毛乌素沙地东南缘沉积物光释光测年与环境变迁研究

发布时间：2018-09-08 17:30

【摘要】：毛乌素沙地位于东亚季风西北边缘区,内部有大量的人类活动遗迹,是气候变化、环境演变与人地关系研究的理想区域。本文于沙地东南缘选取了11个野外剖面,共采集29个光释光年代样品,旨在建立基于光释光测年技术的年代框架,以更准确地重建其环境演变过程。以往报道的关于该区光释光年代结果大多数选用石英矿物作为测年材料,长石矿物应用相对较少。作者在实验中发现,取自该区域的全新世样品大多数石英信号很弱,导致测年误差相对较大,无法满足测年要求。为了解决这一问题,提取了样品中的钾长石矿物,运用50℃激发后150℃高温激发的两步红外(pIRIR150)流程进行测年。同时,选取了3个石英信号较强的湖相沉积样品,运用单片再生剂量(SAR)流程进行石英年代测试,并将得到的3个石英年龄作为独立的年代控制。鉴于测试长石样品需要耗费大量的仪器时间,作者将标准生长曲线(SGC)法与钾长石pIRIR150法相结合,共同测试钾长石样品的等效剂量(De)值。对于3个石英样品,剂量恢复实验显示,每个样品的剂量恢复比均在0.9-1.1之间,平均值为0.98±0.025(n=16)。光释光特性显示,3个样品石英信号较强；循环比大多在0.9-1.1之间,平均值为1.01±0.008(n=78)；热转移效应小于5%；红外检测显示,石英颗粒无长石的污染。D。分布较集中,离散度均小于20%。对于相同3个样品提取钾长石矿物,剂量恢复实验显示,每个样品pIRIR1so信号的剂量恢复比均在0.9-1.1之间,平均值为1.0±0.003(n=9)。释光特性显不,pIRIR150信号比石英信号强很多；循环比和热转移效应均满足要求。剩余剂量实验显示,3个样品pIRIR150信号的剩余剂量值分布在-0.2-0.026 Gy,相当于对所测样品造成小于20年的年龄偏差,因影响很小,故在计算年代时没有将其剔除。异常衰减实验显示,3个样品pIRIR150信号的g-value分布在0.55-1.71%/decade,比IRSL50信号小得多。D。分布集中,离散度较石英小选取2个年代不同的剖面、共6个释光样品,建立了该区域的SGC,并用其计算所有样品的De。对于De在1-70 Gy的样品,SGC De与pIRIR150 De的比值在0.92-1.06之间,均值为].00±0.01；而对于De小于1 Gy的年轻样品,计算误差较大。本文得到的几点主要结论如下：(1)所选3个样品石英SAR流程实验条件合适,其年代可靠；这3个石英年龄可以作为年代对比的基础。(2)相同3个样品钾长石pIRIR150流程实验条件合适,无需进行异常衰减速率的校正；钾长石pIRIR150年代与石英年代一致,年代结果可靠。可用钾长石pIRIR150技术对该区域的样品进行年代测试。(3)本文所建的SGC能准确计算1-70 Gy之间样品的De值,但暂不适用于小于1 Gy年轻样品De的计算。(4)末次盛冰期至末次冰消期(22-11.8 ka)沙丘活化,为干冷气候所致；早全新世至晚全新世初(11.8-2.4 ka)有古湖泊发育,早全新世趋于转暖,至中全新世中期相对最为暖湿；晚全新世至今(2.4-0 ka)沙丘基本活化,1.5 ka前后有固定趋势,人类活动是该时期沙丘活化的主要因素。(5)萨拉乌苏河三岔河段2.4 ka还是浅湖、宽浅曲流状态；2.4-1.5 ka期间河流深切,该河段形成。河流的形成对研究区的地貌格局和沙丘活化影响重大。本文验证了钾长石pIRIR150释光测年技术应用于毛乌素沙地沉积物年代测试的可靠性,以及SGC法计算D。的准确性,可为该区域后续的研究提供可靠的技术支撑。
[Abstract]:Mu Us Sand is located in the northwest edge of the East Asian monsoon. It has a large number of human activities and is an ideal area for the study of climate change, environmental evolution and human-land relationship. Quartz minerals were mostly used as dating materials, feldspar minerals were seldom used. The authors found that most quartz signals from Holocene samples in this area were very weak, which resulted in relatively large dating errors and could not meet the dating requirements. In order to solve this problem, the K-feldspar minerals in the samples were extracted, and the two-step infrared (pIRIRIR150) dating process excited at 150 C after 50 C excitation was used. At the same time, three lacustrine sedimentary samples with strong quartz signal were selected, and the quartz ages were measured by the single regeneration dose (SAR) process. The equivalent dose (De) of potassium feldspar samples was measured by standard growth curve (SGC) and potassium feldspar pIRIR 150. For three quartz samples, the dose recovery ratio of each sample was 0.9-1.1. The average value was 0.98 (+ 0.025) (n = 16). The photoluminescence characteristics showed that the quartz signals of the three samples were strong; the cycle ratios were mostly between 0.9 and 1.1, with an average value of 1.01 (+ 0.008) (n = 78); the heat transfer effect was less than 5%; the infrared detection showed that the quartz particles had no feldspar pollution. D. distribution was concentrated and the dispersion was less than 20%. Dose recovery experiments for potassium feldspar minerals show that the recovery ratios of pIRIR1so signal in each sample are between 0.9 and 1.1, with an average of 1.0 (+ 0.003) (n = 9). The luminescence characteristics are not obvious, the pIRIR150 signal is much stronger than the quartz signal; the cycle ratio and the heat transfer effect are all satisfied. Residual dose experiments show that the residual agents of pIRIR150 signal in three samples are satisfied. The anomalous attenuation experiment shows that the g-value distribution of pIRIR150 signal in three samples is 0.55-1.71%/decade, much smaller than that of IRSL50 signal. D. distribution is concentrated, and the dispersion is smaller than that of quartz. Two samples are selected. The ratio of SGC De to pIRIR150 De ranges from 0.92 to 1.06, with an average value of].00.01 for the samples with De less than 1 Gy. The main conclusions are as follows: (1) The three quartz ages can be used as the basis for chronological comparison. (2) The same three samples of K-feldspar have suitable experimental conditions without correction of abnormal attenuation rate, and the K-feldspar pIRIRIR150 is consistent with the quartz age, and the chronological results are reliable. Feldspar pIRIR150 technique was used to dating the samples in this area. (3) The SGC constructed in this paper can accurately calculate the De values of the samples between 1 and 70 Gy, but is not suitable for the calculation of the De values of the young samples less than 1 Gy. (4) Dune activation from the last glacial maximum to the last glacial depression (22-11.8 ka) was caused by dry and cold climate; from the early Holocene to the early late Holocene (11.8-2. 4 ka) paleo-lakes developed, and the early Holocene tended to warm, and the mid-Holocene was the warmest and wettest relatively; the late Holocene to the present (2.4-0 ka) sand dunes were basically activated, and there was a fixed trend around 1.5 ka. Human activities were the main factors of sand dunes activation in this period. (5) Sarawusu River Sancha reach 2.4 Ka or shallow lake, wide and shallow meandering state; The formation of the river has a great influence on the geomorphological pattern and sand dune activation in the study area. This paper verifies the reliability of the K-feldspar pIRIR150 luminescence dating technique applied to sediment chronology in Mu Us sandy land and the accuracy of calculating D. Support.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P597.3;P941.73

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