Sediment deposited within lake basins can preserve detailed records of past environmental conditions on planetary surfaces, including both Earth and Mars. Establishing how to best characterize these paleoclimate records is thus critical for understanding the evolution of past planetary climates. Here, we present an ~40 k.y. lake sediment record from Lake Towuti, Indonesia, developed using visible to near-infrared (VNIR) reflectance spectroscopy. Source sediment from the main river input to Lake Towuti, the Mahalona River, is spectrally dominated by Mg-rich serpentine; however, we also identify a distinct Al-phyllosilicate component, which we interpret as kaolinite, that increases in relative proportion to serpentine with decreasing grain size. Sink sediment from two cores collected at the distal margins of the Mahalona River delta has similar spectral signatures to the input source sediment. The cores capture systematic variations in the proportion of Alphyllosilicate to serpentine over time, which is also expressed in changes in bulk elemental chemistry of the sediment. We show that the abundance of serpentine relative to Al-phyllosilicate increases dramatically during the globally cooler, regionally drier climate of the Last Glacial Maximum. This change records the grain size-dependent mineralogy of deltaic sediment, which is ultimately driven by forced delta progradation and river incision during lake lowstands. Our analyses show that VNIR reflectance spectroscopy offers a rapid, nondestructive, and effective method for developing paleoenvironmental records from sedimentary phyllosilicate mineralogy. Exposed paleolake deposits on Mars should preserve similar paleoenvironmental information that can be accessed through detailed remote sensing observations of stratigraphy and VNIR reflectance spectroscopy in a source-to-sink framework.
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We express our gratitude to Associate Editor Andrew Cohen and two anonymous reviewers for their insightful and constructive comments, and to David Schofield for editorial handling. We thank Rebecca Greenberger, Io Wicaksono, Danielle Cares, Dave Murray, Joe Orchardo, Tom Kiefer, Taki Hiroi, and especially Kevin Robertson for their help with various components of sample preparation, laboratory techniques, and data analysis. We also thank Ralph Milliken for use of his X-ray diffraction instrument and helpful discussions, and Hendrik Vogel for sharing a preprint of his work and helpful discussions. Goudge gratefully acknowledges support for this work from the Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarships Program (PGSD3-421594-2012). Head acknowledges support from National Aeronautics and Space Administration (NASA) Mars Data Analysis Program grant NNX11AI81G. Russell acknowledges support from National Science Foundation grant EAR-1401448.
© 2017 Geological Society of America.
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