Base level change and depositional filling response of Jurassic in the Qiangtang Basin of Tibet

The base level during the deposition of Jurassic in the Qiangtang Basin shows a complete cycle from rising to falling. The base level change is closely connected with tectonic evolution of the basin, especially connected with Bangonghu-Nujiang ocean evolution process in the formation and evolution of the basin. It is also affected by climate. The Jurassic strata correspond to a long-term base level cycle sequence. The sequence is in fact a non-complete symmetrical cycle, consisting of rising hemicycle and falling hemicycle. It can be divided into 6 intermediate-term base level cycle sequences, including 2 carbonate sequences, 3 mixture sedimentary sequences of carbonate and clastic rocks and one clastic sedimentary sequence. Depositional filling characteristics during base level change show that Bangonghu-Nujiang ocean spreads in Toarcian-Bajocian ages, and is at the height of spreading of Bangonghu-Nujiang ocean in Bathonian-Oxfordian ages. In that process, sea area became smaller because of the dry climate. Eventually, marine depositional filling is ended with the subduction and collision of Bangonghu-Nujiang ocean.

     

西藏羌塘盆地的深部构造与含油气远景评价

羌塘盆地是目前国内石油勘探的热点地区之一,作者综合研究了羌塘盆地的地球物理、石油地质调查资料及INDEPTH-3深部调查结果,得出:1, 盆地内烃源层、储集层、盖层及其组合条件很好, 局部构造发育,有利于形成和保存油气藏,断裂不会成为致命问题,提出了今后工作的主要目的层为上三叠世-中侏罗系组成的中构造层;2,对盆地二级构造作了新的划分,否定羌中隆起,提出盆地表层的主要构造方向为北西-南东向,成“三凹三隆”及“一深凹”的地壳结构特征,其中主沉降带内部及其两侧是最有利的找油气远景地带;3,本区壳幔之间的相互作用较强,盆地北部火山及热活动多,对油气远景评价有较大影响,而盆地南部沉积厚度大,受深层热影响相对较小,是找油气的更有利的地段。4,强调查明深部地层物性、油气赋存状况,烃类物质的来源和上下构造符合情况是当务之急。重点是加强点上的调查和评价研究;5,提出不能轻视伦坡拉陆相第三系盆地找油前景,它可能汇聚有两侧海相地层的油气。     

The deep structures and oil-gas prospect evaluation in the Qiangtang Basin, Tibet

The Qiantang Basin is now one of the topics of general interest in petroleum exploration in China. This paper reports a comprehensive study of geophysical and geological survey data recently obtained in this area and, combined with INDEPTH-3 deep survey results, comes to the following conclusions： 1） The hydrocarbon source formations, reservoirs, and overlying strata and their association within the basin are quite good, local structures are developed, and, therefore, the region is favorable for forming and preserving oil and gas accumulations. Faults are not a fatal problem. The future main target strata are the middle-deep structural strata composed of Upper-Triassic and middle Jurassic rocks; 2） A new classification has been made for second-order tectonic sequences inside the basin to disavow the central Qingtang uplift. It is noted that the main structures at the surface are orientated NW-SE and the crustal structure can be described as three depressions, three risees, and one deep depression, of which the prospective zone with the most potential is the inner main subsided belt and its two sides; 3） Comparatively intensive interaction between the crust and mantle and volcanic and thermal activities in the northern basin play a very important role in petroleum evaluation. The southern deeper sedimentation and less thermal activity make this area a more perfect zone for oil exploration; 4） Currently, the most important objective is determining the physical properties of the deep strata, the status of oil and gas accumulations, the source of the hydrocarbons, and the relationship between the upper and lower structures; and 5） The Lunpola Tertiary basin may be favorable for oil accumulations because petroleum may migrate from marine strata on two sides.     

南盘江盆地二叠系高频沉积旋回的测井响应及海平面变化趋势

利用Fischer图解旋回分析技术识别碳酸盐岩沉积层序、反演长周期海平面变化趋势仍然以露头剖面为对象,人工识别其中的高频沉积旋回.在地下深部,由于旋回识别技术手段的欠缺还未见应用.本文以自然伽玛测井曲线为研究对象,将旋回分析技术首次引入深部地层,利用一阶差分法,在南盘江盆地二叠系测井曲线中共识别出431个高频沉积旋回,...     

