Holocene regression and the tidal radial sand ridge system formation in the Jiangsu coastal zone, east China
Holocene regression and the tidal radial sand ridge system formation in the Jiangsu coastal zone, east China
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DOI：
10.1016/s0025-3227(00)00169-9
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发表时间：
2001-03
期刊：
影响因子：
2.9
通讯作者：
Congxian Li;J. Zhang;D. Fan;B. Deng
中科院分区：
文献类型：
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作者：
Congxian Li;J. Zhang;D. Fan;B. Deng
黄海西南部海域有一条由强港向外海延伸的扇形辐射状潮汐沙脊系统，跨度达2万多km2。 海洋RTSRS位于辐合-辐散潮流场中。在江苏沿海平原，大量钻孔揭露了3000km2的潮汐砂层，与城东向东延伸的、呈扇形、圆心角为130 °的海相RTSRS相邻。潮汐砂体单元位于海侵海岸障壁-泻湖单元之上，两者之间为侵蚀面，后者则位于晚更新世硬泥之上。潮沙单元上覆滨海潮坪单元，共同构成全新世海退序列。古水流研究表明，全新世潮下砂层中存在类似于现代海洋CDTCF的古水流模式。因此，推测该潮下砂体是全新世海退时期形成的古陆坡体，随着长江、黄河三角洲的推移逐渐出露并转化为陆地。陆上和海上的RTSRS应形成于相同的潮汐沉积环境，但处于不同的发育阶段。因此，黄海西南部的辐射状潮汐沙脊应该是在全新世海退过程中形成的，而不是以往研究所认为的全新世海侵过程。矿物学分析表明，该地区的沉积物源最初来自长江，后来主要来自黄河。潮汐流对海底的侵蚀也可能提供形成RTSRS的桑迪物质。钻孔岩心和地质剖面表明，研究区古河谷比现今长江支流小得多。因此，一条大河通过其顶部区域直接供沙形成RTSRS的假设是不成立的。在海平面达到现今高水位后，随着长江三角洲的扩张，江苏海岸线逐渐向外海推移，黄河入海后，江苏海岸线的向外海推移进一步加快。RTSRS的近岸部分逐渐变为陆地，而整个RTSRS向海延伸。在发展过程中，区域社会稳定的顶点由城东向强港转移。目前，海岸线仍在向外海移动，而由于长江三角洲和废弃黄河三角洲的泥沙供应减少，大湄公河次区域的外部受到一定的侵蚀。
A radial tidal sand ridge system (RTSRS) spans more than 20 000km2in the southwest Yellow Sea, is fan-shaped and stretches from Qianggang toward the sea. The marine RTSRS is located in a convergent–divergent tidal current field (CDTCF). Numerous drilling holes reveal an area of 3000km2containing tidal sand strata in the Jiangsu coastal plain on land, adjacent to the marine RTSRS, which stretches eastward from Chengdong and is also a fan-shaped with a central angle of 130°. The tidal sand unit lies on a transgressive coastal barrier-lagoon unit with an erosional surface between them, and the latter unit is in turn lying on late Pleistocene stiff mud. The tidal sand unit is overlain by the littoral–tidal-flat unit and together they constitute the Holocene regressive succession. Paleo-current study reveals that a paleo-current pattern similar to the modern marine CDTCF was present in the Holocene sub-aerial tidal sand strata. Therefore, the sub-aerial tidal sand bodies are deduced to be an ancient RTSRS that was formed during the Holocene regression, and gradually exposed and changed into land as the Changjiang and Huanghe deltas prograded. Both sub-aerial and marine RTSRS should be formed in the same tidal depositional environment but in different development stages. Thus, the radial tidal sand ridges in southwestern Yellow Sea should have formed not during the Holocene transgression, as most previous studies have inferred, but in the process of Holocene regression. Mineralogical analyses demonstrate that the sediment source of the sub-aerial RTSRS initially came from the Changjiang and later predominantly from the Huanghe. Sea-floor erosion by tidal currents may also provide sandy material to form the RTSRS. Drilling cores and ground-penetrating profiles show that the paleo-valleys in the study area are much smaller than the present distributaries of the Changjiang River. Thus, the presumption of direct sand supply by a large river to form the RTSRS through its apical area is cannot be supported. After the sea level reached the present high stand, the Jiangsu coastline has been prograding seaward as the Changjiang Delta expanded and this progradation was accelerated when the Huanghe debouched in the study area. The nearshore part of RTSRS has been gradually changing into land while the entire RTSRS extends seawards. In the process of the development, the RTSRS apex changed from Chengdong to Qianggang. At present, the coastline is still moving seaward while the outer part of the RTSRS suffers from some erosion owing to reduction of sediment supply from both the Changjiang Delta and the abandoned Huanghe Delta.