WETUMPKA IMPACT STRUCTURE, ALABAMA

Wetumpka impact structure is a 7.6 km diameter, semi-circular feature of the coastal plain-piedmont boundary in central Alabama. It is possible that the extant structure is but the inner bowl of a larger impact feature, which has been extensively eroded. The stratigraphic age of this feature is near the Campanian-Santonian boundary during Late Cretaceous. Wetumpka was a marine impact event in the epicontinental Gulf of Mexico. This structure exhibits telltale features of marine impact in 30-100 m of water, including aqueous rim-collapse breccias and structure-filling marine-resurge megabreccias. The lower parts of the drilled structure-filling materials contain impact breccias and other impactites with pervasive shock-metamorphosed quartz and feldspar. Ecosystem perturbation associated with this event was locally devastating, but did not rise to the level of producing biostratigraphic effects. Ejecta from Wetumpka are not known, but are predicted to occur in the lower part of the Mooreville Chalk and laterally equivalent units in the Gulf coastal plain. Distal effects such as tsunami are not known, but the coeval Alabama-Georgia clastic dike injection event may be related to the earthquake effects of Wetumpka.