Jurassic depositional records and sandstone provenances in Hefei Basin, central China: Implication for Dabie orogenesis

Abstract   Detrital composition and major element geochemistry of Jurassic sandstones in the south Hefei Basin, central China, show their provenance to be the Dabie Mountains, whose tectonic attributes are closely related to continent–island arc complexes. It was found that a provenance change, from recycled orogen signatures and mixed orogenic sandstones to arc orogen, occurs from the lower Middle Jurassic to the Upper Jurassic (the Zhougongshan Formation). Dissected magmatic arc sources were gradually exposed in the Dabie Mountains due to intensive exhumation during the Late Jurassic, particularly after the Fenghuangtai depositional phase. Furthermore, it can be infered that the magmatic arc was initially present in both the Early Paleozoic and the Triassic, according to isotopic dating studies in previously published reports. δ¹³C–δ¹⁸O tracing between existing marbles of different strata in the Dabie block and marble gravels of the Fenghuangtai Formation in the Hefei Basin indicate that partial lithostratigraphic units for the Jurassic provenances have entirely disappeared from the Dabie block; therefore, it is impossible to reconstruct integral orogenic processes from studies on the remaining Dabie block alone. These findings, together with basin-fill sequences, also suggest that the Hefei Basin was mainly subjected to compressive mechanical regimes rather than extensional regimes in the Jurassic, which resulted in reverse-grading clastic depositional sequences, and is probably related to the northward intracontinental deep subduction of the Yangtze Plate. Regional exhumation properties and a tectonic model of the Late Mesozoic Dabie orogenesis are discussed in this paper.     

藏北羌塘盆地中部莫霍面形态及其动力学成因

本文通过对羌塘盆地内49个临时宽频带地震观测台阵数据的接收函数分析,采用H-κ叠加和CCP 叠加成像两种方法,获得到了藏北羌塘中部莫霍面深度以及泊松比分布.作为羌塘盆地构造单元的南缘边界,班公湖-怒江缝合带下的Moho存在一个南深北浅、断距约10 km的台阶;把羌塘盆地分为两部分的羌塘中央隆起带下存在一个3 km的Moho台阶;北羌塘盆地下的Moho 平均深度约为60 km,而南羌塘约为63 km.羌塘高原下的近水平Moho结构可能是受到印度大陆北向俯冲作用下的青藏高原隆升过程中Moho再均衡所致或者与其构造演化有关.泊松比值具有明显的构造分区特征,如南羌塘下的泊松比平均为0.31,双湖缝合带下的泊松比接近正常值,为0.265,而北羌塘的泊松比平均为0.285.     

太湖流域土地利用变化的水文响应模拟

以城市化快速发展的太湖流域为研究对象,采用1985、1995和2000年TM/ETM土地利用解译资料,应用区域尺度单元格网分布式水文模型,进行长序列水文模拟,定量评估太湖流域土地利用变化及其水文响应特征,为流域用地规划、水资源管理以及灾害防治提供决策参数.研究显示,自1985年到2000年,太湖流域城镇面积扩展了40.38%,增加量占太湖流域总面积的3.88%.在1980-2000年的雨情下,全流域土地利用变化导致产流量平均增加4.11%,约为7.56×108 m3,最高值为11.76%,约为10.0×108 m3.受土地利用变化空间差异影响,产流量增加具有较大区域差异,城镇快速扩展的苏锡常地区和浦东浦西地区,土地利用变化导致产流量平均增加为10.07%和7.03%,最高增量达20%-30%.     

Disintegration and age of basement metamorphic rocks in Qiangtang,Tibet, China

Comprehensive studies on lithologic association, provenance of metacongelometre, characteristics of metamorphism and deformation, and²⁰⁷Pb/²⁰⁶Pb-dating of single-zircon for metamorphic rocks distributed in Chabu-Chasang areas in Qiangtang block indicate that most of them belong to Middle Proterozoic metamorphic basement except silicilith member ascribed to Triassic. Disintegrated basement strata are called Gemuri group and Guoganjianianri group; they are different in histories of metamorphism and deformation. The single-zircon²⁰⁷Pb/²⁰⁶Pb-ages provide excellent evidence for the existence of an Archean continent nucleus around study areas. Some thermal event ages such as 929–1016 and 509–548 Ma are recorded in Gemuri group.     

