珠江三角洲晚第四纪沉积序列及其对海侵过程的响应

Sedimentary sequences in response to marine transgression during the late Quaternary,Pearl River delta

地处南海北部的珠江三角洲在晚第四纪以来经历了数次海面升降过程,沉积了多套海相、陆相及海陆交互相地层,为研究河口海岸带地区的沉积模式及古环境演变过程提供了良好的研究材料。以江门GC088孔岩芯为主要研究材料,通过岩相分析、粒度分析、磁化率、微体古生物学及年代测试分析等手段,结合区域内其他第四系钻孔剖面资料,综合揭示了珠江三角洲江门新会地区晚更新世以来地层沉积序列及沉积环境演变过程,主要得出如下结论:(1)新会地区第四系存在河床相、潮控河流相、河口湾相、三角洲前缘相、潮坪相、三角洲平原相6种沉积相及风化形成的花斑黏土层;(2)通过本文新获取的14C和OSL年代测试结果并综合对比区域内其他钻孔的测年结果建立了新会地区晚第四纪以来的年代框架,认为珠江三角洲普遍存在2次海侵-海退旋回过程,且下海侵旋回的年代应归属于MIS 5;(3) GC088孔多指标分析结果呈现出较好的周期性,与海平面变化曲线变化较一致;结合区域内部分钻孔沉积相变化及其他各类指标结果(如元素比值、孢粉、有孔虫等),揭示了珠江三角洲MIS 5阶段可能存在次一级海平面波动。本研究结果表明珠江三角洲晚更新世的沉积环境演化过程主要受到全球海平面变化及冰期-间冰期旋回时岸线移动的影响。

The Pearl River Delta,located in the northern South China Sea,has experienced several sea level changes,and deposited several marine-terrestrial strata since the late Quaternary,which provides good research materials for studying the sedimentary model and palaeo-environmental evolution of estuarine and coastal zones.In this study,detailed investigation of lithofacies,grain-size distribution,magnetic susceptibility,microfossils,and chronological analysis were conducted for core GC088.The results were combined with other regional cores and revealed the stratigraphic sequence and the evolution of sedimentary environment in Jiangmen Xinhui area,Pearl River Delta.The Quaternary strata in Xinhui area include six sedimentary facies,namely,river channel,tide-dominated river,estuarine,delta front,tidal flat,and delta plain.Weathered clay layers also present in the Quaternary strata in Xinhui area.Based on the 14C and OSL dating results obtained in this study and in other cores in the study area,the chronological framework of Xinhui area since the late Quaternary was established.Two transgression-regression cycles in the Pearl River Delta were recognized,and the age of the lower transgression cycle should be attributed to MIS 5.3.The multi-index analysis results of core GC088 illustrate clear periodicity in relation to the sea level change.Combined with the changes of sedimentary facies and the results of other proxies(e.g.geochemical elements,pollen,foraminifera,etc.)of regional cores,it is believed that sea level fluctuated in the MIS 5 stage of the Pearl River Delta.This study indicates that the evolution of sedimentary environment in the Pearl River Delta was mainly controlled by global sea level change and shoreline movement during last glacial-interglacial cycles.