BIOSTRATIGRAPHY AND BIOFACIES OF THE PLATAFORMA DELTANA AREA, EASTERN VENEZUELA

Benthic foraminiferal assemblages were studied from seven wells in the subsurface of the Orinoco Delta shelf, Venezuela near the Columbus Basin (Trinidad & Tobago). A biostratigraphic scheme based mainly on benthic foraminifers but also including planktic foraminifers is proposed for the Plio-Pleistocene interval which enables the correlation in the area. Two specific planktonic occurrences are used most extensively across the basin to define the Pleistocene. These are the second evolution of Globorotalia tumida flexuosa and the evolution of Globorotalia truncatulinoides. As noted, the second evolution of G. tumida flexuosa occuurs in the Pleistocene, with its last occurrence (lo) disappearance documented regionally and worldwide at approximately 4.8 Ma. Early Pliocene. The latter defines the base of the Pleistocene at 1.77 Ma.

The assemblages reveal marked differences in taxonomic composition and diversity, reflecting inner neritic to middle bathyal conditions. Three foraminiferal biofacies (FB) are distinguished: FB1 (Erin Formation, Pleistocene). Consists of interbedded sand and clay. The foraminiferal assemblages are: Bulimina marginata d´Orbigny, Brizalina isidroensis, Nonion sp, Uvigerina peregrina, Globocasidulina subglobosa, Elphidium incertum, Quinqueloculina sp and Miliolidae. Paleoenvironments of depositation ranged from inner to middle neritic. FB2 (Palmiste Formation, Late Pliocene). Consists of sands interbedded silts and clay. The dominant species are: Nonionella atlantica, Nonion sp, Miliolidae and Neoeponides sp. Paleoenvironment of depositation is inner neritic. FB3 ( Gros Morne Formation, Early Pliocene). Consists of well bedded gray silts and sands. The foraminiferal assemblages are entirely agglutinated: Glomospira charoides, Glomospira gordialis, Alveovalvulina suteri, Recurvoides sp, Hormosina sp and Saccammina sp . Paleoenvironments of depositation ranged from upper to middle bathyal.