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Abstract: The Wetumpka Asteroid Impact Structure in Alabama, U.S.A.

KING, DAVID T. JR., Auburn University; THORNTON L. NEATHERY, Neathery and Associates.

Summary

The Wetumpka impact crater in Alabama is a 6.5 km-diameter complex crater that likely formed during early Campanian (81.5 ± 1.5 Ma). Its surfical rocks contain level 0 through 2 shock features. Wetumpka's horseshoe-shaped crater rim and associated interior northeast-trending aeromagnetic and gravity anomalies are evidence of an oblique impact by a cosmic object arriving upon a low-angle, northeast-to-southwest trajectory. Wetumpka's impact probably occurred in 0 to 150 m of water and 0 to 50 km offshore from a barrier-island coastline. Wetumpka's complex crater had an estimated original rim height of 210 to 360 m, and the center may have experienced an estimated 59 m of stratigraphic uplift resulting from impact. The impactor, a stony and (or) iron asteroid, is estimated to have been about 350 m in diameter. When the asteroid vaporized upon impact, energy equivalent to between 102 and 103 MT of TNT (or between 4.2 x 1024 and 4.2 x 1025 erg) was released. A 3.3 to 4.2 km-diameter transient crater opened within approximately 11.5 sec. Wetumpka's impact-crater melange, approximately 122 m thick, was likely formed by mass movement from the transient crater rim commencing after the first 18 to 21 sec.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah