首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 511 毫秒
1.
The Himalayan fold-and-thrust belt has propagated from its Tibetan hinterland to the southern foreland since ∼55 Ma. The Siwalik sediments (∼20 - 2 Ma) were deposited in the frontal Himalayan foreland basin and subsequently became part of the thrust belt since ∼ 12 Ma. Restoration of the deformed section of the Middle Siwalik sequence reveals that the sequence is ∼325 m thick. Sedimentary facies analysis of the Middle Siwalik rocks points to the deposition of the Middle Siwalik sediments in an alluvial fan setup that was affected by uplift and foreland-ward propagation of Greater and Lesser Himalayan thrusts. Soft-sediment deformation structures preserved in the Middle Siwalik sequence in the Darjiling Himalaya are interpreted to have formed by sediment liquefaction resulting from increased pore-water pressure probably due to strong seismic shaking. Soft-sediment structures such as convolute lamination, flame structures, and various kinds of deformed cross-stratification are thus recognized as palaeoseismic in origin. This is the first report of seismites from the Siwalik succession of Darjiling Himalaya which indicates just like other sectors of Siwalik foreland basin and the present-day Gangetic foreland basin that the Siwalik sediments of this sector responded to seismicity.  相似文献   

2.
Geochronology is useful for understanding provenance, and while it has been applied to the central and western Himalaya, very little data are available in the eastern Himalaya. This study presents detrital zircon U–Pb ages from the late Palaeocene–Eocene Yinkiong Group in NE India. The samples are from the late Palaeocene to early Eocene Lower Yinkiong Formation, and the Upper Yinkiong Formation deposited during the early to mid‐Eocene within the Himalayan foreland basin. The U–Pb ages of the detrital zircon within the Lower Yinkiong Formation are older than late Palaeozoic, with a cratonic and early Himalayan Thrust Belt affinity, whereas the Cenozoic grains in the Upper Yinkiong Formation indicate a Himalayan Thrust Belt source and possibly a granitic body within the Asian plate. The shift of the sources and the changes in the foreland basin system strongly suggest that the India–Asia collision in the Eastern Himalaya began before or immediately after the deposition of the Upper Yinkiong Formation, i.e., within the early Eocene (c. 56 to 50 Ma).  相似文献   

3.
Najman  Bickle  & Chapman 《地学学报》2000,12(1):28-34
Nd- and Sr-isotopic compositions of Palaeogene foreland basin sediments are used to provide insights into early Himalayan evolution, particularly the timing of exposure of high 87Sr/86Sr units, erosion of which may have caused the late Tertiary increase in oceanic Sr-isotopic ratios. During the late Palaeocene–early Eocene, erosion was from mixed sources including suture zone rocks. Exhumation of the High Himalaya was occurring by the time of deposition of alluvial sediments after mid-Oligocene times and this source has dominated Himalayan sediments from at least this time until the present day. The transition is interpreted to reflect exhumation of 'basement rocks' of the Indian plate, when the High Himalaya became a sufficient topographic barrier to separate suture zone rocks from the foreland basin. The marked rise in seawater 87Sr/86Sr from 40 Ma is consistent with the erosion of a Himalayan source with a high 87Sr/86Sr ratio.  相似文献   

4.
A REINTERPRETATION OF THE OLDEST HIMALAYAN FORELAND BASIN SEDIMENTS: A REVISED AGE FOR THE BALAKOT FORMATION, PAKISTAN1　BossartP .1986 .PhDthesisno .2 6 0 ,ETHZurich ,Switzerland . 2　BossartP ,OttigerR .EclogaeGeologicaHelvetica[j],1989,82 :133～ 16 5 . 3　BurbankDW ,BeckRA ,MulderT .TheTectonicevolutionofAsia[M ],A .Yin ,T .M .Harrison ,eds . 4　CritelliS ,GarzantiE .SedimentaryGeology[J],1994,89:2 6 5～ 2 84. 5　DeCelle…  相似文献   

