Dataset for Sediment Mixing in a Proglacial Catchment at Prestahnukur Volcano, Iceland: Implications for Silicic Deposits at Gale Crater, Mars

Abstract The discovery of silica polymorphs in the Buckskin mudstone at Gale Crater has important implications for understanding high-temperature processes on Mars. Three deposition/formation mechanisms have been proposed: direct deposition of silicic volcanic ash, in-situ hydrothermal alteration of sedimentary bedrock, or fluvial transport and concentration of eroded silicic material from within the Gale Crater catchment in an ancient lake. To evaluate the transport hypotheses, we conducted a source-to-sink study at Prestahnúkur Volcano, Iceland, where silicic materials exist within a predominantly basaltic terrain. Through systematic sampling at 0.2 km intervals along two distinct sediment transport pathways, we characterized the spatial evolution of physical and compositional sediment properties using particle size analysis, X-ray diffraction, and X-ray fluorescence. Our results reveal three key findings: (1) physical sorting of sediments occurs upstream from effective mineralogical and chemical mixing, (2) mixing between silicic and mafic components is extremely efficient once initiated, achieving near-complete homogenization over distances less than 0.4 km, and (3) palagonitic materials significantly influence sediment chemistry during transport, producing characteristic enrichments in FeO, Ni, and Cr. The observed rapid homogenization of sediment compositions reduces the likelihood of catchment-derived transport as a viable mechanism for concentrating silicic materials in the Buckskin mudstone, as any silicic material from Gale Crater's walls or central peak would have been thoroughly mixed with basaltic components before reaching the depositional site. These findings narrow the possible formation mechanisms to either direct volcanic ash deposition or in-situ hydrothermal alteration, providing important constraints for understanding the geological history of Gale Crater.摘要 在盖尔撞击坑（Gale Crater）的巴克斯金泥岩（Buckskin mudstone）中发现二氧化硅同质多象变体（silica polymorphs），对于解析火星上的高温作用过程具有重要意义。目前已提出三种沉积/形成机制：硅质火山灰直接沉积、沉积基岩的原位热液蚀变，或是通过河流搬运盖尔撞击坑集水区内被侵蚀的硅质物质，并在古湖盆中富集。为验证搬运假说，我们在冰岛普雷斯塔赫努库尔火山（Prestahnúkur Volcano）开展了源-汇研究，该火山以玄武岩地貌为主，其中赋存硅质物质。我们沿两条独立的沉积物搬运路径以0.2 km的间隔进行系统采样，借助粒度分析、X射线衍射（X-ray diffraction）与X射线荧光（X-ray fluorescence）光谱分析，表征了沉积物物理与化学成分的空间演化特征。研究结果揭示了三项关键结论：（1）沉积物的物理分选作用发生在有效的矿物学与化学混合作用之前；（2）硅质与镁铁质组分一旦发生混合，效率极高，在不足0.4 km的距离内即可实现近乎完全的均化；（3）橙玄玻璃质（palagonitic）物质在搬运过程中显著改变沉积物的化学组成，使氧化亚铁（FeO）、镍（Ni）与铬（Cr）出现特征性富集。观测到的沉积物组成快速均化现象，降低了集水区来源搬运作为巴克斯金泥岩中硅质物质富集机制的可行性——盖尔撞击坑坑壁或中央峰的任何硅质物质在抵达沉积位点前，都会与玄武岩组分发生充分混合。上述结论将可能的形成机制限定为直接火山灰沉积或原位热液蚀变，为解析盖尔撞击坑的地质历史提供了重要约束。