THE DECOLLEMENT IN THE QIANGTANG BASIN, TIBET

Qiangtang Basin in northern part of Tibet is significant on geological research, and it is also a prospect area for petroleum and gas exploration. Qiangtang Basin mainly consists of Triassic\|Jurassic carbonate strata, extending E—W. The basement of the Qiangtang Basin composed of Lower\|Middle Proterozoic exposed in the central part, and is called Central Upright Zone.The decollement and thrust structure occurred both in Qiangtang Basin and the Central Upright Zone, which have resulted in important influence for petroleum and gas exploration.(1) Tectonic style:① The suprastructure of Qiangtang Basin is dominated by parallel folds (Ramsay’s classification Ib\|Ic) and brittle faults.② Most of the folds are open folds with interlimb angles 80～120°and lack of axial cleavage.③ The 3\|D shape of fold is cylindrical, without or little change on area and volume.④ The folds association is ejective folds (i.e. with the characteristics of the Jura\|type fold).⑤ The plastic bed flowing with the higher zone of the folds formed diapir structure, which is the important evidence indicating decol lement.

TECTONIC CHARACTERISTICS AND EVOLUTION OF THE QIANGTANG BASIN IN NORTHERN TIBET PLATEAU

The Qiangtang basin is located in the north of Qinghai—Tibet plateau and sandwiched by Nianqingtangula continental block and Kekexili\|Bayuankal continental block. Its southern boundary is the Bangongfu—Nujiang suture zone and its northern boundary is the Xijinwulan\|Jinshajiang suture zone.The basement of Qiangtang basin is composed f metamorphic rock of Proterozoic age, which can be divided into two parts. The competent lower part with isotope age of 2056～2310Ma experienced multi\|stage deformation and the soft upper part is dated 1111～1205Ma. Within the basin, it groups into Northern Qiangtang Depression, Central Rise and Southern Depressions and are complicated by a number of subdepressions and subuplifts.The strata of Middle Devonian\|Tertiary are overlain on the basement and composed of marine carbonate rocks, clastic rocks and terrestrial sandstone and conglomerate. Several sets of faults and folds have developed in the cover sequence and the deformation is very strong, characterized by orientation, zonation and equidistance in space and by diversity and disharmony in the profile. The major deformation occurred in Yanshan\|Himalayan period.

The Cretaceous tectonic event in the Qiangtang Basin and its implications for hydrocarbon accumulation

The tectonic event during Cretaceous and its relationship with hydrocarbon accumulation in the Qiangtang Basin is discussed based on zircon U-Pb dating and the study of deformation, thermochronology and hydrocarbon formation. LA-ICPMS zircon U-Pb dating indicates that the tectonic event took place during the Early-Late Cretaceous （125-75Ma）. The event not only established the framework and the styles of structural traps in the basin, but also led to the cessation of the first hydrocarbon formation and the destruction of previous oil pools. The light crude oil in the basin was formed during the second hydrocarbon formation stage in the Cenozoic, and ancient structural traps formed during the Cretaceous event are promising targets for oil and gas exploration.

Evaluation of the oil and gas preservation conditions, source rocks, and hydrocarbongenerating potential of the Qiangtang Basin: New evidence from the scientific drilling project

The Qiangtang Basin of the Tibetan Plateau,located in the eastern Tethys tectonic domain,is the largest new marine petroliferous region for exploration in China.The scientific drilling project consisting primarily of well QK-1 and its supporting shallow boreholes for geological surveys(also referred to as the Project)completed in recent years contributes to a series of new discoveries and insights into the oil and gas preservation conditions and source rock evaluation of the Qiangtang Basin.These findings differ from previous views that the Qiangtang Basin has poor oil and gas preservation conditions and lacks high-quality source rocks.As revealed by well QK-1 and its supporting shallow boreholes in the Project,the Qiangtang Basin hosts two sets of high-quality regional seals,namely an anhydrite layer in the Quemo Co Formation and the gypsum-bearing mudstones in the Xiali Formation.Moreover,the Qiangtang Basin has favorable oil and gas preservation conditions,as verified by the comprehensive study of the sealing capacity of seals,basin structure,tectonic uplift,magmatic activity,and groundwater motion.Furthermore,the shallow boreholes have also revealed that the Qiangtang Basin has high-quality hydrocarbon source rocks in the Upper Triassic Bagong Formation,which are thick and widely distributed according to the geological and geophysical data.In addition,the petroleum geological conditions,such as the type,abundance,and thermal evolution of organic matter,indicate that the Qiangtang Basin has great hydrocarbon-generating potential.

