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A spectroscopy and isotope study of sediments from the Antarctic Dry Valleys as analogues for potential paleolakes on Mars

Published online by Cambridge University Press:  09 March 2004

Janice L. Bishop ,
Brandy L. Anglen ,
Lisa M. Pratt ,
Howell G. M. Edwards ,
David J. Des Marais  and
Peter T. Doran
Janice L. Bishop
Affiliation:
SETI Institute, 2035 Landings Drive, Mountain View, CA 94043, USA e-mail: jbishop@seti.org NASA-Ames Research Center, Mail Stop 239-4, Moffett Field, CA 94035, USA
Brandy L. Anglen
Affiliation:
Department of Geological Sciences, Indiana University, Bloomington IN 47405, USA
Lisa M. Pratt
Affiliation:
Department of Geological Sciences, Indiana University, Bloomington IN 47405, USA
Howell G. M. Edwards
Affiliation:
Department of Chemical and Forensic Sciences, University of Bradford, Bradford BD7 1DP, UK
David J. Des Marais
Affiliation:
NASA-Ames Research Center, Mail Stop 239-4, Moffett Field, CA 94035, USA
Peter T. Doran
Affiliation:
Earth & Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St, Chicago, IL 60607, USA
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Abstract

A spectroscopy and isotope study has been performed on igneous sediments from Lake Hoare, a nearly isolated ecosystem in the Dry Valleys region of Antarctica. The mineralogy and chemistry of these sediments were studied in order to gain insights into the biogeochemical processes occurring in a permanently ice-covered lake and to assist in characterizing potential habitats for life in paleolakes on Mars. Obtaining visible/near-infrared, mid-infrared and Raman spectra of such sediments provides the ground truth needed for using reflectance, emittance and Raman spectroscopy for exploration of geology, and perhaps biology, on Mars. Samples measured in this study include a sediment from the ice surface, lake bottom sediment cores from oxic and anoxic zones of the lake and the magnetic fractions of two samples.

These sediments are dominated by quartz, pyroxene, plagioclase and K-feldspar, but also contain calcite, organics, clays, sulphides and iron oxides/hydroxides that resulted from chemical and biological alteration processes. Chlorophyll-like bands are observed in the spectra of the sediment-mat layers on the surface of the lake bottom, especially in the deep anoxic region. Layers of high calcite concentration in the oxic sediments and layers of high pyrite concentration in the anoxic sediments are indicators of periods of active biogeochemical processing in the lake. Micro-Raman spectra revealed the presence of ~5 μm-sized pyrite deposits on the surface of quartz grains in the anoxic sediments. C, N and S isotope trends are compared with the chemistry and spectral properties. The δ13C and δ15N trends highlight the differences in the balance of microbial processes in the anoxic sediments versus the oxic sediments. The biogenic pyrite found in the sediments from the anoxic zone is associated with depleted δ34S values, high organic C levels and chlorophyll spectral bands and could be used as a potential biomarker mineral for paleolakes on Mars.

Keywords

Antarctic sedimentsisotopesspectroscopylifeMarswater
Type
Research Article
Information
International Journal of Astrobiology , Volume 2 , Issue 4 , October 2003 , pp. 273 - 287
Copyright
© 2003 Cambridge University Press

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