GRAVITY MODELING OF THE WETUMPKA IMPACT CRATER, ALABAMA

Several geologic studies have recently classified an unusual geologic structure located near Wetumpka, Alabama, as an impact event. These studies have provided knowledge about the crater’s near surface geology and mineralogy, but have failed to explore the subsurface geology with depth. This project utilizes high-resolution gravity data to explore the subsurface geology and structure of the crater. Gravity modeling shows that a simple geologic layering cannot explain the observed gravity lows near the impact site. A simplified model based on previous studies adequately explains the extra and crater-rim terrains, but cannot explain the variances in gravity data observed within the crater’s central area. An alternative, more complex geologic model accounts for these variations by incorporating a feature representing a central uplift of the underlying Piedmont rocks. Densities consistent with a zone of thick sedimentary in-fill and brecciated rocks explains the gravity low within the crater. This research proposes that a 400 m uplift of the Piedmont basement occurred in response to the impact and created a large space for sedimentary infill in the eastern portion of the crater.