Secondary Fe and Al in Antarctic paleosols: Correlation to Mars with prospect for the presence of life

详细信息    查看全文

• 作者：William C. Mahaney ; James Dohm ; Barbara Kapran ; Ronald G.V. Hancock ; Michael W. Milner
• 关键词：Extractable Fe/Al in paleosols ; Antarctic paleosols ; Terrestrial analogues of martian paleosols
• 刊名：Icarus
• 出版年：2009
• 出版时间：September 2009
• 年：2009
• 卷：203
• 期：1
• 页码：320-330
• 全文大小：716 K

文摘

Middle-Miocene age paleosols in the Antarctic Dry Valleys were studied for their compositional variation and concentrations of secondary oxides/coatings in c;2 mm matrix material in tills. The paleosols date to between 10–18 Ma by ¹⁰Be, forming prior to and just following the transition from warm-based to cold-based ice, when the climate is thought to have entered a prolonged cold/dry period in which soil moisture would have been frozen most of the year. The progression of release of secondary oxides of Fe and Al shows variable percentages of individual oxihydrites relative to chemical element totals, and thus, to consume total Fe and Al would require tens of millions of additional years. The slow progression of Fe_d/Fe_t, used as a measure of relative age in other warmer alpine and Arctic climates, is shown here to amount to c;15 percent of the total Fe available for weathering. Ferrihydrite variability in paleosols, often used to indicate the presence of fluctuating/perched ground water tables, suggests that liquid water may have accumulated in mid-profile in some instances, perhaps during periods when the climate was somewhat warmer for several weeks during the summer. Variable Fe and Al ratios and arithmetic functions argue for extremely slow but sustainable release of oxides in a cold, polar desert climate, in which temperatures prohibit the formation of clay minerals. The secondary mineral species present likely amount to residue from past climates that were more conducive to clay mineral genesis and aerosolic input over time. The presence of microbial life in Antarctic paleosols, with minor amounts of Fe available for physiological processes to function, argues for the potential existence of microorganisms in ice-enriched paleosols of Mars, particularly given its watery and dynamic geologic past and relatively high concentration of total Fe in subaerial paleosols. The distribution of Fe over a large part of the northern plains of Mars as determined by the GRS instrument is invoked as a comparison with the Antarctic.