5.
碰撞带前陆盆地的建立是大陆碰撞的直接标志和随后造山带构造变形的忠实记录。本文对欧亚板块与印度板块碰撞前后发育在拉萨地块上的冈底斯弧背前陆盆地,同碰撞产生的雅鲁藏布江周缘前陆盆地,以及碰撞后陆内变形产生的喜马拉雅前陆盆地的沉积地层演化以及碎屑锆石物源特征等进行了系统分析,结合前人及我们近些年的研究成果,认为冈底斯岛弧北侧发育一个典型的弧背前陆盆地系统而不是以前普遍接受的伸展盆地。除传统认为的喜马拉雅前陆盆地系统外,在碰撞造山带中还发育一个雅鲁藏布江前陆盆地系统,它是欧亚板块与印度板块碰撞以后,欧亚板块加载到印度被动大陆边缘产生的典型周缘前陆盆地。上述2个造山带前陆盆地系统的识别,大大提高了对新特提斯洋俯冲、碰撞过程的认识。造山带前陆盆地证据指示,新特提斯洋至少于140 Ma以前就已开始俯冲, 110 Ma俯冲速度开始提高,在65 Ma前后印度大陆与欧亚大陆发生碰撞,喜马拉雅山于40 Ma开始隆升,其剥蚀物质大量堆积在喜马拉雅前陆盆地中。  相似文献   

6.
滇西新生代兰坪盆地和剑川盆地分别位于哀牢山–红河断裂带两侧,青藏高原东构造结内,其沉积过程和构造变形对青藏高原东南缘的构造演化有重要的启示意义。通过对这两个盆地古近纪沉积和构造过程的研究,我们发现兰坪盆地和剑川盆地及邻区的构造变形分为三期:始新世早期的强烈挤压变形、始新世中晚期的伸展变形、渐新世的走滑变形。始新世早期的挤压变形主要表现为兰坪地区的褶皱–冲断系统、哀牢山-红河断裂的逆冲活动和剑川盆地的宽缓褶皱。沉积方面,古新统勐野井组(E_1m)较为稳定的细粒滨湖相沉积转变为始新统宝相寺组(E_2b)较粗的具有前陆盆地性质的河流相沉积,特别是宝相寺组底部发育的一套快速堆积的磨拉石建造,可能是对始新世强烈挤压环境下的沉积响应。始新世中晚期伸展变形体现在盆地的构造环境由早期的挤压环境变为伸展环境和该时期大量富钾岩体和岩脉的侵入,沉积学上,下始新统宝相寺组的河流相转变为中始新统金丝厂组(E_2j)具有快速堆积磨拉石特征的曲流河沉积,极可能是对构造体制变革的沉积响应。渐新世的走滑变形则体现在渐新统的缺失和哀牢山–红河断裂的早期左行走滑。因此,我们认为剑川–兰坪地区在始新世中期和渐新世均发生了显著的运动学转换,这一认识也得到了始新世中期兰坪和剑川盆地物源明显变化的支持。结合青藏高原东南部始新世中晚期岩浆的活动,渐新世大型剪切带(崇山剪切带、高黎贡剪切带)的强烈走滑和保山块体的旋转,我们推测青藏高原东南缘古近纪的构造演化为古新世-始新世早期的挤压、始新世中晚期的伸展、渐新世的转换压缩。  相似文献   

7.
藏南古近纪前陆盆地演化过程及其沉积响应   总被引：4，自引：1，他引：3  
藏南地区从三叠纪至古近纪经历了从洋盆(喜马拉雅特提斯)的形成、扩张、衰减、关闭,直至转换成前陆盆地的过程。被动大陆边缘阶段(T-K),在印度陆块北缘形成了从碎屑岩陆架到碳酸盐台地的沉积序列。从古近纪初开始,西藏特提斯关闭,形成周缘前陆盆地体系(由褶冲带、前渊带、前隆带和隆后盆地等单元构成)。随着褶冲带的上叠式逆冲,形成前渊盆地。当前陆推覆体进一步向印度克拉通推进时,前陆隆起亦随之逐渐向克拉通方向迁移。该带表现出一个海平面相对上升的过程,形成碳酸盐缓坡。随着前陆推覆体进一步逆冲,前陆隆起继续隆升并最终露出水面,导致其后的隆后盆地转变为半局限环境。始新世晚期,前陆盆地回返,海水从东向西逐渐退出西藏地区。生物相和沉积相是盆地沉积环境演化的物质表现,在藏南古近纪沉积中可识别出13种生物相和14类沉积相。藏南古近系的超层序,是在印度板块与亚洲板块碰撞背景下形成的,其沉积环境是一个构造活动极为强烈的前陆盆地。前陆盆地在剖面上具明显的不对称性,靠近褶皱山系一侧为陡坡地形,靠近地台一侧为缓坡。每个大型的三级层序都是非对称的,以发育具有独特的岩性和古生物特征的低水位体系域、海进体系域和高水位体系域为标志。藏南前陆盆地的演化符合通行.  相似文献   

