摘要
埋藏古河道沉积物年代学框架的建立对于探讨当地水系演变过程、重建气候演化历史具有重要意义。本文用光释光(OSL)测年中的简单多片再生法(SMAR)和单片再生法(SAR)对南京市区汉府街埋藏古河道堆积物钻孔样品进行了光释光测年,对岩芯中含有的植物碎片进行了AMS1C测年。光释光等效剂量(D_e)的预热坪实验表明,在200～260℃的预热温度范围内均能获得基本一致的D_e值,并得到了剂量恢复实验支持。样品的光释光年龄和树轮校正的AMS ^(14)C年龄吻合,结果显示N06S6孔秦淮河古河道沉积是不连续的,主要堆积于6.6 ka至7.9ka期间和14ka至15ka期间。末次冰盛期期间,秦淮河下切形成深达至少42m的古河谷。
Several previous studies suggest that the ancient Qinhuai River flew from southeast to northwest across Nanjing city and became a confluence of the Yangtze River. However, few geochronological data was available on the sediments in the ancient channel. In this paper, samples from a 39.7-m-long sediment core of the paleochannel deposits in Hanfu bus station in Nanjing city were dated by means of optically stimulated luminescence （OSL） and AMS ^14C. In darkroom, fractions of fine quartz grains（4 -11 μm）were extracted from bulk samples, and their purity was examined using an IRSL scan. All measurements were performed on an automated Daybreak 1100TL/OSL system with blue（470nm）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 spectrophotometry. Firstly, the preheat plateau test and dose recovery test were performed on one sample by the SAR protocol. The results show that the fast component dominates the OSL signals. In preheat plateau test,identical De in the thermal treat from 200 - 260℃ was observed. 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. Secondly, all samples were measured by the SAR and SMAR methods. The results show that the De values from the two methods are well consistent. Three dates on wood fragments from 11.8m to 20. 3m in depth indicate that the depositional ages of this part are between 7317 -7933cal. aB. P. The upper two AMS ^14C ages agree with the OSL ages. Based on the above results,a systematic OSL dating for the cored samples was carried out by unanimously adopting the SMAR protocol. The upper and basal ages of the borehole N06S6 are 6.6ka and 15.4ka. However, OSL dating results show that there is hiat
出处
《第四纪研究》
CAS
CSCD
北大核心
2009年第4期837-844,共8页
Quaternary Sciences
基金
中国地震局地质研究所基本科研业务专项(批准号:DF-1GCEA-0607-1-10)
地震行业科研专项(批准号:200808015)资助
