"Paul H."
In the thread “[meteorite-list] Known Tektite Strewn Fields?”
http://six.pairlist.net/pipermail/meteorite-list/2010-August/068400.html
,
Sterling K. Webb asked:
“So, I have a question for the geologists on the List
(I know you're there), where do I go in the Eastern U.S.
to find Top-O-The-Eocene exposures (beside Georgia
and Texas)?”
First, figure 1 of Heinrich(2009) shows the approximate
distribution of the North American strewn field and
locations from where tektites and microtektites of
the North American strewn field has been reported.
Microtektites have been reported from St. Stephens Quarry
in Alabama from two levels in the North Twistwood Creek
Formation. This suggest that microtektites, possibly even
tektites, can be found within the outcrops within exposures
of the Moodys Branch Group from Georgia to Texas that
expose sediments which are contemporaneous with the
Chesapeake Bay Impact (King and Petruny 2008). The exact
outcrop belt in which find exposures, can be found in local
and regional geologic maps, county geologic reports, field trip
guidebooks and other publications. In Louisiana, the entire
Moodys Branch Group is still somewhat exposed at
Montgomery Landing Bluff on the Red River.
Reference Cited:
Heinrich, Paul V., 2009, Reevaluation of Tektites Reported
from Rapides Parish, Louisiana. Louisiana Geological Survey
NewsInsights. vol. 19, no. 1, pp. 10-14.
The PDF file of this article can be either requested from
the author of downloaded from either:
http://www.scribd.com/doc/18698759/Alleged-Tektites-From-Rapides-Parish-Louisiana
or
http://www.lgs.lsu.edu/deploy/uploads/Summer_09_LGS_Newsletter.pdf
King, D. T., Jr., and L. W. Petruny, 2008, Impact stratigraphy
of the U.S. Gulf coastal states: Gulf Coast Association of
Geological Societies Transactions. vol. 58, pp. 503-516.
Georgia Deposits
In Georgia, the source bed of Georgiaites has been located.
It is "a patchy coarse-grained sand layer up to 10 cm thick that
lies at the boundary between the Twiggs Clay and the underlying
Middle Eocene Huber Formation.” It contains shocked quartz
from the Chesapeake Bay impact. This sand layer, which is the
basal layer of the Twiggs Clay, is a transgressive sheet sand
consists of sand that has been redeposited, reworked, and
bioturbated,
Published papers and abstracts are:
Harris, R. C., M. F. Roden, P. A. Schroeder, S. M. Holland, M. S. Duncan,
and E. F. Albin, 2004, Upper Eocene impact horizon in east-central
Georgia. Geology. vol. 32, no. 8, pp. 717-720; DOI: 10.1130/G20562.1
http://geology.geoscienceworld.org/cgi/content/abstract/32/8/717
Harris, R. S., M. S. Duncan, S. M. Holland, M. Steven, M. F. Roden,
Michael, and P. A, Schroeder, 2002, Probable shocked quartz as
evidence of for an Upper Eocene Impact Horizon in Coastal Plain,
Warren County Georgia. Geological Society of America Abstracts
with Programs. vol. 34, no. 6, pp. 402.
http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_41931.htm
http://gsa.confex.com/gsa/2002AM/finalprogram/session_3270.htm
Schroeder, P. ., and Harris, R. S., 2004, X-ray powder diffraction
evidence for shocked quartz in an upper Eocene sand deposit,
Warren County, Georgia, U.S.A. Southeastern Geology. vol. 42,
pp. 145–150
Schreoder, P. A., R. S. Harris, M. F. Roden, M. Duncan, S. Mack,
and S. M. Holland, 2002, 100% X-Ray Diffraction Evidence for
Shocked Quartz in an Upper Eocene Sand Deposit, Warren
County, Georgia. Geological Society of America Abstracts with
Programs. vol. 34, no. 6, pp. 544.
http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_38959.htm
http://gsa.confex.com/gsa/2002AM/finalprogram/session_3270.htm
In addition, multi-lithic conglomerates and breccias, which
are one to two meters thick have been reported from Georgia.
These enigmatic conglomerates, occur between the middle
Eocene Hawthorne Group and middle Miocene Altahama
Formation. Although their origin is unknown, it has been
suggested that they might be deposits related to the Chesapeake
Bay impact. If so, they might contain ejecta from this impact
(Cocker 2007, King and Petruny 2008). Additional studies of
these conglomerates are definitely needed.
References Cited:
Cocker, M., 2007, Possible impact-related conglomeratic
sediments in the upper coastal plain of southwestern Georgia.
Geological Society of America Abstracts with Programs.
vol. 39, no. 6, p. 311.
http://gsa.confex.com/gsa/2007AM/finalprogram/abstract_131779.htm
King, D. T., Jr., and L. W. Petruny, 2008, Impact stratigraphy
of the U.S. Gulf coastal states. Gulf Coast Association of
Geological Societies Transactions. vol. 58, pp. 503-516.
Yours,
Paul H.
