Systematic paleontology of a densely fossiliferous, upper Pliocene molluscan shell lens, 6th and Flower Streets, Los Angeles, California, with commentary on the stratigraphic nomenclature of the "Fernando Formation"

A richly fossiliferous lens of loose shells and shell materials in the uppermost part of the upper Pliocene Pico Formation in downtown Los Angeles, yielded an exceptionally well-preserved fauna of mollusks and other invertebrates. This lens, and its enclosing matrix of cemented coquina, the result of a turbidity flow initiated 7 km north of the resting site, was exposed in 1969 as the basement of the Arco Towers Plaza at Sixth and Flower Streets was being excavated. Both the lens and the matrix were completely removed along with any chance for further in situ study. This study of these fossils, which have been stored at the Natural History Museum of Los Angeles County, Section of Invertebrate Paleontology, shows a mixed assemblage of nearshore and deep-water species. The lens yielded a total of 138, mostly nearshore mollusks, nearly half of which are neogastropods, and some additional non-mollusks. Thirty-three bivalves, nine archaeogastropods, twenty-eight neotaeniogastropods, sixty-one neogastropods, two chitons, and two scaphopods are listed of which the bivalves, archaeogastropods, neotaeniogastropods, and scaphopods are herein subjected to synonymy. The neogastropods, chitons, non-mollusks, and the final sorting of nearshore and deep-water species have been reserved to future study. The rocks enclosing the ARCO fauna have been referred to the "Fernando Formation" by many early workers, but an exhaustive review of the stratigraphic nomenclature showed that "Fernando Formation" is not applicable because this "formation" has never been adequately defined. I have, therefore, referred the ARCO fauna and its enclosing rocks to the uppermost Pico Formation. The ARCO fauna is herein assigned to the Pliocene based on subjacency to rocks already adequately defined as upper Pliocene and the inclusion in the fauna of the terminal Pliocene fossil, Patinopecten healeyi (Arnold, 1906).