PALEOECOLOGY OF A LATE PLIOCENE MARINE INVERTEBRATE FAUNA FROM SOUTHERN CALIFORNIA

Mount , Jack D., Department of Geology, University of California., Los Angeles, California 90024

      A marine fauna of over 250 species and subspecies of larger invertebrates was collected from the lower part of the Fernando Formation, on the east bluff of upper Newport Bay, Orange County, California. This assemblage occurs in a lens of sandy cobble conglomerate considered to be deposited as a gravitite. The fauna is characterized by a mixture of mollusks from shallow to deep water, including southern and northern extralimital and submergent forms. Based on the present distribution of extant members, this mixed fauna was arranged into depth associations whose hydroclimates were reconstructed separately.
      The presence of a Panamic element in the protected shore to shallow inner sublittoral zone (int.-15 fathoms) suggests somewhat warmer temperatures than at this latitude today. The exposed shore assemblage indicates slightly cooler water, which is attributed to upwelling.
      The majority of the species represents the deep inner sublittoral to shallow bathyal zone (15-200 fathoms) and contains a significant element of frigaphilic species. Twelve mollusks are now restricted to the Aleutian Province. This assemblage suggests that the water at this depth was considerably colder.
      The assemblage from the bathyal zone is poorly represented and indicates no significant differences from conditions at these depths today. The inferred depth of deposition is greater than 300 fathoms.
      Using a two-fold division of the Pliocene in California the fauna is assigned an early Late Pliocene age on the basis of characteristic guide fossils and by its similarity to other Pliocene faunas in southern California.

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