| 湘鄂西地区晚埃迪卡拉世-早寒武世硅质岩成因及其页岩气地质意义 |
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| 引用本文： | 危凯,陈孝红,王传尚,刘安,曾雄伟,李志宏.湘鄂西地区晚埃迪卡拉世-早寒武世硅质岩成因及其页岩气地质意义[J].地质科技通报,2020,39(2):20-30. |
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| 作者姓名： | 危凯 陈孝红 王传尚 刘安 曾雄伟 李志宏 |
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| 作者单位： | 中国地质调查局武汉地质调查中心;古生物与地质环境演化湖北省重点实验室 |
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| 基金项目： | 国家科技重大专项2016ZX05034001-002中国地质调查局地质调查项目DD20160179;DD20190823 |
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| 摘 要： | 湖北宜昌地区在寒武系水井沱组取得页岩气重大突破后,中扬子地区下寒武统富有机质页岩受到了更加广泛的关注。为了查明这套富有机质页岩的成因及其与下伏硅质岩之间的内在联系,系统采集了鄂西宜昌地区鄂宜地2井岩家河组和湘西桃源、张家界地区留茶坡组-牛蹄塘组的硅质岩,利用主量元素和稀土元素数据分析了硅质岩成因,并探讨了不同地区、不同沉积模式及其对下寒武统富有机质页岩形成的意义。结果表明:①鄂宜地2井岩家河组硅质岩的Al/(Al+Fe+Mn)值介于0.30~0.68,在Al-Fe-Mn三角判别图和Fe/Ti-Al/(Al+Fe+Mn)图解上集中分布在沉积成因区;稀土元素Eu异常不明显,配分曲线为平坦模式,且(La/Yb)N介于1.01~1.81,指示岩家河组硅质岩为沉积成因。②湘西桃源和张家界地区的硅质岩明显分为两种成因。留茶坡组硅质岩Al/(Al+Fe+Mn)值介于0.03~0.19,在Al-Fe-Mn三角图上靠近Fe一端,稀土元素表现明显的Eu正异常,且配分曲线以重稀土元素相对富集的左倾斜为主,指示明显的热液成因;牛蹄塘组硅质岩则表现相反,指示沉积成因。③埃迪卡拉纪末期,湘西斜坡地区靠近热液喷流中心,因此留茶坡组硅质岩以热液成因为主,而宜昌地区位于局限台地附近,富硅热液因受到阻隔而无法进入,因此硅质岩为沉积成因;至寒武纪早期,随着气候变暖、海平面上升,湘西和鄂西地区海水连通,因此该时期硅质岩均为沉积成因。埃迪卡拉纪末期的热液活动为海洋生物的繁盛提供了大量的磷等无机营养元素,对下寒武统水井沱组/牛蹄塘组富有机质页岩的形成具有重要的意义。沉积成因的硅质页岩相很可能是页岩气的有利相带,这或许能为页岩气勘探提供一个新的思路。
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| 关 键 词： | 湘鄂西 晚埃迪卡拉世 早寒武世 硅质岩成因 富有机质页岩 |
| 收稿时间： | 2019-09-04 |
Origin of siliceous rocks in west Hunan and Hubei Provinces during Late Ediacaran-Early Cambrian,and its geological significance of shale gas |
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| Wei Kai,Chen Xiaohong,Wang Chuanshang,Liu An,Zeng Xiongwei,Li Zhihong.Origin of siliceous rocks in west Hunan and Hubei Provinces during Late Ediacaran-Early Cambrian,and its geological significance of shale gas[J].Bulletin of Geological Science and Technology,2020,39(2):20-30. |
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| Authors: | Wei Kai Chen Xiaohong Wang Chuanshang Liu An Zeng Xiongwei Li Zhihong |
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| Affiliation: | (Wuhan Center of Geological Survey,CGS,Wuhan 430205,China;Hubei Key Laboratory of Paleontology and Geological Environment Evolution,Wuhan 430205,China) |
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| Abstract: | Followed by the major breakthrough of shale gas in Shuijingtuo Famation of Yichang, Hubei Province, the organic-rich shale in Lower Cambrian has received much wider attention. In order to find out the internal relationship of the organic-rich shale and the underlying siliceous rocks, we have made a systematic study of the west Hubei and Hunan Provinces, including Yanjiahe Formation of YIDI-2 Well, Liuchapo-Niutitang Formation of Taoyuan and Zhangjiajie area. Based on the analysis of major elements and rare earth elements, we discuss in the paper the different origins of siliceous rocks during Late Ediacaran-Early Cambrian, as well as their significance of shale gas. The conclusions are reached: ①The Al/(Al+Fe+Mn) values of YIDI-2 Well are between 0.30-0.68, close to the biogenic origin. In the Al-Fe-Mn and Fe/Ti-Al/(Al+Fe+Mn)decision diagrams, the sample points are also in the non-hydrothermal area. There is no obvious Eu anomaly but flat partition curves in REE, with LaN/YbN values between 1.01-1.81, indicating the lack of hydrothermal activities and the origin of continental margin. Therefore, the siliceous rocks in Yanjiahe Formation of YIDI-2 Well are mainly of nonhydrothermal origin. ② In the Taoyuan and Zhangjiajie area of West Hunan Province, Al/(Al+Fe+Mn) values of Liuchapo Formation are between 0.03-0.19, and the sample points are close to the Fe in the Al-Fe-Mn diagram. Combined with the obvious Eu anomalies and left-inclined partition curves in REE, it is concluded that the siliceous rocks in Liuchapo Formation are hydrothermal origin. However, it has changed into non-hydrothermal origin for the siliceous rocks in Niutitang Formation, which can be inferred by the larger values of Al/(Al+Fe+Mn) (0.29-0.70), the unconspicuous Eu anomalies and flat partition curves of REE. ③During the later period of Ediacara, due to the short distance to the hydrothermal vents, a set of hydrothermal-origin cherts are developed on the west Hunan slope. As for the Yichang area in the restricted basin, because of the blocking of silceous hydrothermal fluid, a set of dolostone is deposited. During the Early Cambrian, followed by the climate warming, sea-level rising and the sea water being connected, a set of biogenic chert is developed both in west Hunan slope and Yichang area. We conclude that the hydrothermal activities that occurred during Late Ediacaran should be of great significance for the generation of organic shales in Shuijingtuo or Niutitang Formations, because of the large supply of nutrient elements, such as phosphorus, for the flourishing of marine organism. Combined with the exploration results of Cambrian shale gas in South China, we consider that the nonhydrothermal siliceous shales are probably the favorable zones, and about to be the main direction of future exploration after more similar discoveries. |
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| Keywords: | west Hunan and Hubei Late Ediacaran Early Cambrian origin of siliceous rock organic-rich shale |
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