Rizwan Sarwar Awan, Chenglin Liu, Ashar Khan, Khawaja Hasnain Iltaf, Qibiao Zang, Yuping Wu, Sajjad Ali, Muhammad Amar Gul
{"title":"从牛蹄塘地层富有机黑色岩石的地球化学特征重建中国湘西湘西地区早寒武纪古环境背景","authors":"Rizwan Sarwar Awan, Chenglin Liu, Ashar Khan, Khawaja Hasnain Iltaf, Qibiao Zang, Yuping Wu, Sajjad Ali, Muhammad Amar Gul","doi":"10.1007/s12583-021-1524-x","DOIUrl":null,"url":null,"abstract":"<p>The Niutitang Formation in the South China Block might be a source of hydrocarbon as it contains an enormous quantity of organic matter. Black rock of the Early Cambrian Niutitang Formation is widely distributed in the Yangtze region, but detailed geochemical understanding of it is still emerging. This research discusses the detailed geochemical characteristics of the Niutitang Formation to reconstruct the paleoenvironmental conditions, employing total organic carbon (TOC) content, major, trace, and rare earth element data. For this purpose, black rock specimens of the Niutitang Formation from two outcrop sections were utilized for geochemical characterization, and the results compared with another eight sections from the South China Block. The average total organic carbon in these sediments is significantly higher (5.80 wt.%). In the platform region, lower quantities of TOC indicate a poor potential to produce hydrocarbons. At the same time, significantly higher TOC is observed in the deep shelf and slope sediments, indicating a significant potential to produce hydrocarbons. The average Ce, Eu and Y anomalies from both Longbizui and Sancha sections studied are 0.74, 0.86, 1.77, 1.07, and 1.19, 1.30, respectively. The chemical index of alteration (CAI) throughout the Yangtze block is higher (averaging 71.32) than that of Post Archean Australian Shale (PAAS 69), indicating a moderately weathered source of the Niutitang Formation relative to PAAS. As the sediments are moderately weathered, this suggests these rocks might have been derived from felsic rocks, mainly granite-granodiorite. The normalization of REEs in the black rocks reveals a reduction of light REEs with increase in heavy REEs enrichment. Similarly, a positive Eu anomaly, negative Ce anomaly, and a moderate Y/Ho (34.61) are clues to a hybrid depositional mechanism associated with hydrothermal action and terrigenous input. These anomalies are also evidence of upwelling in the paleo-ocean and mixing of organic matter, which created anoxic bottom water during the deposition of the Niutitang Formation in the basin and upper oxic water conditions before deposition. The main controlling factors for the distribution of rare earth elements in these black rocks of the Niutitang Formation are pH, terrigenous input, source rock composition, tectonism, an upwelling mechanism, and hydrothermal activity.</p>","PeriodicalId":15607,"journal":{"name":"Journal of Earth Science","volume":"89 1","pages":""},"PeriodicalIF":4.1000,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Geochemical Characterization of Organic Rich Black Rocks of the Niutitang Formation to Reconstruct the Paleoenvironmental Settings during Early Cambrian Period from Xiangxi Area, Western Hunan, China\",\"authors\":\"Rizwan Sarwar Awan, Chenglin Liu, Ashar Khan, Khawaja Hasnain Iltaf, Qibiao Zang, Yuping Wu, Sajjad Ali, Muhammad Amar Gul\",\"doi\":\"10.1007/s12583-021-1524-x\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>The Niutitang Formation in the South China Block might be a source of hydrocarbon as it contains an enormous quantity of organic matter. Black rock of the Early Cambrian Niutitang Formation is widely distributed in the Yangtze region, but detailed geochemical understanding of it is still emerging. This research discusses the detailed geochemical characteristics of the Niutitang Formation to reconstruct the paleoenvironmental conditions, employing total organic carbon (TOC) content, major, trace, and rare earth element data. For this purpose, black rock specimens of the Niutitang Formation from two outcrop sections were utilized for geochemical characterization, and the results compared with another eight sections from the South China Block. The average total organic carbon in these sediments is significantly higher (5.80 wt.%). In the platform region, lower quantities of TOC indicate a poor potential to produce hydrocarbons. At the same time, significantly higher TOC is observed in the deep shelf and slope sediments, indicating a significant potential to produce hydrocarbons. The average Ce, Eu and Y anomalies from both Longbizui and Sancha sections studied are 0.74, 0.86, 1.77, 1.07, and 1.19, 1.30, respectively. The chemical index of alteration (CAI) throughout the Yangtze block is higher (averaging 71.32) than that of Post Archean Australian Shale (PAAS 69), indicating a moderately weathered source of the Niutitang Formation relative to PAAS. As the sediments are moderately weathered, this suggests these rocks might have been derived from felsic rocks, mainly granite-granodiorite. The normalization of REEs in the black rocks reveals a reduction of light REEs with increase in heavy REEs enrichment. Similarly, a positive Eu anomaly, negative Ce anomaly, and a moderate Y/Ho (34.61) are clues to a hybrid depositional mechanism associated with hydrothermal action and terrigenous input. 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引用次数: 0
