Autochthonous and Allochthonous Quaternary Ostracoda from Site 893, Santa Barbara Basin

Abstract

Site 893 of Ocean Drilling Program (ODP) Leg 146 (34°17.25'N,120°02.2'W) was drilled in a 576-m water depth. Recovered from thesite was an extensive marine sequence of late Quaternary sedimentsfrom the Santa Barbara Basin. The benthonic Ostracoda from 29core-catcher samples recovered from the 200-m-thick sequence havebeen analyzed for assemblage composition and population structure.Our studies show that this sequence contains a mixed assemblage ofallochthonous taxa together with some autochthonous deep-watertaxa. The shallow-water taxa are considered to have been transporteddown-slope into the basin.Few of the taxa recorded in the present study have been identifiedto species level because of the high number of juveniles recoveredthat render detailed taxonomy difficult. However, the presence ofspecies which possess well-developed ocular structures (e.g., Ambostracontweedsmuirensis and Cytheromorpha krausei) clearly indicatesan origin within the photic zone and attests to the allochthoneityof part of these assemblages. We believe that the absence of adultspecimens in many of the taxa recorded shows that the juveniles ofboth shelf and upper bathyal taxa have been transported downslope.Only Cytheropteron sp. A and Loxoconchidea dolgoiensis Brouwers,1990, have been recovered with well-represented suites of instars, indicatingautochthoneity.A number of previous studies have described Oligocene to Pleistocenedeep-water Ostracoda from onshore exposed sections insouthern California (Cronin, etal., 1983; Finger, 1983, 1982; LeRoy,1943), some of which are related to the assemblages at Site 893.