钱塘江下切河谷充填物沉积序列和分布模式  

Sedimentary sequence and distribution pattern of filling in Qiantang River incised valley

作　　者：张霞[1] 林春明[1] 高抒[2] Robert W.Dalrymple 曲长伟[1] 殷勇[2] 李艳丽[1] 周健[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,江苏南京210093 [2]海岸与海岛开发教育部重点实验室,南京大学,江苏南京210093 [3]Department of Geological Sciences and Geological Engineering,Queen's University,Kingston

出　　处：《古地理学报》2013年第6期839-852,共14页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号:40872075;41272124);教育部高等学校博士学科点专项科研基金项目(编号:20090091110023);南京大学"内生金属矿床成矿机制研究国家重点实验室"自主研究基金项目(编号:2009-Ⅱ-11);中国石油大学(北京)"油气资源与探测国家重点实验室"开放课题基金项目(编号:PRP/open-1306)共同资助

摘　　要：以最新钻取的SE2孔沉积物为重点研究对象,对晚第四纪以来钱塘江下切河谷充填物的沉积特征和沉积相进行了精细研究,重建了研究区地层结构和层序地层格架,总结了强潮型钱塘江河口湾和下切河谷的沉积模式。钱塘江下切河谷充填物自下而上依次发育河床、河漫滩、古河口湾、近岸浅海和现代河口湾5种沉积相类型,表现为一个较完整的Ⅰ型层序,其内部层序界面、初始海泛面、最大海泛面、海侵和海退潮流侵蚀面、体系域内海侵面发育。钱塘江下切河谷充填物自海向陆可划分为海向段、近海段、近陆段和陆向段4段,各段沉积序列和海陆相互作用程度不同。在钱塘江下切河谷充填物中海陆过渡部位首次明确划分出了古河口湾相,并对其沉积特征和分布模式进行了初步探讨;其形成时间在9000 a BP左右,具有与现代河口湾不同的沉积特征,表现为中部为潮道砂体沉积,向陆渐变为受潮流影响的河流沉积,两侧被潮坪或盐沼沉积包围,沉积物在平面上自陆向海呈现粗—细—粗的分布模式。现代河口湾平面上自陆向海依次发育受潮流影响的河流沉积、粉砂质砂坎、潮道—潮流砂脊复合体和湾口泥质沉积区,沉积物呈现粗—细—粗—细的分布模式,与大多数河口湾常见的粗—细—粗的分布格局明显不同。The present-day Qiantang River （QR） estuary is a world-famous tide-dominated estuary, and is one of the most sensitive areas for postglaeial global sea-level changes in China. Filling of the QR incised valley was initiated by marine inundation during the transgression after the Last Glacial Maximum and has continued during the Holoeene sea-level stillstand. From bottom to top it could be grouped into five sedimentary facies. Fluvial channel, floodplain, paleo-estuary, offshore shallow marine, and pres- ent-day estuary. The QR incised valley deposits occur as a relatively complete type I sequence with the se- quence boundary, initial flooding surface, maximum flooding surface, tidal-ravinement surfaces and tid- al-erosion surfaces well-developed. Filling of the QR incised valley consists of four longitudinal segments： Seaward segment, offshore segment, the third segment and innermost segment, each of which is charac- terized by a distinct stratigraphic succession, and different degrees of marine and fluvial influences. This is the first time the paleo-estuary facies has been recognized, formed about 9000 a BP. It has a distinct sedimentary succession from the present-day estuary, and is characterized by a large number of tidal-chan- nel sand bodies flanked by mudflats and salt-marshes in the landward part of estuary, passing headward into the tidal-fluvial channel. The present-day estuary is mainly composed of bay-mouth sediments, as well as a complex of tidal sand ridges and channels at the mouth, followed headward by a silty bar, which passes landward to a single tidal-fluvial channel. The sediments of paleo-estuary present a coarse-fine- coarse seaward pattern. By comparison, the deposits of present-day estuary show a coarse-fine-coarse- fine pattern from land to the sea, which is in general similar to the grain-size distribution in tide-dominated estuaries, but a significant difference exists in that the bay-mouth sediments of the present-day estuary are mud-dominated.

关 键 词：沉积特征 沉积序列 分布模式 河口湾 下切河谷 钱塘江 

分 类 号：TE121.3[石油与天然气工程—油气勘探]