GUANOCO, Formation

See SAN ANTONIO, Formation and GUANOCO, Shales

SAN ANTONIO, Formation

CRETACEOUS (Senonian)

State of Anzoátegui, Venezuela

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

Original reference: H. D. Hedberg, 1937a, p. 242.

Original description: ibid.

Hedberg (1937-a, p. 242) originally named and described the San Antonio formation as the upper unit of the Guayuta group. The type section is on the Río Querecual, from the base of the first sandstone, 600 meters downstream from Paso Hediondo to the base of the thick gorge-forming sandstone (Santa Anita formation), about 150 meters upstream from Paso Santa Anita. However, the formation was named from Cerro San Antonio just north of the town of Bergantín. On Río Querecual, it is 1,290 feet thick, and consists dominantly of black limestone and shale, similar to that of the Querecual formation, but in addition contains numerous beds of hard, light-gray, calcareous sandstone and common sandstone dikes. The San Antonio formation is in conformable contact with the Querecual formation below and the Santa Anita formation above. Lithologically it represents a zone of transition between these two formations. Based on fossils that probably came from the Querecual formation (Hedberg and Pyre, 1944, p. 12), a Turonian-Senonian age was assigned.

Hedberg (1937-b, p. 1992-1994) more fully discusses this formation and mentions that thin sections of the limestones very often contain tests of pelagic foraminifera as those of the Querecual formation. These tests, in the San Antonio limestones, are filled with carbonaceous matter, whereas those in the Querecual limestones contain calcite. In the San Antonio formation there is usually an association of benthonic forms not found in the Querecual formation. He also indicates that the random occurrence in thickness and direction of the many sandstone dikes, is an outstanding feature of the formation. The presence of sandstones in the San Antonio formation is significant and the development of cherts, although of local variation, is characteristic. The small foraminifera, especially the occurrence of the species Siphogenerinoides ewaldi (Karsten) indicate a correlation of the San Antonio formation with the lower part of the Colón formation of Western Venezuela, which in turn is correlated with the Taylor stage of Texas, and a Senonian age is assigned to it.

Hedberg (1950, p. 1191-1192) indicates that the San Antonio formation is of considerable extent in the Serranía del Interior of northeastern Venezuela and believes that the Guanoco formation in the State of Sucre is quite probably an approximate equivalent of the San Antonio formation. Mencher et al. (1951, p. 774-775, Correlation Chart) indicate the age of the San Antonio formation as ranging from Upper Coniacian to Upper Campanian.

Wm. K. MacFarquhar