摘要:
采用层序地层学基本原理,以海平面升降旋回为主线,根据钻井岩芯、古生物、测年和分析化验等资料,探讨了江苏南通地区晚第四纪地层层序、层序界面、沉积特征及沉积环境的演变。结果表明,研究区晚第四纪发育三期下切河谷,形成了三套沉积层序,自下而上三个层序的地质时代分别相当于晚第四纪早期、晚第四纪中期和晚第四纪晚期。由于后期河流的强烈下切破坏,早期沉积层序往往被剥蚀殆尽,仅残留下部的河床相粗粒沉积,造成不同期河床相的叠置;相对而言,晚第四纪晚期形成的下切河谷沉积层序以不同的沉积相组合被保存下来,自下而上划分为河床、河漫滩、河口湾、浅海和三角洲5种沉积相类型,表现为一个较完整的沉积层序。晚第四纪晚期下切河谷底界面,是末次冰期海面下降,河流下切形成的侵蚀面,与河间地古土壤层顶面的沉积间断面同属一个地史期的产物,一起构成区域不整合面,界面上下岩性突变,其上的冰后期地层属同一个海平面变化旋回,可互相对比,因而具有年代地层学意义。三期下切河谷层序的套叠结构表明,晚第四纪以来,研究区存在三次"低海面-海侵-高海面-海退"周期性海面变化。
Abstract:
This paper studies the sedimentary characteristics, stratigraphic sequence, sequence boundary and environmental evolution of the Late Quaternary incised-valley fills in the Nantong area, Jiangsu Province, based on the detailed analyses of core lithology, paleontology, 14C dating, and so on. The results show that there are three episodes of incised valley developed in the study area resulting in the formation of distinct sedimentary sequences, which correlate to the early stage, the middle stage, and late stage of late Quaternary, respectively, and showing three episodic sea-level change "low sea level-transgression-high sea level-regression". The early two systems are incomplete due to the late strong incision and erosion, and are characterized by the superposition of fluvial sediments; while the last postglacial sequence is relatively complete with five sedimentary facies generated, i.e., the fluvial channel, floodplain, estuary, shallow marine, and delta. The basal erosional surface of the lastglacial incised valley fill, which was formed during the Last Glacial Maximum due to fluvial incision, can be correlated with the surface of stiff clay on the interfluves, indicating a significant chronostratigraphic nature.
点击查看大图
下载:
