摘要： 依据广东省中山地区3个标准孔岩心材料的AMS(加速器质谱)¹⁴C测年、微体古生物有孔虫、介形类、硅藻分析,海相双壳类、腹足类鉴定,沉积构造、沉积物颜色特征,结合已经报道的万顷沙钻孔研究成果,确定小榄镇—万顷沙地区东西向4个钻孔揭露了珠江河口地区LGM(末次盛冰期)河间地与古河谷区两类古地貌单元。由于处在较闭塞的地理位置,下切河谷从9 ka BP(¹⁴C 日历年龄)开始接受泥质沉积物充填,不同于长江三角洲和中国北方沿海平原古河谷充填的砂质沉积;大约7 cal ka BP 出现最大海侵,导致在古河间地LGM风化层之上发生海侵超覆,随后三角洲开始形成。按照河流层序与海面变化对应关系,没有发现海相微体生物的完整河流旋回应该对应MIS(深海氧同位素阶段)3海侵。基于对埋藏阶地的考虑,以及30年来测年技术对这段地层无法取得突破,认为存在着这样的可能性:即区域自上而下第2厚层富铝质红色风化层属于MIS4低水位域沉积,最底部见少量海相双壳类、腹足类的富有机质河口湾沉积单元可能属于MIS5晚期。

关键词: 珠江口, MIS3, 海侵层序, 下切河谷, 海侵超覆, 地层结构

Abstract: Based on AMS(accelerator mass spectrometry)¹⁴C dating data,analysis of microfossils(foraminifera, ostracoda,diatom),identification of marine bivalve and gastropoda,characteristics of sediment structures and color at the core materials from three standard drilling holes in Zhongshan area,Guangdong Province,combining with the study result of the borehole in adjacent Wanqingsha area,this paper noticed that these four drilling holes, located by E-W direction from the Xiaolan Town to Wanqingsha area, represent the interstream and incised-valley palaeogeographic units at LGM(last glacial maximum) in the Zhujiang River estuary area. Since 9 ka BP(¹⁴C cal age), the incised-valley, which was located in a more restricted sedimentary setting, started to accept the mud sediment, and this is different from in the cutting valley in Changjiang River Delta area and northern China coastal plain where occurred the sandy sediments. At about 7 cal ka BP, the maximum transgression occurred, and transgressive onlap happened upon the LGM weathered layer at interstream area,subsequently the delta formed. According to the correspondence relation between riverine sequence and sea level change,the complete river cycle in which no marine microfossil occurred should be correlated to MIS(marine isotope stage)3 transgression. Based on the buried terrance,and the dating technology cannot make a breakthrough for this segment since over 30 years ago,this paper would consider that there is such a possibility that the regional second thick rich-alluvirum red weathered layer from top to bottom would be sediments of the lowstand system tract of MIS4,and the lowest estuarine sedimentary unit which is rich in organic matter, and in which a few marine bivalves and gastropoda shells can be found, would be belonged to sediments of late MIS5.

Key words: Zhujiang River estuary, MIS3, transgressive sequence, incised valley, transgressive onlap, stratigraphic architecture

中图分类号: 

• P534.63