Analysis of Subsurface Geology, including the Parautochthonous Breccias, Flynn Creek Impact Structure, Tennessee

Abstract

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.