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John B. Wagner1
(1) University of Texas at Dallas, Richardson, TX

Abstract: Interaction and Effects of Allocyclic Processes on the Stratal & Sedimentological Expression of Depositional Systems: An Example from the Bolivian Sub-Andean Foreland Basin

The Madre de Dios Basin of Bolivia represents two distinct phases of tectonic development that illustrate the linked stratigraphic responses to a changing basin style. The first phase associated with the Paleozoic is characterized as an intracratonic setting. The second, which began during the late Mesozoic and persists today, is the development of the Sub-Andean Foreland Basin. Hydrocarbons occur primarily within stratigraphic traps, potential reservoirs and seals are Paleozoic to Late Mesozoic in age.

Paleozoic depositional environments identified from core indicate major changes in climatic conditions have occurred and include fluvial/deltaic, eolian dune, coastal sabkha, and shallow marine carbonate facies. A Late Devonian marine source rock with total organic carbon (TOC) content of up to 18% also occurs within the basin. Cretaceous age sediments contain an incised valley system of 10 to 15 kilometers in width and 300 meters in depth. Valley fill facies represent low sinuosity, braided fluvial systems grading upwards into estuarine muds. Terracing of the valley margin formed in response to multiple cut and fill episodes (baselevel fluctuations) of valley formation. Recurrent movements of basement involved fault blocks related to migration of the advancing forebulge, controlled the location and magnitude of valley incision and drainage incisement patterns.

Large-scale variations in depositional environments, duration of geologic time (450 to 60 MY) represented by the stratigraphic section within a changing tectonic style, provides the Madre de Dios Basin as an example of the process to response interplay between tectonics, eustasy, climate and sediment supply.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana