Analysis of the surface microtextures and morphologies of beach quartz grains in Japan and implications for provenance research

The mineral quartz is highly resistant to weathering, and various surface microtextures are formed and preserved on quartz grains. These microtextures are considered to reflect the sedimentary history of quartz: parent rock, transportation process, and depositional environment. Thus, quartz grain surface textures have been widely studied for applications in provenance research. This study focuses on beach sediments in Japan that contain various quartz morphologies resulting from the region's complex geological and geomorphological settings. The goal of the study was to verify the morphological diversity of these quartz grains and reveal the relationship between the quartz morphological features and the sampling site in tectonically active regions. We collected beach sands from backshores in Japan and observed the 15 microtextures of the quartz surfaces using scanning electron microscopy (SEM). The shapes of the quartz grains were also evaluated in terms of roundness parameters based on SEM images. Finally, the particle size distribution and mineral composition of the samples were investigated. The results indicate that quartz roundness can accurately reflect the quartz grain shape and shows a good correlation with the outline observed by SEM. Mechanical features were more frequently observed on the surface of quartz than chemical features. Results show that the coastal areas were under high-energy beach. The coastal sand quartz grains are mainly characterized by (i) v-shaped percussion cracks produced by grain-to-grain collisions in the subaqueous environment and (ii) small holes derived from small inclusion remnants. The v-shaped percussion cracks are related to the sediment source (e.g., a fluvial or marine source), and the holes on the surface are related to the geologic source of the quartz grains. The grain size and mineral composition results support the results of the surface analysis and provide clues regarding sediment provenance. Quartz surface analysis has the potential to show the morphological variation of the coastal sand and provide useful information on the transportation process and parent rock even in areas with complex geological and geomorphological settings such as Japan. The relation between the quartz morphological features and sampling site was based on previous study; however, to develop the analysis, the relation between unweathered quartz shape and parent rock must be clear.