Abstract
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 with synchrotron radiation for X-ray diffraction, pair distribution function analysis, and submicron-scale X-ray fluorescence combined with transmission electron microscopy to better understand the nano-structure and composition of mud-sized sediments from a glacio-fluvial watershed in southwest Iceland. Results from this work demonstrate that sediments in the cold and wet climate of Iceland are more altered than previously thought, as determined from 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 with 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).
