[meteorite-list] Desert Varnish, 100, 000-Year Old Meteorite, and Pluvial Lakes

From: Paul H. <oxytropidoceras_at_meteoritecentral.com>
Date: Tue, 2 Mar 2010 13:39:38 -0600
Message-ID: <20100302143938.TSDHC.814179.imail_at_eastrmwml34>

In ?Science page update / desert varnish on meteorites? at
http://six.pairlist.net/pipermail/meteorite-list/2010-March/061506.html ,
Sonny wrote:

?I have added a thin section picture of desert varnish
on my web page. This picture was taken at ASU of a
meteorite displaying desert varnish estimated to be
on earth for 100,000 years.?

How exactly was the 100,000-year date for this "ancient
dry lake bed meteorite" arrived at?

I ask because if this meteorite was found on a dry lake in
Nevada, the 100,000-year date would not make any sense
in terms of the Pleistocene history of those lakes. Having
a 100,000-year old meteorite lying on a lake bed would
argue that that the lake has been dry for the past 100,000
years and there has been a lack of any sediment
accumulation during the past 100,000 years. Either case
is a physical impossibility for any of the Pleistocene lakes
in the western United States as they were all full of water
and the locations of active sediment accumulation during
various pluvial episodes during the Pleistocene as
discussed in Benson and Thompson (1987), Benson et al.
(1990) Mifflin and Wheat (1979). Even as late as 12,000
to 14,000 BP, many of the western lakes were full of
water and the sites of active sedimentation. Any meteorite
that fell into these lakes before this time would be buried
beneath Pleistocene lake deposits and certainly would not
be lying on the surface of what is now a dry lake. Therefore, if
the meteorite was found on a dry lake bed in the western
United States, the alleged age of the 100,000-year meteorite
is completely contradicted by the age of the dry lake bed
on which it rests.

Benson, L. V., R. I. Currey, R. I. Dorn, K. R. Lajoie, C. G. Oviatt,
S. W. Robinson, G. I. Smith and S. Stine, 1990, Chronology
of expansion and contraction of four Great Basin lake systems
during the past 35,000 years. Palaeogeography,
Palaeoclimatology, Palaeoecology. vol. 78, pp. 241?286.

Benson, L. V., and R. S. Thompson, 1987, The physical record
of lakes in the Great Basin. In: Ruddiman, W. F., Wright Jr.,
H. E., eds., The Geology of North America: North America and
Adjacent Oceans during the Last Deglaciation K-3. Geological
Society of America Bulletin, Boulder, CO, pp. 241? 260.

Mifflin, M. D., and M. M. Wheat, 1979, Pluvial Lakes and
Estimated Pluvial Climates of Nevada, Nevada Bureau of
Mines and Geology, Reno, Nevada, 57 pp.

Yours,

Paul H.
Received on Tue 02 Mar 2010 02:39:38 PM PST