Stratigraphy and sedimentology of Upper Cretaceous rocks in coastal southwest Oregon: Evidence for wrench-fault tectonics in a postulated accretionary terrane

Southwest Oregon is a region of complex juxtaposition of tectonostratigraphic terranes. In southwest Oregon, three Upper Cretaceous (Campanian-?Maastrichtian) formations occur in fault and depositional contact with the Upper Jurassic Otter Point complex, an oceanic assemblage. These four units occur only west of high-angle, north-northwest-trending faults, and they make up a terrane (Gold Beach terrane) unlike any terrane east of these faults.

The patterns of sedimentation and the stratigraphic relationships of the three Upper Cretaceous formations indicate that they were deposited in a tectonically active setting influenced by vertical tectonics. Source areas for clasts in the Cretaceous conglomerates cannot be found in the adjacent Klamath Mountains or other nearby terranes. We postulate that they were deposited in a borderland-type basin with a sediment source at least as far south as southern California. They were translated north during latest Cretaceous to early Paleogene time and were then accreted to the Oregon margin.