Abstract: Slope-Basin Benthic Foraminifera of California Borderland

Robert G. Douglas, Hal Heitman

Recent baseline investigations of slope and basin benthic Foraminifera in the California borderland reveal a complex relation between live and dead populations: the two are not in equilibrium and indicate faunal shifts following environmental changes during the Holocene.

The distribution of live populations is related to variations in dissolved oxygen, sediments, and nutrients. Oxygen levels limit mud-eating macrobenthic predators which control foraminiferal standing crop. Slope and basin environments of the inner borderland occur within the oxygen-minimum zone, and foraminiferal densities exceed 100 individuals/cc, but vary seasonally. The microfaunas of the mainland slope and basin are identical, varying only in species frequencies, and include Epistominella smithi and Suggrunda eckisi. In deeper slope and basin environments of the middle and outer borderland, oxygen levels are higher, and standing crop is ± 1 individual/cc. Common species are E. smithi, Cassidulina delicata, Uvigerina peregrina, many agglutinated taxa, and rare low-oxygen spec es. Microfaunas differ from slope to basin and between basins.

Differences between live and dead populations are greatest in middle and outer borderland environments and, in part, can be attributed to postmortem transport and mixing. Dead populations indicate that present conditions in the outer borderland were more widespread in the Pleistocene.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma