南京附近晚新生代砂砾层和含化石雨花石研究

A STUDY ON LATE CENOZOIC GRAVEL DEPOSITS AND FOSSILS IN YUHUA PEBBLES NEARBY NANJING,EAST CHINA

对南京附近主要砂砾层剖面作沉积相分析,结合已有的化石和年代资料,认为这套地层形成于晚新生代不同时期,反映了古长江及其支流的历史形成和发育过程,以及与新构造运动,尤其是与青藏高原隆起的联系。研究结果支持将砂砾层分为中新世中期洞玄观组、中新世晚期六合组与黄岗组、上新世(或部分至更新世早期)雨花台组的已有划分方案。根据岩相的纵横变化规律,论证了本区中新世时为汇水湖盆和河流相沉积并存,河流作用向上增强,至上新世主要发育河流相堆积的变化过程。通过对雨花石的成因分析和含化石雨花石的综合研究,表明砂砾层的物质来源大多为近源,是南京周边地区古生代和中生代地层经剥蚀后再沉积所致。

Sedimentary facies analysis combined with available fossil evidences and chronological data shows that the gravel deposits nearby Nanjing were formed in the different periods of the late Cenozoic,partly controlled by the development of the ancient Yangtze River and its tributaries,and neotectonic movements related to the uplift of the Qinghai-Tibet Plateau.The current work supports the existing scheme to divide the gravel layers into the Middle Miocene Dongxuanguan Formation,the Late Miocene Luhe and Huanggang formations,and the Pliocene（and Early Pleistocene）Yuhuatai Formation.An analysis of the vertical and spatial distribution of the gravel deposits reveals the co-existence of fluvial and lacustrine deposits in the Miocene,with the fluvial system becoming more dominant in the Pliocene,reflecting the development of the ancient Yangtze River.An analysis of the origin of the Yuhua pebbles and the fossils within the pebbles shows that the majority of these gravel materials were from nearby sources,probably eroded from Paleozoic and Mesozoic strata in the surrounding areas of Nanjing.