SUNDBERG, FREDERICK A., Invertebrate Paleontology Section, Natural History Museum of Los Angeles County, Los Angeles, CA

ABSTRACT: Coniacian and Santonian (Upper Cretaceous) Paleontology and Paleoenvironments of the Santa Ana Mountains

Coniacian and Santonian fossil assemblages are present at several localities in the Santa Ana Mountains. These assemblages

and the containing strata were deposited in outer shelf to slope settings in contrast to the inner to middle shelf settings of the underlying Turonian faunas and sediments. Coniacian strata were deposited under disaerobic to anoxic conditions, perhaps within the oxygen minimum zone. In contrast, the Santonian deposits accumulated in an aerated or slightly disaerobic setting. Several shallow-water taxa in the Santonian assemblages were introduced into a deeper water setting via sediment gravity flows.

Recognition of the Coniacian and Santonian fossil assemblages dispels the proposed hiatus or a phase of slow deposition within the Upper Cretaceous section in the Santa Ana Mountains. In addition, the Cenomanian(?) to early Campanian stratigraphic sequence in the Santa Ana Mountains illustrates an overall transgressive sequence, with a brief regressive or progradational phase during the latest Turonian and/or earliest Coniacian. A similar pattern also has been observed in Upper Cretaceous sequences in other areas of North America.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.