DEFINITING AND ITS GEOLOGIC MEANING OF SOUTH-NORTH TREND FAULTED STRUCTURE BELT IN QIANGTANG BASIN, NORTH PART OF TIBET

There were more expounding to north—west (west) trend fault and north\|east trend fault within Qiangtang Basin, North Part of Tibet, in the past literature. With increasing of geophysical exploration data, nearly east\|west trend structure began to be taken note to. Since the year of 1995, by a synthetic study to geophysical and geological data, that south\|north trend faulted structures are well developed. These structures should be paid much more attention to, because they have important theoretical meaning and practical significance.1 Spreading of south\|north faulted structure belt According to different geological and geophysical data, the six larger scale nearly south\|north faulted structure belt could be distinguished within the scope of east longitude 84°～96° and near Qiangtang Basin. The actual location of the six belts are nearly located in the west of the six meridian of east longitude 85°,87°,89°,91°,93°,95° or located near these meridian. The six south\|north faulted structure belts spread in the same interval with near 2° longitude interval. The more clear and much more significance of south\|north trend faulted structure belts are the two S—N trend faulted structure belts of east longitude 87° and 89°. There are S—N trend faulted structure belts in the west of east longitude 83°,81°, or near the longitudes. The structure belts spreading features,manifestation,geological function and its importance, and inter texture and structure are not exactly so same. The structure belts all different degree caused different region of geological structure or gravity field and magnetic field. There is different scale near S—N trend faulted structure belt between the belts.

BASIN-RANGE TRANSITION AND GENETIC TYPES OF SEQUENCE BOUNDARY OF THE QIANGTANG BASIN IN NORTHERN TIBET

The surface of sequence boundary is a negative record. Its recognition largely depends on the physics of the sediments below and above the boundaries, or on the different sedimentary structures are synthetic marks for the sedimentation and tectonic movements in the sedimentary basin. The Qiangtang Basin that is in 5000m above the sea level is located in Northern Tibet. The Lazhulung—Jinshajiang suture zone now bound it to the north and the Bangong—Nujiang suture zone to the south. Three second\|order tectonic units have been distinguished, i.e. North Qiangtang depression, Central rise and South Qiangtang depression from north to south.The Upper Permian Riejuichaka Formation is built up of mudstone and mud\|limestone, which is represented by sediments in seamarsh. The Lower Triassic Kuanglu Formation, which exhibits the structure unconformable contact with the overlying Upper Permian strata, is characterized by terrigenous clastic rocks in the lower area and is carbonate rocks in the upwarding area and the Middle Triassic Kuangnan Formation. The Upper Triassic Xiachaka Formation consisting of terrigenous clastic rocks, carbonates rocks and mixed sediments, is confined to the uplift zones. The lower Jurassic volcanic rocks are deposited in continental rift. The middle and Upper Jurassic Yangshiping Group are conformable contact and assembled by the gypsum\|bearing terrigenous clastic rock formations and carbonate rock formation. The Middle Cretaceous and the Paleocene strata is built up of the terrigenous clastic rock formations.

