A NEW OCCURRENCE OF THE LATE JURASSIC RHYNCHONELLID COOPERRHYNCHIA (BRACHIPODA) FROM THE GREAT VALLEY GROUP, CALIFORNIA - CONFIRMING A COLD-SEEP COMMUNITY ASSOCIATION

A second occurrence of the rhynchonellid brachiopod Cooperrhynchia is recorded from the Late Jurassic Knoxville Beds (Tithonian, Great Valley Group) of northern California. Cooperrhynchia was first described by Sandy and Campbell (1994) based on material from a single isolated carbonate lens near the town of Paskenta in the western Sacramento Valley. Stanton had originally described this species as "Rhynchonella" schucherti in 1895. The paleoenvironmental setting of these fossils was considered a convergence-related cold seep with associated chemosynthetic worm tube and bivalve taxa (Campbell, Carlson, and Bottjer, 1993). The new material described here is from western Berryessa, 100 kilometers southwest of Paskenta. Similar chemosynthetic or modern vent-seep associated molluscan taxa are associated with both Paskenta and Berryessa brachiopods: lucinid and pectinid bivalves, and provannid, abyssochrysid, fissurellid and cerithid gastropods. The presence of biostratigraphically significant Buchia piochii indicates a similar late Jurassic (~150 m.y.) age. The material is from museum collections but has been described by early collectors (e.g. Angel, 1948) from isolated "limestone reefs" (to 15 m thick, to ~150 m long) and carbonate pods that occur along strike with surrounding fine-grained siliciclastic sediments. The enclosing strata are now attributed to deposition from turbidity currents along an axial forearc of a Mesozoic subduction system. Thus, this second record of Cooperrhynchia is also associated with another cold-seep community. These two isolated occurrences suggest that Cooperrhynchia might be another example of a seep-restricted brachiopod, which were relatively common in Mesozoic and Paleozoic hydrothermal vent and cold-seep settings (e.g., Campbell and Bottjer, 1995; Sandy, 1995). The Berryessa specimens exhibit some minor external differences when compared to the Paskenta specimens, including a larger size and more roundly triangular outline. This may warrant the establishment of a new species.