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

Eltanin Impact Area - A Few References - was "Eltanin - Part 2 of 2 "

Paul bristolia at yahoo.com
Thu Sep 7 09:52:05 EDT 2006

In the post "Eltanin - Part 2 of 2", bernd.pauli wrote:

"Bostwick J.A. et al. (1995) Asteroid sample return
mission II: Eltanin recovered (abs. Meteoritics 30, 490)"

A few of a number of other papers about the Eltanin
Impact Area are:

Kyte1, F. T., 2001, Chapter 9, Data Report: A Search
for Deposits of the Late Pliocene Impact of the Eltanin
Asteroid in Rise Sediments from the Antarctic Peninsula,
Site 1069. In Barker, P. F., Camerlenghi, A., Acton,
G. D., and Ramsay, A. T. S., eds., Proceedings of the
Ocean Drilling Program, Scientific Results. vol. 178

http://www-odp.tamu.edu/publications/178_SR/VOLUME/CHAPTERS/SR178_09.PDF

Kyte1, F. T., R. Gersonde, and G. Kuhn, 2005, Detailed
Results on the Analyses of the Eltanin Impact, Recovered
in Sediments Cores from Polarstern expedition
ANT-XVIII/5A. Lunar and Planetary Science XXXVI (2005)

http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2129.pdf

Gersonde, R., and F. T. Kyte, 2001, Exploration of the
Eltanin Impact Area (Bellingshausen Sea): Expedition ANT
XVIII5a 64th Annual Meteoritical Society Meeting.

http://www.lpi.usra.edu/meetings/metsoc2001/pdf/5421.pdf

Gersonde, R., F. T. Kyte, U. Bleil, B. Diekmann, J. A.
Flores, K. Gohlk, G. Grahl, R. Hagen, G. Kuhn, F. J. Sierro,
D. Volker, A. Abelmann, and J .A. Bostwick, 1997, Geological
record and reconstruction of the late Plioceneimpact of
the Eltanin asteroid in the Southern Ocean. Nature.
vol. 390, pp. 357-363.

Gersonde1, R., F. T. Kyte, T. Frederichs, U. Bleil, and
G. Kuhn, 2003, New Data on the Late Pliocene Eltanin
Impact into the Deep Southern Ocean. Large Meteorite
Impacts 2003.

http://www.lpi.usra.edu/meetings/largeimpacts2003/pdf/4094.pdf
http://www.lpi.usra.edu/meetings/largeimpacts2003/pdf/sess06.pdf

Shuvalov, V. V., 2003, Numerical Modeling of the Eltanin
Impact. Lunar and Planetary Science XXXIV.

+++++ Volume 49, Number 6 (2002) of Deep Sea Research
Part II: Topical Studies in Oceanography +++++

This issue contains the following papers

1. Calcareous plankton stratigraphy around the Pliocene
"Eltanin" asteroid impact area (SE Pacific): documentation
and application for geological and paleoceanographic
reconstruction by J. A. Flores, F. J. Sierro, and R.
Gersonde, pp. 1011-1027.

2. Composition of impact melt debris from the Eltanin
impact strewn field, Bellingshausen Sea by F. T. Kyte,
pp. 1029-1047.

3. Iridium concentrations and abundances of meteoritic
ejecta from the Eltanin impact in sediment cores from
Polarstern expedition ANT XII/4 by F. T. Kyte,
pp. 1049-1061.

4. Unmelted meteoritic debris collected from Eltanin
ejecta in Polarstern cores from expedition ANT XII/4 by
F. T. Kyte, pp. 1063-1071.