THE MESOZOIC QIANGTANG FORELAND BASIN IN QINGHAI—XIZANG PLATEAU,CHINA

Mesozoic Qiangtang foreland Basin is located between Jinshajiang suture belt and Bangong—Nujiang suture belt and an important petroliferous basin in the north of Qinghai—Xizang plateau. This foreland basin is E—W elongated basin with 800km in length and 200km to 300km in width. Both margins of the basin are large suture belt and linked to thrusting of large suture belt, so Mesozoic Qiangtang foreland basin belongs to composite foreland basins according to Jordan’s classification of the foreland basin(1988). The foreland basin is filled with 5000～8000m thick late Triassic to Cretaceous marine sediments. The spacial changes of the stratigraphy indicates that the basin texture looks like a symmetric body, and it can be subdivided into three tectonic geomorphic units from north to south ,such as northern basin, center uplift, and southern basin. The depth in the north varies from 5000 to 8000m,the depth in center uplift varies from zero to 1000m, the depth in the south varies from 5000 to 7000m, Which show that the occurrence of the Mesozoic filling stratigraphy are thicker in the north and the south of the basin, but thinner in the center uplift of the basin. There are two center of subsidence of the basin, both of them are located in south and north foredeep belt, lying in the front of suture belt. The basin is one of common foreland basins between suture belt and belongs to typical symmetric foreland basin.This kind of basin geometry allows large thickness of synsedimentary molasse sediments to be preserved and related to basement uplifts and thrusts in the cratonic edge of the mountain belt.From late Triassic to Cretaceous the foreland basin is filled by four tectonic sequences, including late Triassic tectonic sequence(TS\-1),early Jurassic tectonic sequence(TS\-2), middle Jurassic to early Cretaceous tectonic sequence(TS\-3) and middle to late Cretaceous tectonic sequence (TS\-4).A tectonic Sequence is a body of genetically related strata isolated by unconformity ,deposited in a basining stage responding to a thrusting episode. Late Triassic tectonic sequence(TS\-1) is bounded by Ta and Tb and composed of the Xiaochaka formation which is more than 2500m in depth, it is a coarsing\|upward tectonic sequence,the lower is fan delta sediments with debris conglomerate,the middle is carbonate ramp sediments,the upper is delta sediments; early Jurassic tectonic sequence(TS\-2) is bounded by Tb and Tc and composed of the Nadigangri formation which is more than 1000m in depth, it is a thinning\|upward tectonic sequence,the lower is fan delta sediments with debris conglomerate,the upper is subaquatic detrital sediments; middle Jurassic to early Cretaceous tectonic sequence(TS\-3) is bounded by Tc and Td and composed of the Quemocuo formation,Buqu formation, Xiali formation, Suowa formation and Xueshan formation, which is more than 3000m in depth; middle to late Cretaceous tectonic sequence (TS\-4) is bounded by Td and Tf and composed of the Abushan formation, it is a thinning—upward alluvial fan sediments with more than 1000m in depth.

Depositional features and sedimentary model of Buqu Stage in Mid-Jurassic in Qangtang Basin, Xizang (Tibet), China

The largest Mesozoic northward transgression in Qangtang Basin of Qinghai-Xizang (Tibet) Plateau occurred during the Buqu Stage, Middle Jurassic. Mainly filled with carbonate rocks, the whole basin is composed of transgression-regression sedimentary cycle. Field outcrops and indoor analysis revealed 8 types of sedimentary facies markers in this region. 4 types of sedimentary facies have been recognized: platform facies, platform marginal facies, foreslope facies and basin facies. Influenced by the northern Lazhuglung-Jinshajiang suture zone, central uplift region and southern Bangongco-Nujiang suture zone, these facies belts extended east-west. The sedimentary model was established based on observed depositional features. From their biological features and sedimentary characteristics, it is suggested that the paleoclimate was warm and humid at that time. The Buqu Formation is a promising target for oil and gas exploration in Shuanghu-Duoyong area in future.

PALEOGENE(?) DEPOSYSTEMS AND BASIN EVOLUTION IN THE EASTERN TIBETAN PLATEAU: NANGQIAN AND XIALAXIU BASINS

Paleogene sedimentary basins exposed across much of the central and eastern Tibetan Plateau may record the early history of plateau uplift related to the Indo\|Asian collision. We conducted sedimentological and stratigraphic investigations in the northeastern Qiangtang terrane, eastern Tibetan Plateau. Our results indicate development of several nonmarine basins during Paleogene(?) time, probably synchronous with northeast\|southwest contractional deformation. The Nangqian and Xialaxiu basins (96°～97°E, 32°～33°N) are composed of 500～ 20000m thick successions of primarily clastic sediment indicative of lacustrine and alluvial\|fan depositional processes. Paleocurrent measurements and sediment compositional data indicate local sediment source areas composed of Carboniferous\|Triassic carbonate and sandstone and minor Tertiary volcanic rocks. The large variability of provenance and facies types suggest that each basin evolved independently, as opposed to regional development of a single integrated basin which was partitioned by later deformation.

