Analysis of Subsurface Geology, including the Parautochthonous Breccias, Flynn Creek Impact Structure, Tennessee
Type of DegreeMaster's Thesis
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The present study concerns the Flynn Creek impact structure, Tennessee, which is estimated to have formed approximately 382 million years ago in a shallow marine environment. The present crater is about 3.8 km in diameter at its widest part, and has a non-circular, asymmetric outline. The target was the epicontinental shelf of the Chattanooga Sea, which was underlain by Ordovician carbonates that were deformed during the impact. Impact produced a structure with wide, terraced rims formed by extensive post-impact slumping, a shallow bowl-shaped inner crater of about 2 km in diameter, and slump-derived topographic features, including a central slump-produced mound that has been interpreted in the past as a central peak. Twenty-one drill cores with more than 3 km of total core length have been analyzed using high-resolution photographs in order to provide a detailed analysis of the subsurface stratigraphy of this impact structure. For example, an abundance of previously unknown impact-related breccias have been discovered at depths within and below the crater bowl. Observation and description of these drill cores combined with a petrographic analysis of selected samples from some of the deeper breccia zones suggests a new interpretation of Flynn Creek impact structure as a small simple crater of about 2 km diameter that is surrounded by relatively large concentric slump features. In the rocks beneath the simple crater bowl, i.e. in Flynn Creek’s parautochthonous breccia zone, otherwise rare melt-bearing textures are found to be relatively common.