Kilmichael Structure, Mississippi, Revisited

Paul bristolia at yahoo.com
Tue Sep 26 21:23:49 EDT 2006

Tomorrow afternoon, David T. King of the Department of Geology,
Auburn University, Auburn, AL will talk recent research conducted
on the Kilmichael Structure, Mississippi, at this weeks Gulf Coast
Assicaition of Geological Societies 2006 Annual Meeting in
Lafayette, louisiana. The paper accompanying this talk is;

King, D. T., Jr., and L. W. Petruny, 2006, Cosmic impact in the coastal
plain of Mississippi? The Kilmichael structure. Gulf Coast Association
of Geological Societies Transactions, vol. 56, pp. 341-351.

Its abstract states:

"The Kilmichael structure, a probable impact crater in Montgomery
County, Mississippi, is a circular, structurally disturbed feature
possessing a diameter of approximately 5.6 mi. A refraction seismic
survey reveals subsurface characteristics of an impact structure,
including a central uplift, annular graben, and concentric inward-
dipping faults. A gravity profile like that of some confirmed impact
craters is present. In a key core hole at the structure’s center,
770 ft of section, consisting mainly of breccias and large intact
blocks, was penetrated and sampled. In this paper, we have
reinterpreted the sequence of drilled strata as follows (in reverse
stratigraphic order): (1) soil and colluvium; (2) post-impact
laminated marine sediments; (3) conglomeratic aqueouswashback
or resurge deposits of mixed provenance; (4) interbedded impact
breccias and target rock blocks, i.e., surgeback deposits; (5) large,
deformed and rotated blocks of the Upper Cretaceous Ripley
Formation; and (6) interbedded impact breccias and target rock
blocks, mainly Upper Cretaceous chalks. The stratigraphic age
of this structure is probably late early to early late Paleocene,
based on the fossil age of material from the youngest
recognizable intact block drilled in the key core hole. The
Kilmichael area was in a marginal marine to shallow marine setting
at the time of deformation and the drilled stratigraphy is consistent
with aqueous or “wet-target” impact."

Yours,

Paul