PROVENANCE OF LOWER TERTIARY REDBEDS IN HOH XIL BASIN AND UPLIFT OF NORTHERN TIBET PLATEAU

Eocene Fenghuoshan Group and lower Oligocene Yaxicuo Group are represented by mainly fluvial, lacustrine and fan\|deltaic redbeds cropping out in Hoh Xil basin, the largest redbed basin in northern Tibet plateau. Lithic sandstone, lithic quartzose sandstone, conglomerate, as well as siltstone, consist of the major rock composition of the redbeds. The petrography of sandstone and conglomerate reveals the relationship between regional tectonic uplift events and the provenance of lower Tertiary redbeds.The outcrop rock data show that the detritus were derived from sedimentary rocks, volcanic rocks, and metamorphic rocks. Phyllite and quartzite rock fragments are most common in the metamorphic rock fragments .The sedimentary rock fragments are composed of chert, limestone, siltstone, and mudstone fragments. But volcanic rock fragments are minor and occasionally occur. In Hantaishan area, the northwestern part of Hoh Xil basin, clastic composition of sandstones and conglomerates testify to mainly southward and northeastward provenances. The metamorphic rock fragments, which are more common than volcanic and sedimentary rock fragments, can be directly correlated with metamorphic rock of Triassic metasedimentary Bayankara Group around the basin. In Fenghuoshan area, the southwestern part of the basin, there are less metamorphic rock fragment composition and more limestone fragments than in Hantaishan area.The limestone fragments were obviously derived from Carboniferous—Permian or Jurassic limestone beds. These limestone strata can not be found in the Bayankara block mass at which Hoh Xil basin locates, thus it is deduced that the limestone detritus were derived from the south, that is, Qiangtang blockmass.

青藏高原可可西里盆地晚白垩世—早中新世地层年代学新进展及其对地层和古环境的指示意义

青藏高原构造隆升是新生代重大地质事件之一,是东亚构造—气候演化的重要边界条件之一,也是研究全球气候变化绕不开的一个重要因素。目前,关于青藏高原的隆升历史和机制等存在较大的争议,其中,一个最重要的原因是地层年代学问题,可靠的地层沉积年龄是后续研究的基础。青藏高原中北部可可西里盆地保存有晚白垩世至中新世较连续的沉积,是研究青藏高原构造演化不可多得的研究材料。笔者等基于可可西里盆地最新的晚始新世至中新世地层年龄研究结果,同时,结合其他已发表的、有绝对年龄控制点的地层年龄,认为风火山群和沱沱河组是两套独立的地层单元,即在可可西里盆地,地层划分从老到新可划分为:风火山群、沱沱河组、雅西错组和五道梁组。在可可西里盆地地层沉积年龄最新进展基础之上,综合盆地的古高度、古纬度、古温度、古地磁、沉积相变化、地层接触关系、全球温度、大气二氧化碳以及亚洲季风和高原隆升之间关系的模拟等证据,指出:①青藏高原面上类似于现在向东、东南逃逸的GPS速度运动场方向可能在始新世就已经形成,沱沱河盆地以东的物质向东南逃逸,以西没有这种趋势,沱沱河盆地可能是一个重要的边界;②类似于现在的东亚季风—内陆干旱化格局形成于晚渐新世—早中新世;③青藏高原中北部晚始新世以来发生了明显的两阶段隆升,>38.5~26(24)Ma的隆升主要由印度与欧亚板块的碰撞挤压缩短所致,16 Ma—现在的隆升由岩石圈地幔对流拆沉引起,26(24)~16 Ma是隆升相对平静期;④青藏高原中北部主夷平面可能发育于26(24)~16 Ma期间;⑤角度不整合接触不是构造事件发生的可靠判别标志;⑥石膏等盐类矿物的出现不是干旱化的可靠指标,但似乎表明在盐类矿物沉淀析出之前,区域应该存在至少一期湿润的气候,按此结果,可能暗示了至少在古新世我国中东部可能已经存在季风气候。

冻融影响下生态系统服务价值和生态风险的时空演变特征及关联性——以南羌塘盆地东区为例

气候变化会显著影响冻土、冰川等对温度变化敏感的生态系统,造成区域生态系统服务价值和生态风险发生变化。为揭示气候变化对青藏高原典型冻土区域的生态系统服务价值的影响和可能造成的生态风险,基于2000-2020年土地利用数据,运用生态系统服务价值(Ecosystem Service Value,ESV)评估、生态风险指数(Ecological Risk Index,ERI)评估、双变量空间自相关、地理探测器等模型和方法,分析了南羌塘盆地东区ESV、ERI的时空演变、空间关联和空间分异特征。结果显示:(1)2000-2020年,南羌塘盆地东区ESV呈增长趋势,累计增长5.76%(276.98亿元),草地和水域贡献了超98.70%的ESV。研究区ESV总体呈中部高、四周低的分布格局,以中等价值区为主(面积约占研究区总面积的70.37%)。(2)研究区ERI整体呈上升趋势,总体呈东南低、西北高的分布格局,以极低风险区为主(面积约占研究区总面积的60.68%)。(3)研究区ESV和ERI具有空间负相关性(Moran s I<0),主要LISA聚类为低价值—低风险(面积约占研究区总面积的34.26%)。(4)区域ESV和ERI的空间分异受自然因子和经济因子共同作用影响,其中归一化植被指数为二者空间分异的主导因子(q值分别为0.55和0.19)。研究结果表明需根据研究区ESV和ERI的时空分布和变化特征,采取因地制宜的生态保护措施,推动区域生态环境的可持续发展。

