Structure-filling Sediments of the Wetumpka Marine-target Impact Structure (Alabama, USA)

Abstract

The Wetumpka impact structure is a deeply eroded, arcuate, 7.6-km diameter Late Cretaceous feature located within the inner Coastal Plain, Alabama, which was produced by a Late Cretaceous impact into shallow marine water. Wetumpka has distinctive exposed, geologic terrains produced by impact-related processes. These exposed terrains include Wetumpka's crystalline rim and two sedimentary terrains: (a) an interior unit (resurge unit), and (b) adjacent extra-structure unit (deformed unit) located outside the rim on the structure's southern side. Core drilling near the structure's geographic center revealed that Wetumpka's structure fill has two distinctive units: (1) an upper, resurge-deposited unit (similar to 60 m thick; same as the "interior unit" above) and (2) a lower, structure-filling breccia unit comprised of fall-back ejecta layers, slumped target-rock blocks, and impact-related sandy breccias and sands (> 130 m thick).