海平面对大气压变化的空间响应

海平面对大气压变化的响应在理想情况下接近均衡态海洋响应.在这个假设下,任何海域的大气压变化都会瞬时传播到整个海洋上.通过比较大气压和海平面变化的标准差,可以发现,在空间尺度上,大气压变化主要是长波信号,而海平面变化除了长波信号外,还存在明显的短波长信号.由大气压变化驱动的海平面变化应与大气压变化在空间尺度上具有一致性.因此,可以对海平面数据进行空间高斯低通滤波,来得到与大气压变化更相近的空间标准差分布.通过阶振幅谱分析,表明海平面对大气压变化响应的空间尺度为800 km.     

Disintegration and age of basement metamorphic rocks in Qiangtang,Tibet, China

Comprehensive studies on lithologic association, provenance of metacongelometre, characteristics of metamorphism and deformation, and²⁰⁷Pb/²⁰⁶Pb-dating of single-zircon for metamorphic rocks distributed in Chabu-Chasang areas in Qiangtang block indicate that most of them belong to Middle Proterozoic metamorphic basement except silicilith member ascribed to Triassic. Disintegrated basement strata are called Gemuri group and Guoganjianianri group; they are different in histories of metamorphism and deformation. The single-zircon²⁰⁷Pb/²⁰⁶Pb-ages provide excellent evidence for the existence of an Archean continent nucleus around study areas. Some thermal event ages such as 929–1016 and 509–548 Ma are recorded in Gemuri group.

     

羌塘盆地中部地区地壳S波速度结构及构造意义

羌塘盆地是我国最大的海相盆地.本文根据在羌塘盆地内布设的27个宽频带地震观测台站记录的远震波形数据,利用非线性复谱比反演算法得到各台站下方100 km深度范围内S波速度结构.结果表明,羌塘地区Moho深度较为平缓,平均深度为61 km;北羌塘地壳内低速层广泛分布;北羌塘具有两个较大的沉积盆地,龙尾错和白滩湖坳陷,沉积厚度分别有10 km和15 km.尽管北羌塘下地壳受到强烈的新生代火山岩作用改造,但是这种深部岩浆热作用会加速烃源岩中有机质的热演化历程,北羌塘两个盆地具有很好的油气前景.与北羌塘低速层分布相比,南羌塘下低速层更深,可能与班公怒江洋于中生代的俯冲消减及拉萨地体北向俯冲有关.

     

羌北地块中-晚侏罗世雁石坪群古地磁新结果

本文报道青藏高原羌北地区中-晚侏罗世雁石坪群古地磁新结果.对采自青海省格尔木市唐古拉山乡雁石坪剖面(33.6°N, 92.1°E)11个灰岩采点(118块)和10个碎屑岩采点(99块)定向样品系统古地磁学研究表明,大部分样品的退磁曲线具有双分量特征.低温分量方向在地理坐标系下较为集中,应该为地层褶皱之后的黏滞剩磁.高温特征剩磁分量方向可分为两类:(1)索瓦组(J₃s)和布曲组(J₂b)灰岩,以磁铁矿为主要载磁矿物,高温特征剩磁分量(D_s=355.7°,I_s=42.1°,k=58.2,α₉₅=6°)可通过99%置信度的褶皱检验.(2)雪山组(J₂x)和雀莫错组(J₂q)碎屑岩,以赤铁矿、磁铁矿为主要载磁矿物,高温特征剩磁分量(D_s=3.3°,I_s=28.9°,k=30.7,α₉₅=8.9°)可通过95%置信度的倒转检验和99%置信度的褶皱检验.两组分量都应该是岩石形成时的原生剩磁信息.碎屑岩组的磁倾角比灰岩组偏低13°左右,其剩磁方向很可能存在着与压实作用相关的剩磁倾角变浅的状况.本文取灰岩组平均磁化方向作为雁石坪群的原生剩磁分量,获得羌北地区雁石坪群古磁极位置:80.0°N,295.2°E(dp/dm=7.4/4.5).古地磁结果表明,羌北-昌都地区晚石炭-晚二叠世期间位于南纬中低纬度地区,早三叠世以后开始大规模北向漂移,至中-晚侏罗世已到达24.3°N.其快速北向运动主要发生在早三叠至早侏罗世期间(3500 km左右),与现今位置相比中晚侏罗世之后的北向迁移总量为900 km左右.     

