^1,2Michael T. Thorpe,²Elizabeth B. Rampe,^3,4Juergen Thieme,³Eric Dooryhee,^2,5Seungyeol Lee,⁶Roy Christoffersen
American Mineralogist 110,1689-1701 Open Access Link to Article [https://doi.org/10.2138/am-2023-9290]
¹University of Maryland, NASA Goddard Space Flight Center, and CRESST II, Greenbelt, Maryland 20771, U.S.A.
²NASA Johnson Space Center, Houston, Texas 77058, U.S.A.
³Brookhaven National Lab, NSLS-II, Upton, New York 11973, U.S.A.
⁴Institute for X-Ray Physics, Georg-August University Goettingen, Goettingen University, Göttingen 37073, Germany
⁵Department of Earth and Environmental Sciences, Chungbuk National University, Seowon-Gu, Cheongju, Chungbuk 28644, Korea
⁶Amentum JETS-II contract, NASA Johnson Space Center, Houston, Texas 77058, U.S.A.
Copyright: The Mineralogical Society of America

Mudrocks and mud-sized sediments (i.e., silt to clay) dominate the surface of Earth and Mars. These fine-grained sediments preserve a rich history of sedimentary processes from source to sink and shed light on ancient climates. However, both the physical and chemical nature of these materials make them difficult to fully characterize with traditional laboratory techniques. Here, we explore a cross-disciplinary and high-resolution approach using synchrotron radiation for X-ray diffraction, pair distribution function analysis, and submicrometer-scale X-ray fluorescence, combined with transmission electron microscopy, to better understand the nanostructure and composition of mud-sized sediments from a glacio-fluvial watershed in southwest Iceland. Our results demonstrate that sediments in the cold and wet climate of Iceland are more altered than previously thought, as evidenced by the identification of kaolinite and mixed-layer kaolinite-smectite. Additionally, sediments are enriched in amorphous materials and nanocrystalline phases, as determined from grain morphologies and compositions consistent with allophane, hisingerite, ferrihydrite, and halloysite. These alteration products are present as intimate mixtures that vary across depositional sites, demonstrating the dynamic nature of the secondary assemblage from source to sink. This work has implications for Mars, where, for example, basalt-sourced sedimentary rocks from Gale crater are abundant in clay minerals and amorphous materials. Finally, this work underpins the importance of using high-resolution techniques, a coordinated methodology, and developing innovative approaches for future planetary sample return missions (e.g., Mars sample return).