A FOUR-DIMENSIONAL MODEL OF CRETACEOUS DEPOSITIONAL GEOMETRY AND SEDIMENT FLUX IN THE NORTHERN GREAT VALLEY FOREARC, CALIFORNIA

The Great Valley forearc records Jurassic-Eocene sedimentation along the western margin of North America during eastward subduction of the Farallon plate and development of the Sierra Nevada magmatic arc. This study presents the first 4-D basin model of the northern Great Valley forearc designed to reconstruct its depositional history from the Tithonian through the Maastrichtian. Using >1200 boreholes, we identify the tops of 13 horizons and produce a new series of isopach maps and cross-sections that highlight the spatial and temporal variability along and across the basin. The model shows the southward deepening of the basin during the Cretaceous and eastward onlapping of basin strata onto the Sierra Nevada basement. In addition, the model presents the first basement map of the entire Sacramento sub-basin, highlighting its topography at the onset of deposition of the Great Valley Group. Minimum volume estimates for sedimentary basin fill reveal episodic periods of flux, with peak sedimentation corresponding to deposition of the Sites Sandstone in the Coniacian. Comparison of these results with flux estimates from magmatic source regions shows a slight offset in the timing of peak sedimentation, likely reflecting the residence time from pluton emplacement to erosion in the neighboring basin. This model provides the foundation for the first 4D subsidence analysis on an ancient forearc basin, which in turn will yield insight into the mechanisms driving development of accommodation space along convergent margins.