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新疆准噶尔盆地吉木萨尔凹陷二叠系芦草沟组云质岩地球化学特征
杨焱钧1,2,柳益群2,蒋宜勤3,杨召3,周鼎武4,焦鑫2,周鹏2,5,李旭2,靳梦琪2,6
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(1. 中煤科工集团西安研究院有限公司, 陕西 西安 710077;
2. 西北大学大陆动力学国家重点实验室 西北大学地质学系, 陕西 西安 710069;
3. 中国石油新疆油田分公司实验检测研究院, 新疆 克拉玛依 834000;
4. 山东科技大学地质科学与工程学院, 山东 青岛 266510;
5. 中国石油塔里木油田分公司勘探开发研究院, 新疆 库尔勒 841000;
6. 中国地质调查局西安地质调查中心, 陕西 西安 710054)
摘要:
研究区芦草沟组云质岩主要包含泥晶白云岩、凝灰质白云岩和白云质凝灰岩等类型,对准噶尔盆地吉木萨尔凹陷二叠系芦草沟组广泛发育的云质岩进行详细的地球化学研究,分析了芦草沟组云质岩的物质来源和沉积环境。云质岩的c(Mg)/c(Ca)比值0.03~1.44,磷含量262×10-6~17283×10-6,Th/U比值0.58~2.00,V/(V+Ni)比值0.60~0.89,V/Cr比值1.25~6.38,Sr/Ba比值0.55~8.25,反映了云质岩形成于生物繁盛的还原性咸水湖泊环境,Mg离子主要来源于深部岩浆热液。碳、氧同位素研究反映芦草沟组主要形成于温度较高的咸水环境中,且由早至晚芦草沟组沉积期具有温度升高而盐度降低的趋势。温度的升高引起的蒸发量增大并没有带来湖水盐度的增加,这种碳酸盐碳、氧同位素反向变化关系可能由于芦草沟组沉积后期不断有外源淡水的输入造成。
关键词:  吉木萨尔凹陷  芦草沟组  白云岩  地球化学
DOI:
投稿时间:2017-12-31修订日期:2018-03-20
基金项目:国家自然科学基金(批准号:41272116)、教育部科技发展中心高等学校博导基金(批准号:20126101110020)、大陆动力学国家重点实验室(西北大学)重点基金(批准号:BJ08133-3)联合资助
Geochemistry of the dolomitic rocks from the Permian Lucaogou Formation in the Jimusar depression, Junggar Basin, Xinjiang
YANG Yanjun1,2, LIU Yiqun2, JIANG Yiqin3, YANG Zhao3, ZHOU Dingwu4, JIAO Xin2, ZHOU Peng2,5, LI Xu2, JIN Mengqi2,6
(1. Xi'an Research Institute, China Coal Technological and Engineering Group Company, Xi'an 710077, Shaanxi, China;
2. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, Shaanxi, China;
3. Xinjiang Oil Field Company, CNPC, Karamay 834000, Xinjiang, China;
4. College of Earth Sciences and Engineering, Shandong University of Science and Technology, Qingdao 266510, Shandong, China;
5. Tarim Field Company, CNPC, Korla 841000, Xinjiang, China;
6. Xi'an Center, China Geological Survey, Xi'an 710054, Shaanxi, China)
Abstract:
The dolomitic rocks from the Permian Lucaogou Formation in the Jimusar depression, Junggar Basin, Xinjiang mainly consist of micritic dolostone, tuffaceous dolostone and dolomitic tuff. In the present paper, the highlights are concentrated in the geochemical signatures, provenance and sedimentary environment of the dolomitic rocks widespread in the study area. These dolomitic rocks have P contents ranging from 262×10-6 to 17283×10-6 (with an average of 427.70×10-6, very close to that of North America Shale Composite), c(Mg)/c(Ca) ratios of 0.03-1.44, Th/U ratios of 0.58-2.00, V/(V+Ni) ratios of 0.60-0.89, V/Cr ratios of 1.25-6.38, V/Sc ratios of 3.65-16.19, and Sr/Ba ratios of 0.55-8.25. The analytical results outlined above suggest that the dolomitic rocks in the Lucaogou Formation were formed in the salt-water reducing lake environments with abundant organisms, and magnesium ions are inferred mainly to be originated from deep-seated magmatic hydrothermal solutions. The carbon and oxygen isotopic data also demonstrate that the Lucaogou Formation was laid down in the continental salt-water lake environments with higher temperatures. There is a tendency of gradual increase of temperatures and gradual decrease of salinities from the early to later stages of the deposition of the Lucaogou Formation. However, there is no evidence in favour of salinity increase in the highly-evaporated lake water due to temperature increase. The abnormal changes of the above-mentioned palaeotemperatures and palaeosalinities based on carbon and oxygen isotopic data of the carbonate minerals may be caused by the input processes of allochthonous fresh water in the later stages of the deposition of the Lucaogou Formation.
Key words:  Jimusar depression  Lucaogou Formation  dolostone  geochemistry

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