Paleogene Deep-Water Sandstone Provenance and Reservoir Quality of Offshore Areas of Northern South America

Xiangyang Xie¹, Paul Mann¹, and Alejandro Escalona^2
1University of Texas at Austin, Institute for Geophysics, Austin, TX
²Department of Petroleum Engineering, The University of Stavanger, Stavanger, Norway

Several 3 to12-km-thick Paleogene depocenters occur in shelf to deep basinal settings along the offshore margins of Venezuela, Trinidad and Tobago, and Barbados. Seismic data and limited well ties indicate that these basins contain significant quantities of Paleogene sandstone that were deposited as deep-marine fan lobes. Coeval, outcropping, and quartz-rich sandstone units include the Scotland group of Barbados, the Angostura Formation of eastern offshore Trinidad, the Pampatar Formation of Margarita Island and the Misoa Formation of Maracaibo basin. The provenance and continuity of distal, deepwater sandstones and their better studied onland analogs are not well understood. Based on a regional petrographic study of sandstone composition and age, we are testing two depositional models for Paleogene sandstones: 1) the “in situ” paleodrainage model proposes that the Guyana shield is the main source for a stationary Caribbean plate; and 2) the “transported” paleodrainage model proposes that the eastward-moving Caribbean plate has displaced and “bulldozed” the Paleogene deep water clastic rocks several hundred kilometers eastward as part of the Barbados accretionary prism.

We describe outcrop and core data from widely separated onshore and offshore areas to test the two models. Sandstone petrology and U-Pb detrital zircon geochronology are utilized together to understand provenance evolution, to document reservoir characteristics, and to identify framework composition of those on- and offshore Paleogene sandstones.

Preliminary results show two major source areas are distinguishable using distinctive rock types and age differences. The Andean sources to the west are mainly late Paleozoic to Mesozoic metamorphic and sedimentary rocks; and the Guyana shield sources to the south are dominantly Archean to Paleoproterozoic plutonic rocks.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas