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Mineralogy of Impactite Sands Previous HitfromNext Hit AU Drill Core #09-04, Wetumpka Impact Structure, Alabama

Steven N. Rodesney1, David T. King, Jr.1, and R. Scott Harris2
1Department of Geology and Geography, Auburn University, Auburn, AL 36849
2Office of Materials and Research, Georgia Department of Transportation, 15 Kennedy Drive, Forest Park, GA 30297

The Wetumpka impact structure is a Late Cretaceous shallow-marine impact crater about 6 km in diameter, located in central Alabama. The target consisted of Upper Cretaceous sediments unconformably overlying Piedmont schists and gneisses.

AU drill core #09-04 sampled 217.7 m (715 feet) near the southeastern portion of the rim. The upper ~ 60 m of core is interpreted as a segment of slumped, overturned sedimentary section that was formerly on the rim. Below this section are nearly 160 m of impactite sands with sedimentary blocks, the specific origin of which is not yet understood.

Bulk-sample X-ray Previous HitdiffractionNext Hit was used to preliminarily characterize these impactite sands. This allows us to characterize changes in the bulk mineral composition and possible shock petrology of the section. We analyzed systematic changes in the coherent scattering domain (CSD) lengths for diffracting quartz planes observed in successively deeper samples. We also examined the changes with increasing core depth with regard to CSD length for each indexed crystallographic plane. We have found that the upper impactite sands show little evidence of shock deformation. They may show changes in the degree of deformation associated with {10-13} quartz plane, but the Previous HitdiffractionNext Hit peak associated with these planes may not be reliable. Deeper impactite sands show evidence for moderate shock deformation, similar to the levels responsible for producing {10-12} planar deformation features in quartz. We are working to compare the thin-section petrography of the impactite sand section to the X-ray Previous HitdiffractionTop data.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013