Procedencia como herramienta para la subdivisión estratigráfica del Mesozoico temprano en el noreste de México

Abstract

In northeastern Mexico, early Mesozoic red beds and volcanogenic rocks known as the Huizachal Group have been described as an Upper Triassic to Lower Jurassic fluvial succession (La Boca Formation), overlain by alluvial and lacustrine deposits representing the base of the Jurassic marine transgression (La Joya Formation). We estimate inconvenient to group together different sedimentary successions deposited over such a long period, which results in a loss of resolution concerning the tectonic evolution and paleogeographic interpretation. Petrographic provenance studies and detrital zircon geochronology were used as a tool for stratigraphic subdivision: we separated a exclusively Triassic unit, recently defined as El Alamar Formation, from Lower Jurassic red beds of La Boca Formation, now considered Early Jurassic in age. While the Triassic unit usually displays recycled orogen and subordinate continental block provenances, the Lower Jurassic red beds interlayered with volcanic rocks and epiclastic deposits, indicate a more consistent provenance from magmatic arc settings. Moreover, their maximum depositional ages are Late Triassic (220 Ma) and Late Jurassic (160 Ma), respectively, with several Grenvillian, Pan-African and Permian-Triassic detrital-zircon populations included in El Alamar Formation and Grenvillian, Pan-African, Permian-Triassic and Early Jurassic clusters in La Boca Formation.