A NEW LOOK AT THE SERPENT MOUND IMPACT CRATER, SOUTHERN OHIO

The Serpent Mound structure is a circular area of disturbed Phanerozoic strata in southern Ohio at the junction of Adams, Highland, and Pike Counties (32°02'2.74”N, 83°24'24.09”W). While previously proposed as a cryptoexplosive structure, evidence for a high pressure shock metamorphic event (shatter cones, shocked quartz, etc.) has confirmed Serpent Mound's origin by impact. Although we now understand it to be the final product of a high velocity collision of an asteroid or comet, new questions about the size and timing of the Serpent Mound impact event itself have emerged. Previous field mapping indicates that the Serpent Mound structure represents a complex crater with a central peak of uplifted Ordovician-Silurian sedimentary carbonates transitioning to a ring graben, all within an 8 km radius. The central uplift and surrounding graben however only represent a portion of the morphology of a complex crater (minus the crater rim). This implies that actual outer extent of deformation (i.e. the crater rim) for Serpent Mound has yet to be defined. Recent field work outside of the ring graben and between an arcuate portion of the Allegheny Escarpment to the east may have uncovered a poorly-preserved crater rim. This has allowed us to refine the size of the impact event and the impactor itself. Apparent faulting of Late Devonian-Mississippian strata have led early workers to propose that the Serpent Mound impact was a Post-Mississippian event. Newer data from surface exposures and drill cores, along with the presence of a polymict intra-crater breccia suggest that Devonian-Mississippian strata were not present at the time of impact, but may have later buried the crater itself. If preliminary analyses indicate that these geologic units were not present at the time of impact (i.e. were not target rocks), then the Serpent Mound structure may represent an impact that occurred prior to the Late Devonian.