GARCIA, Member

CRETACEOUS (Aptian)

State of Monagas, Venezuela

Author of name: E. Rod, 1952 (private report).

Original reference: E. Rod and W. Maync, 1954, p. 228, etc.

See BORRACHA, Formation.

BORRACHA, Formation

CRETACEOUS (Aptian)

State of Anzoátegui, Venezuela

Author of name: E. Rod, 1952 (private report).

Original reference: E. Rod and W. Maync, 1954, p. 228, etc.

Original description: ibid.

The name Borracha formation, first used by E. Rod in 1952 (Company Report) for the thick limestone complex overlying the Barranquín formation on La Borracha Island, Anzoátegui, was published in 1954 (Rod and Maync, 1954, p. 228 etc.)

The Borracha formation includes the reefal limestone unit formerly referred to the lower part of the El Cantil formation of authors (Liddle, 1928, p. 134).

R. A. Liddle mentions the El Cantil limestone of La Borracha Island without giving a lithologic description (loc. cit.). H. D. Hedberg and A. Pyre stress the bioherm character of the bluish gray massive El Cantil lime- stone which shows a transitional contact with the Barranquín and Chimana formations. A lateral facies change of this El Cantil limestone into the glauconitic sandstones and shales of the Chimana formation is also observed (Hedberg and Pyre, 1944, p. 8).

E. Rod's name, Borracha formation, taken from La Borracha Island, is applied to the variety of zoogenic limestones with interbeds of varicolored shales and marls which occur between the Barranquín formation and the overlying Chimana formation (Rod and Maync, 1946, p. 228, etc.). A conspicuous body of shales and marls within the biostromal limestones readily allows a subdivision of the Borracha formation into an upper, middle, and lower Borracha member. Tne term García member is also applied to the middle Borracha member.

3.- Upper Borracha member. At the type locality on La Borracha Island, the upper Borracha member is exclusively composed of massive, dark to blue-gray, coquinoid dense or sub-oolitic limestones, sometimes with sideritic infiltrations; coral-bearing and algal limestones; subordinate interbeds of shale and sandstone. Thickness: ?60 to 225 meters (Rod and Maync, 1954, p. 241). Microfauna: Choffatella decipiens Schlumberger, Spiroplectammina goodlandana Lalicker, Textularia rioensis Carsey, etc. Orbitolina concava-texana (Roem.) is rarely found below the Chimana formation (e.g. in the Guariquén section, eastern Sucre). The upper Borracha member is conformable with the subjacent García member; a disconformable (in places unconformable) contact exists with the overlying Chimana formation.

2.- García member (middle Borracha member)

At the type locality (eastern slope of Pico García, north of Aragua de Maturín, Monagas), dark gray to ocre marls with some nodular marry limestone occur at the base. On La Borracha Island, a basal sandstone layer with lenses of coquinoid limestone was observed; higher up in the section appear gray, often marry, varicolored shales, shelly limestone, oyster-bearing sandstone, ironstone seams; shales and sandy shales at the top.

Thickness: 50-105 meters (Rod and Maync, 1954, p. 235).

Fauna: A rich ammonite fauna, collected in 1922 by M. Reinhard at Pico García and described by L. W. Collet, includes typical upper Aptian genera, such as Colombiceras, Dufrenoya, Cheloniceras, etc.; a lower Aptian age is suggested by the occurrence of several species of Deshayesites (see faunal lists in Collet, 1922, p. 16-17; in Rod and Maync, 1954, p. 264-265). The microfauna contains Choffatella decipiens Schlumberger, Ammobaculites subsecretaccus Cush. & Alex. Forms like Cristellaria ex gr. gaultina Berth., Epistomina cf. colomi Sigal, Textularia rioensis Carsey, etc., were also found in other Lower Cretaceous formations.

The García member is conformable with the upper Borracha member; the contact with the lower Borracha member appears to be disconformable, on La Borracha Island even unconformable.

1.- Lower Borracha member.

This member consists of dark-gray massive, crystalline, sometimes oolitic, zoögenic limestones which develop into coarse conglomeratic coquinas; often with sideritic infiltrations and pyrite (Las Cinco Ceibas type); rudistid and coral-bearing limestones, Nerinea limestones, Miliolid limestone, Cuneolina limestone, etc. At the top of the lower Borracha member, a shell-bank limestone is often developed, and rare sandstone beds occur locally in the lower part. Thickness: 10-150 meters (Rod and Maync, 1954, p. 235). Microfossils: Choffatella decipiens Schlumberger, Pseudocyclammina hedbergi Maync, etc.

The lower Borracha member is transitional with the underlying Barranquín Formation, and apparently conformable ( ?disconformable) with the middle Borracha member above; on La Borracha Island, however, the upper boundary represents an unconformity.

Age of the Borracha formation:

The prolific ammonite faunas of the García member are reported to captain genera and species of both upper and lower Aptian age.

The Choffatella biozone of Aptian age includes the interval Barranquín formation to top of Borracha formation. In Western Venezuela, it is represented by the Apón formation. (Maync, 1949 (1950); Rod and Maync 1954).

Wolf Manyc