Abstract:
Stratigraphic, geochronologic, and paleobathymetric data from DSDP sites 475 and 476 offshore of Cabo San Lucas, Baja Sur, Mexico together data from onshore Neogene sequences exposed on (1) Isla Maria Madre in the gulf mouth, (2) Punta Mita on Nayarit coast of mainland Mexico, and (3) the San Jose del Cabo area of Baja Sur, allow rates and style of basin subsidence and margin deformation to be determined for the southernmost Gulf of California through application of backstripping techniques. Tectonic subsidence curves constructed for sequences overlying oceanic, transitional, and continental crust reveal patterns of basin formation as the southernmost gulf evolved from (1) a flooded portion of the Basin and Range province to (2) a rifted setting associated with penetration of the East Pacific Rise. The distribution of Miocene (12 to 6 Ma) and Pliocene marine sediments in this region indicates that major marine depocenters shifted westward ca. 5 Ma in concert with (1) uplift and deformation of the eastern margin of the Miocene proto-gulf and (2) rapid subsidence and formation of the modern Gulf of California as rifting and spreading occurred along the relocated East Pacific Rise during Pliocene time. Subsequent Plio-Pleistocene (ca. 2 to 0.7 Ma) deformation and uplift along the eastern margin of the newly formed peninsula of Baja California again shifted major depocenters to their modern positions within the evolving gulf. Analysis of magnetic anomaly patterns and microplate history in the eastern Pacific and gulf region by Atwater, Curray, Klitgord, Lonsdale, Mammericks, Stock, and others permit tentative correlations of major plate events and individual basin histories.