More About Permian-Triassic Boundary "GREAT DYING" Crater???
Wed May 12 17:38:45 EDT 2004
In the thread "[meteorite-list] FW: NASA ANNOUNCES
SITE OF "GREAT DYING" METEORCRATER", Devin Schrader
makinsomenoise wrote:
>
Thanks for the sites, I've read her papers but it >
never seemed like she had enough conclusive evidence >
to prove her theory, never solid enough. I wonder >
if she found it." Using Google, I found the text concerning the proposed
crater, although the original document is no longer
there, at:
http://216.239.57.104/search?q=cache:CoO-SXKVgLYJ:projects.crustal.ucsb.edu/beckerantarctica/downloads/bedout_lb_4-06.doc+bedout+crater&hl=enIn part, the text read:
"Bedout: A Possible End-Permian Impact Crater Offshore
Northwestern Australia
L. Becker1*, R. J. Poreda2, A. R. Basu2, K. Pope3, M.
Harrison4, C. Nicholson1, R. Iasky5
1Institute for Crustal Studies, Department of
Geological
Sciences, University of California, Santa Barbara
93106,
USA, 2Department of Earth and Environmental Sciences,
University of Rochester, Rochester, NY, USA, 4Geo Eco
Arc Research, Aquasco, MD 20608, 5Australian National
University, Canberra, Australia, 6 Geological Survey
Western Australia, Perth, Australia
______________________________________________________________
* To whom correspondence should be addressed
Abstract
The Bedout High located on the northwestern
continental
margin of Australia has emerged as a prime candidate
for an
end Permian impact structure. Seismic imaging, gravity
data
and the identification of melt rocks and impact
breccias
from drill cores located on top of Bedout are
consistent
with the presence of a buried impact crater. The
impact
breccias contain nearly pure silica glass (SiO2),
fractured
and shock-melted plagioclases and spherulitic glass.
The
distribution of glass and shocked minerals over
hundreds
of meters of drill core implies that a melt sheet is
present. Available gravity and seismic data suggest
that
the Bedout High represents the central uplift of a
crater
similar in size to Chicxulub. A single plagioclase
grain
from the Lagrange-1 exploration well has an Ar/Ar age
of
250.7 1 4.3 million years. The location and age of
the
Bedout crater can account for reported occurrences of
impact debris in Permian-Triassic boundary sediments
worldwide."
++++++
" Geology of the Bedout Structure
The Bedout High is part of the Roebuck basin that
forms the
northwestern continental margin of Australia (Fig.
2.). Existing
studies of the structure include two regional seismic
surveys
conducted by the Australian Geological Survey (AGSO)
and the
Japan National Oil Company (JNOC) and two exploratory
wells
drilled 9 km apart on the top and flank of the Bedout
High,
Bedout -1 and Lagrange-1, that extend to depths of
3052 m
(9986 ft.) and 3273 m (10,738 ft.), respectively (Fig.
3, S-2).
Both wells drilled through ~3 km of marine and fluvial
sediments
consisting of carbonates with occasional interbeded
siltstones and
mudstones (Tertiary to Cretaceous) and sandstones
interbeded
with claystones, siltstones and coal (Cretaceous to
Triassic) before
reaching a breccia. (Late Permian; Fig. S-2, 15). Two
of the 14
AGSO regional seismic lines cross over the Bedout
High (Fig. 2).
In addition, four wells penetrate Permian strata (two
are shown in
Fig. 2.) offshore that help to identify seismic
reflectors that define
the Bedout structure and stratigraphy. In both the
Lagrange-1 and
Bedout -1 cores and cuttings fluviatile and marine
Keraudren
(Middle to Late Triassic) sediments are deposited
directly on top
of the breccia (Late Permian; Fig. 4, S-2, S-3)."
Also, there is:
"GLOBAL EVIDENCE FOR AN END-PERMIAN
EXTINCTION EVENT" at:
http://www.cosis.net/abstracts/EAE03/08101/EAE03-J-08101.pdfand
"BEDOUT: AN END-PERMIAN IMPACT CRATER
OFFSHORE NORTHWESTERN AUSTRALIA"
http://www.exopi.org/pdfs/Becker_Bedout.pdfA map showing the location of the Bedout High can be
found at:
http://www1.industry.gov.au/archive/petr_exploration/2002/goldbook/W02-1to6/Figures/rowley_fig2.pdfYours,
Paul
Baton Rouge, LA
