ABSTRACT: Tectonic Effects on the Stratigraphic Sequences Along the Midland Fault Zone, Southern Sacramento Basin, California

JOHNSON, DANE S., Consulting Geologist, Clovis, CA

Seven stratigraphic sequences have been evaluated in the Upper Cretaceous and Paleogene strata between the base of the Sacramento shale and the Neogene nonmarine sediments within the study area southwest of Sacramento, California. Tectonic events along the Midland fault zone of the southern Sacramento basin have modified the Paleogene stratigraphic sequences across the fault zone.

Syndepositional tectonics along the Midland fault zone have resulted in the formation of domal structures on the downthrown (western) side of the fault zone at the Bunker, Lindsey Slough, and Rio Vista gas fields. Late Paleocene tectonics resulted in the initial formation of the domal structure at the Rio Vista gas field, as evidenced by the thinning of the Anderson Sandstone (uppermost member of the Martinez sequence) over the crest of the domal structure west of the Midland fault. The relatively constant thickness of the McCormick Sandstone and Martinez Shale members of the Martinez sequence also indicates a late Paleocene origin for the Midland fault in the Rio Vista area. Early to middle Eocene movement along the Midland fault zone has resulted in the removal of the Meganos regres ive sequence east of the Midland fault, and the removal of the upper part of the Martinez sequence east of the fault zone, with only the lower part of the McCormick Sandstone member of the Martinez sequence remaining east of the fault zone. Eocene syndepositional movement along the Midland fault has resulted in a thickening of the Eocene strata along the western (downthrown) side of the fault.

AAPG Search and Discovery Article #91016©1992 AAPG-SEPM-SEG-EMD Pacific Section Meeting, Sacramento, California, April 27-May 1, 1992 (2009)