Jurassic Through Oligocene Paleogeography of the Santa Maria Basin Area, California

FRITSCHE, A. EUGENE, California State University, Northridge, CA, and DANIEL A. YAMASHIRO, Groundwater Technology, Inc., Tempe, AZ

Compilation from published reports indicates that the paleogeographic history of the Santa Maria basin area of California (west of the

Sur-Nacimiento fault and north of the Santa Ynez fault) began in the Early Jurassic in an area far to the south with the creation of a spreading-center ophiolite sequence. As the ophiolite rocks moved relatively away from the spreading center, they were covered by Lower Jurassic through Lower Cretaceous basin plain and prograding outer continental margin deposits. During this time, right-lateral movement along faults that were located to the east was transporting the area relatively northward toward its present location.

A mild tectonic event in the middle of the Cretaceous caused formation of a parallel unconformity. Renewed subsidence in the Late Cretaceous brought deposition in trench, slope, sandy submarine fan, shelf, and ultimately in the eastern part of the area, delta and fluvial environments. During the ensuing Laramide orogeny, significant deformation raised the entire area above sea level and erosion created a major angular unconformity.

During the early Tertiary, most of the Santa Maria basin area remained elevated as a forearc highland. The present-day east-west-trending area south of the Santa Ynez River fault was at that time oriented north-south. During the Eocene, this portion of the area was submerged and became a forearc basin that was located to the east of a forearc ridge that served as a source of sediment. The basin filled through the Eocene and Oligocene with submarine fan, slope, shelf, coastal, and finally fluvial deposits. In the medial Miocene, these forearc basin rocks were rotated clockwise into their present position along the southern margin of the basin and the upper Tertiary Santa Maria basin was formed.

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