长江三角洲地区晚第四纪年代地层框架及两次海侵问题的初步探讨  

Chronostratigraphy and two transgressions during the Late Quaternary in Changjiang delta area

作　　者：王张华[1] 赵宝成[1] 陈静[1] 李晓[2] 

机构地区：[1]华东师范大学地理系,上海200062 [2]上海市地质调查研究院,上海200072

出　　处：《古地理学报》2008年第1期99-110,共12页Journal of Palaeogeography：Chinese Edition

基　　金：上海市启明星计划资助项目(编号:05QMX1419);国土资源部“三维城市地质”项目(编号:200413000020)资助

摘　　要：根据对长江三角洲地区两个以细颗粒沉积为主的晚第四纪钻孔进行OSL测年、U系测年、孢粉分析和微体古生物分析,试图建立高分辨率气候地层,从而建立本区晚第四纪的年代地层框架,并探讨本区晚第四纪的标志层和期间发生的两次海侵及其机制。研究结果显示,两孔记录的古气候波动可与深海氧同位素曲线进行对比:对应于深海氧同位素曲线第6阶段(MIS6),堆积厚层的河道相粗颗粒沉积及第3硬土层,反映当时气候寒冷;第5阶段(MIS5),为滨海湖沼沉积,沉积物的颗粒显著变细;第4阶段(MIS4),本区形成第2硬土层;第3阶段(MIS3)的早期,本区也发育滨海湖沼沉积,中晚期则形成潟湖—砂坝体系,在滨海平原区普遍发育粉、细砂层;第2阶段(MIS2),地层由下粗上细的沉积序列构成,下部为黄灰、棕黄色粉砂,上部则为棕黄色或暗绿色硬粘土。其中MIS6、MIS4和MIS2期间发育的3层硬土层可作为本区晚第四纪沉积的标志层。在MIS5和MIS3期间,本区均发生海侵,MIS5时期由于古地势较高、淡水径流和陆源物质输入丰富,因此海水影响微弱;MIS3时期的中晚期为缺乏淡水输入的潟湖—砂坝环境,从而形成广泛的海侵层。The present study focuses on the stratigraphy of two Late Quaternary boreholes that are primarily composed of fine-grained sediments. Analyses of the two boreholes include OSL and U-series dating, pollen and microfossils, tending to reconstruct the high resolution climatic stratigraphy, and therefore to define the chronostratigraphy of the Late Quaternary. It is also our aim to discuss the two transgressions and their mechanisms during that period. Results demonstrate that climate fluctuations recorded by the two boreholes correspond to the marine oxygen isotope stages （MIS）. Thick layer of coarser grained fluvial de-posits and the third layer of “hard mud” were deposited in the study area during MIS 6, reflecting a cold climate. The sediments became fine-grained and indicate a coastal marsh depositional environment during MIS 5. The second layer of “hard mud” was deposited during MIS 4. Fine-grained coastal marsh deposits dominated in the study area during early MIS 3, while lagoon-beach ridges prevailed during middle and late MIS 3, forming a layer of silt and fine sand in the coastal plain. The MIS 2 strata are composed of a typical sedimentary sequence with coarse grain in the lower section and fine grain in the upper section, i.e. yellowish grey or brownish yellow silt and brownish yellow or dark green “hard mud”, respectively. The three “hard mud” layers of MIS 6, MIS 4 and MIS 2 are the marker beds in the upper Quaternary in the Changjiang delta area. Marine incursions occurred during both MIS 5 and MIS 3. Higher topography and abundant freshwater and terrigenous material inputs determined that the marine influence during MIS 5 was weak. By contrast, the lagoon-beach ridges environment lack of freshwater supply led to the formation of the widely developed transgressive strata of middle and late MIS 3.

关 键 词：长江三角洲 晚第四纪 年代地层 气候地层 海侵 

分 类 号：P534.63[天文地球—第四纪地质学]