Clay minerals from tidal flat sediments at Youngjong Island, Korea, as a potential indicator of sea-level change

Clay minerals from the tidal flat sediments along the coast of Youngjong is land, west of mainland Korea, were studied to ascertain their potential as an indicator of sea-level fluctuation. Semi-quantitative analysis of their clay-size fractions by XRD shows that the vertical distribution of clay min erals can be separated into four clay mineral assemblage units. Based on th e relative contents of chlorite, four sedimentary units are distinguishable , and the abundance of chlorite is inversely related to that of smectite. T he kaolinite content is constant, and so it is clear that chlorite originat ing from the Han River was transformed to smectite by pedogenesis during re gression periods. Therefore, the relative contents of clay minerals from th e unconsolidated materials in the tidal flat of Youngjong island can be use d as indicators of transgression and regression in accordance with the sea- level fluctuation.