Luminescence chronology of “Old Red Sand” in Jinjiang and its implications for optical dating of sediments in South China  

作　　者：ZHANG JiaFu YUAN BaoYin ZHOU LiPing 

机构地区：[1]Laboratory for Earth Surface Processes, Department of Geography, Peking University, Beijing 100871, China [2]Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

出　　处：《Chinese Science Bulletin》2008年第4期591-601,共11页

基　　金：Supported by the National Natural Science Foundation of China (Grant Nos. 40471010 and 49925307)

摘　　要：A weathered deposit in South China is widespread on the coastal areas of Fujian and Guangdong provinces,China.This deposit consists of slightly cemented,medium-to fine-grained sands,and is characterized by its colors of red,brown red,light reddish brown or dark yellowish orange,and is usually called "Old Red Sand".The uncertainty in its formation age has been a major obstacle to the study of this type of deposit.In this paper,optically stimulated luminescence(OSL) techniques were used to date the "Old Red Sand" sediments from Jinjiang,Fujian Province,China.The effect of the geochemical behavior of uranium and thorium in sediment during chemical weathering on estimation of annual dose was investigated.The results show that the change in annual dose due to weathering poses a major problem for the optical dating of such weathered sediments.The optical dating of these weathered deposits will produce erroneous ages if average annual dose during burial cannot be correctly estimated.For the profiles studied,the OSL dates obtained on samples from the upper part do not represent the burial age of the samples.It is highly likely that they are underestimated due mainly to the accumulated radioactive elements as a result of chemical weathering.It is concluded that changes in annual dose due to chemical weathering must be considered when dating similar sediments in South China.With a detailed analysis of the OSL dating results,the chronology of the marine terraces in this area was suggested.The lowest terrace was formed at ～3.5 ka and the second terrace was dated to ～74 ka.The age of the highest terrace may not be established accurately,but is inferred to be older than the apparent OSL date of～77 ka and so is the Paleolithic artifacts from it.A weathered deposit in South China is widespread on the coastal areas of Fujian and Guangdong provinces, China. This deposit consists of slightly cemented, medium- to fine-grained sands, and is characterized by its colors of red, brown red, light reddish brown or dark yellowish orange, and is usually called ＂Old Red Sand＂. The uncertainty in its formation age has been a major obstacle to the study of this type of deposit. In this paper, optically stimulated luminescence （OSL） techniques were used to date the ＂Old Red Sand＂ sediments from Jinjiang, Fujian Province, China. The effect of the geochemical behavior of uranium and thorium in sediment during chemical weathering on estimation of annual dose was investigated. The results show that the change in annual dose due to weathering poses a major problem for the optical dating of such weathered sediments. The optical dating of these weathered deposits will produce erroneous ages if average annual dose during burial cannot be correctly estimated. For the profiles studied, the OSL dates obtained on samples from the upper part do not represent the burial age of the samples. It is highly likely that they are underestimated due mainly to the accumulated radioactive elements as a result of chemical weathering. It is concluded that changes in annual dose due to chemical weathering must be considered when dating similar sediments in South China. With a detailed analysis of the OSL dating results, the chronology of the marine terraces in this area was suggested. The lowest terrace was formed at -3.5 ka and the second terrace was dated to -74 ka. The age of the highest terrace may not be established accurately, but is inferred to be older than the apparent OSL date of -77 ka and so is the Paleolithic artifacts from it.

关 键 词：红土 发光年代学 化学风化 第四纪沉淀物 

分 类 号：P597[天文地球—地球化学]