Surface microtextures of quartz grains under intermittent sediment transport in a gravel bed in the Hantan River, South Korea

Abstract

Surface microtextures of quartz grains (SMQs), which are observable using scanning electron microscopy (SEM), provide direct evidence for reconstructing the sedimentary history of individual grains. Detailed SMQ investigations across diverse modern river systems are essential to better understand the factors controlling SMQ formation in fluvial sediments; however, comprehensive studies of diverse modern fluvial systems remain limited. In this study, we examined SMQ characteristics in a gravel bed of the monsoon-influenced Hantan River on the Korean Peninsula. Hantan River sediments maintain angular to subangular grain outlines throughout downstream areas, exhibiting no gradual changes in either grain outlines or other mechanical microtextures. In contrast to typical fluvial sediment characteristics, upturned plates predominate rather than V-shaped percussion cracks. These features reflect episodic sediment transport driven by seasonal discharge variations in this gravel bed river system. Statistical analysis revealed distinct SMQ frequencies between the mainstream and tributaries, with the mainstream showing higher abrasion features (subangular outlines, conchoidal fractures, and V-shaped percussion cracks), whereas tributaries exhibited fresher surfaces (angular outlines and flat cleavage surfaces). These differences primarily reflect variation in transport distance from source areas, as tributaries, which are shorter and surrounded by mountainous terrain, maintained more direct sediment input characteristics, whereas mainstream sediments showed mixed features due to longer transport distance and tributary inputs. Our SMQ study in modern fluvial environments contributes to enhanced interpretations of past depositional conditions and further suggests a need to refine current SMQ classification systems.