藏北羌塘盆地菊花山地区晚三叠世古岩溶不整合面的发现及其意义

菊花山地区出露的肖茶卡组—那底岗日组,其接触关系清楚,是北羌塘盆地代表性的剖面。在对该剖面中两者之间的砾岩进行详细的野外观测和分层取样分析的基础上,确定了肖茶卡组顶部与那底岗日组底部之间的砾岩为上、下两套不同成因、不同性质的砾岩组合。下套角砾岩以钙质、铁泥质胶结为特征,是肖茶卡组沉积期后海平面下降,出现广泛暴露、风化溶蚀形成的岩溶角砾岩;上套砾岩以凝灰质胶结为特征,是岩溶角砾未固结之前,发生构造活动产生的火山碎屑、熔岩流携带、搬运松散岩溶角砾再次沉积形成的那底岗日组底砾岩。从而确定了肖茶卡组与那底岗日组为岩溶不整合接触关系。该岩溶不整合面是羌塘盆地构造演化分析的重要证据,也是油气勘探的重要标志层。

羌塘盆地中部晚三叠世地层特征

羌塘盆地中部以土门格拉断裂带为界,其西南部出露上三叠统土门格拉群,其东北部出露上三叠统结扎群和鄂尔陇巴组,研究认为岩石基本特征大体一致,双壳类化石组合反映地质时代都为诺利期;岩石地球化学分析表明土门格拉群为古盐度较低、氧化、干热、弱碱性浅水环境,结扎群和鄂尔陇巴组为古盐度稍高、弱还原、温暖潮湿的较深水环境;旋回地层研究表明区内经历了一次完整的二级相对海平面变化旋回(由四个三级旋回组成),海水进退规程南北一致。区内古地理格局具有西高东低、南浅北深(水深)的特点,沉积自北东向南西超覆,层位逐渐抬高穿时;岩性、厚度、颜色和沉积相类型上的差异是统一沉积背景下沉积物相变、穿时的结果。前人以土门格拉断裂带为界,将土门格拉群和结扎群分置于两个地层大区(藏滇地层大区,华南地层大区)的认识值得商榷。

羌塘盆地侏罗纪末—早白垩世沉积特征与地层问题

羌塘盆地侏罗纪末至早白垩世地层包括扎窝茸组、雪山组、白龙冰河组和索瓦组上段,目前对它们的划分、对比和相互间关系的认识不一。笔者根据各组的含义和时代依据,指出各地层组为岩石地层单元,目前资料尚不足以作进一步年代学划分。通过全面统计各组的分布情况,分析各组的沉积特征,发现白龙冰河组为陆棚相,仅见于盆地北西部;索瓦组上段为海湾泻湖相,见于盆地中部;雪山组和扎窝茸组为河流—三角洲相,见于北东部。为此,认为各地层组是盆地内同期异相沉积,作为上下关系处理是不妥的,据此又提出了新的地层对比方案,认为盆内最高海相层位应该跨入了下白垩统,海水最终是向北西方向逐步退出盆地的。

羌塘盆地侏罗系—白垩系岩石地层格架厘定

羌塘盆地位于青藏高原腹地,侏罗系—白垩系分布广泛,但由于地处高寒地区,地层厘定工作一直以来较为薄弱,这限制了地质认识水平的提高。本文通过总结前人40年来的野外基础调查资料,结合近年来我们对羌塘盆地的最新研究成果,总结和评述了羌塘盆地侏罗纪—白垩纪的岩石地层格架,并简要探讨了各地质单元的沉积环境和沉积物源,并提出了羌塘盆地侏罗纪—白垩纪地层格架中存在的一些问题。

西藏羌塘盆地古油藏发现及其意义

古油藏带位于羌塘盆地中央隆起带南部羌南坳陷比隆错 -昂达尔错地区 ,东西长 10 0km ,南北宽 2 0km ,为一狭长湿状油苗群 ,露头上岩石的颜色呈暗褐色、褐灰色 ,为中侏罗统布曲组的白云岩。沉积环境以生物礁组合为主。经对比 ,古油藏油气主要来源于下侏罗统烃源岩。生烃过程模拟反映羌塘盆地有两次生排烃过程 ,第一次发生在 14 0～ 15 0Ma ,第二次发生在 2 0Ma至现今。

