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3-D Modeling of a Multi-Staged Turbidite System within a Structurally Complex Basin: The Republic Sandstone Member, San Joaquin Valley, California

M. J. Richey
Texaco California Inc. Bakersfield, CA

3-D modeling and depositional reconstruction of the Republic Sandstone Member of the Monterey Formation indicates that San Andreas Fault-derived deformation played a major role in the geometric and lithologic character of terrigenous-sourced, coarse-clastic turbidite sedimentation along the southwestern margin of the San Joaquin Basin during the late Miocene.

Outcrops and nearby subsurface data of the five sand lenses comprising the Republic Sandstone Member illustrate a near crosssectional view of a developing sandy turbidite system. Deposition of these sands was restricted to a northwest-trending, anticlinebounded, asymmetric, intra-slope basin along the northeastern dipping western slope of the encompassing San Joaquin Basin. This subbasin is one of many anticline-bounded lows that collectively form the structural feature referred to as the Temblor Anticlinorium, a feature believed to be the result of wrench tectonics associated with initiation of strike-slip plate motion along the San Andreas Fault 10 kilometers to the west.

To most accurately determine the influence of the sub-basin margin relief on sedimentation, 3-D surface to subsurface and depositional reconstruction models incorporating both structure and stratigraphy were developed. Initial models focused on defining the general architecture and terminal extent of the sand bodies. The orientation of the sand units within these models revealed offset stacking of the sand bodies to the northwest with time, suggesting that both vertical and horizontal development of the eastern basin margin coincided with sedimentation. 3-D resistivity (lithology) property models were developed to identify the internal architecture of individual sand units. Analyses of all models contradict previous workers interpretations of the tectonic environment during sedimentation of the Republic Sand. Where it was once thought that the sub-basin exhibited only a confining to non-confining nature (accommodation space in-filling) throughout sedimentation, results illustrate a nonconfining to confining to non-confining trend. This trend can best be explained by initiation of sedimentation prior to sub-basin margin development and the continuation of sedimentation through final margin development.

AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California