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Thursday, 13 December 2007

Crow Creek Member of Pierre Shale is Impact Tsunami Generated

Crow Creek Member of Pierre Shale is Impact Tsunami Generated

Paul bristolia at yahoo.com
Wed Dec 12 16:19:38 EST 2007

In “December Media Highlights: Geology and GSA Today” at:
http://www.geosociety.org/news/pr/07-68.htm , there is:

Weber, R. D., and D. K. Watkins, 2007, Evidence from
the Crow Creek Member (Pierre Shale) for an impact-
induced resuspension event in the late Cretaceous
Western Interior Seaway. . Vol. 35, no. 12,
pp. 1119-1122.

http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG24209A.1

The press release stated:

The Crow Creek Member, a unique rock unit in the Upper
Cretaceous Pierre Shale in South Dakota and Nebraska,
has been thought to represent sea-level rise along
the eastern margin of the Western Interior Seaway.
However, Weber et al. show that the presence of impact
ejecta from the Manson Impact Structure, found within
the Member, suggests an impact-induced genesis.
Current investigation of a reworked nannofossil
assemblage occurring within the Crow Creek Member is
consistent with an origin involving gravitational
settling rather than sea-level rise. Additionally,
the reworked assemblage decreases in abundance with
increased distances from the Manson Impact Structure.
These observations support the hypothesis that Manson
Impact may have caused a re-suspension event in the
Western Interior Seaway, resulting in Crow Creek
deposition.”

Yours,

Paul H.

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