四川盆地侏罗系致密砂岩弹性特征及岩石物理建模

近年来围绕四川盆地侏罗系陆相致密砂岩已取得了勘探突破,其中川中—川西过渡带具备形成大气田的地质条件,但对该套致密砂岩弹性性质变化规律的研究还较少,致使利用地震方法进行"甜点"储层预测的精度不高.本文利用四川盆地侏罗系沙溪庙组32块样品开展了系统的声学测量,在此基础上,分析了样品弹性性质的变化规律.结合X射线衍射矿物组分分析、扫描电镜、铸体薄片和岩石薄片特征确定了不同成岩作用对岩石储集性能的影响.研究结果表明,研究区致密砂岩储层表现为孔隙型储层,受差异性成岩作用影响,黏土含量、钙质含量和硅质含量的差异以及它们分布特征之间的差异对岩石弹性性质造成了很大的影响.在研究区对岩石物性及弹性性质有明显影响的成岩作用包括早期的钙质胶结作用、压实作用和溶蚀作用,因此针对不同时期的成岩作用对岩石弹性及物性的影响,利用接触-胶结模型、微分等效模量模型和临界孔隙度校正的Hashin-Shtrikman上限模型建立了研究区致密砂岩的岩石物理模型.     

四川盆地侏罗系致密砂岩弹性特征及岩石物理建模

近年来围绕四川盆地侏罗系陆相致密砂岩已取得了勘探突破,其中川中—川西过渡带具备形成大气田的地质条件,但对该套致密砂岩弹性性质变化规律的研究还较少,致使利用地震方法进行"甜点"储层预测的精度不高.本文利用四川盆地侏罗系沙溪庙组32块样品开展了系统的声学测量,在此基础上,分析了样品弹性性质的变化规律.结合X射线衍射矿物组分分析、扫描电镜、铸体薄片和岩石薄片特征确定了不同成岩作用对岩石储集性能的影响.研究结果表明,研究区致密砂岩储层表现为孔隙型储层,受差异性成岩作用影响,黏土含量、钙质含量和硅质含量的差异以及它们分布特征之间的差异对岩石弹性性质造成了很大的影响.在研究区对岩石物性及弹性性质有明显影响的成岩作用包括早期的钙质胶结作用、压实作用和溶蚀作用,因此针对不同时期的成岩作用对岩石弹性及物性的影响,利用接触-胶结模型、微分等效模量模型和临界孔隙度校正的Hashin-Shtrikman上限模型建立了研究区致密砂岩的岩石物理模型.     

Structural framework and its evolution in Chasang area of Qiangtang Basin in northern Tibetan

Through comprehensive research on the various geophysical and geological data acquired recently, we consider that the Chasang area in the western uplift of Qiangtang is a huge south-dipping block which is overlapped by several east-west trending blocks rather than a simple and palaeo-doming existing for a long time. The structural and geophysical features of the area, which only alone limited between Shuanghu and Rongma districts, are of no regional significance. Their development is closely related with the approximately south-north trending transform faults developed during the Mesozoic era on the east and west sides of the area and their later continuous movement. The compressing, overlapping and uplifting of the Chasang area began at the stage of reversing of the Qiangtang Basin during the Lower Cretaceous, which is in direct relation with Bangonghu-Dingqing limited ocean’s closure and the convergence of the neighboring blocks. The compression and overlapping of the area have further developed and reformed since the Eocene because of the continuing collision and pushing of the Indian Plate to the north.     

On the Jurassic volcanism and on volcanoes in the Shadoron Basin,eastern Transbaikalia

We present new data on the stratigraphy, volcanism, and K–Ar ages of Jurassic features in the Shadoron Basin. Two phases of volcanic eruptions have been identified, a Middle Jurassic and a Late Jurassic, which are separated by a pre-Oxfordian phase of tectogenesis. We show that the Jurassic volcanism in the area of study occurred through fissure vents and mostly evolved in subaqueous conditions.     

