LA PEDRERA, Limestone

TERTIARY (upper Eocene)

State of Anzoátegui, Venezuela

Synonym of TINAJITAS FORMATION

Author of name: unknown.

Original reference: R. A. Liddle, 1946, correlation table.

Original description: none.

In the correlation table by Liddle (1946), there appears in the column headed "Eastern Venezuela and Guayana highlands" the name "La Pedrera". No such formation is described in the text, but the locality of La Pedrera, north of Clarines, appears in the discussion of the "Lower Eocene" (i.e. Paleocene), San Juan de los Morros formation, in which Liddle (1946, p. 308-309) quotes from Kehrer (1937, p. 66-67) to the effect that "Eocene" reef limestones appear in various localities along the south of the Serranía del Interior, between El Pao and Boca de Unare, "...and La Pedrera to the north of Clarines". "To the south of Boca de Unare...Eocene reef limestones form the outcrop of La Pedrera. . . " Liddle continues, "To this erratic Midwayan Eocene horizon may be referred. . . " (the limestone of Cerro El Corazón). It would appear from the context, then, that Liddle considers the La Pedrera limestone as Paleocene.

However, on p. 385 Liddle quotes from Hedberg and Pyre (1944), who mention foraminiferal identifications by Vaughan on material from La Pedrera and Peñas Blancas, the limestones of these localities being referred to the Tinajitas member (now formation) of the Merecure formation (now group). Liddle's geological map may also shows an outcrop of upper Eocene north of Clarines.

In an unpublished paper, J. M. Sellier de Civrieux has studied samples of the limestone which outcrops from La Pedrera on the west bank of the Unare river, over some 7 km. to the WNW, and finds no indication whatever of Paleocene age, but on the contrary, various species of upper Eocene (Jacksonian) age, especially: Lepidocyclina (Pliolepidina) pustulosa, including the forma tobleri; Pseudophragmina (Proporocyclina) tobleri; Discocyclina (Asterocyclina) asterisca; associated with these are Operculinoides spp. and calcareous algae, especially Archaeolithothamnium.

All the paleontological evidence thus indicates that the La Pedrera limestone is upper Eocene. The name is essentially a synonym of the Tinajitas formation, but we leave to the judgment of geologists who may have occasion to make detailed studies in the region, the question of whether the local name La Pedrera might be worth retaining.

(See also PEÑAS BLANCAS HORIZON and MUNDO NUEVO FORMATION)

Frances de Rivero

PEÑAS BLANCAS, Horizon

TERTIARY (upper Eocene)

State of Anzoátegui, Venezuela

Synonym of TINAJITAS Formation

Author of name: W. O. Dietrich, 1924.

Original reference: W. O. Dietrich, 1924, p. 186.

Original description: ibid.

W. O. Dietrich (1924, p. 186) and R. A. Liddle (1932, p. 175) first mentioned the Pefias Blancas limestone to designate a unit of massive reef limestone which outcrops some 6 Km. to the south of Boca de Unare, Distrito Peñalver, State of Anzoátegui. This limestone was considered of Oligocene age, on account of a Lepidocyclina identified by Dietrich as L. panamensis Cushman.

Hedberg (1937, p. 2002) discussing his Merecure formation, says that: "50 kilometers west of Barcelona, between Piritu 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 kilometers 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 ?), Echinolampus ovumserpentis 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 (Mount Moriah formation) and with Bed N° 6 of Soldado Rock, and it is probably equivalent to the Upper Eocene orbitoidal limestone of Woodring from the State of Zamora, Venezuela". Hedberg adds that the Peñas Blancas limestone is probably of Bartonian rather than Ludian age.

R. A. Liddle (1946, p. 337, 357, 385-86) refers to the Peñas Blancas limestone as Peñas Blancas horizon. He mentions a thickness of 300 to 400 ft. of orbitoidal reef limestone, lying over conglomeratic sandstones and shales and interbedded with coal layers, which he considers equivalent to the Naricual beds.

Among the orbitoids, Liddle (1946, p. 385-6) mentions a Lepidocyclina pustulosa forma tobleri H. Douvillé and a L. cf. L. crassimargo Vaughan and Cole, identified by T. W. Vaughan in Peñas Blancas and La Pedrera limestones (see) which he considered as definitely upper Eocene. In the present nomenclature, the Peñas Blancas horizon is generally considered as a synonym of Tinajitas formation of the Merecure group.

R. Laforest