David R. ADRIAN¹, David T. KING Jr.¹, Steven J. JARET², Jens ORMÖ³,Lucille W. PETRUNY¹, Justin J. HAGERTY⁴, and Tenielle A. GAITHER⁴
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12862]

¹Department of Geosciences, Auburn University, Auburn, Alabama 36849, USA
²Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, USA
³Centro de Astrobiologıa (INTA-CSIC), Madrid, Spain
⁴USGS, Astrogeology Science Center, Flagstaff, Arizona 86001, USA
Published by arrangement with John Wiley & Sons

Drill core FC77-1 on the flank of the central uplift, Flynn Creek impact structure, Tennessee, contains 175 m of impact breccia lying upon uplifted Lower Paleozoic carbonate target stratigraphy. Sedimentological analysis of this 175-m interval carbonate breccia shows that there are three distinct sedimentological units. In stratigraphic order, unit 1 (175–109 m) is an overall coarsening-upward section, whereas the overlying unit 2 (109–32 m) is overall fining-upward. Unit 3 (32–0 m) is a coarsening-upward sequence that is truncated at the top by postimpact erosion. Units 1 and 3 are interpreted as debris or rock avalanches into finer sedimentary deposits within intracrater marine waters, thus producing progressively coarser, coarsening-upward sequences. Unit 2 is interpreted to have formed by debris or rock avalanches into standing marine waters, thus forming sequential fining-upward deposits. Line-logging of clasts ranging from 5 mm to 1.6 m, and thin-section analysis of selected drill core samples (including clasts < 5 mm), both show that the Flynn Creek impact breccia consists almost entirely of dolostone clasts (90%), with minor components of cryptocrystalline melt clasts, chert and shale fragments, and clastic grains. Cryptocrystalline melt clasts, which appear isotropic in thin section, are in fact made of exceedingly fine quartz crystals that exhibit micro-Fourier transform infrared (FTIR) and micro-Raman spectra consistent with crystalline quartz. These cryptocrystalline melt clasts are the first melt clasts of any kind to be reported from Flynn Creek impact structure.