Geochronology and Correlation of the Todos Santos group, southern Mexico: Implications for Regional Stratigraphic Relations and the Rift History of the Gulf of Mexico

Abstract

Triassic redbeds record an early rifting phase in western equatorial Pangea. Initial rifting in the northern and southern Gulf of Mexico, respectively, was recorded by deposition of the Eagle Mills Formation (continental sandstone, mudstone, local anhydrite) and poorly-known sub-salt successions in the Bay of Campeche. These units are considered Upper Triassic to perhaps Lower Jurassic. The record of Triassic rifting is also locally exposed in the Sierra Madre Oriental, where continental redbeds are assigned to El Alamar Formation. We present new stratigraphic, sedimentological, and provenance data for another unit thought to relate to rifting, the Todos Santos Group (informal) in southern Mexico. Maximum depositional ages (detrital zircons) and cross-cutting relationships demonstrate that strata of the Todos Santos Group in Mexico belong to two relatively unrelated successions, juxtaposed after Late Jurassic CCW rotation of the Yucatán Block. An older, Upper Triassic fluvial siliciclastic succession in the Sierra Juárez of the western Veracruz Basin is assigned to the informal Valle Nacional Formation. This unit is characterized by diverse zircon ages, with no zircon ages younger than Triassic, and is intruded by the San Juan del Río pluton (194 Ma, U-Pb zircon) along the Valle Nacional Fault, implying a Triassic age. We correlate the Valle Nacional Formation of the Todos Santos Group with El Alamar Formation of northeastern Mexico, the Eagle Mills Formation of the northern Gulf, and sub-salt successions in the southern Gulf of Mexico. Overall, three regional extensional events are recognized in the western Gulf of Mexico Mesozoic margins: (1) Late Triassic early rifting, (2) Early to Middle Jurassic extension within a continental volcanic arc, and (3) Middle Jurassic rifting that culminated with the onset of the rotation of Yucatán and the formation of oceanic crust in the Gulf.

AAPG Datapages/Search and Discovery Article #90369 © 2020 AAPG Hedberg Conference, Geology and Hydrocarbon Potential of the Circum-Gulf of Mexico Pre-salt Section, Mexico City, Mexico, February 4-6, 2020