【作者】 付修根；

【导师】 王剑； 谭富文；

【作者基本信息】 中国地质科学院 ， 古生物学与地层学， 2008， 博士

【摘要】 青藏地区是目前中国大陆上油气勘探程度最低的油气资源战略选区,近年来随着研究程度的不断深入,该区油气调查与勘探越来越受到重视,其中中生代羌塘盆地被认为是该区油气资源潜力最大和最有希望取得勘探突破的首选盆地。论文以“北羌塘中生代沉积盆地演化及油气地质意义”为题,紧密围绕北羌塘盆地的开启时间、盆地的早期演化特征、盆地沉积充填序列、盆地的关闭与消亡等一系列关键的基础地质问题,开展了卓有成效的深入研究。2006年,在羌塘盆地油气地质调查中,笔者与导师等一道发现了肖茶卡组顶部的风化壳,表明那底岗日组与下伏地层之间存在明显的沉积间断,这一发现无疑对羌塘中生代盆地演化具有重要意义。论文以位于古风化壳之上,代表中生代裂谷作用开启的那底岗日组火山岩为研究对象,采用SHRIMP精确定年方法,确定了那底岗日组火山岩早期喷发年龄(SHRIMP U-Pb年龄)在220 Ma左右,晚期喷发年龄(SHRIMP U-Pb年龄)在205 Ma左右。结合前人的生物化石资料,最终确定了塘中生代沉积盆地的开启时间应该在220 Ma左右。沉积相研究表明,羌塘晚三叠世—侏罗纪盆地是在那底岗日组火山—火山碎屑岩基础上发育起来的,盆地的性质与火山岩密切相关。盆地的开启以火山—火山碎屑岩的喷发、沉积为特征,早期沉积作用以冲洪积相为主,之后,盆地发生了相对均匀的沉降作用,显示裂谷盆地的演化特征。论文进一步采用地球化学方法,对那底岗日组火山岩性质进行了研究,确定了该套火山岩性质为板内裂谷玄武岩,结合盆地的演化特征,提出了北羌塘中生代(主要是晚三叠世—早白垩世)盆地性质为裂谷(陷)盆地。这一结论为客观分析羌塘盆地油气资源潜力提供了重要的基础地质依据。北羌塘中生代沉积盆地什么时候关闭?对于这一问题由于地层中生物化石较少,并且缺乏区域上可对比的年代学依据,迄今为止很难对此进行清楚的认识。2006年,笔者和导师等在北羌塘胜利河地区发现了一套海相油页岩,采用新的Re-Os同位素定年方法,确定了油页岩形成年龄为101±24Ma,结合油页岩中的化石组合,确定了油页岩形成时代为早白垩世,并对早白垩世北羌塘地区沉积特征、岩相古地理特征进行了研究。此外,论文把盆地演化与油气的生、储、盖组合相结合,对目前人们关心的羌塘地区油气资源问题进行了讨论。更多还原

【Abstract】 The Qinghai -Tibet Plateau is located in the east part of the well-known Tethys realm that is the largest petroliferous region onshore in China which is under-explored. Because of the special structure, complicated tectonic evolution and badly natural environment, the research level of petroleum exploration in the Qinghai-Tibet Plateau is the lowest in China. Recently, the oil and gas survey and exploration for this area are being given more and more attention.The Qiangtang basin is located in the north and mid position of the Qinghai -Tibet Plateau, where widespread Mesozoic marine deposits. This basin is the No.1 to the potential of the oil and gas resources in major sedimentary basin on the Qinghai -Tibet Plateau. In this paper, based on the early and late evolution of basin, and sedimentary sequences, we present the open age, early evolution and close of Mesozoic sedimentary basin in North Qaingtang.Regionally, a paleo-weathering crust, a new find by us in 2006, occurred widely at the top of the Xiaochaka strata during the early evolution of Mesozoic sedimentary basin in North Qaingtang, revealing that a depositional hiatus was existed between the Nadi Kangri Formation and its underlying strata (Xiaochaka Formation). Then, judged from the basin evolution, the Nadi Kangri deposits in the North qiangtang depression should be assigned in Jurassic structural/tectonic interval but different from Carnian structural/tectonic interval (Xiaochaka Formation). Mesozoic sedimentary basin in North Qaingtang developed on the basis of the Nadi Kangri volcanic rocks. As a result, eruption ages of the volcanic rocks represent the open ages for the basin, and tectonic setting of the volcanic rocks is close related to basin nature. The dacitic tuff from the basal part of the Juhua Mountain section gives a SHRIMP zircon U-Pb age of 225.1±1.4 Ma, which represents an early eruption age of the Nadi Kangri volcanic rocks. While the age obtained in the Nadigangri section is more close to the upper part of the sequences, which may represent a late age of about 205±4 Ma. Therefore, we conclude that open age of Mesozoic sedimentary basin in North Qaingtang is about 220 Ma.The open of Mesozoic sedimentary basin in North Qaingtang is characterized by the eruption and sedimentary of the Nadi Kangri volcanic rocks and early sedimentary is characterized by alluvial-flood plain facies conglomerate, and then basin settled uniformly. This shows a rift basin evolution. On the tectonic discrimination diagrams, such as Ti/100-Zr-3Y, Zr/4-2Nb-Y, Th/Hf-Ta/Hf and Zr-Zr/Y, the Nadi Kangri basaltic rocks plot in the "within-plate" setting field which, in conjunction with the tectono-sedimentary evolution of the basin, indicates that the Nadi Kangri basic lavas did indeed erupt in an intracontinental rift setting (rift basin).The close age of Mesozoic sedimentary basin in North Qaingtang remains unclear due to few fossils and lack of the correlatable dating data at the regional scale. However, during late evolution of Mesozoic sedimentary basin in North Qaingtang, oil shale, a new find by us in 2006, occurred widely in Shengli River region. An isochron is obtained giving an age of 101±24 Ma for the oil shale. The Re-Os age agrees with geological age derived from biostratigraphic data, indicating an end of marine sedimentation within the Middle-late early Cretaceous. Based on oil shale characteristics, this paper also studies the sedimentary characteristics and lithofacies and paleogeography during late evolution of Mesozoic sedimentary basin in North Qaingtang.In addition, this paper also studies the oil and gas resources in the Qiangtang basin and discusses the relation between the evolution of basin and source rocks, reservoir, and cap rocks.更多还原