Middle to late Miocene chronostratigraphy and development of the northern Gulf of California

Geologic models locate Baja California next to mainland Mexico during the Oligocene and propose opening of the Gulf of California during Miocene times. Outcrop information in the northern part of the Gulf indicates late Miocene marine sedimentation on a continental platform. However, the earliest marine sediments in the region are present in basins sampled by oil exploratory wells in the area, which drilled as much as 5591 m  of marine sands to silty clays. graphic and paleontological data in these wells indicate almost continuous marine sedimentation from middle Miocene times, in maximum water depths of approximately 200 m. The presence of the dinoflagellates Cribroperidinium tenuitabulatum, Diphyes latiusculum and Spiniferites pseudofurcatus, together with the nannofossil Cyclicargolithus floridanus in samples from some of these wells, indicates marine deposition during middle Miocene times in the Tiburَn, Consag and Wagner basins in the northern Gulf of California. ta indicate that in the middle Miocene, a marine proto-gulf basin was formed in the central part of the proto-gulf, probably related to Basin and Range extension. Published data indicate that during late Miocene times, the proto-gulf extended from southeastern California and southern Arizona, to central Baja California and Isla Tiburَn. Finally, by Pliocene times, marine sedimentation within the Gulf reached the modern distribution.