CROSS-SECTION OF FLYNN CREEK IMPACT STRUCTURE, TENNESSEE

Flynn Creek impact structure, Jackson County, Tennessee, is one of the original six proven impact structures on Earth and the first one attributed to a marine target setting. The Late Devonian Flynn Creek impact structure is notably asymmetrical and generally averages ~ 3.6 km in diameter. Flynn Creek has a rim terrain characterized by concentric normal faults, a central uplift area with breccia-laden flanks, a crater moat-filling breccia (CMFB) unit ranging from ~ 30 m to ~ 70 m thick, and a poorly known parautochthonous breccia lens of substantial thickness. In 1968, David Roddy produced the first published cross section of Flynn Creek, which showed a faulted rim, shallow basin, central uplift, and CMFB of relatively uniform thickness. This east-west cross section was based on field work plus 6 shallow drill cores in the crater moat area obtained during 1967. Roddy’s 1979 cross section, which relied on several unnamed, post-1967 drill cores, was different in important ways, including a CFMB that thickened considerably near the rim of the structure and intact sub-crater stratigraphy except under the central uplift. Both cross sections showed considerable structural detail in the central uplift based on field work. However, drill cores FC77-1, FC79-12, and -13, which were drilled on the western flank of the central uplift show a flanking breccia unit that ranges from 175 to 50 m thick. This central uplift flanking breccia likely grades laterally into CMFB. Several Flynn Creek drill cores penetrate to depths more than 450 m. These drill cores show that sub-crater stratigraphy was strongly affected by impact at substantial depth. Large intact blocks, with varying degrees of internal deformation, comprise an as-yet-to-be-delineated parautochthonous breccia lens. These large blocks, ranging up to 10s of m thick, are separated by zones of allogenic impact breccia ranging from a few cm to a few m thick. We present a new interpreted cross section based on available drill-core photographs from 12 or more core holes. But, additional drilling and/or geophysical surveying will be needed to more fully understand the actual shape and cross-sectional view of Flynn Creek. Supported by NASA PGG NNH14AY73I.