Serpent Mound disturbance, Adams County, Ohio, USAi

Regional Level Types
Serpent Mound disturbance	Impact Structure
Adams County	County
Ohio	State
USA	Country

Bratton & Franklin townships (unspecified locations).

"Serpent Mound is an archaeological site located in Adams County, Ohio constructed by the Adena tribe between 1000 BCE and 700 CE. Located near the western edge of the Serpent Mound structure, is a unique astrobleme site based on bedrock geology, planar deformed quartz, and shatter cones. The geology at that location is complex, owing to the disturbance caused by the impactor. Detailed studies of the environmental mineralogy of the region are uncommon; such studies provide critical information for long-term archaeological site management and broader understanding of the geologic and environmental history of the region."

"Rock samples were collected from an outcrop of impact breccia in the Silurian Tymochetee Formation northeast of the archaeological site. Those samples were analyzed using X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). Results from the analysis indicate a wide range of minerals in the bedrock, composed of mostly dolomite (CaMg(CO3)2), some calcite (CaCO3), and a minor amount of other mineral phases such as oxide minerals, sulfides, and minerals minor rare earth element (REE) bearing minerals. Euhedral kaolinite crystals approximately 5 micrometers in diameter were also commonly observed. The SEM investigation indicated the dolomite crystals to be anhedral to euhedral and possessed variable twinning textures and pitting. Natural asphalt or tar occurred as tacky infilling that completely filled the pores, which were commonly 10 micrometers to 50 micrometers in diameter. Energy Dispersive Spectroscopy (EDS) analysis indicated an appreciable amount of sulfur in the asphalt or tar material."

"This is the first detailed mineralogical investigation of bedrock at the Serpent Mound archaeological site using SEM. The occurrence of natural asphalt or tar along with information on mineralogical constraints will provide a detailed reference for future environmental impact studies, particularly relating to road traffic, rock face preservation and geoarchaeological investigations of sediment and soil tied to site use." (MINERALOGICAL INVESTIGATIONS OF A METEORITE IMPACT BRECCIA FROM THE SERPENT MOUND ARCHAEOLOGICAL SITE, ADAMS COUNTY OHIO, see reference below).

"The Serpent Mound structure is an 8 km impact crater in southern Ohio. The impact occurred in and affected sedimentary target rock ranging from Cambrian to Silurian (and possibly strata as young as Mississippian) in age. Serpent Mound is a partially-preserved complex crater, with a central uplift, transition zone, and surrounding ring graben. Within the crater lies an anomalous gray, dolomitic polymict breccia with unique characteristics we informally refer to as the Serpent Mound Breccia (SMB). Originally, it was identified in a single (type) location in the western crater. The purpose of this study was to identify and map additional SMB locations and track its lateral distribution, which may allow us to identify a formation/emplacement mechanism. Different breccia generation mechanisms result in a wide variation of lateral distributions. For the 3 most probable mechanisms for the SMB, faulting during rise/collapse of the central uplift, mass wasting from gravitational collapse, or ejecta fallback/resurge, expected distributions range from localized to crater-wide respectively. In order to track the lateral distribution of the SMB, we searched for new potential sites using aerial/satellite imagery, new field exposures, and references from former field investigations. Each potential breccia was compared to the SMB at its type location. Upon positive identification, we mapped each new site and recorded elevations with GPS. GPS elevations and Brunton compass measurements allowed us to determine minimum apparent thicknesses of the SMB. Our team confirmed 8 new exposures in all but the eastern portions of the crater to date, with most of the sites located in the western half. Several other suspected sites are still under investigation. All confirmed and suspected sites lie in the transition zone within the crater. The SMB ranged from 220-246 m above sea level and 3-21m in minimum apparent thickness at individual sites. The widespread distribution of the SMB within the crater does not support an origin by localized fault brecciation or single mass wasting events. It does support generation by a crater-wide geologic process following the impact event, with the most probable mechanism being fallback or resurge of ejecta. Ongoing work continues to address the viability of this hypothesis." (DISTRIBUTION AND FORMATION OF AN ANOMALOUS BRECCIA WITHIN THE SERPENT MOUND IMPACT CRATER - see reference below)

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References