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Reconstruction of the Western Rim, Wetumpka Impact Structure, Alabama: Clues to Excavation Processes in a Foliated Metasedimentary Target

Pascual Tabares Rodenas and David King
[email protected]

The Wetumpka impact structure (near the town of Wetumpka, Alabama) has a semi-circular crystalline rim that is ~ 5 km in diameter. This well-exposed, marine-target impact structure developed in a near-shore setting with a few tens of meters of seawater and about 120 m of poorly consolidated, water-saturated sediments covering a crystalline basement (mainly weathered metasedimentary schists). Our previous studies have described a semi-circular, crystalline rim, an interior structure-filling unit, and an exterior disturbed area developed within the sedimentary target sequence outside the southwestern part of the central, basement crater. Based on field and drill-core observations, we recognize the following specific structural and lithological impact-related terrains: partially preserved overturned crystalline rim flap; slumped interior megablock terrain; central polymict breccia (originating as near-field ejecta); interior marine chalk deposits and reworked glauconitic sands (formed by resurge and post-impact deposition); and a collapsed southern part of the rim with overturned flap (mainly developed within the sedimentary target rocks). This study is aimed at attaining a better understanding of the behavior of foliated crystalline rocks during the cratering process, specifically what are the mechanisms that relate to the deformation and emplacement of the crystalline crater rim. For that reason a series of detailed measurements of strike and dip of foliation and fracture planes were made on the best-exposed (western) part of the crater rim in order to create an inventory of fracture and schistosity plane orientations. [Supported by GCAGS student grant]

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013