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Sediments collected from Lake Towuti, an ultramafic-hosted lake in Indonesia, preserve a visible alternating pattern of red and green sediments due to variations in clay mineral and Fe-oxide composition and abundance consistent with changes in iron oxidation state through time. Spectral, mineralogical, and chemical analyses on soils, river, and sediment samples from across the lake and its catchment were carried out to better understand the starting composition of these sediments and the processes that affected them before and after deposition. Despite high Fe abundances in all samples and abundant Fe oxides in lateritic source regions, mineralogical analyses (X-ray diffraction (XRD) and Mossbauer spectroscopy) of the modern lake sediment show almost no well-crystalline iron oxides. In addition, sequential Fe extractions suggest an increasing proportion of easily extractable, poorly crystalline (X-ray amorphous) material with burial depth. XRD, bulk chemistry, and visible-near infrared (VNIR) spectral reflectance measurements demonstrate that clay mineralogy and bulk chemistry can be inferred from VNIR data. These results provide evidence for variations in Fe mineralogy and crystallinity based on location in this source to sink system. Understanding how the mineralogy and chemistry of sediments within a ferruginous lake basin are affected by transport, chemical alteration, physical alteration, and deposition from source to sink on Earth, and the degree to which these trends and underlying processes can be inferred from chemical and spectral properties, may provide useful direction in assessing paleoenvironmental conditions in other terrestrial lakes as well as ancient lacustrine environments preserved in the stratigraphic record of Mars.

Sediments collected from Lake Towuti, an ultramafic-hosted lake in Indonesia, preserve a visible alternating pattern of red and green sediments due to variations in clay mineral and Fe-oxide composition and abundance consistent with changes in iron oxidation state through time. Spectral, mineralogical, and chemical analyses on soils, river, and sediment samples from across the lake and its catchment were carried out to better understand the starting composition of these sediments and the processes that affected them before and after deposition. Despite high Fe abundances in all samples and abundant Fe oxides in lateritic source regions, mineralogical analyses (X-ray diffraction (XRD) and Mossbauer spectroscopy) of the modern lake sediment show almost no well-crystalline iron oxides. In addition, sequential Fe extractions suggest an increasing proportion of easily extractable, poorly crystalline (X-ray amorphous) material with burial depth. XRD, bulk chemistry, and visible-near infrared (VNIR) spectral reflectance measurements demonstrate that clay mineralogy and bulk chemistry can be inferred from VNIR data. These results provide evidence for variations in Fe mineralogy and crystallinity based on location in this source to sink system. Understanding how the mineralogy and chemistry of sediments within a ferruginous lake basin are affected by transport, chemical alteration, physical alteration, and deposition from source to sink on Earth, and the degree to which these trends and underlying processes can be inferred from chemical and spectral properties, may provide useful direction in assessing paleoenvironmental conditions in other terrestrial lakes as well as ancient lacustrine environments preserved in the stratigraphic record of Mars.

Near-infrared remote sensing data of Mars have revealed thousands of ancient deposits of Fe/Mg-rich smectitic clay minerals within the crust with relevance to past habitability. Diagnostic metal-OH infrared spectroscopic absorptions used to interpret the mineralogy of these phyllosilicates occur at wavelengths of 2.27-2.32 mu m, indicating variable Fe/Mg ratios in the clay structures. The objective of this work is to use these near infrared absorptions to constrain the mineralogy of smectites on Mars. Using Fe/Mg-rich seafloor clay minerals as mineralogical and spectroscopic analogs for Martian clay minerals, we show how crystal-chemical substitution and mixed layering affect the position of the diagnostic metal-OH spectral feature in smectitic clay minerals. Crystal-chemistry of smectites detected on Mars were quantitatively constrained with infrared data and categorized into four mineralogical groups. Possible alteration processes are constrained by comparisons of clay chemistry detected by remote sensing techniques to the chemistry of candidate protoliths. Of the four groups identified, three of them indicate significant segregation of Fe from Mg, suggestive of alteration under water-rich and/or oxidizing conditions on Mars. The fourth group (with low Fe/Mg ratios) may result from alteration in reducing or water-limited conditions, potentially in subsurface environments. Some samples are interstratified di-trioctahedral clay minerals that have characteristics of dioctahedral clay minerals but clear chemical evidence for trioctahedral sheets. Approximately 70% of smectite deposits previously detected on Mars are classified as Fe-rich (FeO/MgO > 10). Only 22% of detections are trioctahedral and relatively Mg-rich. An additional similar to 8% are difficult to characterize, but might be very Fe-rich. The segregation of Fe from Mg in Martian clay minerals suggests that Mg should be enriched in other contemporaneous deposits such as chlorides and carbonates. (C) 2015 T

Near-infrared remote sensing data of Mars have revealed thousands of ancient deposits of Fe/Mg-rich smectitic clay minerals within the crust with relevance to past habitability. Diagnostic metal-OH infrared spectroscopic absorptions used to interpret the mineralogy of these phyllosilicates occur at wavelengths of 2.27-2.32 mu m, indicating variable Fe/Mg ratios in the clay structures. The objective of this work is to use these near infrared absorptions to constrain the mineralogy of smectites on Mars. Using Fe/Mg-rich seafloor clay minerals as mineralogical and spectroscopic analogs for Martian clay minerals, we show how crystal-chemical substitution and mixed layering affect the position of the diagnostic metal-OH spectral feature in smectitic clay minerals. Crystal-chemistry of smectites detected on Mars were quantitatively constrained with infrared data and categorized into four mineralogical groups. Possible alteration processes are constrained by comparisons of clay chemistry detected by remote sensing techniques to the chemistry of candidate protoliths. Of the four groups identified, three of them indicate significant segregation of Fe from Mg, suggestive of alteration under water-rich and/or oxidizing conditions on Mars. The fourth group (with low Fe/Mg ratios) may result from alteration in reducing or water-limited conditions, potentially in subsurface environments. Some samples are interstratified di-trioctahedral clay minerals that have characteristics of dioctahedral clay minerals but clear chemical evidence for trioctahedral sheets. Approximately 70% of smectite deposits previously detected on Mars are classified as Fe-rich (FeO/MgO > 10). Only 22% of detections are trioctahedral and relatively Mg-rich. An additional similar to 8% are difficult to characterize, but might be very Fe-rich. The segregation of Fe from Mg in Martian clay minerals suggests that Mg should be enriched in other contemporaneous deposits such as chlorides and carbonates. (C) 2015 T

