LOWER AND MIDDLE TERTIARY SEQUENCE STRATIGRAPHY AND PALEOGEOGRAPHY OF THE SOUTHERN SAN JOAQUIN BASIN, CALIFORNIA

The establishment of a sequence-stratigraphic framework for the lower and middle Tertiary succession of the entire southern San Joaquin basin permits greater resolution of the paleogeographic changes within the basin and its margins. Most previous paleogeographic reconstructions were prepared for broad intervals of time, thus resulting in the mixing of highstand, lowstand, and transgressive systems tracts and obscuring stratigraphic relationships between the various parts of the basin. In these reconstructions, the effects of various geologic controls on the evolution of the paleogeography and depositional systems, such as eustatic and regional variations in sea level, differing basin-margin and basin-center tectonic activity, and varying provenance areas, were generally not fully resolved. By focusing on narrower time intervals and applying sequence-stratigraphic principles to the thick succession, basinwide reconstructions, including the deeper parts of the basin where data is limited, become more precise and consistent. Lower Tertiary submarine-fan systems can be related to sequence boundaries and regional lowstands of sea level affected by accretion of outboard terranes that formed new provenance areas to the west and south. Middle Tertiary coarse-grained turbidite systems can be related to high-order sequence events that resulted from episodic uplift associated with the lateral migration of provenance areas along the newly active San Andreas fault system on the western and southern margins of the basin. In contrast, the eastern basin margin was affected mostly by regional sea-level changes in a tectonically more quiescent area.