末次冰消期以来黄海海平面变化与黄海暖流的形成
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摘要
ＹＳＤＰ１０２孔和ＹＳＤＰ１０３孔位于南黄海东南侧冷涡所对应的泥质沉积区，它们揭示了自末次冰消期以来的海侵沉积序列：海侵滞留沉积→潮流砂脊／潮坪～海滩沉积→陆架泥质沉积。该沉积序列上部的陆架泥质沉积厚度可达５０余米，在浅地震剖面上其内部存在一个明显的反射界面，从而将泥质沉积体分为上、下两个单元。泥质沉积体呈灰绿色调，含少量自生黄铁矿，但其内反射界面以上的沉积物含水量高。根据两个钻孔岩心中有孔虫的分布规律、泥质沉积层的化学组分、沉积磁组构特征以及现有测年数据，得到如下结论：（１）黄海暖流形成于大约６ｋａＢ．Ｐ．，（２）泥质沉积层内反射界面以上的沉积物是与黄海暖流伴生的冷涡沉积，（３）黄海地区末次冰消期海侵自略早于１４ｋａＢ．Ｐ．之前开始，至约６ｋａＢ．Ｐ．海平面达到最高位置。从６ｋａＢ．Ｐ．至今，海平面经历了几次波动，即在６～４ｋａＢ．Ｐ．和３～１．９ｋａＢ．Ｐ．海平面超过现今海平面位置；在４～３ｋａＢ．Ｐ．和１．９ｋａＢ．Ｐ．～现代，海平面有所降低，可能与现今海平面高度相当。
This paper focuses on boreholes YSDP 102 and YSDP 103 which were drilled in the southeastern South Yellow Sea,an area covered by muddy sediment and coinciding with an anticlockwise eddy(a cold water mass).Both cores reveal the post glacial transgressive sedimentary sequence in the region,which can be described as follows in an ascendant order:transgressive lag deposit,tidal sand ridge/tidal flat beach deposit,and muddy deposit of shelf.More than 50 meters in thickness,the muddy deposit in the upper part of the sequence can be subdivided into two subunits by a clear reflector,is greenish grey in color and contains authigenic pyrite,but the muddy sediment above the reflector is characterized by a higher water content.This paper analyses the downcore distributions of foraminifera in both cores,the chemical composition and sedimentary magnetic fabric of the muddy sediment in core YSDP 102. Based on these data,in conjunction with 14 C dates,we conclude:(1)the Yellow Sea Warm Current took shape about 6 ka B.P.,(2)the muddy deposit above the reflector resulted from the cold water mass associated with the Yellow Sea Warm Current,and (3)the post glacial transgression in the Yellow Sea commenced a little earlier than 14 ka B.P. and peaked around 6 ka B.P. with a sea level higher than the present day’s;from then on,the sea level fluctuated several times,that is,on higher positions than today between 6 ka and 4 ka B.P. and between 3 ka and 1 9 ka B.P.,and on relatively lower positions possibly the same as today between 4 ka and 3 ka B.P. and between 1 9 ka B.P. and today.
This paper focuses on boreholes YSDP 102 and YSDP 103 which were drilled in the southeastern South Yellow Sea,an area covered by muddy sediment and coinciding with an anticlockwise eddy(a cold water mass).Both cores reveal the post glacial transgressive sedimentary sequence in the region,which can be described as follows in an ascendant order:transgressive lag deposit,tidal sand ridge/tidal flat beach deposit,and muddy deposit of shelf.More than 50 meters in thickness,the muddy deposit in the upper part of the sequence can be subdivided into two subunits by a clear reflector,is greenish grey in color and contains authigenic pyrite,but the muddy sediment above the reflector is characterized by a higher water content.This paper analyses the downcore distributions of foraminifera in both cores,the chemical composition and sedimentary magnetic fabric of the muddy sediment in core YSDP 102. Based on these data,in conjunction with 14 C dates,we conclude:(1)the Yellow Sea Warm Current took shape about 6 ka B.P.,(2)the muddy deposit above the reflector resulted from the cold water mass associated with the Yellow Sea Warm Current,and (3)the post glacial transgression in the Yellow Sea commenced a little earlier than 14 ka B.P. and peaked around 6 ka B.P. with a sea level higher than the present day’s;from then on,the sea level fluctuated several times,that is,on higher positions than today between 6 ka and 4 ka B.P. and between 3 ka and 1 9 ka B.P.,and on relatively lower positions possibly the same as today between 4 ka and 3 ka B.P. and between 1 9 ka B.P. and today.
引文
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