Seafloor hydrothermal sites generate abundant Mg- and Fe-rich clays. These clays are structurally and compositionally interesting because these environments are characterized by large, dynamic temperature and chemical gradients in their deposition environment, which promote the formation of chemically and structurally complex clays, including interstratified phases. The system is also interesting as a proxy for the study of the large Mg- and Fe-rich phyllosilicate deposits on Mars, which are broadly characterized as smectitic clay of hydrothermal, volcanic or sedimentary origin. Thirty submarine samples and four terrestrial ones, for comparison, were studied by means of X-ray diffraction (XRD), thermogravimetry (TG), mid-IR and Mössbauer spectroscopies and chemical analysis. The samples include nontronite and the mixed-layer phases glauconite-nontronite, talc-nontronite and talc-saponite. Some of the talc-saponite samples have Fe contents well above those typical for these Mg-rich, trioctahedral phases (up to 1.69 Fe per O10[OH]2, in the tetrahedral and octahedral sheets). Tetrahedral Fe ranges from 0 to 0.66 atoms per O10[OH]2 across the samples. As found in previous studies of similar specimens, Fe promotes the retention of molecular water that is released upon heating above 200 C, and is mainly emplaced in non-expandable layers (talc and glauconite layers). In talc-nontronite and talc-saponite octahedral Fe (both di- and trivalent) appears to be bound to this trapped molecular water, whereas in glauconite-nontronite the bond appears to be with tetrahedral Fe. Samples typically show more than one dehydroxylation event in the TG analysis. The weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of XRD, but there is no good correlation between both. By contrast, the weight loss at each dehydroxylation event correlates with the chemistry of the layers, where certain cations promote chemical do

Seafloor hydrothermal sites generate abundant Mg- and Fe-rich clays. These clays are structurally and compositionally interesting because these environments are characterized by large, dynamic temperature and chemical gradients in their deposition environment, which promote the formation of chemically and structurally complex clays, including interstratified phases. The system is also interesting as a proxy for the study of the large Mg- and Fe-rich phyllosilicate deposits on Mars, which are broadly characterized as smectitic clay of hydrothermal, volcanic or sedimentary origin. Thirty submarine samples and four terrestrial ones, for comparison, were studied by means of X-ray diffraction (XRD), thermogravimetry (TG), mid-IR and Mössbauer spectroscopies and chemical analysis. The samples include nontronite and the mixed-layer phases glauconite-nontronite, talc-nontronite and talc-saponite. Some of the talc-saponite samples have Fe contents well above those typical for these Mg-rich, trioctahedral phases (up to 1.69 Fe per O10[OH]2, in the tetrahedral and octahedral sheets). Tetrahedral Fe ranges from 0 to 0.66 atoms per O10[OH]2 across the samples. As found in previous studies of similar specimens, Fe promotes the retention of molecular water that is released upon heating above 200 C, and is mainly emplaced in non-expandable layers (talc and glauconite layers). In talc-nontronite and talc-saponite octahedral Fe (both di- and trivalent) appears to be bound to this trapped molecular water, whereas in glauconite-nontronite the bond appears to be with tetrahedral Fe. Samples typically show more than one dehydroxylation event in the TG analysis. The weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of XRD, but there is no good correlation between both. By contrast, the weight loss at each dehydroxylation event correlates with the chemistry of the layers, where certain cations promote chemical do

Seafloor hydrothermal sites generate abundant Mg- and Fe-rich clays. These clays are structurally and compositionally interesting because these environments are characterized by large, dynamic temperature and chemical gradients in their deposition environment, which promote the formation of chemically and structurally complex clays, including interstratified phases. The system is also interesting as a proxy for the study of the large Mg- and Fe-rich phyllosilicate deposits on Mars, which are broadly characterized as smectitic clay of hydrothermal, volcanic or sedimentary origin. Thirty submarine samples and four terrestrial ones, for comparison, were studied by means of X-ray diffraction (XRD), thermogravimetry (TG), mid-IR and Mössbauer spectroscopies and chemical analysis. The samples include nontronite and the mixed-layer phases glauconite-nontronite, talc-nontronite and talc-saponite. Some of the talc-saponite samples have Fe contents well above those typical for these Mg-rich, trioctahedral phases (up to 1.69 Fe per O10[OH]2, in the tetrahedral and octahedral sheets). Tetrahedral Fe ranges from 0 to 0.66 atoms per O10[OH]2 across the samples. As found in previous studies of similar specimens, Fe promotes the retention of molecular water that is released upon heating above 200 C, and is mainly emplaced in non-expandable layers (talc and glauconite layers). In talc-nontronite and talc-saponite octahedral Fe (both di- and trivalent) appears to be bound to this trapped molecular water, whereas in glauconite-nontronite the bond appears to be with tetrahedral Fe. Samples typically show more than one dehydroxylation event in the TG analysis. The weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of XRD, but there is no good correlation between both. By contrast, the weight loss at each dehydroxylation event correlates with the chemistry of the layers, where certain cations promote chemical do