Sedimentation rates and provenance analysis in the Southwestern Okinawa Trough since the mid-Holocene  

作　　者：LI ChuanShun JIANG Bo LI AnChun LI TieGang JIANG FuQing 

机构地区：[1]Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China [2]Graduate University, Chinese Academy of Sciences, Beijing 100049, China [3]China Ocean Press, Beijing 100081, China

出　　处：《Chinese Science Bulletin》2009年第7期1234-1242,共9页

基　　金：Supported by National Basic Research Program of China (Grant No. 2007CB815903);Key Project of National Natural Science Foundation of China (Grant No. 90411014);National Natural Science Foundation of China (Grant Nos. 40776030 and 40506016)

摘　　要：As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transpor-tation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS 14C dating, coarse size fraction (>63 μm) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 14C dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21.2 m ka?1, which is well consistent with the modern observations from sediment traps. We identified five 70―200 a periods of abnormally rapid sedimentation events at 6790―6600 a B.P., 5690―5600 a B.P., 4820―4720 a B.P., 1090―880 a B.P., and 260―190 a B.P., during which the highest sedimentation rate is up to 21.2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (>63 μm). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earth-quakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transportation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XⅡ MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS ^14C dating, coarse size fraction （〉63μm） extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 ^14C dating points. The sediments span across the mid-Holocene （6.8 ka B.P.） and have remarkablely high sedimentation rates between 1.8 and 21.2 m ka^-1, which is well consistent with the modern observations from sediment traps. We identified five 70-200 a periods of abnormally rapid sedimentation events at 6790-6600 a B.P., 5690-5600 a B.P., 4820-4720 a B.P., 1090-880 a B.P., and 260-190 a B.P., during which the highest sedimentation rate is up to 21.2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction （〉63μm）. As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earth-quakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.

关 键 词：南冲绳海槽 沉积速率 河流沉积物 异常事件 中期 西南 泥沙来源 马可波罗 

分 类 号：P736.1[天文地球—海洋地质] P736.21[天文地球—海洋科学]