Print this pageRecognition and Development of an Incised Valley System, Madre De Dios Basin, Bolivia
WAGNER, JOHN B., and RICHARD J. MOIOLA
The Late Cretaceous foreland basin sequence of the Madre De Dios Basin, Bolivia, contains an excellent example of a valley-fill system (up to 15 kilometers in width and 300 meters in depth) formed in response to changes in tectonics, sea-level, climate and sediment supply.
Seismic data suggests that potential reservoir facies are located near the base of the incised valley. They are interpreted to represent low sinuosity to braided fluvial deposits emplaced during the end of a relative sea-level fall and initial rise in sea- level. The terraced morphology of the valley margin formed in response to multiple cut and fill episodes (baselevel fluctuations) of valley formation, with basement involved faulting influencing the location and magnitude of valley incision. Isopach mapping demonstrates that the valley incises more deeply in a landward direction than in a seaward direction. Recurrent movements of basement that involved fault blocks and pre-existing topography, appears to have controlled the drainage incisement patterns and possibly had influence on petroleum migration pathways. Sealing facies are the infill units deposited during subsidence and associated transgression, interpreted to be fine-grained estuarine muds and/or possible marginal marine deposits. It is our interpretation that finer-grained estuarine deposits filled the upper portions of the valley during a slow relative sea-level rise as the downdip reaches of the incised valley were flooded.
Our work suggests incised valleys should contain multiple channel systems within the confines of the valley margins, as a key criterion for their recognition.