鄂尔多斯盆地天环坳陷北段桌子山组白云岩碳氧同位素特征及意义

Characteristics and implications of carbon and oxygen isotopes in dolomites of the Ordovician Zhuozishan Formation in northern Tianhuan Depression, Ordos Basin

薛时雨 付斯一 侯明才 高星 苏中堂 呼尚才 朱莉娟

Xue Shiyu Fu Siyi Hou Mingcai Gao Xing Su Zhongtang Hu Shangcai Zhu Lijuan

油气藏地质及开发工程国家重点实验室(成都理工大学), 成都 610059 2. 成都理工大学 沉积地质研究院, 成都 610059 3. 中国石油 长庆油田分公司 勘探开发研究院, 西安 710021 4. 天津市环鉴环境监测有限公司, 天津 300384 5. 江西省核工业地质调查院(江西省核工业地质局266大队), 南昌 330038

State Key Laboratory of Oil & Gas Reservoir Geology and Exploration(Chengdu University of Technology), Chengdu, Sichuan 610059, China 2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China 3. Exploration and Development Research Institute of Changqing Oil Field Branch Company, PetroChina, Xi'an, Shsanxi 710021, China 4. Tianjin Huanjian Environmental Testing Co. Ltd., Tianjin 300384, China 5. Nuclear Industry Geological Bureau of Jiangxi Province(Brigade 266), Nanchang, Jiangxi 330038, China

通过空间展布和不同类型白云岩的碳氧同位素特征，诠释了鄂尔多斯盆地西部天环坳陷北段奥陶系桌子山组白云岩的成因和储层地质学意义。研究区白云岩主要有微-粉晶白云岩、残余砂屑细晶白云岩和细-中晶白云岩3种，其中微-粉晶白云岩δ13C、δ18O平均值为0.78‰和-5.0‰；残余砂屑细晶白云岩δ13C、δ18O平均值为0.53‰和-6.5‰；细-中晶白云岩δ13C、δ18O平均值为0.47‰和-6.3‰。桌子山组白云岩碳氧同位素的组成位于正常海相碳酸盐岩范围之内，说明其白云石化流体来源于囚禁的古海水。白云岩碳氧同位素演化特征及成岩作用特征，指示微-粉晶白云岩为准同生阶段白云石化的产物，而残余砂屑细晶白云岩及细-中晶白云岩则为浅埋藏白云石化的产物。

The origin and geological significance of dolomites in the Ordovician Zhuozishan Formation in the northern Tianhuan Depression of the western Ordos Basin were interpreted based on spatial distribution and the characteristics of carbon and oxygen isotopes of different types of dolomites. There are three main types of dolomites in the study area, including powder-microcrystalline, residual sand-fine crystalline and fine-medium crystalline ones. The δ13C values of powder-microcrystalline, residual sand-fine crystalline and fine-medium crystalline dolomites are 0.78‰, 0.53‰, and 0.47‰, while the δ18O values are -5.0‰, -6.5‰ and -6.3‰, respectively. These values belong to normal marine carbonates, indicating that the dolomite fluid might come from ancient seawater. Carbon and oxygen isotope evolution and diagenetic effects showed that the powder-microcrystalline dolomites were formed during the quasi-synchronic stage, and the residual sand-fine crystalline and fine-medium crystalline dolomites were formed during the shallow burial stage.

国家自然科学基金项目（41302087）资助。

https://doi.org/10.11781/sysydz201706842