Abstract: Salinian Block of California, an Enigma

D. G. Howell, J. G. Vedder

The Salinian block is an allochthonous granitic terrane bounded on the east and west by fore-arc basin and accretionary-prism terranes of Late Jurassic to Late Cretaceous age. This linear, fault-bounded block is made up mainly of granitic plutons of Late Cretaceous age (80 to 100 m.y. old) with local roof pendants of Paleozoic(?) metasedimentary rock. The probable root zone of the Salinian block lay well inboard of the leading edge of a late Mesozoic arc complex. The original source terrane of the Salinian block is equivocal; speculations, however, based on large-scale plate movements, include southeastern California, Central America, and even Asia.

The oldest rocks that lie depositionally on Salinian basement are Late Cretaceous strata (late Campanian and Maestrichtian) that crop out in five separate areas. From north to south, these are Gualala, Pigeon Point, northern Santa Lucia Mountains, Nacimiento Lake, and the La Panza Range. Sedimentary lithofacies vary abruptly, both laterally and stratigraphically, and include numerous progradational and retrogradational sequences in environments ranging from nonmarine to subsea-fan complexes. Conglomerate clast suites and paleocurrent data suggest that each of five outcrop areas represents a discrete basin or clastic wedges deposited along an irregularly shaped coastline.

Many aspects of the early geodynamic history of the Salinian block are unknown, but its latest Cretaceous history seems to have involved uplifting and basin-forming tectonics. Crustal instability lasted through early Paleogene time with the formation of additional small basins. By Eocene time the west margin of the proto-Salinian block was tectonically removed and replaced by an allochthonous terrane consisting of fore-arc and accretionary complexes. Most of the strike-slip displacement between these two terranes occurred along the Sur-Nacimiento fault system and all related strike-slip movement ceased by Oligocene time.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California