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January 2020 Bulletin

Stratigraphy Of The Glen Rose Formation In Big Bend National Park, Texas
John N. Casiano III
The University of Texas at San Antonio, 2017
Supervising Professor: Alexis Godet, Ph.D.
During the Early Cretaceous, a broad carbonate platform developed on the northern margin of the ancestral Gulf of Mexico. Although its sedimentary succession has been studied in most other areas of Texas, its Lower Cretaceous succession has been overlooked in Big Bend National Park (BBNP). This is particularly the case of the Glen Rose Formation, which lacks a precise facies description and age control. The aim of this study is to fill this gap in knowledge by describing the Glen Rose Formation in BBNP, analyze its microfacies and constrain its age by carbon utilizing stable isotope chemostratigraphy and sequence stratigraphy.
Facies of the Glen Rose Formation at BBNP belong to a low-profile ramp formed in a shallow carbonate shelf environment. This is consistent with the reconstruction of depositional environments performed in central and southern Texas. Carbon isotope chemostratigraphy indicates that the δ13C values in BBNP match the δ13C trend of the Comanche platform of Central Texas and other locations worldwide. The δ13C trend also suggests that part of the Glen Rose Formation is not sampled in this study and permits the identification of OAE1b near the base of the Glen Rose Formation in BBNP. This chemostratigraphic correlation is supported by the sequence stratigraphic interpretation of the studied sections. The unconformity at the base of the Glen Rose Formation, identified as the composite sequence boundary is followed by a transgressive systems tract, maximum flooding surface and a highstand systems tract. This reinforces the comparison and correlation of the Glen Rose Formation from BBNP with the other areas of Texas.
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