Abstract
Outburst sediments are widely distributed in the Upper Jinsha River in the Southeastern (SE) Tibetan Plateau. In order to understand the sedimentary characteristics of these sediments, gravel fabric, particle size distribution and quartz sand surface textures were used to analyze the mesotextures and microtextures of the Xuelongnang outburst sediments. It was determined that these sediments usually have a short transport distance, and are distributed over a distance of approximately 3.5 km. The gravel fabric and particle size distribution analysis represent the different mesotextures with different transport distances and suggest gradually changing hydrodynamic conditions. The statistical data of quartz surface textures exhibit the transformation process of quartz sands by outburst flood. The variation from abundant sub-angular shapes (> 75%); to common V-shaped percussion cracks, solution crevasse, medium relief, and chatter marks (50% to 75%); to rare meandering ridge, underwater polished surface, large conchoidal fracture (> 100 μm), directional etch pits, and crystalline overgrowths (< 5%), present the features in different combinations to other sedimentary environments. The microtexture characteristics of landslide-dam outburst deposits are also consistent with those of the mesotextures. As the distance from the residual dam increased, the quartz grain microtextures showed gradual or abrupt changes, such as increased frequencies of V-shaped percussion cracks, decreased frequencies of the adhering particles, and growth of the solution crevasses. These findings could potentially be used as a discriminant mark to distinguish outburst sediment from other types of sediments, e.g., subaqueous, eolian, glacial, etc.
Highlights
Scanning electron microscopy (SEM) has been widely utilized to collate the observed surface microtextures of quartz grains characterized by grain migration and sedimentary environments. (KRINSLEY & TAKAHASHI, 1962; HAMILTON & KRINSLEY, 1967; WHALLEY & KRINSLEY, 1974; HELLAND & DIFFENDAL, 1993; MAHANEY et al, 2001; KRINSLEY, 2011, IMMONEN, 2013; VOS et al, 2014; CHEN et al, 2019)
It can be difficult to determine the exact shape of parent-rock quartz grains and their microtexture characteri stics, it can be deduced from previous research on mechanically-released quartz in cave walls (MAHANEY & KALM, 1995), and weathering release processes (MOLEN, 2014)
It has been found that dam-burst flooding induces special gravel fabric characteristics, variable particle size distributions, and significant damage to the quartz grains
Summary
Scanning electron microscopy (SEM) has been widely utilized to collate the observed surface microtextures of quartz grains characterized by grain migration and sedimentary environments. (KRINSLEY & TAKAHASHI, 1962; HAMILTON & KRINSLEY, 1967; WHALLEY & KRINSLEY, 1974; HELLAND & DIFFENDAL, 1993; MAHANEY et al, 2001; KRINSLEY, 2011, IMMONEN, 2013; VOS et al, 2014; CHEN et al, 2019). The transported grains in the outburst deposits were affected by the non-uniform stresses within different parts of a large water mass It included many variable factors, such as transport distances, velocity and sediment concentration, which resulted in the formation of a variety of different sedimentary characteristics (e.g., gravel fabric; quartz surface textures, and particle size distribution)
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