藏北羌塘盆地早侏罗世中侏罗世早期沉积构造特征

侏罗纪早期是研究羌塘盆地形成过程、判别盆地性质的重要时期。通过开展早侏罗世 中侏罗世早期的沉积相、古流向、沉积厚度统计等分析 ,恢复了该时期羌塘盆地的古地理面貌 ,提出了侏罗纪早期羌塘盆地并非前陆盆地 ,而是伸展构造背景下形成的裂陷型盆地。该时期盆地以中央隆起带为界 ,南部为陆缘开阔海盆地 ,形成滨岸 浅海陆棚相碎屑岩沉积 ;北部为陆缘近海湖盆 ,成盆初期 (托尔期 )发生强烈的裂陷活动 ,形成一套火山碎屑岩沉积体系 ,可识别出三个北西向分布的裂陷槽 ,巴柔期快速下沉 ,沉积一套厚达 2 0 0 0m以上的冲积扇 湖泊三角洲 湖盆相碎屑岩夹少量灰岩和石膏沉积 ,沉降中心位于湖盆南部 ,表现出明显的继承性 ,随后逐步向北东迁移 ,海水自中央隆起带中段频繁向湖盆浸漫。巴通期中央隆起带进一步下沉 ,南、北羌塘连成一个统一的拗陷盆地 ,从此沉积作用进入稳定发展阶段 ,形成稳定的碳酸盐岩台地沉积体系。

青藏高原中侏罗世—早白垩世羌塘复合型前陆盆地充填模式

根据沉积物碎屑组分、粗碎屑楔状体、边缘相、古流向和沉积、沉降中心等重建了盆地结构、古地理和古地貌 ,认为该盆地是在中侏罗世—早白垩世多岛洋体制下形成的一种复杂的、特殊类型的复合前陆盆地 ,它的形成和发展同金沙江缝合带与班公湖—怒江缝合带的碰撞和对冲有关 ,是盆地两侧板块边缘的大型逆冲作用的产物。在此基础上 ,根据中央隆起地貌景观交替性变化和盆地中“三砂二灰”的幕式沉积特点 ,将中侏罗世—早白垩世羌塘前陆盆地演化过程分为 5个阶段 ,其中巴通期和牛津—提唐期是羌塘盆地南北两侧构造活动相对平静期 ,而巴柔期、卡洛期、提唐—贝里阿斯期是羌塘盆地南北两侧构造活动强烈时期 ,强烈的逆冲推覆作用产生大量的构造负载 ,导致中央隆起强烈地挠曲隆升 ,造成了盆地中的幕式沉积 ,产生构造层序和层序 。

西藏羌塘盆地———中国油气资源战略选区的首选目标

研究表明羌塘盆地在油气资源的许多方面可与中东特提斯油气集聚区相类比,因而成为中国油气资源战略选区的首选目标之一。羌塘盆地的构造部位相当于中东特提斯构造域的北亚带和中亚带,羌塘盆地晚古生代是一个被动大陆边缘盆地,中生代是一个复合式前陆盆地,新生代叠置成为第三纪走滑断陷盆地;羌塘盆地内发育有极为良好的生储盖组合,生油岩主要为三叠系—侏罗系的泥岩、灰岩和油页岩,烃源层处于成熟 过成熟阶段,生油高峰期为晚侏罗世—古近纪,局部发现厚达70余米的油页岩,初步估计油气资源总量为50亿吨左右;盆地内发育有孔渗极佳的碎屑岩、白云岩以及生物礁(滩)岩等储集层,其次生孔隙的形成期与烃岩的生油高峰期一致;盆地内发育泥岩、泥灰岩和石膏等多套盖层,累计厚度可达3000多米,尤其是发育中东油田最好的石膏储层,累计厚度达177m,其中,仅中侏罗统布曲组最大单层厚度达93m;盆地内发育数十个形态好、保存完整的大中型背斜和穹隆圈闭构造,它们均定型于侏罗纪末期,为油气运移和圈闭创造了良好的条件;盆地内共发现油气显示190余处,其中包括5处液态油苗,数处见厚达数厘米的板状沥青,并发现面积约10km2的古油气藏一个;藏北高原的抬升属整体的均一抬升,剥蚀强度不大,岩浆活动广泛,但除盆地东南部外,规模小,对油?