Abstract:

The fluvial terrace has plenty of paleoclimate and paleoenviromental information which play an important role in paleoclimate and paleoenviromental researches.In this paper,we drilled a 42.85m-long core(N06S2)in 2007,which was located in the south bank of Yangtze River at Shifuqiao in Qixia district of Nanjing City.Firstly,fine quartz grains(4～11μm)were extracted from bulk samples in dark room,and the quartz purity tests were conducted.The results show that purity can satisfy the experiment.All measurements were performed on an automated Daybreak 2200 TL/OSL system with blue(470±5nm)light stimulation and U-340 luminescence detection filters.Thick source alpha counting(TSAC)was used to measure the uranium and thorium concentrations.The potassium content was determined using flame spectrophotometer.Secondly,the preheat plateau test and dose recovery test were performed on one sample using the SAR protocol.The results indicate that the fast component dominates the OSL signals.In preheat plateau test,identical D_e in the thermal treat from 160～260℃ was observed,thus we use the preheat temperature of 220℃ for 10 seconds.The recuperation ratios of zero point are below 2％and the recycling ratios lie between 0.9 and 1.1.In dose recovery test,OSL signal sensitivity changes are well corrected.Tests of luminescence characteristics confirm the suitability of the material for OSL dating.At last,samples from this drilling core were systematically dated by optically stimulated luminescence(OSL)dating method,and samples which contain organic matters were dated by AMS¹⁴ C.The results show that the D_e values from the two methods accord with each other very well.However,OSL dating results show that there is a hiatus in this core,and the hiatus,which ranges from 1.9ka to 7.9ka,may be the result of change of Yangtze River's channel or the erosion of the river.The ages of the fluvial deposition mainly range from 0.26ka to 1.9ka and 7.9ka to 9.1ka,it could be attributed to the results of paleoclimate and sea levels change.Meanwhile,study results on pollen and spores show that the paleoclimate has changed from warm wet to temperate wet during the stage of hiatus.

Key words: Yangtze River terrace, OSL dating, SAR, ¹⁴ C dating, paleoclimate

摘要：

河流阶地作为古气候和古环境的重要载体,在研究古气候、古环境变化方面有着极其重要的作用。文中对南京市长江南岸全新世河流阶地的23m厚钻孔沉积物,采用细颗粒石英单测片再生法技术进行了系统的光释光(OSL)测年,并对沉积物中的植物碎片等进行了¹⁴ C测年,样品的OSL年龄和经树轮校正后的¹⁴ C 年龄吻合。测年结果表明,这批样品的光释光信号较强,部分层位释光测年分辨率可达百年尺度。该阶地堆积并不连续,主要堆积于距今0.26～1.9ka和7.9～9.1ka期间且沉积速率较快,而在1.9～7.9ka BP之间即全新世大暖期内存在一个明显的沉积间断期或地层缺失,这有可能是受长江河道摆动或侵蚀下切所致。钻孔的孢粉分析结果表明,古气候由7.9ka BP之前的相对温暖湿润转为1.9ka BP之后的相对温和湿润。

关键词: 长江阶地, 光释光测年, 单测片再生法, ¹⁴C测年, 古气候