藏北羌塘中央隆起带果干加年山晚三叠世珊瑚化石发现及其地质意义   总被引：3，自引：0，他引：3  

纪占胜  姚建新  武桂春 《地质学报》2010,84(8):1095-1104

藏北羌塘盆地中央隆起带果干加年山北坡首次发现了较丰富的珊瑚化石。珊瑚主要属种有8属10种及未定种:Distichophyllia norica(Frech),Gablonzeria irregularis DengZhang,Margarophyllia stylophylloides(Vinassa deRegny),M.zogangensisDengZhang,Margarophyllia? sp.,Montlivaltia tenuise DengZhang,Pamiroserisrectilamellosa(Winkler),Paradistichophyllum verticalis DengZhang,Paradistichophyllum?sp.,StylophyllopsismosjvariFrech等。产出这些珊瑚化石的灰岩地层原来被认为是混杂在晚三叠世望湖岭组碎屑岩中的古生代灰岩断块,而新发现的珊瑚指示地层时代并非是古生代,而是晚三叠世。这说明果干加年山地区不存在上三叠统碎屑岩和古生界灰岩混杂的现象。果干加年山地区的晚三叠世沉积不仅包含有望湖岭组的碎屑岩,还包含有夹在碎屑岩之间的浅海相灰岩。本次研究和前人的资料表明羌塘中央隆起带在晚三叠世并非是隆起剥蚀区,而是海洋沉积区。因而,以往建立在中央隆起带为隆起剥蚀区认识基础上的羌塘盆地晚三叠世沉积古地理环境和"一隆两坳"的大地构造格局认识需要重新考虑。  相似文献   

Episodic Cenozoic tectonism and the development of the NW European ‘passive’ continental margin     

D. Praeg  M.S. Stoker  P.M. Shannon  S. Ceramicola  B. Hjelstuen  J.S. Laberg  A. Mathiesen 《Marine and Petroleum Geology》2005,22(9-10):1007

The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations <1° over distances of 100s of Kilometres) and sagging (strongly differential subsidence, rotations up to 4° over distances <100 km). Each epeirogenic episode involved relatively rapid (<10 Ma) km-scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity-bounded stratigraphic units. Early Cenozoic tilting (late Paleocene to early Eocene, c. 60–50 Ma) caused the basinward progradation of shelf-slope wedges from elongate uplifts along the inner continental margin and from offshore highs. Mid-Cenozoic sagging (late Eocene to early Oligocene, c. 35–25 Ma) ended wedge progradation and caused the onset of contourite deposition in deep-water basins. Late Cenozoic tilting (early Pliocene to present, <4±0.5 Ma) again caused the basinward progradation of shelf-slope wedges, from uplifts along the inner margin (including broad dome-like features) and from offshore highs. The early, mid- and late Cenozoic epeirogenic episodes coincided with Atlantic plate reorganisations, but the observed km-scale tectonic movements are too large to be accounted for as flexural deflections due to intra-plate stress variations. Mantle–lithosphere interactions are implied, but the succession of epeirogenic episodes, of differing form, are difficult to reconcile with the various syn-to post-rift mechanisms of permanent and/or transient movements proposed in the hypothetical context of a plume beneath Iceland. The epeirogenic movements can be explained as dynamic topographic responses to changing forms of small-scale convective flow in the upper mantle: tilting as coeval upwelling and downwelling above an edge-driven convection cell, sagging as a loss of dynamic support above a former upwelling. The inferred Cenozoic succession of epeirogenic tilting, sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening, a process that may also be the underlying cause of plate reorganisations. The postulated episodes of flow reorganisation in the NE Atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin, as well as on other Atlantic-type ‘passive’ margins.  相似文献   

Wave pressures and uplift forces on and scour around submarine pipeline in clayey soil     

A. Vijaya kumar  S. Neelamani  S. Narasimha Rao 《Ocean Engineering》2003,30(2):304-295

Experimental investigations are carried out on wave-induced pressures and uplift forces on a submarine pipeline (exposed, half buried and fully buried) in clayey soil of different consistency index both in regular and random waves. A study on scour under the pipeline resting on the clay bed is also carried out. It is found that the uplift force can be reduced by about 70%, if the pipeline is just buried in clay soil. The equilibrium scour depth below the pipeline is estimated as 42% of the pipe diameter for consistency index of 0.17 and is 34% of the pipe diameter for consistency index of 0.23. The results of the present investigations are compared with the results on sandy soil by Cheng and Liu (Appl. Ocean Res., 8(1986) 22) to acknowledge the benefit of cohesive soil in reducing the high pore pressure on buried pipeline compared to cohesionless soil.  相似文献   

喀喇昆仑断裂带走滑过程中伴随的快速隆升作用:热年代学证据   总被引：4，自引：0，他引：4  

李海兵  陈松永  许志琴  司家亮  邱祝礼 《岩石学报》2008,24(7)

