Tectonic setting of pre-Oxfordian units from central and northeastern Mexico: A review
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abstract
There are five widely recognized stratigraphic units underlying the transgressive Oxfordian deposits in central to northeastern Mexico: (1) the submarine-fan deposits of the Zacatecas Formation, (2) the volcanogenic products of the Nazas Formation, (3) the continental deposits of the Huizachal Formation in northeastern Mexico (which contains several volcanogenic products comparable to those in the Nazas Formation), (4) the Lower to Middle Jurassic redbeds of the La Boca Formation (which overlies the Huizachal Formation), and (5) the clastic basal sequence of the Oxfordian transgression, known as La Joya Formation. Field, petrographic, and petrological observations as well as published geochemical data and isotopic or paleontologic ages suggest five main tectonic settings that correspond to five main events which may explain the origin and nature of the five stratigraphic units recognized: (1) Upper Triassic turbiditic sedimentation along the western passive margin of North America (Zacatecas Formation), (2) arc volcanism related to the evolving active continental margin of western North America during the Late Triassic to Early Jurassic (Nazas Formation), (3) a probable backarc extension related to the same active continental margin (Huizachal Formation), (4) rifting and continental deposition related to the break up of Pangea(?) or to the same backarc (La Boca Formation), and (5) the Gulf of Mexico opening and Oxfordian transgression (La Joya Formation). The present location of some parts of the early Mesozoic western margin of North America (pre-La Joya units) in central to northeastern Mexico may be explained by the nearly 800 km of left-lateral displacement of Mexico along the Oxfordian Mojave-Sonora megashear.
