DEPOSITIONAL AGE, PROVENANCE, AND BASIN DEVELOPMENT OF THE BASAL GREAT VALLEY FOREARC BASIN, NORTHERN CALIFORNIA

The Great Valley Forearc (GVF) basin, California contains sedimentary strata that reflect deposition along the western margin of North America during active oceanic subduction in Mesozoic-early Cenozoic time. Residing between the Franciscan accretionary complex to the west and the Sierra Nevada magmatic arc to the east, the GVF basin is divided into two subbasins: the Sacramento and the San Joaquin. This study targets basal GVF strata of the northwest Sacramento subbasin to address the following questions: (1) When did sedimentation begin along the length of the basin? and (2) What was the original location of the GVF relative to the western margin of North America at the onset of sedimentation? This study employs U-Pb detrital zircon geochronology and sandstone petrography on 13 detrital zircon samples from basal GVF strata to constrain maximum depositional ages and identify provenance signatures. Detrital zircon data yield Jurassic and Cretaceous maximum depositional ages that range from ~151 Ma to ~132 Ma. Prominent detrital zircon age populations comprise Early-Late Jurassic and Early Cretaceous ages, which are likely derived from Mesozoic igneous and volcanic rocks of the Sierra Nevada-Klamath magmatic arc. Modal point counting results support this interpretation, with the majority of samples comprising litharenites that plot in the magmatic arc tectonic provenance field. Pre-Mesozoic detrital zircon age populations contain peak populations of 2200-2000 Ma, 1900-1600 Ma, 1500-1400 Ma, 1300-950 Ma, 700-550 Ma, and 450-250 Ma, consistent with North America affinity sources. Where GVF strata are in depositional contact with the underlying ophiolitic basement, variation of basal GVF maximum depositional ages supports the interpretation of diachronous initiation of sedimentation in the basin during Late Jurassic-Early Cretaceous time. Detrital zircon peak age populations are consistent with previous studies that link the GVF to the central-western margin of North America at the onset of deposition.