A. T. Picarelli1,
(1) Perez Companc, Caracas - DF, Venezuela
Abstract: Tectonic and eustatic controls on reservoir architecture on the distal zone of foreland basins: Shallow marine Cenozoic sediments in Eastern and Western Venezuela
La Concepción oil field (Maracaibo Basin) and Mata oil field (Eastern Venezuela Basin) record shallow marine sedimentation in the distal zone of two foreland basins formed by the eastward migration of the Caribbean Plate in oblique convergence with the South American Plate. A foredeep unconformity was followed by two 2nd-order sequences, where a retrogradational stacking pattern characterizes the lower sequence and a progradation the upper sequence. In La Concepción, the foredeep unconformity was formed during the early Eocene and the sequences range in age from early Eocene to Oligocene. In Mata, the foredeep unconformity was formed in lower Miocene and the sequences range from early to late Miocene.
The shallow marine paleophysiography, distal to the collision front, allowed the incision of several valleys and the development of multiple sequence boundaries. The lower sequence was subdivided in 16 3rd-order cycles in Mata (Merecure, Oficina and Freites formations) and 12 in La Concepción (Misoa Formation). The 2nd-order cycles were interpreted as a result of the foreland basin subsidence, crustal relaxation, and rebound. The internal stacking patterns were the result of 3rd- to 5th-order eustatic cycles, which controlled the geometry and quality of the reservoir rocks.
During periods of 3rd-order LST, the best reservoir rocks were developed as channel sand bodies within 50-100ft incisions at 4th- and 5th-order LST’s. During 3rd-order TST, the 4th- and 5th-order LST’s formed incised valley fills, associated with beachridges. During 3rd-order HST, the 4th- and 5th-order LST’s were marked by a few incised valleys and deltaic lobes.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana