Occurrence of authigenic siderites in the Early Holocene coastal deposit in the west coast of Korea: an indicator of depositional environment

The macrotidal muddy deposits around Youngjong Island in the west coast of Korea with a radiocarbon dating of ca. 8000 yr BP contain micro-scale (ca. 150 μm) siderite concretions. The authigenic siderites exhibit the aggregated spherulitic textures with well-developed rhombs on the grain surfaces, which reflects good preservation. Geochemical analyses indicate that the concentrations of Mg (mean 2.6 mol%) and Ca (mean 9.4 mol%) are low whereas those of Fe (mean 70.4 mol%) and Mn (mean 17.6 mol%) are relatively high. The chemical composition suggests that the authigenic siderites might have precipitated in a non-marine environment. The occurrence of such siderites in the early Holocene sediments, considering the stratigraphic level with respect to the well-established sea-level curve helps recognize the non-marine depositional environment existed before the formation of modern tidal flats along the west coast of Korea.