GEOCHEMISTRY OF THE GREAT VALLEY GROUP, SACRAMENTO VALLEY, CALIFORNIA: IMPLICATIONS FOR CRETACEOUS PALEOGEOGRAPHY

Analysis of fine-grained sediment, often overlooked in provenance studies, can provide critical information about source characteristics. Sedimentary provenance techniques tend to focus on the coarse-grained fraction of the sedimentary system, potentially biasing data toward more local and/or more resistant detrital components. Major and trace element geochemical analysis of fine-grained sedimentary rocks complements petrographic study and detrital zircon analysis and can provide a more robust characterization of sedimentary provenance. Geochemical analysis of the Great Valley Group (GVG) in the Sacramento Valley suggests that the fine-grained sediment in the basin is characterized by largely mafic provenance and likely includes minor ophiolite input into the basin. The lack of zirconium enrichment in the GVG mudstone is characteristic of active margin sources and suggests little sediment recycling in the source region. The geochemical signature of the GVG mudstone is relatively consistent throughout the depositional history of the basin, with no significant difference between Lower and Upper Cretaceous samples, or between southern and northern Sacramento Valley samples. These geochemical results are consistent with provenance in the Klamath Mountains and northern Sierra Nevada Mountains throughout basin deposition, with significant mafic and even ultramafic sediment provided by the accreted island arc terranes and ophiolite slivers present in these source regions. These results do not support a translational basin model because a southern sediment source for the lower GVG would likely include recycled miogeoclinal sediment and would lack the significant mafic source rocks that characterize the mudstone geochemical signature throughout the basin’s depositional history. These results suggest that the fine-grained component of basin deposition can record different information than that contained in the coarser-grained sediment, providing more complete characterization of sedimentary provenance.