摘要
The sedimentary facies of the subaqueous Changjiang （Yangtze） River delta since the late Pleistocene was studied based on lithology and foraminifera analysis for two boreholes, CJK07 and CJK11, along with 14C dating. Four sedimentary facies were identified, namely fluvial, tidal flat, offshore, and prodelta facies. The fluvial sedimentary facies is comprised of fluvial channel lag deposits, fluvial point bar deposits, and floodplain deposits, showing a fining-upward sequence in general with no benthic foraminifera. A layer of stiff clay overlies the fluvial deposits in core CJK07, indicating a long-term exposure environment during the Last Glacial Maximum （LGM）. During the postglacial sea-level rise around 13-7.5 cal ka BP, the tidal flat facies was deposited in core CJK11, characterized by abundant silt-clay couplets. Euryhaline species dominate the subtidal fiat foraminiferal assemblages, while almost no foraminifera was found in the intertidal fiat. The offshore environment was the major sedimentary environment when the sea level reached its highest level around 7.5 cal ka BP, with a maximum accumulation rate of 10 mm/a found in core CJK11. Prodelta sediments have been deposited in core CJK11 since -3 cal ka BP, after the formation of the Changjiang River delta. The difference in sedimentary facies between core CJK07 and CJK11 is due to their location： core CJK07 was in an interfluve while core CJK11 was in an incised valley during the LGM. Furthermore, AMS 14C dating of core CJK07 shows poor chronological order, indicating that the sediments were reworked by strong tidal currents and that sediment deposited since -7.7 cal ka BP in core CJK07 was eroded away by modem hydrodynamic forces caused by the southward shift of the Changjiang River delta depocenter.
自从迟了的更新世，水下的 Changjiang (Yangtze ) 河三角洲的沉积外形为二地上凿穿， CJK07 和 CJK11 基于岩性学和有孔虫类分析被学习，与标明日期的 14C 一起。四沉积外形被识别的、也就是河的、潮汐的公寓，近海，并且 prodelta 外形。河的沉积外形由河的隧道组成落后扔，河的点酒吧扔，并且泛滥平原扔没有 benthic 有孔虫类一般来说显示出一个鳍向上的序列。生硬泥土的层在核心 CJK07 躺河的存款，显示在最后冰川的最大值(LGM ) 期间的长期的暴露环境。在在 13-7.5 cal ka BP 附近的冰期后的海平面的上升期间，潮汐的扁平的外形在核心 CJK11 被扔，由丰富的淤泥泥土两行诗描绘了。能在不同盐分之环的种类统治 subtidal 公寓有孔虫目的集合，当几乎没有有孔虫类完全在 intertidal 被发现时。近海当海水平在 7.5 cal ka BP 附近到达了它的高水平时，环境是主要沉积环境，与 10 的最大的累积率， mm/a 在核心 CJK11 发现了。自从 3 cal ka BP， Prodelta 沉积在核心 CJK11 被扔了，在 Changjiang 河三角洲的形成以后。在在核心 CJK07 和 CJK11 之间的沉积外形的差别由于他们的地点：当核心 CJK11 在 LGM 期间在一条切入的山谷时，核心 CJK07 在一块河间地。而且，核心 CJK07 标明日期的 AMS 14 C 给穷人看按年代先后的顺序，显示沉积被自从在核心 CJK07 的 7.7 cal ka BP 被 Changjiang 河三角洲 depocenter 的向南方的移动引起的现代水动力学力量离开侵蚀，扔的强壮的潮汐的水流和那沉积重做。
基金
Supported by the Marine Public Welfare Research Project(No.200805063)
the National Natural Science Foundation of China(Nos.41076023 and 41106065)
the Basic Fund Project of National Science and Technology Ministry(No.2008FY220300)
the Coastal Investigation and Research Project of China(No.908-02-02-05)
