Optically stimulated luminescence (OSL) dating for Late Quaternary sediments using fine grain (4-11 mum) quartz and climatic stratigraphic significance in western hilly area of Yangzhou, Jiangsu
江苏省扬州地区西部的岗地地貌受控于区域内的NW向走滑并正断的无锡-宿迁断裂的长期活动,同时该断层的活动性也是一个关系到长三角地区地壳稳定性的重要地质问题,而研究该问题的一个关键是对该断层两侧晚第四纪地层的划分及绝对年代的确定。本文对17个采自岗地的样品使用光释光(OSL)测年法中的细颗粒(4-11 mum)石英测试技术,采用SMAR法和TT-OSL法进行De值的测试及年龄对比,较系统地对江苏扬州西部岗地晚第四纪沉积物年代和地层层序进行了探讨。结果表明:SMAR法较适用于D_e <300 Gy的样品;TT-OSL法对于较低剂量的样品效果差,而对D_e >200 Gy的样品测试更适宜,误差相对SMAR法结果更小,与地层的沉积层序符合的更好。17个样品的OSL年龄结果表明:本区岗地主要为晚更新世沉积物,沉积速率约0.1 mm · a~(-1);在水系及湖岸的附近有少量全新世沉积发育。根据所有样品的宏观岩性和年龄分布,本文初步认为晚更新世沉积物主要形成于MIS5-MIS4阶段、MIS2阶段,沉积物主要为风成,对应区域上的下蜀土,堆积期间本区地壳相对稳定,无锡-宿迁断裂无明显活动。在冰后期-全新世随着气候的变暖,海平面上升,河湖泛滥,水系边缘发育少量湖沼相沉积。总体而言,本区的晚更新世-全新世沉积形成主要受到气候变化影响,构造影响不明显。
英文摘要:
Background, aim, and scope The formation of hill geomorphology in western Yangzhou, Jiangsu Province is related to the long-term activity of NW strike-slip and continuous Wuxi-Suqian fault in the region. The division of the formation age of the Late Pleistocene-Holocene strata on the hill and the lack of systematic absolute age data restriction on the stratigraphic sequence are helpful for discussing the formation of sediments in the region since the Late Quaternary. The relationship between tectonic activity or climate change is unfavorable. In this paper, the sedimentary age of the Late Quaternary sediments in the western hilly area of Yangzhou, Jiangsu Province, has been measured by optically stimulated luminescence (OSL) dating. Based on the age results and the characteristics of sediments, the possible tectonic-climatic origin is discussed. Materials and methods In this paper, the shallow Late Quaternary sediments near Gongdao Town in western Yangzhou City were studied. The fine quartz (4-11 mum) extracted from the sediments were measured by SMAR method and TT-OSL method in OSL dating, and the age of De was obtained. Results The test results show that SMAR method is suitable for samples with De value less than 300 Gy, TT-OSL method is less effective for samples with low dose, but more suitable for samples with De value greater than 200 Gy. The error is smaller than that of SMAR method, and it is better in accordance with the sedimentary sequence of formation. Discussion OSL age shows that the sediments in the study area developed from Late Pleistocene to Holocene. The outcropped Late Quaternary depositional epoch is concentrated in the middle-late Late Pleistocene, and the Holocene depositional development is very limited. The dating of borehole samples shows that the sedimentation rate since the Late Pleistocene is about 0.1 mm · a~(-1), which is very low. For the area with altitude >20 m, it is in denudation for a long time, while for the area with altitude of 10-20 m, there may be a process of denudation before sedimentation. The time of acceptance of sedimentation may be 30 ka from now on. For the area with altitude less than 10 m, near the lake system and so on, there are deposits formed in Holocene, and the provenances come from it. Deposits in the Yugang area are transported and then accumulated at the edge of the river system. According to the age distribution of 17 samples, the hill deposits were mainly formed in MIS5-MIS4, MIS2 and Holocene, and the Late Pleistocene deposits were mainly dust deposits in dry and cold climate, corresponding to Xiashu soil. Holocene is a small amount of lake and marsh deposits on the edge of river and lake system, which is related to the rise of sea level and flooding of rivers and lakes. In the dry and cold accumulation stage of aeolian dust, the tectonic activity in this area should be in a very weak state, which is conducive to the stable development and retention of aeolian soil. The Late Pleistocene sediments in the Gangdi are not obviously related to tectonic activities, but are genetically related to climate. Conclusions SMAR protocol can be used for photoluminescence dating of fine-grained quartz in shallow hilly sediments in this area.