PLIOCENE CHANNEL DEPOSITS OF OYSTER SHELLS IN THE SALTON TROUGH REGION, CALIFORNIA

The Imperial Formation, Salton Trough region, California, consists of rift-related deltaic sediments deposited at the head of the early Pliocene Gulf of California. Shell beds of the small plicate oyster Lopha vespertina (Conrad) form a widespread and distinctive sedimentary component of the deltaic deposits. Consisting of a mixture of skeletal material, calcite cement and siliciclastic sand, and reaching thicknesses of 5 m, the shell beds formed as lateral accretion deposits of meandering distributary channels on shallow marine portions of the delta. Shell beds consist mainly of planar cross-stratified shell gravels of point bar origin and also include facies representing channel lag and overbank deposits. Skeletal material in the shell beds was derived from an oyster-dominated community which inhabited overbank areas along channel margins. In addition to oysters, this community also included small numbers of other epifaunal bivalves, gastropods, corals, bryozoans, barnacles, echinoids, annelids and a shell-boring assemblage representing the Typanites ichnofacies. © 1990.