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Integrated Multidisciplinary Biostratigraphic and Paleoecologic Study of Southern California Neogene Coastal Sections

G. H. Blake, R. G. Arends, M. V. Filewicz, M. L. Cotton Thornton, D. R. Vork

This integrated biostratigraphic and paleoecologic study of several Neogene sections of coastal southern California is based on the use of diatoms, calcareous nannofossils, palynology, and benthic foraminifera. The study included the Naples Bluff, Topanga Canyon, and Newport Bay sections, and DSDP Site 468.

These sequences commonly contain well-preserved diatom floras and moderately preserved calcareous nannofossil floras. The integration of diatom and calcareous nannofossil biochronology allowed construction of sediment accumulation curves for these stratigraphic intervals. The sediment accumulation curves can then be used to determine the timing of faunal variations associated with the provincial Miocene benthic foraminiferal stages of R. Kleinpell. These data allow reconstruction of basin history models, including the age and duration of regional hiatuses and unconformities. Palynologic stratigraphy can also support the hiatuses and allows extrapolation of the model out to the marginal and nonmarine basin edges.

The diatom assemblages for these sections are relatively abundant and range from the early Miocene Actinocyclus ingens zone to the early Pliocene Thalassiosira oestrupii zone of J. A. Barron. The diversity and abundance of these assemblages made precise age control for the sections possible. A major unconformity or severely compressed interval exists between 14.8 and 9.3 Ma in the majority of the sections.

The benthic foraminiferal faunas are generally abundant and are representative of the Saucesian through Repettian Stages. The inner continental margin sections are dominated by lower-middle to upper bathyal assemblages. In contrast, the outer continental margin sequence is dominated by lower bathyal species, which are found in rare occurrences in some parts of the inner continental margin sections.

Early Neogene calcareous nannofossil assemblages are moderately to poorly preserved and typically nondiverse, but contain age-diagnostic species representative of the early Miocene CN2 zone through the middle Miocene CN5 zone. Several samples from the type upper Mohnian contain the temperate species Discoaster mendomobensis, which suggests correlation with the late Miocene CN9 zone.

Palynomorph recovery is generally good in the early Miocene through Pliocene-Pleistocene sequences of this study, and the data in part supports the absence of a section at the Naples Bluff section. The early Mohnian to early late Mohnian palynomorph equivalent is very thin and overlies the Luisian palynomorph equivalent at the hiatus.

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