INNER FAN CHANNEL DEPOSITS IN THE GERMAN RANCHO FORMATION NEAR SALT POINT STATE PARK, SONOMA COUNTY, CALIFORNIA

Inner fan channel deposits in the Paleocene/Eocene German Rancho Formation (GRF) crop out in sea cliffs in the area of Salt Point State Park (SPSP), northwestern Sonoma County, California. These deposits contrast sharply with more distal facies of the GRF exposed both north and south of SPSP. The channel deposits are composed of basal conglomerates and sandstones (Turbidite Facies A and B) averaging 2-4 m thick overlain by thinner bedded sandstones with rare shales. The basal contacts of the individual flow units are curved and incise into the underlying beds. Groove casts and flame structures are common. The entire channel system is incised into shales and siltstones (Turbidite Facies G) exposed in the inner cliffs at Stump Beach Cove. An exceptional channel just north of Stump Beach Cove is approximately 50 m across and 8 m thick. The basal sandstones and conglomerates of the channel fills are more resistant than the thinner bedded upper intervals and interchannel deposits and form the small hills that are prominent on the marine terrace at SPSP. Channel-fill conglomerates are composed of granitoid (40%), limestone (19%), quartzite (14%), and volcanic (7%) clasts with minor chert, sandstone, and siltstone. Locally gastropod (Turritella sp.) shells are abundant (up to 24%) in the conglomerate matrix. In deposits north of Stump Beach Cove, purple micrite clasts are very abundant and contain poorly preserved large globigerine-like planktic foraminifers, probably Cretaceous in age, and suggest an open marine environment for the source rocks. Rarer smaller foraminifers are also present. The clast compositions vary drastically between individual conglomerates (even vertically adjacent units) suggesting that the channel system was fed by a complex submarine canyon system that delivered sediments from different sources at different times.