Origin of the name Peñas Blancas formation
(Origen del termino, formación Peñas Blancas)

by R. M. Stainforth


En el Léxico Estratigráfico de Venezuela se indica W. O. Dietrich (1924) como autor del término, caliza de Peñas Blancas, y se menciona el uso del mismo nombre por R. A. Liddle (1932). La verdad es que la designación Peñas Blancas no aparece ni en la primera ni en la segunda de las dos referencias citadas, y que el originador del término es H. D. Hedberg (1937, p. 2002).

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In a forthcoming paper on the geology of the Guárico Mountain Front A. L. Peirson will expound the reasons for applying the name Peñas Blancas Formation to the Upper Eocene limestones there, despite their close similarity to the Tinajitas limestones in the mountains east of the Barcelona Gap. A point which will be mentioned briefly is the faulty citation, in the Stratigraphical Lexicon of Venezuela, of W. O. Dietrich (1924) as the originator of the term. Peñas Blancas limestone. Reinstatement of this long-disused term makes it desirable to state its origin correctly, and this is the purpose of the present note,

The Lexicon includes an item entitled “Peñas Blancas horizon” by R. Laforest (p. 445-446 of English edition, p. 512-513 of Spanish edition). This starts with the words: “W. O. Dietrich (1924, p. 186) and R. A. Liddle (1932, p. 175) first mentioned the Peñas Blancas limestone to designate a unit of massive reef limestone which outcrops some 6 km. to the south of Boca Unare…” In the Spanish edition this is rendered as “W. O. Dietrich (1924, p. 186) y R. A. Liddle (1932,p. 175) usaron por vez primera el nombre, caliza de Peñas Blancas, para designar una unidad de caliza arrecifal maciza, que aflora a unos 6 kilómetros al sur de Boca de Unare…” (Both versions are quoted to show that the error to be demonstrated is not due to a slip in translation).

On consulting the two references mentioned, it is surprising to find that neither author uses the name Peñas Blancas, not even in a purely geographic sense. Since both papers are difficult to obtain, it seems opportune to quote them in full.

Dietrich’s short reference is tucked in at the end of a description of the fossiliferous Cretaceous limestones of northeast Venezuela, and runs as follows: “Am Morro del Unare und weiter unterhalb bei Clarines; nahe der Mündung des Unare Flusses, steht prachtvoller, bunter Lepidocyolinenkalk an; ausser Nummulitiden und Rotaliiden baut er sich aus kleinen Lithothamnienstöckchen von kugeligem oder fingerförmigem Wuchs, vereinzelten Seeigeln und Pectiniden auf. Unter den Lepidocyclinen, die häufig von der Kalklage umkrustet sind, steht eine 3-8 mm grosse Form mit breiter Embryonalkammer L. panamensis sehr nahe; eine zweite, ähnliche Form, zeigt runde Embryonalkammern, eine dritte Form hat einen Durchmesser von 30-40 mm und ist flach. Das genauere oligocäne Alter dieser ebenfalls bituminösen Kalke lässt sich mit den vorhandenen Proben nicht sicher bestimmen. Dieser Lepidocyclinenkalk schliesst eine bisher bestehende grosse Lücke in der Kenntnis der oligocänen festländischen Umrahmung des Karibischen Meeres…”

A free translation is: “At the Morro del Unare and farther down near Clarines, near the estuary of Río Unare, there is a conspicuous light-colored Lepidocyclina-limestone. Besides nummulitid and rotaliid foraminifera, it is built up of little globular or finger-shaped colonies of Lithothamnion, occasional echinoids and pectinid mollusks. Among the Lepidocyclinas, which are frequently encrusted by the calcareous algae, is a 3-8 mm. form with wide embryonic chambers, very near to L. panamensis. A second similar form displays round embryonic chambers, and a third form has a diameter of 30-40 mm. and is flat. The precise Oligocene age of this bituminous limestone is not settled with certainty by the specimens at hand. This Lepidocyclina-limestone closes a hitherto persistent gap in the knowledge of the Oligocene continental framework of the Caribbean Sea…”

Liddle’s 1932 reference is even shorter, as follows: “Six kilometers south of Boca de Unare, in the northern part of the State of Anzoátequi (sic), in northeastern Venezuela, is an outcrop of foraminiferal, dark-gray limestone 300 to 400 feet thick, which correlates with similar middle Oligocene limestone of the Falcon region. This is the only outcrop of the horizon in central, or eastern, Venezuela; but others may be found after a thorough study of the foothills of the Coast range is made.”

Undoubtedly the beds described by both authors belong to the Peñas Blancas Formation of current usage, but that name is not applied. Consequently, the introduction of te name to the literature must be attributed to Hedberg (1937, p. 2002) in the following passage, which is also cited by Laforest in the Lexicon: “50 kilometers west of Barcelona, between Piritú and the Río Unare, sediments believed to be the time equivalents of the Merecure formation are exposed. They include conglomerates and coals similar to those of Naricual but also in part consist of massive orbitoidal reef limestones, which are particularly well exposed on Cerro Peñas Blancas and El Picacho a few miles east of the river, The Peñas Blancas limestone contains Lepidocyclina trinitatis H. Douvillé, Lepidocyclina (Pliolepidina) tobleri H. Douvillé, Lepidocyclina sp. (microspheric form of L. tobleri ?), Echinolampas ovumserpenti Guppy, Rotularia sp., and an abundance of Lithothamnium sp. It may be rather definitely correlated with the Upper Eocene limestone of Vista Bella quarry in Trinidad, …”

For clarity, it might be noted that Liddle (1946, p. 385-386) later rejected his reference of the limestones to the Oligocene and, like all subsequent authors, placed these beds definitely in the Upper Eocene.


DIETRICH, W. O., 1924
Zur Paläontologie und Stratigraphie der Kreide und des Tertiärs in der ostkaribischen Kordillere Venezuelas”, Zentralblatt für Mm., Geol., Paläont., no. 6, p. 181-187. (Stuttgart)

HEDBERG, H. D., 1937
“Stratigraphy of the Río Querecual section of northeastern Venezuela”, Geol., Soc. Am. Bull., vol. 48, no. 12, p. 1971-2024

LIDDLE, R. A., 1932
“Outlines of Venezuelan Stratigraphy”, Pan-American Geologist, vol. 57, no. 3, p. 161-185

—, 1946
“The geology of Venezuela and Trinidad” (2nd ed.), Paleontological Research Institution, Ithaca, N.Y.: 890 p.

“Stratigraphical Lexicon of Venezuela” Dirección de Geología, Bol. Geol., Spec. Publ. No. 1 (also in Spanish: “Léxico Estratigráfico de Venezuela)