NEOGENE MARINE MOLLUSKS IN BAJA CALIFORNIA AND THE ANCIENT GULF OF CALIFORNIA HAVE HOLOCENE AND FOSSIL RECORDS IN THE CARIBBEAN PROVINCE

High tech methodologies and theoretical models currently prevail in paleogeographic reconstructions of complex plate boundary areas, but low tech, collections-based paleontological research provides a time frame for tectonostratigraphic events and the geographic connections between marine embayments and plate slivers.

Updated nomenclature for Pacific and Caribbean, Holocene and fossil index species and subspecies is critical because the same taxon may have multiple names for living and fossil specimens from different basins. Taxonomic splitting obscures conspecific and phylogenetic relationships that indicate distribution patterns in time and space, and that correlate sediments along the complex Pacific/North American Plate boundary. This area includes the southwestern Basin and Range Province, southern San Andreas Fault system, Gulf Extensional Province, the northern East Pacific Rise and the California Continental Borderland.

Tertiary marine fossils from Baja California and the Salton Trough of California have newly refined ages based on associated radiometrically-dated volcanic rocks. They correlate particular embayments in west Mexico and southern California with classic sections in Panama, Costa Rica, Dominican Republic, Trinidad, Venezuela, Colombia and Ecuador. They also relate western Baja California to slivers of tectonic terranes in southern California. Field work and the extensive Paleobiology and Systematic Biology collections in the Smithsonian Institution’s National Museum of Natural History provide comparative data on molluscan biodiversity, morphologic variability, geographic distributions and ecology.

Work in progress suggests that some taxa are time-transgressive: early Middle to Late Miocene age in west Mexico and the ancient Gulf of California, Miocene, undifferentiated in Panama, Colombia, Venezuela, and Trinidad, and living in the eastern Caribbean. Attention to specific and subspecific nomenclature will greatly improve Bioinformatics databases that aim to include all organisms, living and fossil, world-wide.