摘要
华南地块的牛蹄塘地层可能是碳氢化合物的来源,因为它含有大量的有机物质。早寒武世牛蹄塘地层黑岩在长江流域分布广泛,但对其详细的地球化学认识仍处于起步阶段。本研究利用总有机碳(TOC)含量、主要元素、痕量元素和稀土元素数据,讨论了牛底塘地层的详细地球化学特征,以重建古环境条件。为此,利用两个露头剖面的牛泥塘地层黑色岩石标本进行地球化学特征描述,并将结果与华南地块的另外八个剖面进行比较。这些沉积物的平均总有机碳含量明显较高(5.80 wt.%)。在平台区域,较低的总有机碳含量表明生产碳氢化合物的潜力较低。同时,在深海陆架和斜坡沉积物中观察到的总有机碳明显较高,表明生产碳氢化合物的潜力很大。龙鼻嘴和三岔剖面的平均 Ce、Eu 和 Y 异常值分别为 0.74、0.86、1.77、1.07 和 1.19、1.30。整个扬子地块的化学蚀变指数(CAI)(平均 71.32)高于后阿尔坎澳大利亚页岩(PAAS 69),表明相对于后阿尔坎澳大利亚页岩,牛蹄塘地层的风化程度为中度。由于沉积物为中度风化,这表明这些岩石可能来自长英岩,主要是花岗岩-花岗闪长岩。黑色岩石的REEs正態化顯示輕REEs減少,而重REEs則增加。同样,正的 Eu 异常、负的 Ce 异常和适度的 Y/Ho (34.61) 也是与热液作用和陆相输入有关的混合沉积机制的线索。这些异常也是古海洋上升流和有机质混合的证据,在盆地牛尾塘地层沉积过程中形成了缺氧底层水,而在沉积之前则形成了上层缺氧水条件。牛塘地层黑色岩石中稀土元素分布的主要控制因素是 pH 值、土著输入、源岩成分、构造作用、上升流机制和热液活动。
Geochemical Characterization of Organic Rich Black Rocks of the Niutitang Formation to Reconstruct the Paleoenvironmental Settings during Early Cambrian Period from Xiangxi Area, Western Hunan, China
The Niutitang Formation in the South China Block might be a source of hydrocarbon as it contains an enormous quantity of organic matter. Black rock of the Early Cambrian Niutitang Formation is widely distributed in the Yangtze region, but detailed geochemical understanding of it is still emerging. This research discusses the detailed geochemical characteristics of the Niutitang Formation to reconstruct the paleoenvironmental conditions, employing total organic carbon (TOC) content, major, trace, and rare earth element data. For this purpose, black rock specimens of the Niutitang Formation from two outcrop sections were utilized for geochemical characterization, and the results compared with another eight sections from the South China Block. The average total organic carbon in these sediments is significantly higher (5.80 wt.%). In the platform region, lower quantities of TOC indicate a poor potential to produce hydrocarbons. At the same time, significantly higher TOC is observed in the deep shelf and slope sediments, indicating a significant potential to produce hydrocarbons. The average Ce, Eu and Y anomalies from both Longbizui and Sancha sections studied are 0.74, 0.86, 1.77, 1.07, and 1.19, 1.30, respectively. The chemical index of alteration (CAI) throughout the Yangtze block is higher (averaging 71.32) than that of Post Archean Australian Shale (PAAS 69), indicating a moderately weathered source of the Niutitang Formation relative to PAAS. As the sediments are moderately weathered, this suggests these rocks might have been derived from felsic rocks, mainly granite-granodiorite. The normalization of REEs in the black rocks reveals a reduction of light REEs with increase in heavy REEs enrichment. Similarly, a positive Eu anomaly, negative Ce anomaly, and a moderate Y/Ho (34.61) are clues to a hybrid depositional mechanism associated with hydrothermal action and terrigenous input. These anomalies are also evidence of upwelling in the paleo-ocean and mixing of organic matter, which created anoxic bottom water during the deposition of the Niutitang Formation in the basin and upper oxic water conditions before deposition. The main controlling factors for the distribution of rare earth elements in these black rocks of the Niutitang Formation are pH, terrigenous input, source rock composition, tectonism, an upwelling mechanism, and hydrothermal activity.
期刊介绍:
Journal of Earth Science (previously known as Journal of China University of Geosciences), issued bimonthly through China University of Geosciences, covers all branches of geology and related technology in the exploration and utilization of earth resources. Founded in 1990 as the Journal of China University of Geosciences, this publication is expanding its breadth of coverage to an international scope. Coverage includes such topics as geology, petrology, mineralogy, ore deposit geology, tectonics, paleontology, stratigraphy, sedimentology, geochemistry, geophysics and environmental sciences.
Articles published in recent issues include Tectonics in the Northwestern West Philippine Basin; Creep Damage Characteristics of Soft Rock under Disturbance Loads; Simplicial Indicator Kriging; Tephra Discovered in High Resolution Peat Sediment and Its Indication to Climatic Event.
The journal offers discussion of new theories, methods and discoveries; reports on recent achievements in the geosciences; and timely reviews of selected subjects.