Geochemical characteristics and geological significance of shale in the lower member of Wufeng-Gaojiabian Formation of Well Gudi 1 in Chaohu area, Lower Yangtze region
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摘要:
下扬子巢湖地区鼓地1井揭示了上奥陶统五峰组(WF2-3带)和下志留统高家边组下段(LM2带和LM5-6带)页岩。基于该套地层的页岩岩心样品的元素地球化学测试分析,对其沉积构造背景、物源区背景、古气候、古生产力、海水深度和盐度、氧化还原条件进行了研究。结果表明,鼓地1井五峰组-高家边组下段页岩主量元素、微量元素以及稀土元素纵向分布不均匀,LM2带与WF2-3带和LM5-6带相比明显异常。沉积时期的构造环境主要为活动大陆边缘,同时兼具大陆岛弧的特征。物源具有长英质物源和成熟大陆石英物源混合物源的特征。WF2-3带和LM5-6带为浅水环境,底层海水含氧高,气候温暖湿润,古生产力较低,海水较浅且盐度较低;LM2带为深水环境,海水盐度高、滞留程度较弱,底层海水缺氧,气候干燥炎热,古生物生产力较强。
Abstract:Well Gudi 1 reveals the strata of the WF2-3 member of Wufeng Formation (Upper Ordovician) and the LM2 and LM5-6 members of lower member of Gaojiabian Formation (Lower Silurian). The element geochemistry characteristics of shale samples from the studied strata has been analyzed, and its sedimentary tectonic background, provenance background, paleoclimate, paleoproductivity, seawater depth and salinity, redox conditions are thus studied subsequently. The results show that the vertical distribution of major elements, trace elements and rare earth elements in the shale of the lower member of Wufeng Formation-Gaojiabian Formation of well Gudi 1 is uneven, and the LM2 member is obviously abnormal compared with WF2-3 member and LM5-6 member. The tectonic environment during the sedimentary period is mainly the active continental margin environment, which also has the characteristics of continental island arc. The provenance is characterized by a mixture of felsic provenance and mature continental quartz provenance. WF2-3 and LM5-6 are in shallow water environment, with high oxygen content in bottom seawater, warm and humid climate, low paleoproductivity, shallow seawater and low salinity; LM2 member is a deep-water environment with high seawater salinity and weak retention. The bottom seawater is anoxic, dry and hot climate and strong paleontological productivity.
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图 2 鼓地1井五峰组-高家边组下段地层特征[5]
Figure 2.
图 6 鼓地1井五峰组-高家边组下段页岩沉积构造背景判别[24]
Figure 6.
图 7 鼓地1井五峰组-高家边组下段页岩物源区背景判别[23]
Figure 7.
图 8 鼓地1井五峰组-高家边组下段页岩A-CN-K图解[30]
Figure 8.
表 1 鼓地1井五峰组-高家边组下段与下扬子区地层对比[5]
Table 1. Stratigraphic correlation between the lower member of Wufeng-Gaojiabian Formation and Lower Yangtze region of Well Gudi 1[5]
下扬子地层 鼓地1井 阶 笔石带 井深/m 埃隆阶 LM8 / LM7 / LM6 1 175.5 鲁丹阶 LM5 1 224.5 LM4 缺失 LM3 LM3 1 226.2 赫南特阶 LM1 缺失 WF4 凯迪阶 WF3 1 237.8 WF2 WF1 缺失 表 2 鼓地1井五峰组-高家边组下段主量元素测试结果
Table 2. Test results of major elements in the lower member of Wufeng-Gaojiabian Formationof Well Gudi 1
