川西南地区下寒武统细粒沉积岩高精度层序地层特征及其充填演化模式

【作者】 袁钰轩； 李一凡； 樊太亮；

【Author】 YUAN Yuxuan;LI Yifan;FAN Tailiang;School of Energy, China University of Geosciences (Beijing);

【机构】 中国地质大学(北京),能源学院；

【摘要】 上扬子地区下寒武统页岩展现出了良好的页岩气勘探前景,是中国乃至全球开展古老层系海相页岩气勘探研究的重要领域。利用高分辨率层序地层学的方法在海相细粒沉积岩中建立高精度层序地层格架,对川西南地区下寒武统进行层序划分与对比,可有效预测富有机质发育层段,指导非常规油气勘探。本文以川西南地区下寒武统麦地坪组-筇竹寺组细粒沉积岩为研究对象,选取金石103井,通过岩心精细描述和高精度薄片分析,将麦地坪组-筇竹寺组划分为(1)磷质岩、(2)弱纹层硅质泥岩、(3)硅质粉砂质泥岩、(4)变形层理泥质粉砂岩、(5)块状硅质粉砂岩、(6)暗纹层粉砂质泥岩、(7)透镜状粒序泥质粉砂岩、(8)波状纹层泥质粉砂岩、(9)贫纹层粉砂质泥岩、(10)富纹层泥质粉砂岩、(11)钙质胶结硅质粉砂岩等11种岩相类型,并以此为基础识别了混积潮坪、泥质深水陆棚、砂泥质深水陆棚、泥质浅水陆棚、砂泥质浅水陆棚5类沉积相;通过岩心精细观察,识别出了3个三级层序界面,包括震旦系—寒武系不整合面SB1、麦地坪组—筇竹寺组岩性突变面SB2、岩性组合转换面SB3。根据岩相叠加样式及沉积构造定量统计,在麦地坪组-筇竹寺组中划分了35个准层序,14个准层序组,总结了由潮汐流控主导的"磷质颗粒灰岩+磷质—钙质砂岩+钙质—磷质泥质粉砂岩"(HST1准层序单元)、受重力流和底流协同作用的"钙质胶结粉砂岩+块状粉砂岩/变形层理泥质粉砂岩+暗纹层粉砂质泥岩"(HST2准层序单元)、受风暴浪作用为主导、底流作用协同影响的"透镜状粒序泥质粉砂岩/波状纹层泥质粉砂岩/变形层理泥质粉砂岩+暗纹层粉砂质泥岩"(TST3准层序单元)、受波浪和重力流共同影响的"钙质胶结粉砂岩+富纹层状泥质粉砂岩+贫纹层状粉砂质泥岩"(HST3准层序单元)等4类典型准层序叠加样式,识别了6个体系域,划分出3个完整的三级层序单元;结合沉积相和层序特征,建立了麦地坪组—筇竹寺组"混积陆棚—深水陆棚—浅水陆棚"的演化过程。更多还原

【Abstract】 The Lower Cambrian shale in the Upper Yangtze region shows a good prospect of shale gas exploration, which is an important field for the exploration and research of marine shale gas in ancient strata in China and even in the world. Using the method of high-resolution sequence stratigraphy to establish a high-precision sequence stratigraphic framework in marine fine-grained sedimentary rocks, the sequence division and comparison of the Lower Cambrian in southwestern Sichuan can effectively predict the organic-rich development intervals and guide unconventional oil and gas exploration. This paper takes the fine-grained sedmentary rocks of the Lower Cambrian Maidiping Formation-Qiongzhusi Formation in southwestern Sichuan as the research object,selects Jinshi 103,and through the elaborate description of core and trough high-precision analysis of thin sections divides the Maidiping FormationQiongzhusi Formation to 11 lithofacies types, as follows:(1) Phosphatic rocks,(2) Weak-laminar siliceous mudstone,(3) Siliceous silty mudstone,(4) Deformed bedding argillaceous siltstone,(5)Massive siliceous siltstone,(6) Dark-laminar silty mudstone,(7) Lenticular sequence argillaceous siltstone,(8)Wavy lamellar argillaceous siltstone,(9)Lean laminated silty mudstone,(10)Laminar-rich argillaceous siltstone,(11)Calcareous cementation siliceous siltstone. On this basis, five types of sedimentary facies are identified: mixed tidal flat facies, muddy deep-water shelf facies, sandy argillaceous deep-water shelf facies, muddy shallow-water shelf facies and sandy muddy shallow-water shelf facies. Three third-order sequence boundaries were identified by fine core observation, including Sinian-Cambrian unconformable surface SB1, lithofacies catastrophe surface SB2 of MaidipingQiongzhusi formation, lithologic assemblage transform surface SB3. According to lithofacies superposition style and the quantitative statistics of sedimentary structure, 35 parasequences and 14 parasequence sets are divided in Maidiping Formation-Qiongzhusi Formation, four types of parasequence styles are summarized, such as "phosphorite grainstone + phosphorite-calcareous sandstone + calcareous-phosphorite argillaceous siltstone parasequence"(HST1 parasequence unit) dominated by tidal flow control, "calcareous cemented siltstone + massive siltstone/deformed bedding argillaceous siltstone + dark laminated silty mudstone parasequence"(HST2 parasequence unit) by the synergy of gravity flow and bottom flow, "lenticular graded argillaceous siltstone/wavy laminated argillaceous siltstone/deformed bedding argillaceous siltstone + dark laminated silty mudstone parasequence"(TST3 parasequence unit) led by storm wave action and co-influenced by bottom flow,"calcareous cemented siltstone + rich laminated argillaceous siltstone + poor laminated silty mudstone parasequence"(HST3 parasequence unit) influenced by wave and gravity flow, 6 system tracts are identified, and three complete third-order sequence units are divided; Combined with characteristics of sedimentary facies and sequence, the evolution process of ’mixed shelf-deep shelf-shallow shelf’ of Maidiping Formation-Qiongzhusi Formation was established.更多还原