Abstract: Eustatic and Tectonic Cycles During the Tertiary of Eastern Venezuela and Their Relationship to the Distribution of Hydrocarbon Reservoirs

Guerra, Clara De; Cabrera, Sandra De; Di Gianni, Nieves; and Sanchez, Humberto - PDVSA

Integrated geological studies indicate that during Tertiary time, three main transgressive events occurred due to the collision of the South American plate and the Caribbean plate. These events are proposed to explain the Eastern Venezuela Basin evolution and its tilting to the east.

The sedimentation associated with the first transgression occurred in the Guárico subbasin. Sedimentation of Oligocene littoral sands, known as La Pascua Formation began overlaying directly over upper Cretaceous.

As the transpression moved forward to the east, it produced a deep water pelagic regime known as the Guárico foredeep (approx. 33-30 My), represented by the basal shaly Roblecito Formation. In this period, the southern flank of the basin was exposed and therefore eroded away.

During the late Oligocene on the regressive phase of the cycle, the upper part of the Roblecito Formation was deposited in inner neritic environments and the overlaying Chaguaramas Formation was also deposited in even shallower conditions. To the east, in the north Anzoategui area, the equivalent Merecure Formation was deposited along with the Los Jabillos, Areo and Naricual formations in the north Monagas area.

The transpressive offset of the Caribbean allocthonous continued toward the east from early Miocene to middle Miocene, producing the Eastern Venezuela Basin tilting to the east and the displacement of the depocenters from the Guárico subbasin to the Maturín subbasin.

During lower Miocene, NN3/NN2 Zones (approx. 20-18 My), the sedimentation of deep water Carapita Formation began. Meanwhile to the south of the Anaco fault, the basal sands of the Oficina and Merecure formations were being deposited in deltaic and inner neritic environments.

The maximum flooding of Carapita Formation occurred at the end of early Miocene (approx. 18-15 My). This sedimentation continued through middle Miocene. At this time upper Oficina Formation and Freites reached a bathyal paleobathymetry (14-11 My). To the west of the Urica fault, thick continental to inner neritic packages of sediments were deposited, which are associated with the Quiamare Formation.

The upper limit of the second cycle is an unconformity which is a result of a relative sea level fall during middle Miocene, associated with the uplifting of the Serranía del Interior, producing a fluvial-continental sedimentation to the north and south of the Anaco fault. The progressive increase of the sea level during upper Miocene-Pliocene, reached its maximum deepening to the east (Paria Gulf and Orinoco Delta). These sediments are represented by La Pica Formation.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil