MIS 3晚期以来江苏中部海岸的层序地层

Sequence Stratigraphy of the Central Part of North Jiangsu Coasts since Late MIS 3, Eastern China

通过对苏北岸外西洋潮流通道内钻孔和地震剖面的地层沉积学、年代地层学、地震地层学和层序地层学等多学科再研究,以及区域钻孔再对比,本文确定该海域约从35kaBP(14C惯用年龄)开始经历了滨岸砂坝、淡水湖沼、河流泛滥平原、滨岸沼泽、潮流沙脊和潮流通道一系列的环境演变,主要受控于MIS3晚期以来的海平面旋回以及古河流入海沉积物供给,而构造沉降是相对次要的,由此形成了五级层序地层中的末次冰期晚间冰阶准层序和冰后期准层序,以及前者的高水位体系域和强制海退楔体系域、后者的海侵体系域和高水位体系域。海域中潮流沙脊可能开始发育于冰后期海侵淹没本区(约9calkaBP)之后,但一直只是水下暗沙且处在不断调整之中,直到1128～1855AD间黄河夺淮从苏北入黄海,大量泥沙充填潮道,部分水下暗沙出露海面成为明沙。西洋潮流通道并非是晚全新世期间通过沙脊的蚀低而形成,而在全新世高海面前后就已具雏形并持续至1128AD,1128～1855AD和1855AD至今分别经历了充填淤浅与冲刷成型的过程,且今后具有进一步展宽刷深的趋势。

Based on the re-study of core 07SR01 and the seismic profile in Xiyang tidal channel off north Jiangsu coasts using multidisciplinary methods, such as geomorphology, sedimentology, chronostratigraphy, seismic stratigraphy and sequence stratigraphy, and the further stratigraphic correlation between core 07SR01 and adjacent studied cores, this paper confirmed that the sea area experienced a series of environmental changes mainly controlled by sea level changes since about 35 ka BP（late MIS 3）, sediment supply of paleo-rivers that flowed to the South Yellow Sea and minor structural subsidence, which are coastal barrier island, freshwater lacustrine-swamp, river-floodplain, coastal marsh, tidal sand ridges and tidal channel. Thus, the parasequence of the late period of the last interstadial, including high-stand system tract and forced regressive wedge system tract, and the parasequence of the postglacial period, including transgressive system tract and highstand system tract, belonged to the fifth-order sequence stratigraphy have developed. The tidal sand ridges in sea area might begin to develop since the seawatercovered the study area during the postglacial transgression about 9 cal ka BP, just were submerged sand ridges until the Yellow River switched its river mouth southward to north Jiangsu during 1128~1855 A. D.. Especially when the Yellow River totally captured the Huaihe River after 1494 A. D. , a huge amount of sediments filled the tidal channel, some submerged sand ridges could develop to emerged ones. The development of Xiyang tidal channel was not due to the erosion of tidal sand ridges during the late Holocene, it has had an embryonic form since the highest sea level period in Holocene and lasted until 1128 A. D. , and became a modern tidal channel, experiencing a process of silting during 1128~1855 A.D. and scouring during 1855 A. D. ~now, influenced by the Yellow River. Xiyang tidal channel had a tendency of broadening and deepening to some extent in the future, influenced by strong tidal current scouring and human beings activities.