SIPHOGENERINA TRANSVERSA, Zone

TERTIARY (upper Oligocene)

State of Falcón, Venezuela

Author of name: H. H. Renz, 1948.

Original reference: H. H. Renz, 1948, p. 50-53.

See ACOSTIAN, Stage

ACOSTIAN, Stage

TERTIARY (middle to upper Oligocene)

State of Falcón, Venezuela

Author of name: H. H. Renz, 1948.

Original reference: H. H. Renz, 1948, p. 44-55.

Original description: ibid.

The Acostian stage is defined and describeed as a time-stratigraphic unit with type-locality at El Mene de Acosta, Eastern Falcón. It covers a section of sediments within the lower part of the Agua Salada group (Renz, 1948, p. 44-55) and is in conformable contact with both yhe underlying "Uvigerinella" sparsicostata zone and the overlying Araguatian stage.

The stratigraphic thickness of the Acostian in the type area is 171 meters. It includes 116 meters of sediments beloging to the Menecito clay member of the San Lorenzo formation; 10 meters belonging to the Policarpio greensand member and 45 meters of the Husito mearly clay member of the Pozón formation. At Pozón the thickness of the Acostian probably exceeds 500 meters, and in the coastal regions to the north it may be as great as 2000 meters.

The Acostian is extremely rich in foraminifera and biostratigraphically wel defined. The top coincides with the disappearance of Siphogenerina transversa Cushman and the base is characterized by the appearance of many foraminiferal species not occurring in older strata.

The Acostian can be subdivided into two distinctive faunal zones, a lower Robulus wallacei zone and an upper Siphogenerina transversa zone, each containing two zonules. Fossil evidence suggests that the Acostian stage ranges from high middle Oligocene (Rupelian) to the upper Oligocene (upper Chattian lower Aquitanian).

The Acostian has a very wide geographic extent. It can be recognized throughout the Agua Salada basin of Eastern Falcón; more in Easter Venezuela, as well as in many localities in the Caribbean region and tropical America.

H. H. Renz