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Abstract: Fold and Thrust Structure and Exploration Concepts Along the Southwestern Margin of the San Joaquin Basin, California

DAVIS, THOM, Davis and Namson Consulting Geologists, San Fernando, CA; JAY NAMSON, Davis and Namson Consulting Geologists, San Fernando, CA

The deformed south and west margins of the San Joaquin basin have been interpreted by several investigators including us to be a seismically active fold and thrust belt. Despite the belt being extremely prolific (8 Bbbl produced, +1 Bbbl proven reserves) the more complex and deeper portions of the belt remain under explored. In part this is due to poor quality seismic reflection imaging due to a host of problems including steep dips, complex folding, and rugged topography Over the past decade we have constructed a sequence of restorable cross sections to better understand the geometry and kinematic history of the belt and its exploration potential. These cross sections incorporate well data and unpublished surface mapping. Using thrust belt concepts we have field mapped a number of previously unknown thrust faults and folds that significantly impact the subsurface geometry of the belt. Thrust faults are east vergent and the deeper and more basinward faults do not reach the surface and fault slip is consumed in folds or removed along unconformities. The Temblor and San Emigdio Mountains are a result of late Pliocene and Quaternary folding and not mountain front faulting. Anticlinal folding results from ramps in the thrust surfaces or fault propagation folding. The belt is very complex along strike as a result of stratigraphic changes and the influence of older structures. Exploration leads such as subthrust anticlines and footwall traps are defined in a dip sense but need additional cross section work to develop a well constrained three-dimensional image(s).

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California