TOMAS VILLAMIL, PEDRO A. RESTREPO-PACE, and K. SVELA, Advance Exploration Organization, Conoco Inc., Houston,TX

Abstract: Campanian-Oligocene Evolution and Tectonostratigraphic Development of Northwestern South America

Stratigraphic evidence on depocenter evolution combined with the structural/tectonic causes for such changes allow us to understand the Campanian Oligocene of northwestern South America within a tectonostratigraphic framework.The central axis of deposition migrated from west to east; this migration had a structural origin and it happened in combination with tectonically-driven changes in accommodation space. The tectonostratigraphic evolution can be divided into the following phases: (1) The axis of the Campanian depocenter was located west of the present Central Cordillera. (2) The axis of late Maastrichtian deposition runs approximately over the present day western foothills of the Eastern Cordillera, crosses over Santander into Venezuela. Accommodation space decreased as reflected in a facies change from distal marine shales to shallow-water sandstones and isolated carbonates. (3) In Paleocene times, the central axis of deposition was located along the spine of the Eastern Cordillera, extending into western Venezuela.Accommodation space continued to decrease. (4) In latest Paleocene-early Eocene times the axis of deposition shifted to the eastern foothills of the Easter Cordillera and accommodation space decreased markedly leading to a major regional  unconformity. (5) In Middle-Late Eocene times the axis of deposition continued to shift east-wards but accommodation space increased allowing sporadic marine invasions. (6) In Oligocene times initial uplift of the Eastern Cordillera divided the main depocenter into two central axes, accommodation space diminished in uplifted regions and continued to increase in the depocenters. (7) As uplift of the Eastern Cordillera continued, the eastern depocenter axis (proto Orinoco) migrated east and the western depocenter axis (proto Magdalena) migrated west. The changes discussed here were controlled by the structural/tectonic evolution of the margin.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England