ABSTRACT

Miocene strata in the Cuyama basin of southern California exemplify syntectonic and post-tectonic stratigraphic development in a strike-slip basin. Integrated seismic, well-log, and outcrop data provide a detailed portrayal of the seismic stratigraphy and sedimentary facies in the previously unstudied middle and upper Miocene sequences. Results show sharp contrast among syntectonic and post-tectonic strata from composition and texture of sediments to lateral distribution and thickness of facies.

Seven post-tectonic sequences were mapped across the basin. Sequences contain eolian to fluvial terrestrial facies, wave- and tide-dominated nearshore facies, biosiliceous, dolomitic, and phosphatic outer-shelf and slope mudstones, and shale-rich submarine fans in basinal environments. Authigenic dolomites and phosphates are pervasive in outer-shelf and slope facies and indicate the possibility of restricted sediment supply. Post-tectonic sequences are thin but laterally continuous, and they exhibit little depositional asymmetry. Minor erosion is distributed equally among regressive and transgressive relative sea-level changes.

Asynchronous changes in tectonism, sediment supply, and eustatic sea-level change created dramatic differences among syntectonic and post-tectonic sequences. Interbasinal tectonic quiescence led to the abrupt end of stratigraphic mismatches and the accumulation of sediment during brief, episodic periods. Multiple points of progradation persisted through several million years of post-tectonic basin development and highlight the importance of extrabasinal sediment supply to the development of all sequences. The eventual loss of most accommodation space promoted the importance of eustatic sea-level change and reduced the prominence of asymmetric facies and abrupt lateral facies changes.