Older Rocks of Van Horn Region, Texas

Abstract

Some new facts are given, based on recent detailed surveys, regarding the pre-Cambrian, possible Cambrian, and early Ordovician rocks of the Van Horn region. A geosyncline existed here in later pre-Cambrian time, and in this a thick mass of sediments accumulated, constituting the Allamoore and Hazel formations. These were afterwards deformed, and were overridden from the south by a thrust block of an older formation, the Carrizo Mountain schist. After the deformed rocks were deeply eroded, the clastic, unfossiliferous Van Horn sandstone was laid down over them. Its age is unknown, but may be late pre-Cambrian or early Cambrian. It was tilted, faulted, and eroded before the first marine Paleozoic deposits were spread over it. These are of early Ordovician age, and correlat with the Bliss sandstone farther west. The type Bliss has hitherto been classed as Cambrian, but paleontological evidence for this is questionable. If the suggested correlation is correct, wide areas in western Texas and southern New Mexico, where the Bliss is the basal Paleozoic formation, may never have been covered by the Cambrian seas.