8.
<正>Foreland basin represents one of the most important hydrocarbon habitats in central and western China.To distinguish these foreland basins regionally,and according to the need of petroleum exploration and favorable exploration areas,the foreland basins in central and western China can be divided into three structural types:superimposed,retrogressive and reformative foreland basin(or thrust belt),each with distinctive petroleum system characteristics in their petroleum system components(such as the source rock,reservoir rock,caprock,time of oil and gas accumulation,the remolding of oil/gas reservoir after accumulation,and the favorable exploration area,etc.).The superimposed type foreland basins,as exemplified by the Kuqa Depression of the Tarim Basin, characterized by two stages of early and late foreland basin development,typically contain at least two hydrocarbon source beds,one deposited in the early foreland development and another in the later fault-trough lake stage.Hydrocarbon accumulations in this type of foreland basin often occur in multiple stages of the basin development,though most of the highly productive pools were formed during the late stage of hydrocarbon migration and entrapment(Himalayan period).This is in sharp contrast to the retrogressive foreland basins(only developing foreland basin during the Permian to Triassic) such as the western Sichuan Basin,where prolific hydrocarbon source rocks are associated with sediments deposited during the early stages of the foreland basin development.As a result, hydrocarbon accumulations in retrogressive foreland basins occur mainly in the early stage of basin evolution.The reformative foreland basins(only developing foreland basin during the Himalayan period) such as the northern Qaidam Basin,in contrast,contain organic-rich,lacustrine so urce rocks deposited only in fault-trough lake basins occurring prior to the reformative foreland development during the late Cenozoic,with hydrocarbon accumulations taking place relatively late(Himalayan period).Therefore,the ultimate hydrocarbon potentials in the three types of foreland basins are largely determined by the extent of spatial and temporal matching among the thrust belts,hydrocarbon source kitchens,and regional and local caprocks.  相似文献   

