Elemental composition of siderite grains in early-Holocene deposits of Youngjong Island (west coast of Korea), and its palaeoenvironmental implications

Abstract

Macrotidal muddy coastal deposits around Youngjong Island (west coast of Korea, eastern Yellow Sea) comprise four lithostratigraphic units (unit I, unit II, unit III and unit IV). Overlain unconformably by unit I of modern muddy intertidal sediments, Unit II of early-Holocene age (ca. 8000 yr BP) is characterized by a distinct color, peat fragments, rootlets, and especially microscale (ca. 150 μm) siderite grains whose mineralogy was confirmed by X-ray diffraction. Siderite concretions occur as aggregated spherulitic forms with texturally well-developed rhombs on the grain surface, as verified by means of scanning electron microscopy. Electron microprobe analyses indicate that the siderite grains have low contents of Mg (<3 mol%) and Ca (<8 mol%). In contrast, high contents of Fe (ca. 70 mol%) and Mn (ca. 15 mol%) suggest that the siderite precipitated in a non-marine depositional environment such as freshwater bogs. The occurrence of such diagenetic and authigenic siderites in early-Holocene sediments highlights a potential for providing information on depositional environments for which unequivocal sedimentological evidence is otherwise lacking, such being the case for the muddy coastal deposits in the eastern Yellow Sea. © 2000 Elsevier B.V. All rights reserved.