Stratigraphy of the Permian-Triassic boundary in southeastern New Mexico and west Texas

Abstract

Abstract ________ At the Permian-Triassic boundary everywhere in west Texas and southeastern New Mexico, Upper Permian (late Ochoan = Changxingian), or older Guadalupian strata are overlain by Upper Triassic (late Carnian = Tuvalian) strata. The youngest Upper Permian strata are the Quartermaster Formation ( = Pierce Canyon red beds = Dewey Lake Formation); the Late Permian age of the Quartermaster is verified by invertebrate fossils, magnetostratigraphy and K-Ar ages. Vertebrate fossils document the late Carnian age of overlying Triassic strata of the Santa Rosa Formation and Camp Springs Member of the Dockum Formation. No Lower or Middle Triassic strata are present in southeastern New Mexico and west Texas. The Permian-Triassic boundary in this area thus is a major unconformity that encompasses at least 25 million years. Because the Permian-Triassic boundary in southeastern New Mexico and west Texas is bracketed by nonmarine siliciclastic red beds, it has often been incorrectly placed. Upper Permian Strata are distinguished by being brick-red, not variegated, texturally and mineralogically relatively mature, ripple-laminar to laminar and unfossiliferous, whereas Upper Triassic strata are grayish red, variegated texturally and mineralogically relatively immature, trough-crossbedded and fossiliferous. We describe 12 reference points in southeastern New Mexico and west Texas where the Permian-Triassic boundary is well exposed.