Abstract

Sandstone petrography and detrital zircon U-Pb analysis of Upper Cretaceous–Paleogene sandstones in the foreland basin of the Sierra Madre Oriental in northeastern Mexico indicate long-distance sediment transport from arc, basement, and thrust-belt sources lying to the west, northwest, and south. The basin fill, termed the Difunta Group, consists of sublitharenites, litharenites, feldspathic litharenites, and lithic arkoses derived from mixed sources that included sedimentary rocks, magmatic arc rocks, and subordinate basement rocks. Six age populations comprise the detrital zircon content of the sandstones: Proterozoic (1900–900 Ma), early Paleozoic (500–400 Ma), late Paleozoic–Early Triassic (288–235 Ma), Jurassic (180–151 Ma), Early Cretaceous (150–111 Ma), and Late Cretaceous–Paleogene (110–54 Ma). These grains were derived from several arc terranes, ranging in age from Permian to Paleogene, in western Mexico and the southwestern United States, from sedimentary rocks and possibly interbedded tuffs of the Sierra Madre Oriental orogen and from basement sources or their derivative sandstones of the southwestern United States. The petrographic and geochronologic provenance data corroborate existing models for derivation of much foreland detritus from arc sources to the west, identify the Sierra Madre orogen itself as an important source for sediment, and these data modify the Late Cretaceous–Paleogene paleogeography of Mexico to include a long, orogen-parallel fluvial system with headwaters in the southwestern United States. The difference in average ages of the youngest grains in the sandstones and their inferred depositional ages is 10.5 m.y., indicating that the initial coarse fill of the foreland basin was derived from early Laramide uplift and eastward arc migration in northwestern Mexico and the southwestern United States.

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