SAN GREGORIO, Formation

TERTIARY (Pliocene)

State of Falcón, Venezuela

Author of name: C. Wiedenmayer and M. F. Fredea, 1928 (private report).

Original reference: H. D. Hedberg and L. C. Sass, 1937, p. 107.

Original description: none published heretofore.

Hedberg and Sass (1937, p. 107) were the first to mention a "San Gregorio horizon" in published literature. Correlating their "Onia beds" with the "Codore formation" -as used by Mencher et al. (1951, correlation chart"- they mentioned that fossils contained in the "Codore formation" (San Gregorio horizon) indicate a lower Pliocene age.

Senn (1940, p. 1580) showed a "San Gregorio horizon" in parentheses after the "Upper Codore formation" of Pliocene age in the column on central Falcón of his correlation chart. The unit is shown to overlie the La Vela formation unconformably.

Liddle (1946, correlation chart) showed the "San Gregorio" as the lowermost of three units of the "Upper Codore" in the lower Pliocene of central Falcón. These units were shown to be overlain unconformably by the "Coro conglomerate" and to rest on the La Vela formation unconformably.

Mencher et al. (1951, correlation chart) showed the San Gregorio formation as lower Pliocene and uppermost Miocene in western Falcón conformably overlain by the Seco River (Río Seco) formation and resting unconformably on the Algodones formation.

Information taken from private reports indicates that the type section of the San Gregorio formation is located two kilometers east of the village of San Gregorio in north-central Falcón and one kilometer east of, and roughly paralleling the Ulé-Amuay pipeline. The formation consists of siltstones, sandstones, conglomerates, occasional claystones and fossiliferous beds. Most geologists have extended the use of the name San Gregorio to make the Río Seco its upper member, thus including all the Pliocene beds of the area within the San Gregorio formation. The thickness of the San Gregorio formation at its type locality is 430 meters and including the Río Seco as a member of the San Gregorio formation, the over-all thickness is 572 meters. The San Gregorio formation rests unconformably on the Algodones formation. The outcrops of the formation occur in northwestern and in north-central Falcón. If the Río Seco is regarded as a member of the San Gregorio formation, this latter is synonymous with the "Codore formation" of Mencher et al. (1951, correlation chart). It is then also synonymous with the "Upper Codore" of Senn (1935 and 1940, correlation charts) and with the "Coro conglomerate" of Liddle (1946, correlation chart) and also with the "Coro conglomerate" of González de Juana (1937, p. 191). The Tablazos formation of Garner (1926, p. 683) is also considered to be a synonym of the San Gregorio formation of enlarged usage.

Leo Weingeist