Sedimentological and Petrographical Data of Cretaceous Evaporites in Barinas Subbasin (Venezuela) and their Relation to Petroleum Occurrence: ABSTRACT

Abstract

Detailed sedimentological and petrographical studies of cores from the phosphatic-shale of the Cretaceous La Morita Member of the Navay Formation have allowed the identification of evaporites towards the top and base of this unit. The study shows enterolithic spotted textures consisting of the minerals silica, anhydrite and dolomite. There are also evaporate levels diagenetically altered to calcite, whose texture shows a crystallization in the shape of a chevron pattern. One of them has abundant planktonic foraminifers towards its base, and, it is a stratigraphic marker possible to follow for 28 km. The crystalline textures mentioned above allow us to establish that at the end of its sedimentation, the La Morita Member displayed environments varying from mud flats to salterns, suggesting that unusual conditions of evaporation existed during this period. It confirms the common association found by researchers of evaporites overlying oil-bearing carbonate intervals in zones where the paleogeographic conditions have played an important role in the generation of organic matter. The geochemical results of total organic carbon, rockeval pyrolysis and organic petrography of La Morita Member support this assumption.