样品编号 深度/m 主量元素含量/% SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO TiO2 P2O5 GD-1 1 063 61.15 17.79 6.62 2.69 0.36 1.39 4.11 0.05 0.791 0.138 GD-2 1 100 59.9 18.56 6.75 2.78 0.28 1.22 4.51 0.05 0.809 0.133 GD-3 1 135 60.51 18.02 6.82 2.71 0.31 1.16 4.34 0.05 0.796 0.135 GD-4 1 162 60.48 18.42 6.6 2.65 0.31 1.15 4.51 0.04 0.815 0.136 GD-5 1 165.7 58.72 19.62 6.54 2.9 0.36 0.963 4.47 0.03 0.842 0.129 GD-6 1 185 60.76 17.75 6.55 2.51 0.30 1.15 4.42 0.05 0.789 0.135 GD-7 1 205 61.5 17.63 5.59 2.13 0.29 1.03 4.81 0.05 0.762 0.131 GD-8 1 215 63.67 15.81 4.9 1.64 0.29 1.15 4.4 0.02 0.692 0.102 GD-9 1 225.5 55.19 9.84 6.69 3.89 6.32 0.396 2.65 0.15 0.433 0.074 GD-10 1 235 60.32 16.88 5.57 2.63 0.52 0.781 5.11 0.04 0.695 0.077 表 3 鼓地1井五峰组-高家边组下段微量元素测试结果
Table 3. Test results of trace elements in the lower member of Wufeng-Gaojiabian Formationof Well Gudi 1
样品编号 深度/m 微量元素含量/(μg/g) Sc V Cr Co Ni Cu Mo Sr Ba Th U Zr Hf GD-1 1 063 17.3 83.4 89.8 17.2 44.4 71.5 0.302 69.9 708 22.6 3.96 114 3.71 GD-2 1 100 18.1 98.8 85.4 17 43.4 64.7 0.301 69.8 818 23.9 4.15 111 3.72 GD-3 1 135 17.4 89.4 85 18 50.8 83.5 0.339 73.2 949 23.3 4.13 129 4.06 GD-4 1 162 17.1 105 85.7 18 46 66.7 0.518 76 880 22.9 4.47 107 3.36 GD-5 1 165.7 18.7 87.3 68.2 21.1 49.3 69.5 0.353 77.6 831 24.8 4.42 99.8 3.27 GD-6 1 185 17.3 86.3 83.6 16.8 42.7 75.1 0.492 78 1162 24.1 4.48 110 3.57 GD-7 1 205 16 85.7 61 16.8 38.7 33 0.617 70.2 1561 21.7 4 106 3.44 GD-8 1 215 13.6 135 75.8 16.8 79.6 75.6 6.51 74.2 1656 18.3 7.02 122 3.96 GD-9 1 225.5 7.27 81.3 34 5.76 29.8 28.4 12.4 233 1705 12.6 5.69 98.9 2.9 GD-10 1 235 15.5 71.6 66.8 11.4 39.5 59.5 0.626 74.1 1315 23.9 2.89 101 3.88 表 4 鼓地1井五峰组-高家边组下段稀土元素测试结果
Table 4. Test results of rare earth elements in the lower member of Wufeng-Gaojiabian Formationof Well Gudi 1
样品
编号深度/m 稀土元素含量/(μg/g) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu GD-1 1 063 59.4 124 13 41.6 7.97 1.47 6.66 1.08 5.72 1.11 3.08 0.569 3.14 0.5 GD-2 1 100 63.9 133 13.9 43.4 8.63 1.54 6.92 1.14 6.15 1.21 3.41 0.608 3.38 0.54 GD-3 1 135 61.9 131 13.8 45 8.51 1.62 6.77 1.16 5.98 1.2 3.33 0.599 3.33 0.535 GD-4 1 162 68.1 140 14.7 47.5 8.9 1.53 7.06 1.17 6.31 1.25 3.58 0.646 3.55 0.555 GD-5 1 165.7 66.1 140 14.4 44.4 8.5 1.52 6.77 1.12 6.04 1.19 3.29 0.605 3.48 0.547 GD-6 1 185 62.8 131 13.9 43.2 8.62 1.56 7.03 1.17 6.22 1.25 3.5 0.636 3.44 0.532 GD-7 1 205 58.2 107 12.1 41.1 7.02 1.27 5.59 0.909 5.06 0.971 2.79 0.513 2.97 0.464 GD-8 1 215 47.8 85.3 10.5 37.8 6.51 1.14 5.33 0.908 4.81 1.03 2.86 0.526 2.94 0.468 GD-9 1 225.5 26.5 47.9 5.92 21.3 4.13 0.842 3.59 0.59 3.22 0.597 1.71 0.324 1.84 0.286 GD-10 1 235 50.1 99.4 10.6 37.2 6.3 1.04 5.05 0.801 4.18 0.835 2.31 0.453 2.53 0.405 -
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