. This is one of those pitfalls encountered due to the quite
different lengths of time required for processing manuscripts in the various
journals. Globigerinoides triloba has checked out as appearing at the base of the Aquitanian, as this stage is defined in the Philippine paper. This species is one of the planktonics which was not used in the major zonation within the Miocene and, in retrospect, it was a regrettable omission.
The comments of Stainforth are much appreciated and should serve to stimulate additional thought and research on the problems discussed. Scientists must continually re-examine data, relationships, and principles in light of new discoveries and new suggestions. Although there is no unanimity of opinion about the manner of subdividing the Miocene, many scientific papers in the past have favored the usage recommended by Stainforth; however, Bacon has said that books must follow sciences, and not sciences books. It will be some time before the problem about methods of subdividing the Miocene will be resolved to the satisfaction of most investigators.
(In addition to those cited in
Stainforth’s discussion)
Bandy, O. L., 1964, Cenozoic planktonic foraminiferal zonation: Micropaleontology, v. 10, no. 1, p. 157.
Blow, W. H., 1959, Age, correlation and biostratigraphy of the upper Tocuyo (San Lorenzo) and Pozon Formations, eastern Falcon, Venezuela: Bull. Am. Paleontology, v. 39, no. 178, p. 1-251.
Bolli, H. M., 1957, Planktonic Foraminifera from Oligocene-Miocene Cipero and Lengua Formations of Trinidad, B. W. I.: U. S. Natl. Mus. Bull. 215, p. 97-123.
— 1959, Planktonic Foraminifera as index fossils in Trinidad, West Indies, and their value for worldwide stratigraphic correlation: Eclogae Geologicae Helvetiae, v. 52, p. 627-637.
Durham, J. W., Jahns, R. H., and Savage, D. F., 1954, Marine-nonmarine relationships in the Cenozoic section of California: Calif. Div. Mines Bull. 170, pt. 1, chap. 3, p. 59-71.
Grill, R., 1963, Exkursion Inneralpines Wiener Becken nördlich der Donau, Molassegebiet und Waschbergzone: Exkursions-führer für das Achte Europäische Mikropaläontologische Kolloquium in Österreich, Geologische Bundesanstalt, Wien, p. 20-40.