Sequence stratigraphy, diagenesis and mechanical behavior of the Glen Rose Formation at Canyon Lake Gorge, Comal County, Texas




Bridges, Chase E.

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During the Albian stage (104 to 110 Ma), intertropical conditions allowed the development of a broad carbonate platform along the northern margin of the proto-Gulf of Mexico. Carbonate-rich sediments were deposited in various environments belonging to the shallow marine realm. Their production is mostly controlled by the type and efficiency of benthic ecosystems. In 2002, a major flooding exposed a 63m-thick carbonate succession belonging to the Glen Rose Formation in Canyon Lake Gorge, located northwest of San Antonio. The deposition of these rocks in shallow-water environments facilitated their subaerial exposure during times of low sea-level. Consequently, weathering due to their interaction with freshwater ensued. Diagenetic modifications comprise dissolution and early cementation promoting the early lithification of carbonate sediments. With this study, we aim to highlight a potential link between the sequence stratigraphy, geochemistry and the mechanical behavior of carbonate rocks of the Glen Rose Formation, using microfacies and diagenetic history to confirm the results. Identification of the standard microfacies characteristic of this formation is assessed by the petrographic analysis of acetate peels, further complemented by cathodoluminescence microscopy performed on selected thin sections. Sequence stratigraphy helps to pinpoint the stratigraphic location of subaerially exposed surfaces, which may thus exhibit post-depositional modifications. Carbon and oxygen isotopic analyses are used to complement sequence stratigraphic analysis; chemostratigraphic correlation with biostratigraphically-constrained series refines the dating of the Glen Rose Formation at Canyon Lake Gorge to 108-110 Ma. Fracturing potential is examined using a Schmidt hammer, assessing various geomechanical properties and especially the stiffness of the rock samples. Microfacies type and degree of cementation seems to be the main controlling factors.


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Albian stage, Broad carbonate platform, Glen Rose Formation