羌塘盆地中部中上地壳三维密度和磁性结构及构造意义

羌塘盆地位于青藏高原中部,经历了多期复杂构造运动,是研究青藏高原演化的良好窗口.本文利用1 ∶ 20万重力和磁力数据,基于1 ∶ 50万地表地质信息约束,反演获得了羌塘盆地中部区域中上地壳的三维密度和磁性结构,揭示了南、北羌塘坳陷、班公湖—怒江缝合带、可可西里—金沙江缝合带和龙木错—双湖缝合带的密度和磁性特征.根据反演结果,认为：主要构造单元与密度和磁化率异常有良好的对应关系,下地壳和上地幔是羌塘盆地大范围低值重力异常的重要来源;可可西里—金沙江缝合带向下切割较深,引起磁异常的岩浆岩大量存在于中地壳;双湖至唐古拉山一线不存在贯穿羌塘盆地的“中央隆起带”;北羌塘广泛分布的火山岩主要存在于上地壳,来源可能是下地壳和上地幔的低密度岩浆岩体;印度板块俯冲的前缘可能影响到了羌塘盆地下方.

     

羌塘中央隆起带深部结构特征研究及其意义

羌塘含油气盆地是我国境内最大的中新生代海相沉积盆地.羌塘地体内的中央隆起将盆地分为南北两个盆地.中央隆起带构造属性认识存在两种截然不同的分歧,一是伸展环境下形成,整个羌塘盆地有着同一的基底.而另一认识其是一古特提斯缝合带,其两侧盆地具有不同的演化机制.调查羌塘中央隆起的深部结构特征及其与南北两侧的盆地间的构造关系是认识羌塘盆地基底性质及其油气远景之关键科学问题.尽管羌塘地体在青藏高原形成演化过程中遭到了强烈改造,但在收集并分析已有地球物理资料基础上认为其深部结构仍有可能被完整保存.因此,利用密集宽频带流动台网观测,获取其深部结构,进而研究其与两侧盆地关系,是当前羌塘含油气盆地研究之重要突破口,同时该项研究符合我国当前国家油气资源战略评估政策.     

Sedimentological and petrochemical studies of Jurassic clastic rocks,Habo Dome Basin,Kachchh Mainland,Northwest India: Implications for depositional environment,provenance, and tectonic setting

Mesozoic rocks are extensively and excellently preserved in the western Indian shield in several basins. The Kachchh Mainland Basin (KMB), comprising six small sub‐basins, is the main repository of these sediments. Habo Dome Basin, situated in the easternmost part of KMB and largest among the six basins, hosts clastics of the Chari Formation of Jurassic age. The fluctuating transgressive–regressive facies cycle, developed during the Callovian and Late Early Oxfordian in the Habo Dome Basin, was mainly controlled by local tectonics and not by global eustatic fluctuations. Near magmatic relationships are displayed by various elements of the clastic rocks of Habo Dome Basin. Two litho‐chemical groups have been identified in Habo Dome Basin, which are cyclically repeated over entire lithostratigraphic sequence, indicating alternate pulses of sediment inputs from two different sources under palpitating tectonic conditions. Provenance indicator elements and their ratios coupled with source modeling indicate predominantly felsic source with basic and alkalic components. Integrated analysis of petrograhic and geochemical characteristics suggests two source terranes for these rocks: a granitoid source with significant basic volcanics (Banded Gneissic Complex) and a granite–gneissic source with minor alkaline volcanics (Nagarparkar Massif) lying to northeast and NNW respectively. The petrochemistry of Habo Dome clastics suggests their deposition in a fault controlled sink which was influenced by sea level changes. Drifting of the Indian plate resulted in the opening of series of rifted basins in the Kachchh Mainland during Late Triassic/Early Jurassic, which were closed later during collision of Indian plate with Eurasia at early Eocene. The Habo Dome Basin which opened up as a half graben in response to the initial stress regime, remained tectonically unstable until the cessation of pre and post collisional stress regimes.     

羌塘盆地冻土层结构核磁共振信号响应研究与实践

为了了解羌塘盆地冻土层的结构,利用核磁共振测深(MRS)技术对羌塘盆地的两个研究区进行了野外勘探。结合室内实验及野外实际资料,冻土层基本无法引起仪器核磁共振响应是划分冻土层和探测水合物的重要证据。在钻井附近进行的MRS方法对试验点进行测量并采集到了NMR信号,分析认为是天然气水合物处在亚稳定状态,分解产生水或者液态烃,形成水-水合物-气三相共存的情况,引起了NMR反应。实践表明可以将MRS方法运用于探测陆域冻土带分布以及冻土带,该方法对于冻土层的结构划分具有十分重要的科学意义和应用价值。