摘要
The mineralogical and geochemical characteristics of sediments of Core CSH1, which was collected from the northern Okinawa Trough, indicate that large amounts of volcanic materials have deposited in the northern Okinawa Trough during the Holocene. On the basis of down-core variations in mineral and element contents of sediments, two layers in the uppermost section of Core CSH 1 characterized by high quartz, Na2O, MnO, K20, uranium contents and low contents of clay minerals, volatiles, Fe2O3, MgO, CaO and strontium, have been identified as the tephra deposits. Systematic grain-size measurements also suggest that sediments from the northern Okinawa Trough are made up of terrigenous materials and volcanic ashes with different proportion during the Holocene. The sedi- ments of tephra layers in Core CSH1 show bi-modal patterns in grain-size distribution with modal grain-sizes of 74.3 and 7.81 μm, respectively. According to the radiocarbon dating on shells of zooplankton foraminifera, two tephra layers in Core CSH1, formed at 7 250 and 10 870 a BP （cal）, approximately correspond to the K-Ah tephra [7 300 a BP （cal）] and the eruption of Kuju Volcano （12-10 ka BP）, respectively.
The mineralogical and geochemical characteristics of sediments of Core CSH1, which was collected from the northern Okinawa Trough, indicate that large amounts of volcanic materials have deposited in the northern Okinawa Trough during the Holocene. On the basis of down-core variations in mineral and element contents of sediments, two layers in the uppermost section of Core CSH 1 characterized by high quartz, Na2O, MnO, K20, uranium contents and low contents of clay minerals, volatiles, Fe2O3, MgO, CaO and strontium, have been identified as the tephra deposits. Systematic grain-size measurements also suggest that sediments from the northern Okinawa Trough are made up of terrigenous materials and volcanic ashes with different proportion during the Holocene. The sedi- ments of tephra layers in Core CSH1 show bi-modal patterns in grain-size distribution with modal grain-sizes of 74.3 and 7.81 μm, respectively. According to the radiocarbon dating on shells of zooplankton foraminifera, two tephra layers in Core CSH1, formed at 7 250 and 10 870 a BP （cal）, approximately correspond to the K-Ah tephra [7 300 a BP （cal）] and the eruption of Kuju Volcano （12-10 ka BP）, respectively.
基金
supported by the International Cooperation Project"High-Resolution Sequence of Quaternary:Paleoenvironmental and Paleoclimatic Evolution in the East China Sea"under contract No.2002DFG00034
the Youth Science Foundation Project of S0A under contract No.2003305
the Key Program of National Natural Science Foundation of China under contract No.40431002.
