长江三角洲晚第四纪沉积地质学研究述评

A REVIEW ON LATE QUATERNARY SEDIMENTARY GEOLOGY OF THE YANGTZE RIVER DELTA

长江三角洲已有的晚第四纪沉积地质学研究成果阐明了区域内晚第四纪沉积分区和沉积序列,建立了层序地层格架及其内部构型,对千年级和百年级事件沉积进行了初步探讨,总结出了长江三角洲发育模式和控制因素。但同时仍有一些涉及长江三角洲沉积和演化的重要问题尚未得到很好的阐述。目前,对末次冰盛期的长江三角洲存在与否尚存在较大分歧,长江古河口湾向三角洲的转换机制与模式尚不清楚,三角洲系统“源到汇”的研究尚未开展,长江三角洲对人类活动的响应也刚受到重视。对这些问题的探讨,需要以沉积地质学的手段对海区三角洲进行精细解剖。目前,长江三角洲沉积地质学研究中存在着陆区三角洲研究程度高、海区三角洲研究程度低的现状,因此,进一步的研究需在海区三角洲加大力度。

Late Quaternary strata of the Yangtze River delta are divided into three sedimentary areas,namely the incised-valley area, and northern and southern parts of interfluve areas. In these areas, stratigraphic frameworks are quite different, reflecting different processes of the post-glacial transgression. From the viewpoint of sequence stratigraphy, all the late Quaternary strata of the Yangtze River delta belong to a six-order sequence, which stretches across the shelf of the East China Sea. In the Yangtze River delta, different superimposing patterns of lowstand systems tract, transgressive systems tract and highstand systems tract were recognized between land and subaqueous parts of the delta. Sediments formed during the Younger Dryas event and by storm surges and periodic tides in the Yangtze River delta were also been identified by preliminary study on millennial and centennial geological events. Based on the sedimentary geological investigation, the sedimentation pattern of the Yangtze River delta was summarized, implying the late Quaternary development of the Yangtze River delta was controlled by continuous subsidence and sediment supply. There are still several crucial questions unsolved in the sedimentary geology of the late Quaternary Yangtze River delta. First of all, existence of the Yangtze River delta during last glacial proximal was still a controversy. Secondly, the transition pattern and model of the paleo-Yangtze estuary to the Yangtze delta were not elucidated clearly. Thirdly, the concepts of ＂source to sink＂ have not been applied to systematic sedimentary geological research on the Yangtze River delta. At last, the influence of human activity on the Yangtze River delta has just been noticed in recent decades. Further researches on these above key issues are fundamentally based on the sedimentary geological study on the subaqueous part of the Yangtze River delta. Furthermore, the subaqueous part of delta has been less studied compared to the land part of the delta at present. Therefore, emphasis should be placed on the subaqueous part in the future sedimentary geological study on the Yangtze River delta.