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.