ROSSI, DENIS, Consultant, Houston, TX, and JAMES A. NOEL,* Consultant, Ashland, OH

ABSTRACT: Sedimentary Environment of the La Rosa Formation, Maracaibo Basin

The La Rosa formation, Miocene consists of three facies: basal sand, the Santa Barbara, a middle shale, and the upper La Rosa Sand. The sands are variably productive. Paleontologic studies by others have shown the La Rosa formation to be of marine origin.

The shape of the SP curve of the Santa Barbara in bell shaped, caused by fining upward of the sand. This shape is typical with a beach deposit formed during transgression. The shale, because of its lithology and fossil content, represents shallow marine origin. The wine glass shape of the SP of the La Rosa sand is a beach sand, the result of a oarsening upward grain size during regression.

An isopach of the La Rosa formation and isoliths of the two sand units show a thickening trend from northeast to southwest. The thickest area trends diagonally across the center of the Basin.

The study shows that the Miocene sea entered the basin from the northeast, transgressed southwesterly depositing the Santa Barbara sand on top of the unconformity as it went. The movement was constricted by the highlands on three sides of the basin. The shale was then deposited in the resulting shallow marine environment. As the highlands gradually rose, the sea regressed to the northeast depositing the La Rosa sand as it went.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.