RELICT OF A LOST PACIFIC COAST: LATE CRETACEOUS (CAMPANIAN) REEF FAUNA FROM THE BLACK STAR CANYON QUADRANGLE, SANTA ANA MOUNTAINS, SOUTHERN CALIFORNIA

A Late Cretaceous marine invertebrate fauna with several species of rudists and scleractinian corals has been discovered in the Campanian age strata of the Santa Ana Mountains, southern California. This new fauna is significant because the Late Cretaceous rocks along the Pacific Coast of southern California typically do not yield sedimentologic or faunal evidence for the coastal and shallow-marine depositional environments which must have existed during this time. Therefore, this recently discovered Campanian marine invertebrate fauna provides a unique insight to the paleoecology of the environments along this segment of the Pacific Coast. The specimens were collected from conglomeratic beds at the base of the Schulz Ranch Sandstone Member of the Williams Formation. This fossiliferous horizon is just above the disconformable contact with the Holz Shale Member of the Ladd Formation. Although the fossils from these conglomeratic sandstone beds do not appear to be in situ, the preservation of specimens with intact ornamentation indicates that they have not been reworked.

The presence of colonial scleractinian corals, rudist bivalves, and a species of calcareous alga indicates a warm, shallow environmental setting along the coast. The fauna contains at least three species of rudist bivalves, including abundant valves of the caprinid Coralliochama orcutti White, 1885, which is a relatively common species in other localities along the Pacific Coast; several specimens of the hippuritid Barrettia sparcilirata Whitfield, 1897, the first hippuritid to be reported from the Pacific Coast of North America; and large fragments of an undetermined species of radiolitid. The scleractinian coral species are massive, colonial taxa with plocoid, cerioid, and thamnasteroid growth forms that are typical of extant zooxanthellate reef-building corals. The taxonomically diverse fauna also contains many other mollusks which are characteristic of the middle to late Campanian strata in the Santa Ana Mountains and surrounding region, including species of the bivalves Crassatella, Glycymeris, Cymbophora, Pterotrigonia, Opis, Cucullaea, Indogrammatodon, Eriphyla, and Pachycardium, and species of the gastropods Volutoderma, Ampullina, Euspira, Perissitys, and Pyktes.