珠江三角洲PRD16孔微体生物记录与晚更新世以来的古环境重建

对珠江三角洲PRD16孔的微体动物群进行了分析,共发现底栖有孔虫12属24种,介形类9属13种,它们可分别划分为3种生态类型。根据有孔虫和介形类微体动物群的分布特征、并结合岩性和沉积粒度特征,推断PRD16孔研究区晚更新世以来沉积环境演化经历了5个阶段:①34 600 cal a BP以前为河流相环境,形成了研究区最早的第四纪河床相砂砾沉积;②34 600～23 900 cal a BP推测为河口湾环境;③23 900～7 960 cal aBP受末次盛冰期影响,研究区暴露地表遭受风化剥蚀,形成花斑黏土;④7 960～2 810 cal a BP为全新世大海侵时期,研究区为河口海湾环境,发育以广盐性有孔虫和中盐-多盐性介形类为主的微体动物群,其间发生了2次小规模海平面波动,受地块区域沉降作用影响,研究区在3 873 cal a BP左右水深达到最大,主要有孔虫和介形类属种的丰度达到全新世最高值;⑤2 810 cal a BP以来海平面持续下降,研究区由潮坪环境变为河口砂坝,随后河流作用增强,又逐渐变为河流冲积-潮上带环境。

Microfossil Records of Borehole PRD16 and Palaeoenvironment since the Late Pleistocene in the Pearl River Delta

Microfaunas of borehole PRD16 in the Pearl River Delta have been quantitatively analyzed in this paper. A total of 24 benthic foraminifera species referred to 12 genera and 13 ostracod species referred to 9 genera were found in the borehole. They can be divided into 3 ecological groups. The microfaunal analytical results, combined with lithological and sedimentary grain characteristics, suggest that the study area experienced environmental changes since the Late Pleistocene. A riverine environment began to develop before 34 600 cal a BP. Between 34 600 and 23 900 cal a BP, the environment generally changed to an estuarine condition. Between 23 900 and 7 960 cal a BP, the sediments experienced weathering and erosion, characterized by a layer of mottled clay. At around 7 960 cal a BP, sea level rose rapidly and an estuary environment with euryhaline foraminifera and brackish ostracod faunas existed until 2 810 cal a BP. Two second order sea level fluctuations can be recognized based on the composition and abundance of microfaunas. The maximum water depth occurred at approximately 3 873 cal a BP, demonstrated by the highest abundance of foraminifera and ostracods in the borehole. Since 2 810 cal a BP, the environment gradually changed into a fluvial supratidal zone with increased influence of river processes.