Drill-Core And Geophysical Investigation Of The Western Part Of The Crystalline Rim Of Wetumpka Impact Structure, Alabama

Abstract

The present research project on Wetumpka impact structure, Elmore County, Alabama, is focused on understanding the effects of hypervelocity impact upon sedimentary target rocks and underlying crystalline bedrock in the impact of a modest-sized asteroid. In particular, this study focuses on the development of the crystalline rim at Wetumpka. This study will improve our knowledge about how a liquid layer (here marine water) as part of the target materials affects the cratering process not only on our planet, but on other celestial bodies such as Mars. The Wetumpka impact structure is a complex crater located in Elmore County, central Alabama (N32˚31’; W86˚ 10’). It was first was proposed as an impact feature in 1976 by Thornton L. Neathery, Robert D. Bentley, and Gregory C. Lines. The size of the Wetumpka apparent crater (about 5 km in diameter) indicates that it most likely has a buried central uplift (the central uplift is not evident topographically). The diameter of this structure is based on field mapping of the outer reaches of impact deformation and has been shown to be a marine-target impact. This study is aimed at attaining a better understanding of the behavior of the crystalline rocks in this kind of explosive event, specifically what are the mechanisms that relate to the deformation of the border rim and the emplacement of the crystalline border crater rim. The present study includes: a complete descriptive analysis of drill core #09-01, which penetrates through the crystalline crater rim; a 3D resistivity survey on the western part of the iii rim, near the drill site, which reveals crystalline rim rock fractures in a detailed way; and maps and cross-sections derived from Light Detection And Ranging (LiDAR) for the a very accurate construction of maps and cross-sections used for interpretation of the surface and shallow subsurface geology of the impact structure. LiDAR data with approximately two-meter resolution allows for construction of Digital Elevation Models (DEMs) and others derivative images, which have helped the present study greatly.