제주도 주변 대륙붕 퇴적물의 지화학적 조성과 기원지 연구

Abstract

Geochemical compositions sedimentation rates and Sr-Nd isotopic ratios of surface and core sediments around Jeju Island were analyzed for the identification of sediment origins. The sediments in the study area are composed of fine sand and silt with a mean grain size of 2.43??8.54?X and their CaCO3 contents ranged from 1.92 to 11.7 wt. %. The ratios of TOC over total nitrogen(TN) showed that the study area sediments contained more organic matters of marine origin than those of terrigenous origin. The regional distribution patterns of major elements, which showed the high concentration of Fe/Al, Mn/Al and Ti/Al figures, were found in the southwestern part near the Changjiang esturay, indicating that it seemed to result from the influence of the Changjiang River. The discrimination diagrams including Sc/Al vs Cr/Th, Th/Sc vs Nb/Co and Ti/Nb vs Th/Sc were thus used as provenance indicators to identify the sediment origins around Jeju Island. Based on these discriminated diagrams, it clearly showed that most of the sediment in the western part originated from the Huanghe River, but the sediments in both the southwestern and southern part near the Changjiang esturay might come from the Changjiang River. In contrast, the sediment samples from the northwestern part and the northern coast of Jeju Island were originated from the Korean rivers. In the REE distribution from the study area, sediments relatively enriched in most of LREEs(La(N)/Sm(N))>4 and negative Eu anomaly and are similar to that of the average of upper continental crust shale. The ucc-nornalized REE pattern in the most of the sediment samples in the southwestern offshore regions showed similar to that of Changjiang sediments with more convex REE patterns and middle REE enrichment relative to the western part sediments which were originated from the Huanghe River. The accumulation rate, which can be obtained using Pb210 geochronologies of the muddy sediments in the northeastern area, showed 0.29cm/yr. The sedimentation rate from core SYS 20009, located in the northwestern near the side, showed 0.13cm/yr indicating that the mud deposits in the Central Yellow Sea may have received influence from the Huanghe River discharge sediments. In the isotopic composition of the 87Sr/86Sr ratios versus ?`Nd(o) values of the study area, sediments can be divided into three potential isotopic end-menber group. The sediments in the western and northwestern region are ultimately sourced from the Chinese Rivers especially from the Huanghe River. The sediments in the southwestern part near the Changjiang estuary might come from Changjiang River, whereas the sediments in the northeast part might come from the Korean river and Jeju Island suggesting multiple sources of the sediment in the area.