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Monday, 24 October 2011

Volcano... Or Giant Impact?

Volcano... Or Giant Impact?


In [meteorite-list] Volcano... Or Giant Impact? at
http://six.pairlist.net/pipermail/meteorite-list/2011-October/080522.html
Michael Fowler asked:

"My guess is that the impact was at an oblique angle, 
since we have many other impact structures without 
such pyroclastic like flows. 

Anyone know where the impact crater (if preserved) 
is in relationship to the flow deposits?"

The crater is hypothesized to lie under the Minch, which is a 
strait that separates the Isle of Lewis in the Outer Hebrides 
from the north-west Highlands of Scotland. If this is the case,
then it lies at the bottom of the Minch Basin and buried beneath 
Precambrian Torridonian strata and a thickness of Permo-Triassic 
and Liassic sediments that fill this basin.

The paper is;

Amor, K., S. P. Hesselbo, D. Porcelli, S. Thackrey, and J. 
Parnell, 2008, A Precambrian proximal ejecta blanket 
from Scotland. Geology. vol. 36, no. 4, pp. 303-306.
http://geology.gsapubs.org/content/36/4/303.short
http://geology.geoscienceworld.org/cgi/content/abstract/36/4/303

A related paper is:

Related paper, in which, the ejecta blanket is interpreted
as volcanic rocks is:

Young, G. M., 2002,  Stratigraphy and geochemistry of 
volcanic mass flows in the Stac Fada Member of the 
Stoer Group, Torridonian, NW Scotland. Royal Society 
of Edinburgh Transactions: Earth Sciences. vol.  93, 
no. 1, pp. 1-16.

Web pages

The Minch
http://en.wikipedia.org/wiki/Minch

Stac Fada Member
http://web2.ges.gla.ac.uk/~mlee/stac_fada/stac_fada.html

Biggest UK space impact found by Paul Rincon
BBC News, March 26, 2008
http://news.bbc.co.uk/2/hi/science/nature/7314329.stm

A PhD. dissertation about possible impact ejecta deposits is:

Aden, D. J., 2011, An Anomalous Breccia in the 
Mesoproterozoic (~1.1 Ga) Atar Group, Mauritania: 
Endogenic vs. Exogenic Genesis. Unpublished PhD.
dissertation, Ohio University, Athens, Ohio.
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1276614508
http://etd.ohiolink.edu/view.cgi/Aden%20Douglas%20J.pdf?ohiou1276614508

PDF file at:
http://etd.ohiolink.edu/send-pdf.cgi/Aden%20Douglas%20J.pdf?ohiou1276614508

Another interesting paper is:

Reimold, W. U., V. von Brunn, and C. Koeberl, 1997, Are 
Diamictites Impact Ejecta?—No Supporting Evidence from 
South African Dwyka Group Diamictite. The Journal of 
Geology. vol. 105, pp. 517–530.

PDF file at:
http://www.univie.ac.at/geochemistry/koeberl/publikation_list/128-diamictites-not-impact-J-Geol1997.pdf

A related paper is:

Huber, H., C. Koeberl, I. MacDonald, and W. U. Reimold,
2001, Geochemistry and petrology of Witwatersrand
and Dwyka diamictites from South Africa: Search for an
extraterrestrial component. Geochimica et Cosmochimica
Acta. vol. 65, no. 12, pp. 2007–2016.

The PDF file for this paper can be downloaded from:

http://www.univie.ac.at/geochemistry/koeberl/publikation_list/184-Dwyka-geochem-GCA2001.pdf

Best wishes,

Paul H.

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