台湾海峡西部海域表层沉积物m值与地层分布

An approach to m value and stratigraphic distribution of surface sediment in western Taiwan Strait

由台湾海峡西部海域中表层沉积物的m值分布和14C测年资料，发现出露于该海域海底表层的沉积物有6层。其中层（3）是以韩江和九龙江古河口沉积物为代表的低海面时期的沉积物，形成于距今9000～7000a间，出露的古河口沉积物的m值小于10。层（4）为低海面前海面逐渐下降过程中形成的，沉积物的m值为10～26．5，且由上向下渐增。其形成时代为距伞12500～9000a。层（2）为低海面后海面逐渐抬升过程中形成的，沉积物的m值为10～25．2，且由该层下部向上渐增。层（1）分布于沿岸和河口区，m值〈15，且由河口或岸边向海渐增，可能为距今3000多年以来的沉积物。层（5）出露于台湾浅滩中南部，为晚更新世冰期的沉积物，其m值为33，8～38．0。层（6）仅在台湾浅滩南部874站出露，m值为200，反映该沉积物形成或被改造于热带海洋或相当于热带海洋环境。上述地层的m值特征及其分布揭示，距今9000～7000a期间台湾海峡西部海域处在低海面时期。最低海面时，韩江和九龙江古河口海淡水混合区曾分别延伸至118°E和1190167E。

According to the data of m value distribution and radiocarbon dating of surface sedimentfrom the western Taiwan Strait, it is found out that there are six layers of sediment occurredon the surface of seafloor in the sea area. Among them, Layer' is the sediment in lowsealevel stage, represented by ancient rivermouth sediments of Hanjiang and JiulongjiangRivers, formed in 9000~7 000 a, B. P., with m value of less than 10. Layer Ⅳ is formed inthe process of gradual sealevel lowering before the low sealevel stage,with m value of 10~26. 5 increasing downwards and forming age of 12 500~9 000 a, B. P. Layer Ⅱis formed inthe process of gradual sealevel rising after the low sealevel stage, with m value of 10~25. 2increaing upwards' layer I is distributed in the coastal and rivermouth regions,with m valueof less than 15 increasing seawards,and may be the sediments since 3 000 a,B. P.. Layer Ⅴoccurs in the central and southern parts of Taiwan Shoal and belongs to the sediment of LatePleistocene Glacial Stage,with m value of 33. 8~38. Layer M is only found in Stati0n 874 inthe southern part of Taiwan Shoal, with m value of 200, reflecting that the sediment isformed or reformed in the environment of tropical ocean or so.The m value characteristics and distribution of the layers mentioned above reveal that9 000~7 000 a,B- P. is the low sealevel stage in the western Taiwan Strait. When the sealevel is the lowest, the mixing region of sea water and fresh water in ancient rivermouths ofHanjiang an Jiulong Rivers extends even to 118°E and 119°E respectively.