[meteorite-list] "Desert Varnish"

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:35 2004
Message-ID: <20020626014328.48899.qmail_at_web10401.mail.yahoo.com>

Regarding recent questions related to "Desert
Varnish":

GSA Today: Vol. 11, No. 8, pp. 4–10.

Rock Varnish: Recorder of Desert Wetness?

Wallace S. Broecker and Tanzhuo Liu
Lamont-Doherty Earth Observatory of Columbia
University, P. O. Box 1000, Palisades, NY 10964, USA

    ABSTRACT

      Rock varnish is a thin coating (<200 µm) of a
cocktail rich in Mn, Fe, and clay minerals that is
ubiquitous in desert regions. It has become the center
of a contentious
    controversy revolving around its use to date
geomorphic surfaces and/or to evaluate past climate
conditions. We observe pronounced temporal variations
in Mn and Ba concentration that are similar over large
regions and that likely relate to variations in
paleo-wetness. The mode of formation of varnish
remains uncertain, but anthropogenic Pb concentrated
in outermost varnish layers indicates its continued
formation, and experiments using cosmogenic Be suggest
that, while precipitation is a primary control, dust,
dew, and aerosols may also be important in delivering
the ingredients of varnish. We suggest several steps
that may lead to rejuvenation and future break-through
in varnish studies.
--------------------

To see the complete paper with images of thin-sections
of "rock varnish", go to:

<http://www.gsajournals.org/gsaonline/?request=get-document&issn=1052-5173&volume=011&issue=08&page=0004>

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Received on Tue 25 Jun 2002 09:43:28 PM PDT