| 摘要: |
| 河南省安阳市内黄县三杨庄遗址是由于黄河下游洪水快速掩埋而保存的汉代文化遗址，是研究黄河流域历史气候变化与古河道变迁的理想载体。近年来，石英的光释光（OSL）测年技术广泛应用于水成沉积物的定年。本文选取三杨庄文化遗址区的一个深度为10.40 m 的剖面，使用细颗粒石英单片再生剂量（SAR）法OSL 技术测量了该剖面的8个样品的年龄，建立了剖面年代标尺，并与前人测得的加速器质谱（AMS）14C年龄进行了对比，结果显示：（1）三杨庄剖面年龄分布在约12.43 — 1.21 ka，沉积于整个全新世时期，剖面沉积速率波动幅度较大，在约3.91 — 3.15 ka（深度9.60 — 5.00 m）沉积速率很快，而3.91 ka 之前的早 — 中全新世时沉积速率较慢；（2）剖面深度8.60 — 5.00 m，14C年代相对OSL 年代出现严重高估，高估值随深度增加而增大，由约2 ka 变化到约7 ka，推断三杨庄剖面14C年代的高估可能是由于碳库效应的影响；（3）三杨庄剖面细颗粒石英OSL 测年结果指示细颗粒石英在河流-洪积相沉积物测定中的潜力。 |
| 关键词: 全新世 光释光测年 14C测年 碳库效应 三杨庄 |
| DOI：10.7515/JEE182050 |
| CSTR：32259.14.JEE182050 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41772177）；中国科学院青年创新促进会人才项目 |
| 英文基金项目:National Natural Science Foundation of China (41772177); Youth Innovation Promotion Association of CAS |
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| Optically stimulated luminescence dating of Sanyangzhuang profile, Henan Province |
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YANG Ming, WANG Songna, KANG Shugang, LIU Haiwang, WANG Xulong
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Henan Provincial Institute of Cultural Heritage and Archaeology, Zhengzhou 450002, China
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| Abstract: |
| Background, aim, and scope Sanyangzhuang archaeological site of the Han Dynasty was deeply buried and well preserved by the Yellow River alluvium. It has the ruins of ancient villages from the late Western Han Dynasty to the early Eastern Han Dynasty, and provides ideal material for studying the historical climate and river channel changes in the lower reach of the Yellow River. Most of the existing studies on Sanyangzhuang site focus on the division of stratigraphic sequence and the description of site villages. Except for some absolute age data measured by accelerator mass spectrometry (AMS) 14C method, there is still a lack of support for high resolution age data. Quartz optically stimulated luminescence (OSL) dating protocol has been successfully applied to the dating of various aeolian sediments, such as loess, sand dunes, etc. The precise dating of hydatogen sediments and some human cultural sites often use 14C dating method. In recent years, OSL dating protocol has been widely applied to determine the ages of alluvial/fluvial sediments. In this study, we tried to obtain an OSL chronology of the 10.40 m Sanyangzhuang archaeological profile and to compare it with AMS 14C chronology. Materials and methods We collected OSL dating samples near a courtyard in the northeast corner of Sanyangzhuang archaeological site. The luminescence sample tubes were processed under subdued red light conditions in the luminescence laboratory. The samples (~100 g) were first treated with 30% (mass percentage) H2O2 and 30% (volume percentage) HCl to remove organic materials and carbonates, respectively. The samples were washed with distilled water until reaching pH neutral, and then 4—11 μm diameter polymineral grains were separated according to Stokes’ law. These grains were immersed in 30% hydrofluorosilicic (H2SiF6) for 3—5 days to extract the fine-grained quartz component. The resultant fluoride was removed using 30% HCl. Finally, the purified quartz was deposited on 9.7-mm-diameter stainless steel discs using ethanol and dried prior to measurement. All of the OSL measurements were performed using an automated Daybreak 2200 OSL reader equipped with infrared ((880±60) nm) and blue ((470±5) nm) LED units and a 90Sr/90Y beta source for irradiation. For dose rate determination, U and Th concentration was measured using inductively coupled plasma mass spectrometry (ICP-MS), and inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the K concentration. The fine-grained quartz single aliquot regenerative dose (SAR) OSL dating protocol is used for obtaining the eight ages of the upper 10.40 m sediments at Sanyangzhuang (SYZ) archaeological site. Conventional tests in fine-grained quartz SAR protocol and the OSL ages variation with depth indicate the reliability of quartz OSL dating in this study. Results (1) The equivalent dose distribution of the 8 samples in Sanyangzhuang profile is about 37.70—3.50 Gy, and the dose rate fluctuates greatly, which is 2.90—4.80 Gy·ka−1. According to the values of equivalent dose and dose rate, the ages of eight samples can be obtained. Quartz OSL dating results show that, the profile deposited between 12.43—1.21 ka, covering almost the entire Holocene, with sediment accumulation rate fluctuated rapidly. Except for the samples at 8.60 m, the age of the remaining seven samples basically conforms to the stratigraphic sequence. The cause of age reversal at 8.60 m is unknown, and this study will treat it as an abnormal age point for the time being. During the period of about 3.91—3.15 ka (depth of 9.60—5.00 m), the deposition rate is extremely high, while that before about 3.91 ka and after about 3.15 ka is low. (2) The 14C ages of depth between 8.60—5.00 m is significantly overestimated, the 14C age at 8.50—4.96 m of Sanyangzhuang section is 10.20—5.16 ka BP, and when compared with the OSL ages the difference between them generally becomes larger as depth increasing, varying from about 2 ka to 7 ka. Discussion In the measurement of hydrous sediments, organic matter samples such as peat used in 14C dating could be mixed with samples from older strata before joining the closed watershed system and are polluted by “old carbon” from surrounding rocks, which makes the samples older. It is suggested that the discrepancy between OSL ages and 14C ages mainly results from radiocarbon reservoir effect. The OSL dating results of Sanyangzhuang section indicate the great potential of fine-grained quartz dating into fluvial-alluvial sediments. Conclusions Fine quartz OSL dating results show that, the profile deposited between about 12.43—1.21 ka, covering almost the entire Holocene, with sediment accumulation rate fluctuated rapidly, the accumulation rate of about 3.91—3.15 ka is very fast. It is suggested that the discrepancy between OSL ages and 14C ages mainly results from radiocarbon reservoir effect. Recommendations and perspectives In the future, more efforts need to be put on the high-resolution construction of Sanyangzhuang archaeological site. Fine-grained quartz OSL dating into fluvial-alluvial sediments has great potential. Meanwhile, radiocarbon reservoir effect of hydrogenic sediments needs to be studied further. |
| Key words: Holocene OSL dating 14C dating radiocarbon reservoir effect Sanyangzhuang |
