PALEOECOLOGY OF MARINE MOLLUSC ASSEMBLAGES IN LOS ANGELES BASIN DURING THE QUATERNARY: DARK DATA SEE THE LIGHT

Los Angeles Basin has experienced continuous subsidence and deposition throughout the Quaternary, resulting in an especially complete and thick succession. These deposits contain the richest and most diverse marine mollusc assemblages of any sedimentary basin in western North America. A long history of fossil collection, museum curation, and scholarly publication makes available a rich dataset to assess the consequences of changing environments on regional biodiversity and ecology, and determine the environmental and taphonomic constraints on this fossil record. The Natural History Museum of Los Angeles County has substantial collections from this basin (2.5 million specimens), of which a considerable number have been digitized through past NSF-funded initiatives. Out of the collections already digitized more than 900,000 specimens from 234 sites within Los Angeles Basin are determined to be suitable for quantitative paleoecological analyses. These appear to have been bulk sampled or were collected from stratigraphically constrained areas and with thought given to preserving abundance patterns. These specimens represent nearly 1300 species of molluscs, brachiopods, and echinoderms, whose ecological preferences are well understood from modern observations and data.

These data were analyzed with multivariate tools, including cluster and detrended correspondence analysis (DCA), to explore controls of bathymetry and related environmental parameters on community composition, and provide an environmental framework for interpreting the completeness of this fossil record. Despite the considerable data heterogeneity of these museum collections (e.g., sampling methodology), very clear lithostratigraphic groupings of samples could be observed using both techniques. DCA indicates a strong bathymetric control, with samples representative of shoreface through mid-shelf depths oriented along the principal axis. These data, when analyzed in a stratigraphic sequence or spatial arrangement reveal paleoenvironmental patterns associated with proximity to shoreline and syndepositional tectonic deformation.

Ongoing digitization activities as part of the NSF-funded Eastern Pacific Invertebrate Cenozoic Communities (EPICC) TCN will soon make even more data accessible to researchers.