9.
Nepal can be divided into the following five east–west trending major tectonic zones. (i) The Terai Tectonic Zone which consists of over one km of Recent alluvium concealing the Churia Group (Siwalik equivalents) and underlying rocks of northern Peninsular India. Recently active southward-propagating thrusts and folds beneath the Terai have affected both the underlying Churia and the younger sediments. (ii) The Churia Zone, which consists of Neogene to Quaternary foreland basin deposits and forms the Himalayan mountain front. The Churia Zone represents the most tectonically active part of the Himalaya. Recent sedimentologic, geochronologic and paleomagnetic studies have yielded a much better understanding of the provenance, paleoenvironment of deposition and the ages of these sediments. The Churia Group was deposited between ∼14 Ma and ∼1 Ma. Sedimentary rocks of the Churia Group form an archive of the final drama of Himalayan uplift. Involvement of the underlying northern Peninsular Indian rocks in the active tectonics of the Churia Zone has also been recognised. Unmetamorphosed Phanerozoic rocks of Peninsular India underlying the Churia Zone that are involved in the Himalayan orogeny may represent a transitional environment between the Peninsula and the Tethyan margin of the continent. (iii) The Lesser Himalayan Zone, in which mainly Precambrian rocks are involved, consists of sedimentary rocks that were deposited on the Indian continental margin and represent the southernmost facies of the Tethyan sea. Panafrican diastrophism interrupted the sedimentation in the Lesser Himalayan Zone during terminal Precambrian time causing a widespread unconformity. That unconformity separates over 12 km of unfossiliferous sedimentary rocks in the Lesser Himalaya from overlying fossiliferous rocks which are >3 km thick and range in age from Permo-Carboniferous to Lower to Middle Eocene. The deposition of the Upper Oligocene–Lower Miocene fluvial Dumri Formation records the emergence of the Himalayan mountains from under the sea. The Dumri represents the earliest foreland basin deposit of the Himalayan orogen in Nepal. Lesser Himalayan rocks are less metamorphosed than the rocks of the overlying Bhimphedis nappes and the crystalline rocks of the Higher Himalayan Zone. A broad anticline in the north and a corresponding syncline in the south along the Mahabharat range, as well as a number of thrusts and faults are the major structures of the Lesser Himalayan Zone which is thrust over the Churia Group along the Main Boundary Thrust (MBT). (iv) The crystalline high-grade metamorphic rocks of the Higher Himalayan Zone form the backbone of the Himalaya and give rise to its formidable high ranges. The Main Central Thrust (MCT) marks the base of this zone. Understanding the origin, timing of movement and associated metamorphism along the MCT holds the key to many questions about the evolution of the Himalaya. For example: the question of whether there is only one or whether there are two MCTs has been a subject of prolonged discussion without any conclusion having been reached. The well-known inverted metamorphism of the Himalaya and the late orogenic magmatism are generally attributed to movement along the MCT that brought a hot slab of High Himalayan Zone rocks over the cold Lesser Himalayan sequence. Harrison and his co-workers, as described in a paper in this volume, have lately proposed a detailed model of how this process operated. The rocks of the Higher Himalayan Zone are generally considered to be Middle Cambrian to Late Proterozoic in age. (v) The Tibetan Tethys Zone is represented by Cambrian to Cretaceous-Eocene fossiliferous sedimentary rocks overlying the crystalline rocks of the Higher Himalaya along the Southern Tibetan Detachment Fault System (STDFS) which is a north dipping normal fault system. The fault has dragged down to the north a huge pile of the Tethyan sedimentary rocks forming some of the largest folds on the Earth. Those sediments are generally considered to have been deposited in a more distal part of the Tethys than were the Lesser Himalayan sediments.The present tectonic architecture of the Himalaya is dominated by three master thrusts: the Main Central Thrust (MCT), the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). The age of initiation of these thrusts becomes younger from north to south, with the MCT as the oldest and the MFT as the youngest. All these thrusts are considered to come together at depth in a flat-lying decollement called the Main Himalayan Thrust (MHT). The Mahabharat Thrust (MT), an intermediate thrust between the MCT and the MBT is interpreted as having brought the Bhimphedi Group out over the Lesser Himalayan rocks giving rise to Lesser Himalayan nappes containing crystalline rocks. The position of roots of these nappes is still debated. The Southern Tibetan Detachment Fault System (STDFS) has played an important role in unroofing the higher Himalayan crystalline rocks.  相似文献   

10.
青藏高原东缘新生代构造层序与构造事件   总被引：28，自引：7，他引：28       下载免费PDF全文
新生代龙门山前盆地和盐源盆地是青藏高原东缘龙门山－锦屏山冲断带内及前缘地区发育和保存最好的新生代沉积盆地，本次以地层不整合面和ESR测年资料为主要依据，将该区新生代构造地层序列划分为5个构造层序，即TS1（65－55Ma)、TS2(40-50Ma)、TS3（23－16Ma)、TS4(4．7-1.6Ma)和TS5（0．74－0Ma)，据此将青藏高原东缘新生代构造变形和隆升事件划分为5期，其中TS1与喜马拉雅地体和拉萨地体拼合事件相关，TS2与印亚碰撞事件相关，TS3与青藏高原第一次隆升事件相关，TS4与青藏高原第二次隆升事件相关，TS5与青藏高原第三次隆升事件相关。  相似文献   

11.
The physical characteristics of sedimentary record are governed largely by grain size distribution in Mohand area where Middle and Upper Siwalik successions are investigated to characterize the sediments deposited in response to the prevailing tectonic activities and climatic conditions. Here we show with the help of cluster analysis that precipitation and tectonic perturbations generate characteristic patterns of grain sizes and stratigraphic succession. Previous studies suggested an increase in precipitation represented by the abrupt accumulation of sediments to foreland Siwalik basin around 11 to 10 Ma. First appearance of diagnostic minerals of the Great Himalayan complex in Siwalik sediments at 9.2 Ma implies the accelerated erosion of Himalaya during Middle to Late Miocene. The response of sedimentation to tectonic activity is resulted by the presence of coarse grained gravel units in Siwalik succession of Mohand area. Apatite fission-track dates and muscovite cooling ages confirm the strong activity on boundary thrusts during 8-6 Ma. Although the responses are non-linear and transient, we clusterize these non-linear responses to tectonics and climate and quantify them to find out the role of tectonics and climate in architecture of sedimentary succession.  相似文献   

