Structural Deformation in the Offshore Santa Maria Basin, California

WILLINGHAM, C. RICHARD, Explorametrics, Carpinteria, CA, RONALD G. HECK, R. G. Heck & Associates, Carpinteria, CA, and JAN D. RIETMAN, Rietman Consultants, Santa Ana, CA

We divide the offshore Santa Maria basin into the southern, central, and northern provinces based on the pattern, style, and timing of late Cenozoic deformation. From our analyses of over 2000 km of CDP seismic data and offshore well data we prepared time structure contour maps for three basin-wide unconformities: top of basement, top of Miocene, and the unconformity between early and late Pliocene chronostratigraphic units. Isochron maps were constructed between these horizons and between the early/late Pliocene unconformity and the sea floor to evaluate timing of the deformation. All maps were converted to depth and isopach values based on a three-dimensional velocity model.

The southern province is characterized by near-coastal uplift that increases southward from the latitude of Point Sal. This uplift is coupled with northwest-trending folding. Folding occurred episodically from the early Miocene to the Holocene. The central province is relatively undeformed except for the northern extension of the Queenie structure and along the Hosgri fault zone in the east. In these areas up to 2.5 km of Miocene-Holocene sediments have accumulated. The northern province extends northward from the latitude of Point Estero and displays strong near-coastal uplift and folding culminating in the Piedras Blancas antiform. Seaward the effects of deformation diminish and are restricted to lower Pliocene and older rocks.

The regional structure contour and isopach maps show that the offshore Santa Maria basin is characterized by localized crustal shortening orthogonal to the Pacific/North America plate margin and indications of post-Miocene to recent lateral slip along the eastern basin boundary, the San Simeon/Hosgri fault system.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)