MERECURE Formation

See MERECURE Group

MERECURE GROUP

TERTIARY (upper Eocene to Oligocene)

State of Anzoátegui, Venezuela

Author of name: H. D. Hedberg, 1937.

Original reference: H. D. Hedberg, 1937a, p. 244-245.

Original description: ibid.

This major lithostratigraphic unit was originally defined and named by Hedberg (1937a, p. 244-245; 1937b, p. 2000-2004) as a formation with its type locality in Quebrada Merecure, a sidebranch of the Río Querecual. On this river, the formation extends from the base of the light-colored quartzitic sandstone which forms a gorge and waterfalls about 600 meters downstream from Paso Santa Anita to a point about 400 meters downstream from the mouth of Quebrada La Haciendita. Only the lower part of the formation is well exposed in the river, but outcrops in the quebradas Merecure and Carapita supplement the river section. Here, it is about 5725 feet thick and is made up largely of massive, whitish-gray to pinkish- gray, pure, quartzitic sandstones, with intervals of light-colored shales, which weather red-mottled, and brownish siltstones.

On the basis of a subsequent study by Hedberg and Pyre (1944, p. 15-21) on Río Capiricual and in the vicinity of Naricual, the Merecure formation was divided into three members which are from bottom to top: the Tinajitas, Los Jabillos sandstone and Naricual members Later, Hedberg (1950, p. 1196) raised the formation to group rank and the members to the rank of formations. Lithologically, besides sandstones and shales, the group is characterized by orbitoid-algal reef limestones in the basal part and by coal beds in the middle and upper parts. In northeastern Anzoátegui, the group reaches a thickness from 5500 to 7500 feet.

According to Hedberg (1950, p. 1198) the Merecure group is generally unconformable on older sediments along the northern edge of the Eastern Venezuela Basin. In the Barcelona area, it rests on the weathered lower part of the Caratas formation. In northwestern Anzoátegui it rests on the Vidoño formation, and in northern Guárico it is usually in contact with Guayuta sediments. Eastward from the Barcelona area, indications of unconformity between the Santa Anita and Merecure groups become less distinct, and near the Anzoátegui-Monagas boundary there appears to be a transition zone between these two groups. The contact between the Merecure group and the overlying Santa Inés group appears to be transitional everywhere throughout northeastern Anzoátegui, although the general distinction between the two groups is clear (Hedberg and Pyre, 1944, p. 18). Likewise, in the Anaco fields the Periquito formation (Funkhouser et al., 1948, p. 1870-1872), probably equivalent to the Naricual formation, underlies conformably the Oficina formation, included by Hedberg in the Santa Inés group. Furthermore, it is interesting to note that the basal Oficina "U-sands" of the Greater Oficina area grade laterally into the uppermost Periquito formation of the Anaco fields (Hedberg, 1950, p. 1205). In northwestern Anzoátegui and northern Guárico, the relation existing between the Merecure group and basal Santa Inés sediments is not only gradational, but the differences noted farther east become indistinct with the appearance of a somewhat different facies known as the Caño Dulce formation. Hedberg (1950, p. 1204) considers that the La Pascua sandstone of central Guárico and Kamen-Kaye's (1942, p. 128-133) Guarumen group of western Guárico are probably equivalents to the upper part of the Merecure and lower part of the Santa Inés groups of northeastern Anzoátegui.

In northwesternmost Monagas and northeasternmost Anzoátegui, a lateral facies of the lower part of the Naricual formation was named Areo shale by Hedberg (1950, p. 1197-1198). In the Quiriquire field, reefal limestones and sandstones of the Eocene Mundo Nuevo formation (Borger, 1952, p. 2302-2303) appear to correlate with the Tinajitas formation.

Paleontologic data suggest an upper Eocene to Oligocene age for the Merecure group of northeastern Anzoátegui (Hedberg and Pyre, 1944, p. 18-21). In the type section the sediments are barren of fossils. (Hedberg, 1937b, p. 2001).

Gustavo Feo-Codecido