苏北射阳河口NTCJ1钻孔沉积序列与年代再认识

Rethinking on sedimentary sequence and geochronological framework of Core NTCJ1 in the Sheyang estuary of Northern Jiangsu, East China

  • 摘要: 射阳河口位于苏北粉砂淤泥质海岸上,处在苏北废黄河三角洲侵蚀岸段与江苏中部淤积岸段之间的过渡区域,是淤蚀交替地带,系现代海岸地貌演变的节点处,同时也是晚第四纪古黄河古长江交互作用的关键区域之一。为了深入研究不同大河交互作用下的海岸、陆架晚第四纪沉积层序模式,最近就苏北射阳河口NTCJ1孔沉积序列和年代,根据该孔的岩性、粒度、介形虫、有孔虫、黏土矿物、地球化学元素和ESR测年等结果,并结合邻近其他钻孔和浅层地震剖面资料进行再研究和再认识,主要得到以下两点新认识:① NTCJ1孔22.00 m岩芯记录了MIS 5以来的沉积环境演化过程,可能缺失形成于MIS 4—2的第一陆相沉积层,MIS 1海相沉积层直接上覆于MIS 5海相沉积层,且尚未钻及形成于MIS 6的第二陆相沉积层;② NTCJ1孔中上部0~17.95 m颗粒较细,以粉砂质为主和暗黄色为基调,明显上粗下细,基本为AD 1128—1855年间形成的废黄河三角洲沉积,为一进积序列,底部可能含有少量全新世滨浅海沉积,但目前尚难以甄别;下部17.95~22.00 m颗粒较粗,以细砂质为主和深灰色为基调,尚未钻穿,是受到古黄河明显影响的MIS 5潮汐河口的水道充填沉积。

     

    Abstract: The Sheyang estuary is located in the muddy coast of Northern Jiangsu, East China, in the transition zone between the eroded coast of the abandoned Yellow River delta in Northern Jiangsu and the silted coast in central Jiangsu, which is characterized by the alternation of erosion and siltation as a node of modern coastal geomorphic evolution, as well as one of the key areas of geo-interactions between the old Yellow River and old Changjiang River during the Late Quaternary. To investigate deeply the Late Quaternary sedimentary sequence models of the coasts and continental shelves under the interactions among different large rivers, the sedimentary sequence and geochronology of 22.00 m-long Core NTCJ1 drilled at the Sheyang estuary were recently re-studied in lithology, grain size, ostracods, foraminifera, clay minerals, elemental geochemistry, and ESR dating, and the results were compared with those of other adjacent cores and shallow seismic profiles. The new results show that: (1) Core NTCJ1 recorded the sedimentary environment evolution since Marine Isotope Stage 5 (MIS 5), the first continental facies layer formed from MIS 4 to MIS 2 may be missing, the MIS 1 marine facies layer overlain directly the MIS 5 marine facies layer, and the second continental facies layer formed in MIS 6 has not been drilled yet; (2) The middle-upper part of Core NTCJ1 sediments (0~17.95 m) are characterized by fine grain size, mainly silty, and dark yellow in color, and obvious reversal graded bedding, which could be interpreted as the abandoned Yellow River deltaic deposits formed between AD 1128 and 1855 with a progradational sequence, and may contain a small amount of the Holocene coastal-shallow marine deposits at the bottom, but it is difficult to identify them yet. The lower part sediments (17.95~22.00 m) are characterized by coarse grain size, mainly fine sandy, and dark grey in color; they had not been drilled through and could be explained as a channel-fill deposit in the MIS 5 tidal estuary and were obviously influenced by the old Yellow River.

     

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