Stratigraphy and paleontology of Upper Cretaceous to Paleocene strata on the western Rosillos Mountain Ranch, Brewster County, Texas

Abstract

This study focused on unstudied exposures of Cretaceous and Paleogene rocks on the western portion of the Rosillos Mountain Ranch, a private 25,000 acre ranch enveloped on three sides by Big Bend National Park (BBNP). The field studies focused on mapping and recovery of fossils, accomplished during five visits, mostly during 2013. Field studies were aided by the col- lection of many georeferenced high resolution images. The goals of this thesis were production of the first accurate geological map of the area and the collection of fossils for biostratigraphic calibration. A new geologic map corrected errors in older published maps. A new measured sec- tion aids our understanding of the regional lithostratigraphy. Fewer vertebrate fossils were col- lected than anticipated but we added to the relatively poor fossil record of this interval of time in BBNP. Fossils include a subadult cf. Alamosaurus humerus, an indeterminate juvenile hadrosaur ischium and a fragmentary turtle.