Dating climatic change in hot deserts using desert varnish on meteorite finds

Lee, M.R. and Bland, P.A. (2003) Dating climatic change in hot deserts using desert varnish on meteorite finds. Earth and Planetary Science Letters, 206(1-2), pp. 187-198. (doi: 10.1016/S0012-821X(02)01078-6)

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A thin coating of desert varnish occurs on Forrest 009 and Nurina 004, both equilibrated ordinary chondrite (L6) finds from the Nullarbor Plain, Australia. This finely laminated deposit is chemically and petrographically comparable to the varnish found on terrestrial rocks. Forrest 009, which has a terrestrial age of 5.9 kyr, has a 100-130 micrometre thick coating of desert varnish that has a laterally consistent chemical microstratigraphy comprising a narrow Ba- and Mn-poor lower region, a thick Ba- and Mn-rich central area and a narrow outer zone almost devoid of both cations. The interior of the meteorite contains Fe-oxide and oxyhydroxide veins that have formed by chemical weathering of metals and sulphides. As these veins do not cross-cut the varnish, it must have accreted rapidly relative to the weathering rate of the meteorite. The less than or equal to 70 mum thick varnish on Nurina 004, which has a terrestrial age of 33.4 kyr, lacks a consistent chemical microstratigraphy, but it is cross-cut by Fe-oxide and oxyhydroxide veins, some of which have supplied Fe to the varnish. This implies that the chemical weathering rate of Nurina 004's interior was slow in comparison to the accretion rate of the varnish. The petrography and chemical composition of varnish on Forrest 009 indicates that this meteorite may have resided in a relatively humid environment for most of its 5.9 kyr terrestrial history and that the Nullarbor recently became more arid. This conclusion supports results from an analysis of Fe-bearing weathering products in the interior of the meteorite by Mossbauer spectroscopy, which also indicate that Forrest 009 experienced an early period of rapid weathering under relatively humid conditions. The petrography of varnish on Nurina 004 shows that the interior of the meteorite weathered relatively slowly, probably because it fell during an and time, which is again in agreement with previous Mossbauer spectroscopy results. Results from both meteorites are in agreement with palaeoclimate data derived from a number of other proxies. The implications of this work are that the large number of meteorites that have been collected from several hot deserts of the world may be a powerful source of information on climate change over the last 30-35 kyr.

Item Type:Articles
Additional Information:NOTICE: this is the author’s version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Earth and Planetary Science Letters 206(1-2), Jan 03, DOI: 10.1016/S0012-821X(02)01078-6
Keywords:Meteorite, desert varnish, nullarbor, weathering
Glasgow Author(s) Enlighten ID:Lee, Professor Martin
Authors: Lee, M.R., and Bland, P.A.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Earth and Planetary Science Letters
Publisher:Elsevier Science B.V
Copyright Holders:Copyright © 2002 Elsevier Science B.V
First Published:First published in Earth and Planetary Science Letters 206(1-2):187-198
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
286201Quantifying chemical weathering rates of silicate mineralsMartin LeeNatural Environment Research Council (NERC)NER/B/S/2000/00SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES