AN EXTENDED PLIOCENE FORAMINIFERAL RECORD FOR THE EASTERN SANTA BARBARA BASIN

In 2007, the California Academy of Sciences (CAS) received the microfossil collection of Union Oil of California (Unocal). The collection represents the accumulated micropaleontological collection of Unocal for much of its operation during the 20th century, and those of companies acquired by Unocal during its existence. It consists of more than 750,000 vials of residues from marine and terrestrial sampling, including cores, grabs and surface samples. Since its acquisition, the collection has been transferred from a Unocal storage facility in La Brea, California, to the CAS collections in San Francisco, where a process of compactorization, sample rehousing, and data exploration was initiated to understand the scope of the collection. One focus of this effort is to determine the extent to which the collection supplements or extends publicly accessible micropaleontological data.

Here we present foraminiferal assemblage data from Unocal core D273, the first exploratory oil well core drilled from the Dos Cuadras oil field located in the eastern Santa Barbara Basin (SBB), California (34.331°N, 119.6269°W), in March, 1968. Assemblages were constructed and diversity indices calculated for 125 sample residues spanning a 955 m continuous depth transect from 195-1150 m below sea floor. The stratigraphy of the Dos Cuadras oil field, combined with benthic foraminiferal assemblage data, suggest that the sampled transect represents the Pliocene Pico Formation, most notably the “Repetto” biozone of the early Pliocene Repettian Stage (4.8-2.58 Ma), extending the available temporal range of foraminiferal data for the SBB. Preliminary examination of foraminiferal assemblages reveals a trend in decreasing diversity downcore, and increasing dominance of Cibicides, Epistominella, Bolivina, and Uvigerina– genera which indicate lower middle bathyal depths and intermediate hypoxic conditions. Further examination of D273 and related warm-interval Pliocene cores may provide proxy data for SBB conditions under IPCC “business as usual” scenarios for the end of this century.