PAPARRO, Formation

See MOSTRENCOS, Formation.

MOSTRENCOS, Formation

TERTIARY (middle Eocene)

State of Zulia, Venezuela

Author of name: J. A. Tong and A. E. Getzendaner, 1925 (private report).

Original reference: H. D. Hedberg and L. C. Sass, 1937, p. 91-93.

Original description: ibid.

The name Mostreneos shale was first used by Tong and Getzendaner (private report) for the formation exposed near the Los Mostrencos corral, about 15 kilometers west-southwest of Carrasquero, between the Socuy and Guasare rivers in the northern part of the Mara District. Outcrops of the formation are exposed along strike-ridges and stream beds near the corral, and good reference sections are exposed in the Caño Paso del Diablo, Río Socuy and Río Guasare.

Hedberg and Sass (1937, p. 92) described the formation as consisting predominantly of thin-bedded, light gray, medium to fine-grained sandstones, gray sandy shales, and finely interlaminated light gray sandstone and dark gray shale with micaceous-carbonaceous bedding planes. Massive caleareous sandstones and coals are rare. On the basis of lithologic and mineralogic variation, the formation was subdivided into two members (Hedberg, 1929, private report; Hedberg and Sass, 1937, p. 92): the Barqueta member includes the lowermost 900-1200 feet of the formation at the type locality of Pozo de la Barqueta on the Caño Paso del Diablo. It is characterized by the predominance of dark carbonaceous shale and distinctly laminated sandstone and shale. This member is referred to as the Paparro formation by Liddle (1946, Correlation Chart). The Taparito member is 1500 to 2000 feet thick at the type locality between Taparito and Los Mostrencos. It is a sequence of tabular to massive light gray, cross-bedded, friable sandstones and laminae of gray, carbonaceous sandy shale; the sand is predominant. Near the base of the Taparito is a limestone phase eontaining fossiliferous, tabular, sandy limestone.

Molluscan fossils are common in the Taparito limey phase, but are rare elsewhere; ostraeods and foraminifera are fairly common throughout the entire formation. The age is believed to be middle Eocene (L. W. Stephenson, 1924, private report) based upon stratigraphic position and such mollusca as: Ostrea sellaeformis Conrad, Ostrea var. O. alabamiensis Lea, Arca aff. A. rbomboidella Lea, Anomia aff. A. lisbonensis Aldrich. The Mostrencos formation overlies the Paso Diablo formation conformably with transitional contact, and is overlain conformably by the Orumo formation.

The outcrops of this formation are in the western Mara District but are found in the subsurface in the Districts of Mara and Maracaibo, and is correlated with the El Mene formation encountered in the subsurface of the Bolívar Coastal fields. In present day usage, the Mostrencos is the equivalent of the upper part of the Potreritos formation and the lowermost part of the Las Flores as used in the Mara field.

Gordon A. Young