Abstract:
Neogene marine and non-marine sediments exposed within the Salton Trough, California, in Baja California, Mexico and along the Pacific coast of mainland Mexico, together with data from DSDP sites and limited seismic reflection profiles, provide evidence of the tectonic and depositional history of the Gulf of California. Geochronologic, stratigraphic, and paleobathymetric data from five stratigraphic sections arrayed from the northern reach of the gulf (Fish Creek section, California) to the mouth of the modern gulf (Maria Madre Id., Mexico) allow application of backstripping techniques to derive rates and patterns of basin subsidence throughout the gulf province in a variety of crustal and depositional settings. The resulting subsidence curves clearly reflect the two-phase evolution of the gulf from (a) a flooded portion of the Basin & Range extensional province beginning 12-10 Ma to (b) a rifted setting associated with penetration and spreading of the East Pacific Rise beginning about 5 Ma. The areal distribution of Miocene marine sediments indicates that major marine depocenters shifted westward about 5 Ma in concert with (a) uplift and deformation of the eastern margin of the Miocene proto-gulf and (b) rapid subsidence and formation of the modern Gulf of California by spreading along the relocated EPR during Pliocene time. Subsequent Plio-Pleistocene (2.5-0.7 Ma) deformation along the eastern margin of the newly formed peninsula of Baja California shifted major depocenters to their modern positions within the evolving gulf and exposed older basin fill, including Colorado River deltaic deposits, along the west side of the Salton Trough. Variations in rates of sediment accumulation and Neogene lithofacies reflect (a) tectonic events which dictated the location and dimensions of gulf basins and (b) the impact of major Neogene climatic and oceanographic events which controlled water mass character, circulation, productivity, and runoff within the gulf.