The Echo Cliff structure: identification and analysis of a possible Kansan impact structure

Abstract

This study examines an ovoid drainage feature southwest of Topeka, Kansas, whose discovery sparked a flurry of activity. Geomicrobial and surface gamma ray surveys indicated possible vertical migration of hydrocarbons, and a ground magnetic survey produced anomalies that resemble the profile of a crater. The area was dubbed the Echo Cliff structure and considered analogous to the Ames structure in Oklahoma, an Ordovician impact structure remarkable for significant hydrocarbon recovery. However, four wells drilled in the area were dry and abandoned. The Echo Cliff structure did yield further indications of its origins by the discovery of possible shocked quartz in drill cuttings from the Ordovician Simpson Group. Our study integrated well log analysis, geophysical modeling, and petrographic analysis to verify or refute the proposed identity of the Echo Cliff structure. Well logs from the area were used to create a structural and stratigraphic cross-section in Petrel® 2016. A gravity survey was conducted in the study area and combined with an aeromagnetic survey, donated by Applied Geophyics, Inc., to use as the basis for geophysical modeling within GM-SYS®. Finally, drill cuttings from the Simpson Group of two wells in the study area were mounted for thin sectioning. These thin sections were examined for planar deformation features, which are indicative of an impact event. The structural and stratigraphic cross sections indicated minimal variation in the subsurface, which is uncharacteristic of an impact event. The GM-SYS® geophysical models seem to indicate that variations in the topography of the Precambrian basement and faulting from the Bolivar-Mansfield Tectonic Zone are responsible for the geophysical anomalies and possibly the current drainage pattern of the study area. Finally, no planar deformation features were observed in any of the examined thin sections. Therefore, there is currently no evidence in support of the claim that the Echo Cliff structure is an impact structure.