12.
A sedimentary succession more than 5800 m thick, including the Lower Eocene to Lower Oligocene Fenghuoshan Group, the Lower Oligocene Yaxicuo Group, and the Lower Miocene Wudaoliang Group, is widely distributed in the Hoh Xil piggyback basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan plateau. The strata of the Fenghuoshan and Yaxicuo groups have undergone strong deformation, whereas only minor tilting has occurred in the Wudaoliang Group. We analyze their sedimentary facies and depositional systems to help characterize continental collision and early uplift of the Tibetan plateau. The results indicate fluvial, lacustrine, and fan-delta facies for the Fenghuoshan Group, fluvial and lacustrine facies for the Yaxicuo Group, and lacustrine facies for the Wudaoliang Group. Development of the Hoh Xil basin underwent three stages: (1) the Fenghuoshan Group was deposited mainly in the Fenghuoshan-Hantaishan sub-basin between 56.0 and 31.8 Ma ago; (2) the Yaxicuo Group was deposited mainly in the Wudaoliang and Zhuolai Lake sub-basins between 31.8 and 30.0 Ma ago; and (3) the Wudaoliang Group was deposited throughout the entire Hoh Xil basin during the Early Miocene. The Fenghuoshan and Yaxicuo groups were deposited in piggyback basins during the Early Eocene to Early Oligocene, whereas the Wudaoliang Group was deposited in a relatively stable large lake. The Hoh Xil basin underwent two periods of strong north–south shortening, which could have been produced by the collision between India and Asia and the early uplift of the Tibetan plateau. The study suggests the Hoh Xil region could reach a high elevation during the Late Oligocene and the diachronous uplift history for the Tibetan plateau from east to west.  相似文献   

13.
Whole rock major, trace and rare earth element (REE) compositions of Paleogene to Neogene sedimentary rocks of the NW shelf succession (Province 1) of Bangladesh contain a record of interaction of the India and Asian plates, Himalayan tectonism, and climatic development. Analyses of 66 sandstones and mudrocks from the Tertiary succession of Bangladesh were made to examine provenance, source weathering, and the influence of paleoclimate and tectonism. The sediments display linear geochemical trends due to quartz dilution, and varying quartz–clay ratios produced by hydrodynamic sorting. Chondrite-normalized REE patterns for both sandstones and mudrocks from different groups are similar to upper continental crust, with moderate to high LREE enrichment (lithotypes within formations average LaN/YbN 5.31–11.41) and marked negative Eu anomalies (Eu/Eu* 0.51–0.69). Based on geochemical criteria the succession can be divided into three parts (Jaintia; Barail–Surma; and Dupi Tila). Very high silica contents in Jaintia Tura sandstones and high Chemical Index of Alteration (CIA) indices in Kopili mudrocks (Fe-shales) suggest derivation from a deeply weathered and stable cratonic source (India). The Tura sandstones are interpreted as first-cycle quartz arenites, produced while the Indian plate drifted across equatorial regions during the Paleocene–Eocene Thermal maximum (PETM). The Barail–Surma and Dupi Tila sediments were derived from a felsic orogen (the Himalaya). The Barail–Surma sediments were mainly derived from the Trans Himalayan Batholith and associated granitoids, with significant contribution from the Lesser Himalaya. Mafic input is also evident, probably from intraoceanic arc material within the Himalaya. Barail mudrocks have uniformly high CIA values (92–95), suggesting intense steady-state weathering of their proto-Himalayan source, and warm and humid climate. In contrast, CIA values of Surma mudrocks range from 66 to 93 (average 84), suggesting non-steady state weathering related to active uplift in the Himalaya. The Dupi Tila sediments were derived from a more felsic Lesser Himalaya source, with significant contribution from the Trans-Himalaya and very little or no ophiolitic or arc material. Dupi Tila mudrocks have CIA ratios of 62–99 (average 72), also indicating non-steady state weathering in the rising Himalayan source. Geochemical compositions of the NW shelf sediments are comparable to coeval successions in the Surma basin (Province 2) of Bangladesh and the Siwaliks (India), indicating similar source. Evolution of the Indian monsoon and associated high precipitation caused intense chemical weathering of the Surma and Dupi Tila source, despite rapid uplift. The Surma Group thus bears the signature of evolution of the Asian monsoon in the Bengal basin at 21 Ma, simultaneous with the development of the East Asian monsoon. This supports proposals that both monsoon systems developed at the same time.  相似文献   

