Evidence for Late Cretaceous Volcanism in Trans‐Pecos Texas

Abstract Cretaceous basaltic pyroclastic strata have been discovered in a fault block on the southern edge of the Rosillos Mountains laccolith in the Big Bend area of Trans‐Pecos Texas. The sequence comprises base‐surge and pyroclastic‐fall deposits inferred to have accumulated on the flanks of a small phreatomagmatic volcano. A diverse assemblage of freshwater turtles (including Aspideretes), crocodile teeth, and dinosaur bones have been recovered from the uppermost part of the sequence. The fauna indicate a Late Cretaceous, probably Campanian age. An outward‐dipping normal fault bounding the pyroclastic strata on the southeast juxtaposes sediments of the Upper Cretaceous Javelina Formation in the hanging wall with pyroclastic rocks in the footwall, indicating the pyroclastic strata must be Maastrichtian or older. U‐Pb SHRIMP‐RG analyses of zircons separated from a basaltic block thrown out of the volcano yield an inferred igneous crystallization age of \documentclass{aastex} \usepackage{amsbsy} \usepack...