OSL ages of sedimentary layers in Linhe Depression since Late Pleistocene
Many studies have been carried out in the Hetao Basin between Inner Mongolia and Ningxia Province,China because of the thick Quaternary lacustrine sedimentary layers. However,the lack of absolute ages,especially in the west part,is the major obstacle to compare the regional Quaternary strata in the Hetao Basin. Samples from three drill cores in the north of the Linhe Depression were collected. OSL signals from fine grain quartz were used to determine the ages of sedimentary layers. The method used in the paper is the Simplified Multiple Aliquot Regenerative-dose(SMAR)protocol. The residual signals from modern water-laid sediment show that the sediments had been bleached well,which is the basis for OSL dating. And the results of the dose recovery test indicate that a sample having been given a dose of 249.67 Gy was determined as 257.50±25.67 Gy. The error was 3.13%,within acceptable limits. In addition,no saturation was observed in the curves of the samples. As a result,it is proper to determine the ages of sediments in this area using OSL method.Based on the lithology and the OSL ages of 3 cores in the Linhe Depression,the bottom margin of Late Pleistocene series was about 150 m,while the top boundary ranged from9 m in the west to 15 m in the east. Moreover,The OSL data of the Linhe Depression are indispensible for analyzing climate changes and regional comparing for the Hetao basin. The results illustrate that there were five change stages of climate in the Linhe Depression:(1)During the late period of Middle Pleistocene(200-130 ka),the climate was humid;(2)During the early period of Late Pleistocene(130-80 ka),it became arid;(3)During the middle period of Late Pleistocene(80-40 ka),the weather was relatively humid;(4)During the late period of Late Pleistocene(40-10ka),it was dry;(5)During the Holocene(10ka up to now),the climate was humid at first and then getting drier.