A PETROGRAPHIC LINK BETWEEN THE LATE CRETACEOUS PIGEON POINT CONGLOMERATE AND FELSITIC VOLCANIC ROCKS NEAR PESCADERO, CALIFORNIA

The Late Cretaceous (Campanian) Pigeon Point Formation is located west of the San Gregorio fault and crops out for about 16 km along the California coast between San Francisco and Santa Cruz. The formation locally overlies 86-90 Ma felsitic volcanic rocks (Ernst and others, 2009). An on-going provenance study of igneous clasts in the Pigeon Point Formation reveals that ~5 percent of them appear to be a match with the underlying Pescadero felsite. These conglomerate clasts exhibit similar texture and composition, and significantly they contain prehnite and pumpellyite, as does the Pescadero felsite, indicative of low temperature burial metamorphism. This metamorphic assemblage is otherwise absent in clasts of the Pigeon Point Formation and associated sedimentary section, suggesting the Pescadero felsite is the source of the felsitic conglomerate clasts and significant uplift and erosion of the felsite prior to, or during deposition of the Pigeon Point Formation. Discovery of Pescadero felsite clasts in the Pigeon Point Formation corroborates the depositional relation between the Pigeon Point Formation and the felsite inferred by Ernst and others and partly clarifies the context of the Pigeon Point Formation in the tectonic history of western California.