Tectonic Generation of Early Miocene Transgressive Fill of the Eastern Venezuela Basin (Maturín Sub-Basin)

Santiago, Nubia¹, Kaolu Parra², Ronald Steel³ (1) PDVSA-, Puerto La Cruz, Venezuela (2) PDVSA, Puerto La Cruz, Venezuela (3) University of Texas, Austin, TX

The Lower Miocene succession, derived mainly from the craton and examined here in the Maturín sub-basin, shows a clear transgressive development trend caused by the earliest downwarping of the foredeep. Although the main paleo-Orinoco system drained into the area from Middle-Miocene, and the bulk of the thrust tectonics is from Middle Miocene, the Early Miocene saw the initiation of foredeep subsidence, and shows that a deepwater shelf margin had been created at this time.

The Lower Miocene succession of the area is composed of six thick (300-370 m) stratigraphic units that record discrete phases of subsidence and successive backfilling of the basin. Each of these units has a stacked architecture of higher frequency (4th-order) sequences created by northward prograding deltas that drained the south-southwesterly craton. Units S3-S4 as they approach the deepest part of the foredeep, develop a shelf margin with channelized deepwater turbidites.

The vertical transgressive-regressive stacking analysis allowed the differentiation of three prominent features that reflects the clear tectonic control on the development of the stratigraphy: (1) thicker regressive deltaic units on the outer shelf area (up to 200 m), as a result of a subsidence increment, at the sequences S2 and S5; (2) coarser-grained, distributary channels reflecting falling sea level in unit S3 with the overlying shelf deposits of the unit S4; and (3) the overall transgressive trend of the succession despite the vigorous activity of the deltas. The Lower Miocene succession is capped by deeper water shales that persist into the Middle Miocene.