南羌塘依桑日剖面中侏罗统布曲组沉积相与氧化还原条件  

Sedimentary facies and redox conditions of the Middle Jurassic Buqu Formation in Yisangri section,South Qiangtang Basin

作　　者：文跃 韦恒叶 邹怡 付修根 WEN Yue;WEI Hengye;ZOU Yi;FU Xiugen(School of Geosciences and Technology,Southwest Petroleum University,Chengdu 610500,China;Qiangtang Institute of Sedimentary Basin,Southwest Petroleum University,Chengdu 610500,China)

机构地区：[1]西南石油大学地球科学学院,四川成都610500 [2]西南石油大学羌塘盆地研究院,四川成都610500

出　　处：《沉积与特提斯地质》2025年第1期31-47,共17页Sedimentary Geology and Tethyan Geology

基　　金：国家自然科学基金专项项目(42241203)及面上项目(42272118)。

摘　　要：羌塘盆地中侏罗统布曲组为海相碳酸盐岩沉积,可作为良好的储集层,但目前对于布曲组早期的沉积环境以及古海水氧化还原条件还有争议。本文针对南羌塘盆地依桑日剖面布曲组下部地层开展岩相、沉积相以及古水体氧化还原条件分析,研究结果表明:(1)南羌塘盆地毕洛错地区依桑日剖面布曲组下部地层中识别出远端变陡的碳酸盐岩缓坡沉积体系,划分为内缓坡、中缓坡以及外缓坡沉积亚相。(2)划分出5个岩相组合:风暴岩岩相、核形石石灰岩岩相、滑塌透镜体灰岩岩相、瘤状灰岩岩相、钙质泥岩岩相;11种微相类型:钙质泥岩(MF1)、泥晶灰岩(MF2)、似球粒灰泥石灰岩(MF3)、含鲕粒粒泥灰岩(MF4)、粪球粒粒泥灰岩(MF5)、核形石粒泥灰岩(MF6)、含内碎屑、似球粒泥粒石灰岩(MF7)、生物碎屑泥粒灰岩(MF8)、内碎屑颗粒灰岩(MF9)、内碎屑角砾灰岩(MF10)、内碎屑灰砾灰岩(MF11)。(3)依桑日剖面布曲组整体古水体处于贫氧—氧化环境,并且总有机碳(TOC)含量较低,可能跟氧化还原条件有关,但其关键控制因素可能是水体营养以及初级生产力水平。布曲组下部较深水相泥岩TOC值较低说明布曲组晚期沉积的白云岩古油藏的油气来源并不是同时期沉积的深水烃源岩,而可能是更深部古老的烃源岩地层。The Middle Jurassic Buqu Formation in the Qiangtang Basin represents marine carbonate sedimentation and is regarded as a promising reservoir.However,ongoing debates surround its earlier depositional environment and the ancient seawater redox conditions.This study focuses on the lower strata of the Buqu Formation in the Yisangri section of the South Qiangtang Basin,conducting a thorough analysis of lithofacies,sedimentary facies,and ancient water body redox conditions.The results are as follows:(1)In the Yisangri section of the Biluo Co area in the South Qiangtang Basin,the lower strata of the Buqu Formation reveal a distally steepen carbonate ramp deposition system,delineated into inner ramp,mid ramp,and outer ramp sedimentary subfacies.(2)Five lithofacies associations are identified,encompassing tempestite lithofacies,oncolite limestone lithofacies,slumping lens-body limestone lithofacies,nodular limestone lithofacies,and calcareous silt mudstone lithofacies.Additionally,11 microfacies types are identified,including calcareous mudstone(MF1),mudstone(MF2),pelletoid mudstone(MF3),ooid wackstone(MF4),fecal pellet wackstone(MF5),oncolite wackstone(MF6),intraclast and pelletoid packstone(MF7),bioclastic packstone(MF8),intraclast grainstone(MF9),intraclast calcareous limestone(MF10),and intraclast rudstone(MF11).(3)The overall paleowater conditions in the Yisangri section of the Buqu Formation indicate a dysoxic–oxic environment,accompanied by a relatively low TOC content.The low TOC values may be associated with redox conditions,but they are more likely influenced by water nutrient levels and primary productivity.The TOC values in the lower part of the Buqu Formation suggest that the oil and gas of the dolomite reservoir did not originate from contemporaneous deep-water hydrocarbon source rocks but may have originated from deeper strata.

关 键 词：布曲组 沉积相 碳酸盐岩缓坡 风暴沉积 草莓状黄铁矿 羌塘盆地 

分 类 号：P586[天文地球—岩石学]