ORUMO, Formation

TERTIARY (upper Eocene)

State of Zulia, Venezuela

Author of name: H. D. Hedberg, 1929 (private report).

Original reference: H. D. Hedberg and L. C. Sass, 1937, p. 93-95.

Original description: ibid.

The Orumo formation was applied by H. D. Hedberg (1929, private report) to a shale series outcropping in the vicinity of a former ranch known as El Orumo, about 1.5 kilometers southwest of the village of La Burra, on the bank of the Río Guasare, in the northern part of the Mara District. A good reference section occurs in the Río Socuy, from a point one kilometer upstream from Los Caballos to a point about 500 meters above the mouth of the Río Mache. Other sections are found on the Río Guasare and Caño Salado.

The formation was described by Hedberg and Sass (1937, p. 94) as being composed largely of soft, incompetent, gray clayshale with minor amounts of medium hard, friable, light gray sandstone. J. T. Scopes (1930, private report) also described a 100-foot limestone facies near La Burra on the Río Guasare that contained fossiliferous, tabular, sandy, gray and brown limestone.

The contact between the Orumo formation and the underlying Mostrencos formation is gradational but a major unconformity ts present at the top of the Orumo and accounts for the variation in stratigraphic thickness throughout the western part of the Maracaibo basin. In northwest Mara, the maximum thickness is about 2100 feet, exposed on Río Guasare.

Fossils are fairly common but not very diagnostic. The foraminifera are largely limited to Ammobaculites, Haplophragmoides, Trochammina, Anomalina, Quinqueloculina, Siphonina and Rotalia.

Hedberg and Sass (1937, p. 94-95) correlated the Orumo with the upper part of the Las Flores formation, and González de Juana (1951, p. 284) believed it to be equivalent to the upper Las Flores and the Mene Grande formation.

Gordon A. Young