Characterization of Iron in Lake Towuti sediment

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 Mössbauer 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.