旧石器遗址强烈化学风化沉积物细粒混合矿物的光释光信号特征及其测年应用  

Luminescence signals from polymineral fine-grains in strongly chemically-weathered sediments from a Paleolithic site and their usefulness for dating

作　　者：黄先可 罗泊宁 周力平[1] Huang Xianke;Luo Boning;Zhou Liping(Key Laboratory for Earth Surface Processes,Department of Geography,Peking University,Beijing 100871)

机构地区：[1]北京大学城市与环境学院,地表过程分析与模拟教育部重点实验室,北京100871

出　　处：《第四纪研究》2019年第2期438-447,共10页Quaternary Sciences

摘　　要：从湖南省北部赤山岛枫树嘴旧石器遗址剖面第2、第3和第4考古层位采集的3个沉积物样品中提取的细粒混合矿物,尝试对其红外释光(IRSL)信号进行研究。实验表明,虽然长石IRSL信号很弱,但仍可以测得信噪比足够高的红外激发后高温红外激发释光(post-IR IRSL)信号。与此同时,样品存在明显的红外激发后蓝光释光(post-IR OSL)信号,并且样品的IRSL与post-IR OSL信号均以快组分为主,这为该地区沉积物利用长石光释光信号定年提供了新的可能。鉴于长石IRSL信号较弱,根据剂量恢复实验结果,本研究采用post-IR IRSL SAR法(50℃红外激发后270℃高温红外激发,pIRIR270℃)进行等效剂量测量,同时也应用post-IR OSL SAR法定年进行比较。实验结果表明,细粒混合矿物的pIRIR270℃等效剂量分别为418.8±13.2 Gy、562.3±18.2 Gy和694.8±17.9 Gy,相对应的post-IR OSL SAR等效剂量结果为345.0±29.4 Gy、409.6±33.7 Gy和424.7±32.2 Gy。假设强烈化学风化未对沉积物的剂量率造成很大影响,基于长石pIRIR270℃信号的释光年龄为89±6 ka、118±8 ka和152±9 ka,比前人所得的石英OSL SAR法年龄老30%~55%(约20~55 ka)。通过对比不同测量条件下获得的等效剂量值来评估长石IRSL信号是否存在晒退问题,没有发现长石post-IR IRSL信号存在晒退不完全的证据。根据本研究post-IR IRSL SAR法测年结果,赤山岛枫树嘴旧石器遗址似阿舍利技术类型的石器出现在倒数第二次冰期(MIS 6)后期至末次间冰期(MIS 5)前期,比湖南道县福岩洞现代人类牙齿化石年龄(80~120 ka)稍老。作为似阿舍利技术石器制造者的赤山岛古人与福岩洞现代人的关系将是我国旧石器时代考古学和古人类学研究的一个重要课题。Sediments from some of the archaeological sites in South China which have undergone strong chemical weathering are fine and hard to isolate feldspar extracts.Hence fine-grained quartz has been utilized for luminescence dating.Here we report a study which was specifically designed to probe the infrared stimulated luminescence(IRSL)signals from feldspar fractions in the polymineral fine-grains from three of the samples,from archaeological Layers 2,3 and 4 at Fengshuizui site(28°56'47"N,112°17'22"E)of Chishan Island in northern Hunan,South China.The IRSL signals,albeit relatively weak,were observed,so were post-IR IRSL and post-IR OSL signals.This prompted us an opportunity of using feldspar signals for dating the strong chemically weathered sediments at the site.Both the infrared and post-IR OSL measurements of these samples showed a dominant fast component.The application of the single-aliquot regeneration dose(SAR)protocol to the IRSL and post-IR IRSL signals as well as that of post-IR OSL signals was then made for dating.On the account of the weak IRSL and post-IR IRSL signals apparently due to the strong weathering and on the basis of the dose recovery test,a protocol employing measurement temperatures of 50℃and 270℃was used for the determination of the post-IR IRSL equivalent dose(pIRIR270℃De).As the post-IR OSL signals in these samples were intense and decayed fast,an attempt was also made to obtain equivalent doses(post-IR OSL De)for comparison.We obtained pIRIR270℃De values of 418.8±13.2 Gy,562.3±18.2 Gy and 694.8±17.9 Gy for the three samples respectively.The corresponding post-IR OSL De values are 345.0±29.4 Gy,409.6±33.7 Gy and 424.7±32.2 Gy respectively.These De values are all higher than the respective De values of 278.1±3.9 Gy,330.4±6.0 Gy and 381.2±5.1 Gy published previously for the fine-grained quartz.Using our post-IR IRSL signals and assuming minimal effects of the strong weathering on the dose rate calculation based on the previous dating study,the luminescence ages are 89±6

关 键 词：湖南赤山岛枫树嘴旧石器遗址 混合矿物 光释光 红外激发后高温红外光释光 强烈风化 

分 类 号：P597.3[天文地球—地球化学]