A SPECTROSCOPY AND ISOTOPE STUDY OF SEDIMENTS FROM THE ANTARCTIC DRY VALLEYS AS ANALOGS FOR POTENTIAL PALEOLAKES ON MARS

A spectroscopy and isotope study has been performed on igneous sediments from the Dry Valleys region of Antarctica in an effort to characterize aqueous processes in potential paleolake environments on Mars.  Gaining VNIR, mid-IR, and Raman spectra of such sediments provides compositional information for missions to Mars, as well as ground truthing for reflectance, emittance and Raman spectroscopy of the geology, and perhaps biology, on Mars.  C, N, and S isotope analyses provide additional information about biological and chemical activity in the samples studied here and may be utilized in future martian missions.  Sediments measured in this study are dominated by feldspar, quartz and pyroxene, and were collected from the perennially ice-covered Lake Hoare in the Taylor Valley and include surface sediments and sediment cores from below oxic and anoxic zones of the lake. 

Calcite, organics, clays, sulfides, and iron oxides/hydroxides are also present in these igneous sediments and result from chemical and biological alteration processes.  Chlorophyll bands are observed in spectra of the sediment-mat layers from the surface of the lake bottom, especially in the anoxic region sediments.  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 have revealed the presence of ~5 µm-sized sulfide deposits imbedded in quartz grains in an anoxic sediment.  The d¹³C and d¹⁵N trends show a more complex organic history for the anoxic region sediments than for the oxic region sediments.  Correlations are observed between the d³⁴S values for sulfate and pyrite and the organic C abundances. 

Magnetic grains were separated using a hand magnet for the surface sand and one oxic region sediment.  The VNIR spectra of the magnetic grains in each sample are substantially darker than spectra of the bulk sediments, the mid-IR spectra of the magnetic grains do not exhibit the quartz bands present in the bulk sediment spectra and Raman spectra show the presence of magnetite (and maybe some Ti-spinel) in the magnetic grains.  However, all three spectroscopic techniques show that other minerals including feldspar, pyroxene, Fe-Ti oxide, and Fe-rich clays are also present in the magnetic grains.