5. Impact tsunami-Eltanin by S. N. Ward and E. Asphaug,
pp. 1073-1079(7)

+++++ Bathymetric Maps of the Eltanin Impact Area +++++

AWI Bathymetry & Geodesy - Eltanin Impact Survey: Analyses
of High Resolution Bathymetric Data in the Eltanin Impact
Area by Merijn J. Jacops at:

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin.html

The maps of the Eltanin Impact Area consist of:

1. Eltanin Impact Area at 57°25'00'' overview map, 1:200.000
- 4.0 MB PDF file available at;

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin_overview.pdf

2. Bathymetric chart Eltanin Impact Area northwest, 1:100.000,
sheet 1 - 2.6 MB Pdf file available at;

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin_1a.pdf

3. Bathymetric chart Eltanin Impact Area northeast, 1:100.000,
sheet 2 - 3.1 MB Pdf file available at;

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin_2a.pdf

4. Bathymetric chart Eltanin Impact Area southwest, 1:100.000,
sheet 3 - 5.7 MB Pdf file available at;

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin_3a.pdf

5. Bathymetric chart Eltanin Impact Area southeast, 1:100.000,
sheet 4 - 4.7 MB Pdf file available at;

http://www.awi-bremerhaven.de/GEO/Bathymetry/eltanin/eltanin_4a.pdf

Yours,

Paul

Re: Geological History of terrestrial "Olivine Bomb"?

Paul bristolia at yahoo.com
Mon Sep 4 19:39:16 EDT 2006

Gerald Flaherty wrote:

"I picked up an Olivine Bomb from Norbert and
Helke Kammel of "Rocks On Fire" a couple of
years ago when I knew less than I know now of
meteorites. It's Location is listed as Mt.
Shadwell, Victoria, Australia. At the time the
very word "olivine" immediately brought pallasite
to mind. I think I'd just invested in my first
Imilac. This piece is tantalizing in every way,
from is thick jet black volcanic crust, to its
beautifully polished green interior. Is this
terrestrial mantle tossed up in a violent
volcanic blast? Are these common?"

Technically speaking, they are not volcanic bombs, which are
thrown out of volcanoes during eruptions. Rather, they are
exotic chunks of rocks, called xenoliths, carried upward by
magma as it ascended through the crust. The best preserved
xenoliths are those carried up rapidly from deep in the
mantle by the formation of diatremes.

Mount Shadwell is the highest of a cluster of basaltic scoria
cones. It is well known as a source of olivine and augite
ultramafic xenoliths and clinopryoxene and orthoclase
megacrysts contained in basalts and scoria. My understanding
that although such xenoliths can be found in many basaltic
lavas, the ones found at Mount Shadwell are uncommon for
their size and preservation. The xenoliths found at Mt.
Shadwell are inferred to have come from both the lower
crust and upper mantle.

Some web pages:

1. Mount Shadwell - Victorian Resources Online
http://www.nre.vic.gov.au/dpi/vro/coranregn.nsf/pages/eruption_points_shadwell

2. Coexisting Andesitic and Carbonate Melts in a
Lherzolite Xenolith from Mt. Shadwell, Victoria

http://www.es.mq.edu.au/geology/MNAGC98.html
http://www.es.mq.edu.au/geology/MNHP.html

3. Melting and Metasomatism in the Lithospheric Mantle Beneath
SE Australia: Trace Element Studies by Laser Microprobe by
Marc Norman and Suzanne O'Reilly

http://www.es.mq.edu.au/GEMOC/annrep97/abs96/Norm396.htm

4. Roach, I. C., 2004, Mineralogy, Textures and P-T
Relationships of a Suite of Xenoliths from the Monaro
Volcanic Province, New South Wales, Australia. Journal of
Petrology. vol. 45, no. 4, pp. 739-758.

http://petrology.oxfordjournals.org/cgi/content/abstract/45/4/739

5. Ellis. D. J., 1976, High pressure cognate inclusions
in the Newer Volcanics of Victoria. Contributions to
Mineralogy and Petrology. vol. 58, no. 2, pp. 149-180.

http://www.springerlink.com/content/r02x704tlm23w415/

6. Xenolith

http://en.wikipedia.org/wiki/Xenolith

Yours,

Paul H.