Paleo-Oceanographic Controls on Lithofacies and Biofacies Patterns in Neogene Basins of California

James C. Ingle, Jr.

Collision of the Pacific and North American plates (about 29 Ma) and subsequent birth of the San Andreas transform system led to the rapid formation of a Miocene borderland stretching across 20° of latitude from Baja California, Mexico, to northern California. The resulting complex of basins, ridges, and islands was much larger than the modern borderland off southern California and was astride an unusually dynamic oceanographic and climatic hinge line dominated by the California Current. Studies of borderland basins have generally emphasized the role of tectonism in controlling basin evolution, including aspects of basin stratigraphy. This paper focuses on faunal and lithofacies evidence of the paleo-oceanographic history of this region and the role of global and pro incial oceanographic and eustatic events in dictating the strikingly similar stratigraphic pattern expressed throughout the Neogene borderland. Early Miocene, late Miocene, and Pliocene paleogeographic maps of the borderland clearly illustrate the highly irregular configuration of the evolving Miocene coastline, which may well have been a major factor in dictating the position and stability of major upwelling plumes and creating areal variations in the flux of organic materials delivered to various segments of the borderland. Invasion by Pacific Intermediate Water and associated oxygen minima into the evolving borderland was in turn responsible for creating sub-oxic slope and basin-plain environments capable of enhancing preservation of organic-rich sediments. This condition was further nhanced through sill control of basin geochemistry and/or episodic expansions of the oxygen minimum layer. Climatically induced variations in the character, age, and flow of Pacific Deep Water into the Neogene borderland are clearly reflected by variations in benthic foraminiferal biofacies and apparent episodes of intense carbonate dissolution. Correlation of Neogene O¹⁸ and C¹³ trends analyzed in DSDP corehole sequences from the deep Pacific Ocean with quantitative planktonic and benthic faunal patterns from the Miocene borderland of California demonstrate the impact of global events in controlling provincial biostratigraphies through the manipulation of local species ranges.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.