燕辽裂陷槽辽西坳陷中元古界黑色页岩沉积环境和生烃潜力

The Depositional Environment and Hydrocarbon Potential of the Mesoproterozoic Black Shale in the Western Liaoning Depression of the Yanliao Rift Zone

[目的]前人对中元古代生命演化、氧气含量、古海洋条件等研究均表明中元古代存在适宜优质烃源岩生成和保存的环境。加之近年来元古宇油气资源的相继发现,使得我国中元古界黑色页岩沉积环境和生烃潜力的认识亟需加强。华北地台燕辽裂陷槽沉积了巨厚的中新元古代地层,发育串岭沟组、高于庄组、洪水庄组、铁岭组和下马岭组5套烃源岩层系,前人在冀北地区对这些烃源岩层系已开展了大量研究,但是目前对辽西坳陷研究还处于初级阶段。[方法]基于大量的野外露头、钻井、薄片和有机地球化学数据对辽西坳陷洪水庄组、铁岭组和下马岭组这三套烃源岩层系开展了沉积环境和生烃潜力分析。[结果]洪水庄组主要为一套富含有机质的黑色页岩,黄铁矿非常发育,指示海槽深水沉积。多个露头点在洪水庄组顶部见白云岩滑塌沉积,表明水深向上变浅,逐渐过渡为碳酸盐岩台地斜坡沉积环境。铁岭组底部广泛发育高能颗粒白云岩沉积,中部以灰色页岩为主,局部地区灰色页岩与含锰白云岩交互沉积,顶部为叠层石白云岩和泥岩互层,反映碳酸盐岩台地边缘—潟湖—潮坪沉积环境,并同洪水庄组组成了两个整体水深向上变浅的沉积旋回。待建系下马岭组底部发育石英砂岩、中上部则以灰色页岩沉积为主,为无障壁碎屑海岸—浅海陆棚沉积。有机地球化学数据表明多数黑色页岩TOC含量大于1.0%,为中到优质烃源岩,Tmax介于435℃~480℃,指示烃源岩处于成熟阶段,有利于油气的生成。[结论]中元古界黑色页岩沉积环境和生烃潜力综合分析表明,辽西坳陷具有良好的油气勘探潜力。

[Objective]Recent years'research advance on the life evolution,oxygen content,and paleo oceanic con-ditions of the Mesoproterozoic all indicate that during the Mesoproterozoic era there were suitable environments for the formation and preservation of high-quality hydrocarbon source rocks.The discoveries of the Proterozoic oil and gas resources in recent years,also suggests a need to enhance our understanding of the China's Mesoproterozoic black or-ganic shale depositional environment and its potential for generating hydrocarbons.The YanLiao rift belt in the North China Craton has deposited thick Proterozoic strata,developing five sets of source rock systems:Chuanlinggou For-mation,Gaoyuzhuang Formation,Hongshuizhuang Formation,Tieling Formation,and Xiamaling Formation.Previ-ous studies have conducted extensive research on these source rock systems in the northern Hebei region but current research on the Western Liaoning Depression is still at an early stage.[Methods]This study is based on field out-crops investigation,drilling core observation,thin sections analysis and geochemical data to reveal the sedimentary environment and hydrocarbon potential for the Proterozoic Hongshuizhuang,Tieling,and Xiamaling Formation in the Western Liaoning Depression.[Results and Discussions]The study found that the Hongshuizhuang Formation main-ly consists of organic-rich black shales with abundant pyrite indicating a deep-marine trough depositional setting.Multiple outcrop sections show carbonate debris flow deposits at the top of the Hongshuizhuang Formation,suggesting a gradually decreased water depth and depositional environment transition into a carbonate platform slope setting.The Tieling Formation consists of the grain dolostone formed under high energy at the bottom,gray shale and locally devel-oped manganese-bearing dolostone in the middle,and interbedded stromatolite dolomite and thin mudstone at the top,suggesting a carbonate platform margin-lagoon-tidal flat depositional environment.The Xiamaling Formation is dominated by quartz sandstone at the bottom and grey shale in the middle-upper part indicating a clastic coast-shal-low marine shelf depositional environment.Organic geochemical test data shows that most black shales have TOC con-tent>1.0%,which are medium to high-quality source rocks.The majority of the Tmax ranges from 435°-480°,indicat-ing that the source rock is mature and favorable for oil and gas generation.[Conclusions]Given the widely develop-ment of the black shale,favorite depositional environment,along with the high shale TOC and suitable thermal evolu-tion degree,we believe the Proterozoic black shales in the Western Liaoning Depression have great hydrocarbon po-tential.