喀喇昆仑断裂带是青藏高原西部的一条大型右旋走滑断裂带,它是喜马拉雅山脉西段北侧重要的地质边界.本文在岩石学、变形构造的研究基础上,对喀喇昆仑断裂带东南段阿伊拉日居山-噶尔盆地地区的喀喇昆仑韧性剪切带中变质岩石的同构造矿物进行了40Ar/39Ar热年代学研究.显微构造研究表明,剪切带中的矿物记录了从高温(>600℃)到低温(<250℃)条件下的连续变形,表现为近水平的右旋剪切运动转变成斜向的右旋正滑,使绿片岩相的变形作用叠加在中-高温变形之上.暗示出走滑过程中存在隆升作用,热年代学结果显示其连续剪切变形作用从早中新世以来至少持续到4Ma,并且出现三个快速冷却阶段:第一个快速冷却阶段为从25～22Ma到21～18Ma期间,可能代表的是浅部高温剪切过程中变形局部停止或减慢的过程;第二个快速冷却时期为从15Ma到12～10Ma,是喀喇昆仑断裂带走滑过程中,阿伊拉日居山的快速隆升、噶尔盆地开始形成以及主要河流深切过程阶段;9Ma以来是第三个快速冷却过程,使阿伊拉日居山脉进一步快速隆升、噶尔盆地定形过程.根据不同年代地表地貌特征的右旋错位距离以及不同层次变形特征,估算出喀喇昆仑断裂带长期滑移速率为8～10mm/a,伴随的隆升速率为1mm/a.从显微构造和热年代学证据表明,晚第四纪以来该断裂经历了强烈的右旋走滑运动的同时伴随强烈的隆升作用.  相似文献   

青藏高原西北缘晚新生代沉积岩古流向的磁化率各向异性确定及其构造意义   总被引：9，自引：4，他引：5  

裴军令  孙知明  李海兵  司家亮  潘家伟  刘静  刘雪刚  赵越 《岩石学报》2008,24(7)

古流向的确定是重建沉积物来源及沉积过程的有效方法,而磁化率各向异性作为古流向恢复的可靠信息载体在室内沉积实验和具体工作中已得到认可.本文对青藏高原西北缘柯克亚剖面晚新生代地层鸟恰群、阿图什组和西域组80块样品开展了磁组构研究,磁面理与磁线理图、磁化率各向异性度与磁化率椭球体形状因子图直观地说明研究对象均具有磁面理较磁线理发育的特点,代表了原生沉积组构特征.柯克亚剖面乌恰群、阿图什组和西域组的磁化率各向异性测量则恢复了三个时期的古流向.古流向在不同时期的变迁显示了重要的青藏高原西北缘的隆升信息.乌恰群与阿图什组、阿图什组与西域组之间的古流向的改变反映出西昆仑山北缘具有西早东晚的构造隆升过程.  相似文献   

New Riphean microbiotas of the Billyakh Group,the north Anabar region (Fomich River basin): To Riphean biostratigraphy of the Siberian platform     

V. N. Sergeev  N. G. Vorob’eva  P. Yu. Petrov 《Stratigraphy and Geological Correlation》2007,15(1):1-11

Excellently preserved organic-walled and silicified microfossils are first found in the Lower Riphean Ust-Il’ya and Kotuikan formations of the Billyakh Group in the northern slope of the Anabar Uplift (the Fomich River basin). Similar assemblages were previously known only from sections located southward in the Kotuikan River basin, and taxonomic composition of organic-walled microbiotas from the Ust-Il’ya and Kotuikan formations became a corner stone in competitive microphytological models that are based on different approaches. In their composition and general appearance, microbiotas from the Kotuikan and Ust-Il’ya formations in the Fomich River basin are similar to microbiotas reported from the Kotuikan River basin, although northern sections of the above formations characterize deeper sedimentation settings than in localities known before. The Ust-Il’ya and Kotuikan assemblages of organic-walled microfossils include sphaeromorphic Chuaria circularis and Leiosphaeridia, two-layer vesicles the genus Simia, filamentous Plicatidium and Taenitrichoides, and some others. The silicified microbiota from the lower Kotuikan Subformation is largely composed of akinetes of Anabaena-like cyanobacteria Archaeoellipsoides, spherical Myxococcoides grandis, and short trichomes Filiconstrictosus and Orculiphycus representing initial germination stages of Anabaena-like cyanobacterial spores. Acanthomorphic acritarchs known from lithology-similar Lower and Middle Riphean (Mesoproterozoic) formations of Australia and China have not been observed in the Ust-Il’ya and Kotuikan microbiotas, which are probably of older age. The found microbiotas outline substantially wider distribution area of organic-walled and silicified microfossils, supplement microphytological characteristics of Riphean sediments in the Anabar Uplift, provide information on taxonomic composition of microbiotas from a wider spectrum of facies, and specify relationships between Early and Middle Riphean assemblages of microorganisms from different continents.  相似文献   

Paleomagnetic constraints on the paleogeography and oroclinal bending of the Devonian volcanic arc in Kazakhstan   总被引：1，自引：0，他引：1  

Alexandra Abrajevitch  Rob Van der Voo  Natalia M. Levashova  Mikhail L. Bazhenov   《Tectonophysics》2007,441(1-4):67-84

