MAGNETOSTRATIGRAPHY OF CORE DZS2 OFF THE YANGTZE RIVER ESTUARY
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摘要: 长江河口区外海域是陆源物质沉积以及向外海输送的重要地带。DZS2孔采自长江河口外海域(东海陆架西北部),是我国现今最深,年代最久远的大陆架海底全取心钻孔。对其进行了细致的古地磁研究,结合岩心岩性特征、微体古生物鉴定以及AMS14C测年等的分析,建立了可靠的长江河口外海区年代地层框架序列。磁极性地层研究揭示了清晰的M/B极性转换界线,且沉积地层中出现了多个可与标准极性柱对比的反极性漂移事件,这其中包括Gothenburg、Blake、Emperor、Jaramillo和Olduvai事件,这为钻孔年代约束以及长江三角洲区域地层对比提供了重要的依据。钻孔DZS2沉积物岩性特征较为简单,相对来说泥质层位较多,与长江三角洲陆上典型第四纪钻孔的岩性特征以及沉积演化旋回存在一定差别。这可能与整个长江三角洲区域下覆基岩的起伏有关,根据单道地震剖面的资料,长江河口区西南部有一系列岛屿分布,海底明显存在较高隆起的基岩,松散沉积物厚度较薄,这很可能阻挡了部分长江物质,特别是粗颗粒沉积物向外海的输送。Abstract: The outside estuary of the Yangtze River, as a link between the land and sea, is an important area for the study of sea-land interactions and terrestrial materials transportation into the sea. The core DZS2, collected from the northwest of East Sea shelf, is the longest and oldest core so far in this region. Combined with the methods of paleomagnetism, sediment lithological analysis and AMS14C dating, a relatively complete and reliable chronostratigraphic framework of the Core DZS2 in the outside estuary of Yangtze River estuary has been established. The paleomagnetic data of the Core DZS2 reveals a distinct M/B geomagnetic polarity boundary in the sequence, in addition to several magnetic excursions, which can be correlated with the standard palaeomagnetic polarity record, including the Gothenburg, Blake, Emperor, Jaramillo and Olduvai events. The events have provided further age constraints on stratigraphic sequences. Comparing to other cores drilled in the Yangtze River delta, the core DZS2 does not have similar sedimentary cyclicity, probably due to the swollen bedrock in the estuary preventing transportation of a part of the materials from the Yangtze River to the offshore.
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Key words:
- outside estuary of Yangtze River /
- DZS2 core /
- Quaternary /
- Paleomagnetism /
- Magnetostratigraphy
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