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Wetumpka impact structure (Alabama), a Late Cretaceous marine-target crater


, : Wetumpka impact structure (Alabama), a Late Cretaceous marine-target crater. Abstracts with Programs - Geological Society of America 32(7): 161

Wetumpka impact structure (N32 degrees 31.5'XW86 degrees 10.5') is a deeply eroded 6-km diameter feature characterized by a substantial impact-deformed crystalline rim and a crater-filling melange unit. Wetumpka's age (Campanian?) is constrained by youngest target fragments within its resurge deposits, whereas its position within shallow (100 m?), epicontinental Gulf waters is determined from well-documented paleogeographic reconstructions of the target area. Borehole drilling shows that Wetumpka's melange has two main parts: [1] a surficial resurge unit (approximately 50 m thick) and [2] an underlying impact-breccia unit (over 140 m thick). Wetumpka's resurge deposits are conglomeratic clayey sands and sandy clays, which display graded and contorted bedding and incorporate local, megablocks of target strata. Wetumpka's impact breccia contains intercalated monomict and polymict (shocked-quartz bearing) breccias and sizeable (up to 10 m) blocks of target strata and crystalline basement. Wetumpka's inferred cross-section is more like a partially filled, simple bowl-shaped crater than a typical land-target, complex (or "terraced") crater of comparable size. Wetumpka's bowl could be the deep, central part of the characteristic 'inverted sombrero' form, which is typical of impact excavation in marine-target situations involving relatively shallow marine waters. Unlike some marine-impact craters, Wetumpka may not have preserved resurge channels, and its potentially broad, shallow outer rim is not evident based upon our studies thus far. However, this situation may be attributable entirely to substantial post-impact erosion.


Accession: 020613984

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Related references

Petruny Lucille W.; King David T.; Neathery Thornton L., 2006: Structure-filling stratigraphy of the Late Cretaceous Wetumpka marine-target impact structure, Alabama. Wetumpka impact structure is the only known impact feature in the inner coastal plain of the southeastern U.S. Wetumkpa is a deeply eroded, arcuate, 7.6-km diameter Late Cretaceous feature located near the fall line in Elmore County, Alabama. This...

King D.T.J.; Ormoe J.; Petruny L.W.; Morrow Jared R.; Neathery T.L., 2006: Excavation and modification of the Late Cretaceous Wetumpka impact structure (Alabama), a shallow marine impact feature. Abstracts of Papers Submitted to the Lunar and Planetary Science Conference 37: (unpaginated

Anonymous, 2007: Marine impact craters on Earth; field investigation of the Wetumpka impact structure, a well-preserved marine impact crater, and the K-T boundary in the Alabama Gulf Coastal Plain. GSA Today 17(9): 57-58

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King David T.J.; Neathery Thornton L.; Petruny Lucille W., 2004: Structure-filling sediments of the Wetumpka marine-target impact structure; Alabama, USA. Pages 97-113 2004

King David T.; Petruny Lucille W.; Neathery Thorton L., 2002: Upward-facies transition analysis in interpretation of stratigraphic sequence within the Wetumpka impact structure, a Cretaceous marine impact in Alabama, USA. Eos, Transactions, American Geophysical Union: 7, Suppl., Pages F796. 2002.

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King David T.Jr., 1997: The Wetumpka impact crater and the Late Cretaceous impact record. Pages 25-56 1997