石油与天然气地质 ›› 2016, Vol. 37 ›› Issue (4): 483-489.doi: 10.11743/ogg20160404

• 油气地质 • 上一篇    下一篇

羌塘盆地南部隆鄂尼地区布曲组鞍形白云石成因

张帅1, 夏国清2, 伊海生2,3, 蔡占虎2, 李启来2   

  1. 1. 成都理工大学 地球科学学院, 四川 成都 610059;
    2. 成都理工大学 沉积地质研究院, 四川 成都 610059;
    3. 成都理工大学 油气藏地质及开发工程国家重点实验室, 四川 成都 610059
  • 收稿日期:2015-05-14 修回日期:2016-06-06 出版日期:2016-08-08 发布日期:2016-09-06
  • 通讯作者: 夏国清(1982-),男,博士、讲师,沉积地质学。E-mail:xiaguoqing2012@cdut.cn。 E-mail:xiaguoqing2012@cdut.cn
  • 作者简介:张帅(1985-),男,博士研究生,储层矿物岩石学。E-mail:zsdolomite@mail.com。
  • 基金资助:
    国家自然科学基金项目(41572089,41402099)。

Origin of saddle dolomites from the Buqu Formation of Longeni Area in southern Qiangtang Basin

Zhang Shuai1, Xia Guoqing2, Yi Haisheng2,3, Cai Zhanhu2, Li Qilai2   

  1. 1. College of Earth Sciences, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    3. State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China
  • Received:2015-05-14 Revised:2016-06-06 Online:2016-08-08 Published:2016-09-06

摘要: 羌塘盆地南部隆鄂尼地区中侏罗统布曲组砂糖状白云岩中发育有大量的鞍形白云石,其岩相学特征表现为正交偏光下的波状消光以及弯曲的晶面和解理,阴极发光整体呈暗红色,无明显的环带。鞍形白云石中流体包裹体均一温度主要分布于152.8~174.1℃,盐度均值(23.3% NaCl)远高于现代海水盐度,表明其形成经历了高温高盐度的演化过程。微区同位素分析显示鞍形白云石δ13C值介于-4.81‰~4.29‰,δ18O值为-11.2‰~-7.51‰,根据白云石-流体氧同位素分馏方程得到成岩流体δ18O (SMOW)值为5‰~11‰。综合分析认为,鞍形白云石形成于相对封闭的深埋藏环境,是热液流体调整改造作用的产物。地层水加热再循环过程中在孔隙或裂缝较为发育的部位沉淀形成鞍形白云石,高盐度的地层水可能来自沉积期古海水与埋藏期地下热卤水的混合。鞍形白云石的成因研究表明,晶粒相对较粗大的砂糖状白云岩是地表/近地表形成的白云岩重结晶作用的产物。

关键词: 碳、氧同位素, 埋藏白云石化, 鞍形白云石, 布曲组, 中侏罗统, 羌塘盆地

Abstract: Saccharoidal dolostones in the Middle Jurrasic Buqu Formation of Longeni Area in southern Qiangtang Basin were found to contain large number of saddle dolomites.Petrographic study shows typical sweeping extinction,curved crystal faces and cleavage traces under cross polarized light and dark red luminescence and unzoned textures.Fluid inclusions in the saddle dolomite were measured to have homogenization temperature ranging between 152.8 and 174.1℃ and salinity averaged at 23.3%NaCl,much higher than the salinity of modern seawater,indicating a high temperature and high salinity diagenetic environment.In-situ isotopic analysis shows δ13C value ranging from -4.81‰ to 4.29‰,and δ18O value varying from -7.51‰ to -11.2‰.The δ18O(SMOW) value of diagentic fluid was calculated to be 5‰ -11‰ by using the fractionation equation of dolomite-fluid oxygen isotope.It is believed based on a comprehensive analysis that the saddle dolomites were formed in a relatively closed deep burial setting and were the products of thermal fluid modification.The saddle dolomites were probably formed in places where pores and fractures were well developed during a recirculation of heated formation water.The high salinity formation water could be the mixture of paleo-seawater during sedimentation period and underground hot brine during burial period.Origin of the saddle dolomite reveals that the saccharoidal dolostones with coarse grains are the result of recrystalization of surface or near surface dolostones.

Key words: carbon and oxygen isotope, burial dolomitization, saddle dolomite, Buqu Formation, Middle Jurassic, Qiangtang Basin

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