MID-MIOCENE CETACEAN FOSSILS, PAULARINO MEMBER, TOPANGA FORMATION, WESTERN SAN JOAQUIN HILLS, ORANGE COUNTY, CALIFORNIA

Cetacean skeletal remains contained within the mid-Miocene Paularino Member of the Topanga Formation were exposed during land development in 1997 on the western edge of the San Joaquin Hills, Orange County, California. The site represents a dense concentration of fossil material that includes articulated and semi-articulated whale skeletons, an abundance of mostly cetacean bone fragments, shark skeletal fragments, and shark teeth and other marine vertebrate dentary. Irvine Valley College became the recipient of the fossil assemblage, and preparation work began during the Spring, 2004 semester on select jacketed skeletal fragments.

To date, preparation and identification of fossils from a dozen jackets has yielded the following: fragments of cetacean spinous and transverse processes, cetacean rib fragments, partial cetacean scapula. One incomplete molariform tooth, species unknown, was prepared from a small jacket, containing pebble-sized matrix material. Bioturbation and trace fossils are rarely observed, however one of the jackets containing a sandy siltstone matrix did contain burrows. Small fish scales and shell fragments have been seen in several matrix samples.

The matrix material from various jackets ranges from moderately well sorted to very poorly sorted, and commonly varies from gray siltstone to light-brown to gray silty sandstone. Patches of subrounded to rounded granules of mostly gray to white quartz, with lesser amounts of potassium feldspar, commonly concentrate around the bones in some of the coarser-grained fossil samples. Preliminary grain analyses indicate at least two distinct quartz grain populations in some matrix samples. One population of quartz consists of subrounded to subangular, lightly colored grains that appear abraided, and often iron stained. The second quartz population is comprised of subangular to angular, clear, colorless grains. Secondary minerals include fine grained micas, and oxidized metallic minerals. Fine-grained, subrounded volcanic rock fragments were also noted. Gypsum cements were present in all samples analyzed.