Numerical modelling, incorporating coupling between surface processes and induced flow in the lower continental crust, is used to address the Quaternary evolution of the Gulf of Corinth region in central Greece. The post-Early Pleistocene marine depocentre beneath this Gulf overlies the northern margin of an older (Early Pleistocene and earlier) lacustrine basin, the Proto Gulf of Corinth Basin or PGCB. In the late Early Pleistocene, relief in this region was minimal but, subsequently, dramatic relief has developed, involving the creation of  900 m of bathymetry within the Gulf and the uplift by many hundreds of metres of the part of the PGCB, south of the modern Gulf, which forms the Gulf's main sediment supply. It is assumed that, as a result of climate change around 0.9 Ma, erosion of this sediment source region and re-deposition of this material within the Gulf began, both processes occurring at spatial average rates of  0.2 mm a^− 1. Modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is  4 × 10¹⁹ Pa s, indicating a Moho temperature of  560 °C. It predicts that the  10 mm a^− 1 of extension across this  70 km wide model region, at an extensional strain rate of  0.15 Ma^− 1, is partitioned with  3 mm a^− 1 across the sediment source,  2 mm a^− 1 across the depocentre, and  5 mm a^− 1 across the ‘hinge zone’ in between, the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the Gulf. This modelling confirms the view, suggested previously, that coupling between this depocentre and sediment source by lower-crustal flow can explain the dramatic development in local relief since the late Early Pleistocene. The effective viscosity of the lower crust in this region is not particularly low; the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity. In detail, the effective viscosity of the lower crust is expected to decrease northward across this model region, due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere; in the south the two are separated by the subducting Hellenic slab. The isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why, since  0.9 Ma, the modern Gulf has developed asymmetrically over the northern part of the PGCB, leaving the rest of the PGCB to act as its sediment source.  相似文献   

Holocene crustal movements and sea-level changes in Great Britain     

Ian Shennan 《第四纪科学杂志》1989,4(1):77-89

Crustal downwarping has occurred throughout southern and south-eastern England and most of Wales for at least the last 4000 years, but the type of movement in some areas of southern and eastern England is more complicated than simple linear subsidence. Highest estimated rates of subsidence (since 4000 BP) are for the Thames Estuary and Norfolk (up to 2 mm/yr). Glacio-isostatic processes have resulted in uplift in northern England and mainland Scotland. The rates of uplift have decreased throughout the Holocene; estimates for the present range from zero in south Lancashire and the Tees Estuary to over 1 mm/yr (though less than 2 mm/yr) in central Scotland. Over 400 sea-level index points, from the databank of 904 cases collected for IGCP Project 200, are grouped into 15 main areas and used to investigate the nature of crustal movements in Great Britain since 8800 BP, but there are significant deficiencies in available data which constrain the analysis.  相似文献   

黔中隆起的形成时间及形成机制探讨   总被引：6，自引：0，他引：6  

牛新生  冯常茂  刘进 《海相油气地质》2007,12(2):46-50

黔中隆起经历了水下和陆上两个发育阶段;都匀运动是这一发育转变的成因。问题的焦点是水下隆起的开始时间和都匀运动发生的具体时间。根据沉积相研究,受郁南运动控制,黔中隆起在下奥陶统桐梓组沉积期间已具雏形。对贵阳乌当发现的珊瑚化石Plasmoporella、Heliolites、Amsassia等重新厘定后认为黔中隆起大规模露出水面的时间为晚奥陶世五峰组沉积期结束之时,这也是都匀运动发生的时间。都匀运动本身,受到自南而北方向的滇桂—北越地块的挤压和南东—北西方向的加里东造山运动的挤压,因此在黔中及周缘地区形成了以黔中背斜、乌当—二比向斜为代表的东西向构造和以麻江背斜为代表的南北向构造并存的地质现象。  相似文献   

鲁西隆起和济阳坳陷新生代隆坳耦合关系   总被引：2，自引：0，他引：2       下载免费PDF全文

李理钟大赉  时秀朋 《地质学报》2007,81(9):1215-1228

为探讨鲁西隆起的抬升史,研究鲁西隆起和济阳坳陷之间的隆-坳演化关系,进一步揭示渤海湾盆地的演化特征,主要利用裂变径迹分析和裂变径迹t-T模拟方法建立了新生代鲁西隆起的抬升史和济阳坳陷的沉降史。鲁西隆起三期抬升史分别为62～53Ma、44～37Ma和23～20Ma,济阳坳陷在65～46Ma和46～38Ma期间为快速构造沉降期,构造沉降量大,23Ma左右坳陷抬升。对比研究表明,新生代鲁西隆起的抬升与济阳坳陷沉降之间存在隆-坳耦合关系。鲁西隆起的抬升控制了济阳坳陷烃源岩的形成、油气运移时间和油气分布由南向北迁移,并为济阳坳陷古潜山油藏提供了有效的储集空间。研究还认为,鲁西隆起与济阳坳陷的隆坳耦合关系是渤海湾盆地及周边山系盆山耦合事件的一个组成部分。  相似文献