南京—仪征地区新近纪砂砾层层序及古长江的形成与演化

Sandy Gravel Sequence in Neogene in Nanjing and Yizheng Area and Genesis and Evolution of the Old Yangtze River

对南京—仪征地区新近纪砂砾层层序、时代进行了讨论。该地区新近纪砂砾层地层层序为中新世中期的洞玄观组 (N1d)、中新世晚期的六合组 (N1l)、黄岗组 (N1h)及上新世的雨花台组 (N2 y) ,认为雨花台组沉积是位于六合组之上的另一套砂砾层 ,其沉积时代为上新世晚期。还分析了新近纪砂砾层在中新世中期、中新世晚期、上新世的沉积环境 ,探讨了区内古长江的形成与演化 ,认为古长江是在古近纪断陷盆地的基础上 ,经历了中新世多个汇水盆地的发育阶段至上新世形成古长江雏形 ,并于更新世早期基本定型 ,其形成及演化过程均与新构造活动息息相关。

The lithostratigraphy in Neogene along Nanjing-Yizheng region is characterized by a wide development of sandy gravel and basalt. Since the twenties in 20 th century,many scholars and institutes made a great deal of studies and acquired abundant fruits. Yet up till now, a unified acknowledgement fails to be reached towards the sequence, time and genesis. Based on the previous work, sandy gravel sequence and time in Neogene are discussed along Nanjing-Yizheng region. The sandy gravel sequence in Neogene in the study area are consisted of Dongxuanguan Fm.(N 1d) in middle Miocene, liuhe Fm.(N 1l) and Huanggang Fm.(N 1h)in late Miocene and Yuhuatai Fm.(N 2y) in Pliocene. It is deemed that the sedimentation in Yuhuatai formation is another set of sandy gravel overlain the Liuhe formation with sedimentary time as late Pliocene. The sedimentary environment is analyzed for Neogene sandy gravel in middle Miocene, late Miocene and late Pliocene. The genesis and evolution of the old Yangtze River in the study area is discussed,the old Yangtze River is deemded to, on the basis of Paleogene fault basin, undergo many developing stages of the catchbasin in Miocene up to the formation of a rudimentary of the old Yangtze River in Pliocene, and finalize basically in early Pleistocene. It is concluded that the genesis and evolution of the old Yangtze River in the study area is closely relatd with the neotectonism.