Occurrence of authigenic gypsums from deep-sea core sediment in the Korea Plateau, and their paleoceanographic implications

Abstract

A piston core was obtained from the Korea Plateau at a water depth of 1259 m to study paleoceanographic changes that occurred in the late Pleistocene. The core sediments consisted of four lithologic facies: bioturbated mud (BM), crudely laminated mud (CLM), massive muddy sand (MS), and tephra layers (TL). Alternating layers of BM and CLM facies were distributed widely throughout the core, implying variation in glacial and interglacial paleoceanographic conditions. The chronostratigraphy of the core was established using five radiocarbon ages, the oxygen isotope curve of the planktonic foraminifera, total organic carbon content, and variation in the lightness of sediments. The core bottom represents marine isotope stage 8, and spans more than 300 kyr of the paleoceanographic history of the East/Japan Sea. Considerable amounts of authigenic gypsum were found throughout the core. Mineralogic identification of the gypsum was confirmed by x-ray diffractometry and energy dispersive spectrometery. The authigenic gypsums in this core can be classified into four types: hexagonal tabular, hexagonal columnar, spheric, and prismatic forms. The grain size of the gypsums are varied markedly and averageed about 1000, 700, 2000, and 300 ㎛ in the greatest dimension for each type respectively. Scanning electron microscopy revealed numerous sharp leaching grooves on the surface of the gypsum in several