CHRONOLOGY STUDY OF THE QUATERNARY STRATA IN YBK1 CORE IN THE NORTH WING OF THE YANGTZE RIVER DELTA
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摘要: 第四纪钻孔岩芯时间标尺的建立是分析平原覆盖区第四纪环境演变过程的重要基础。通过分析江苏扬州市施桥镇运河大桥东侧YBK1孔岩芯中总厚度95.50 m的第四纪沉积物的岩性、颜色、物质组成、沉积结构和接触界面形态等特征，并对地层进行详细分层基础上，综合采用AMS14C、光释光、宇生核素埋藏和古地磁等年代测试，建立了YBK1孔的第四纪地层年代标尺。结合地层的结构、构造、标志层等的标志，确定YBK1孔第四纪沉积物下覆地层为白垩系浦口组红色粉砂岩，第四纪地层自上而下可分为4套地层，从老到新分别为：中更新世晚期的启东组上段，发育时代为0.1~0.3 Ma，厚度30.20 m，以河床相砂砾层为主，成分较杂；晚更新世早期的昆山组下段，发育时代为0.1~0.045 Ma，厚度仅1.80 m，以残留的河床相砂砾为主；晚更新世晚期的滆湖组中段，发育时代为0.045~0.01 Ma，厚度仅3.40 m，以海滨形成的灰色粉细砂和灰黄色砂砾层为特征，晚更新世晚期的上段及下段均未见残留；全新世如东组沉积厚度较大，达55.10 m，可进一步分为上、中、下三段，分界年龄约为2.5 Ka和7.5 Ka。该区的全新世以滨海、河口、河漫滩沉积物为主，其厚度突然增大与全新世时期的河床改道密切相关。从YBK1孔的岩性特征分析，研究区域缺失早更新世及中更新世早期沉积物，中更新世晚期至晚更新世时期受河流侵蚀作用影响，以少量残留粗颗粒河床相沉积物为特征；全新世时期，因河流改道，地表水动力条件减弱，沉积了较厚的全新世沉积物。Abstract: The establishment of Quaternary drilling core time rulers is an important basis for analyzing the evolution of the Quaternary environment in the plain areas. After analyzing the lithology, color, material composition, sedimentary structure and interface of the Quaternary sediments with a total thickness of 95.5m in YBK1 core in the east side of Yunhe Bridge in Shiqiao Town, Yangzhou City, dividing the stratum in detail, and using dating methods like AMS14C, OSL, cosmogenic nuclide and paleomagnetism, we finally establish the Quaternary stratigraphic-time ruler of YBK1 core. Combining with the stratigraphic structure, key bed and so on, we determine that the Quaternary sediments is overlying the Pukou group red siltstone, and it is composed of four sets of strata, which from old to new respectively are:the upper part of the early Late-Pleistocene Qidong Group, with age of 0.1~0.3Ma, thickness of 30.20m, sand bed gravel layer as the main stratum with complicated composition; the lower part of the early Late-Pleistocene Kunshan Group, with age of 0.1~0.045Ma, thickness of 1.80m, residual sand bed gravel layer as the main stratum; the middle part of the later Late-Pleistocene Gehu Group, with age of 0.045~0.01Ma, thickness of only 3.40m, littoral facies grey clay sand as the main stratum, no upper and lower parts; the Holocene Rudong Group, with large thickness of 55.10m, which can be further divided into upper, middle and lower sections with demarcation ages of~2.5Ka and~7.5Ka. The Holocene in this area is dominated by coastal sediments, estuaries and floodplains. It is the Holocene river diversion that made the stratum thickness increase suddenly. According to the lithological characteristics of YBK1 core, Early-Pleistocene and Early-Middle-Pleistocene sediments are non-existent, sediments of Late-Middle-Pleistocene to Late-Pleistocene are affected by river erosion, resulting of depositing a small amount of residual coarse grain river bed sediments. Up to Holocene, the weakening of surface hydrodynamic forces caused by river diversion produced the thicker Holocene sediments.
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Key words:
- chronology /
- Quaternary Strata /
- the north wing of the Yangtze River Delta
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图 3 YBK1孔孢粉含量百分比图式
Figure 3. The YBK1 drill hole percentage diagram of sporopollen content
表 1 扬州施桥YBK1孔第四系光释光环境剂量率结果
Table 1. The OSL enviroment dose rates of the YBK1 drill hole at shiqiao of Yangzhou city in Jiangsu province
实验室编号 钾含量K(%) 铀含量U(ppm) 钍含量Th(ppm) 实测含水量(%) B1 1.71±3.2 2.55±4.0 11.1±2.8 35.52 B2 1.55±3.5 2.55±4.0 10.9±2.8 38.81 B3 1.65±3.3 2.27±4.1 13.1±2.8 23.54 B4 1.75±3.2 2.14±4.2 10.1±2.9 37.99 B5 1.94±3.1 3.16±3.7 14.3±2.6 34.43 B6 1.61±3.4 1.68±4.6 8.13±3.1 27.05 B7 1.56±3.5 1.45±4.9 4.41±3.6 5.17 B8 1.91±3.1 2.32±4.1 6.73±3.4 15.49 B9 1.63±3.4 1.64±4.6 7.08±3.3 13.87 B10 2.22±2.9 0.75±6.2 3.20±4.5 18.41 注：数据误差为百分相对误差，表内省略了%。 
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表 2 扬州施桥YBK1孔第四系光释光(OSL)测年结果
Table 2. The OSL age results of the YBK1 drill hole at shiqiao of Yangzhou city in Jiangsu province
采样地点 样品编号 原始编号 采样深度
/m等效剂量
/Gy剂量率
Gy/KaOSL年代
/ka备注 扬州施桥镇YBK1 B1 YZ-OSL-4 9.3~9.5 4.99±0.44 2.09±0.15 2.38±0.27 结果基本可信 B2 YZ-OSL-5 11.7~11.8 6.3±0.05 1.86±0.14 3.38±0.25 B3 YZ-OSL-7 20.2~20.3 8.18±0.09 2.52±0.19 3.25±0.24 B4 YZ-OSL-9 28.4~28.6 10.29±0.2 1.87±0.14 5.50±0.43 B5 YZ-OSL-10 34.0~34.2 9.26±0.2 2.50±0.19 3.70±0.29 B6 YZ-OSL-11 45.8~46.0 17.98±1.36 1.94±0.15 9.28±0.99 B7 YZ-OSL-13 59.6~59.7 249.48±8.91 2.23±0.17 111.73±9.54 B8 YZ-OSL-15 65.8~66.0 321.50±3.60 2.60±0.20 123.50±9.40 B9 YZ-OSL-16 74.2~74.6 303.24±7.43 2.28±0.17 132.86±10.59 B10 YZ-OSL-18 94.75~94.9 337.89±32.17 2.15±0.17 157.51±19.63
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表 3 YBK1孔第四纪沉积物14C测年结果表
Table 3. The 14C age results of the YBK1 drill hole at shiqiao of Yangzhou city in Jiangsu province
原始编号 Beta实验室编号 采样地点 深度 14C年龄/a 备注 YZ-C-7 NJ-7 扬州施桥镇 19.8 m 3650+/-30B.P. 结果均有效 YZ-C-2 NJ-4 35.4 m 5390+/-40B.P. YZ-C-5 NJ-5 58 m 12720+/-50B.P. YZ-C-6 NJ-6 74.8 m ＞43500B.P.
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