Weathering of Ordinary Chondrites from Algeria and Australia as a Climatic Indicator

Details Weathering of Ordinary Chondrites from Algeria and Australia as a Climatic Indicator Weathering of Ordinary Chondrites from Algeria and Australia as a Climatic Indicator

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..487b&link_type=abstract

Meteoritics, vol. 30, no. 5, page 487

Computer Science

Ages, Terrestrial, Chondrites, Ordinary, Meteorites, Hot Desert, Spectroscopy, Mossbauer, Weathering

Scientific paper

Introduction: Recently it has been recognized that ordinary chondrite meteorites resident in desert regions may preserve information about the climate at the time of their arrival on Earth in the degree to which they are weathered [1], providing that a stable surface has existed at the accumulation site. We present here a comparison of ^57Fe Mossbauer spectroscopy data for additional meteorites for which terrestrial ages exist, recovered from Reg el Acfer, Algeria and the Nullarbor Region, Australia. Results and Discussion: The data presented in Fig. 1 compare abundance of ferric iron oxide/oxyhydroxide species against terrestrial age [2, 3] for ordinary chondrites from Australia (a) and Algeria (b). Even with an increased dataset for Australian meteorites (compared to that already presented [1]) the initial hypothesis remains intact i.e. meteorite weathering over time is sensitive to changes in climate. Peaks in oxidation at around 2,000, 7,000 and 23,000 years correspond to periods of speleothem formation [4] and high lake level status [5]. Similarly, a period of low oxidation between 12,000-20,000 years is mirrored in low lake level status [5] and aridity in the Nullarbor [6]. The mechanism by which meteorites may record palaeoclimatic information is given in [1]. A correlation that strengthens our case is that where data from both H and L(LL) chondrites are available (i.e. around 7,000-8,000 years) the two plots are similar, indicating a broadscale environmental effect. In contrast, the distribution for meteorites from the Acfer region appears to be more random, with no correlation between H and L(LL) data. The difference may be related to the stability of the respective accumulation surfaces. The surface of the Nullarbor appears to have been stable over the last 30,000 years [7]. The Algerian and Libyan Sahara, however, has experienced several episodes of active fluvial processes over the last 10,000 years [8] which may have profoundly effected the meteorites residing in this area [9]. If Reg el Acfer has experienced surface drainage during the last few thousand years this could disrupt the signature of a climatic effect, as meteorites in a topographic low would be more likely to be more highly weathered. References: [1] Bland P. A. et al. (1995) LPS XXVI, 129-130. [2] Jull A. J. T. et al. (1994) Workshop on Meteorites from Cold and Hot Deserts, LPI, Houston, in press. [3] Jull A. J. T. (1995) personal communication. [4] Goede A. et al. (1990) J. Quat. Sci., 5, 29-38. [5] Street F. A. and Grove A. T. (1979) Quat. Res., 12, 83-118. [6] Martin H. A. (1973) Australian J. Botany, 21, 283-316. [7] Lowry D. C. and Jennings J. N. (1974) Zeits. Geomorph., 18, 35-81. [8] Pachur H-J (1980) The Geology of Libya, 781-788, Academic, London. [9] Benoit P. H. et al. (1993) Meteoritics, 28, 196-203.

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