14.
特提斯喜马拉雅北亚带江孜地区上古新统-下始新统甲查拉组记录了喜马拉雅碰撞造山带的早期地壳加厚和沉积历史。本文我们报道了甲查拉组详细的碎屑锆石U-Pb年龄和全岩Sm-Nd同位素数据。甲查拉组由青灰色厚层的岩屑砂岩夹泥岩组成,不整合覆盖在宗卓组之上,碎屑锆石主要的峰值介于350～80 Ma, 900～470 Ma以及1 300～950 Ma,次要的峰值介于2 800～1 500 Ma。全岩87Sr/86Sr介于0.707 505～0.713 174,143Nd/144Nd介于0.512 206～0.512 355,εNd(0)介于-5.52～-8.43。甲查拉组物源区以再循环的日喀则弧前盆地和上三叠统郎杰学群为主,少量物质来自雅鲁藏布江缝合带。上述研究表明,甲查拉组沉积在周缘前陆盆地的背景下,且特提斯喜马拉雅北亚带在始新世期间经历了明显的地壳加厚。  相似文献   

15.
The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.  相似文献   

16.
崔宇驰  曹立成  乔培军  陈淑慧  庞雄  邵磊 《地球科学》2018,43(11):4169-4179
长期以来,由于地质资料的限制,有关南海早期裂陷过程中的沉积演化问题一直缺乏相对深入的认识与了解.采用碎屑锆石U-Pb定年方法,对南海北部古近纪沉积物进行"源-汇"对比分析.结果表明,该时期南海北部不仅接受来自北部河流搬运的陆源碎屑物质,同时还受到盆地内部局部隆升区物源的影响.其中,始新世沉积物以下白垩统物源为主,至早渐新世,琼东南盆地接受了来自海南岛及西沙隆起带的沉积物,珠江口盆地珠一坳陷同时期的锆石磨圆度较高,年龄谱系同华南沿海地区一致,说明很可能接受了来自华南沿海地区的陆源物质;而处于盆地南侧的白云凹陷同时期存在自形程度极高的锆石,反映其物源极可能为盆地内近源的局部隆起区.到晚渐新世荔湾凹陷沉积物中开始出现较多元古代锆石,与其北部同时期沉积物明显不同,琼东南盆地N6井也开始出现较多元古代锆石,其物源可能与南海西侧隆起有关.资料显示,在古近纪,现代意义上的珠江并未形成,其在早渐新世仅影响到珠一坳陷,到晚渐新世影响到珠二坳陷北侧.因此,珠江在古近纪具有从小到大逐步演化的特点.   相似文献   

17.
昝立宏  程捷 《古地理学报》2008,10(6):647-656
吐鲁番盆地是天山山脉中的一个山间盆地,古近系保存完好,是研究中国西北地区古近纪气候变迁的良好地区。通过对吐鲁番盆地连木沁剖面古近系多种气候代用指标（Fe2O3、FeO、CaCO3、有机碳、有机碳同位素）的研究,探讨了吐鲁番盆地古近纪的气候变迁和重要气候事件。利用Fe3+/Fe2+值,恢复了吐鲁番盆地古近纪的气温：古新世的年均气温为22.35℃,始新世为21.82℃,渐新世为15.69℃,并且在渐新世的早期和晚期发生较大幅度的降温事件。对地层中CaCO3（碳酸钙）含量的研究表明,古新统和始新统碳酸钙平均含量分别为468％和666％,指示该沉积时期气候相对比较湿润,而渐新统达15.01％,指示渐新世气候明显干旱化,并且渐新世的早期和晚期气候更为干旱。有机碳同位素（δ13Corg）值分布于C3植物的范围内,表明其受C3植物的影响。对地层中的δ13Corg值研究显示,该值与地层中碳酸钙含量呈负相关,与气温呈正相关,即该值偏负时,地层中碳酸钙含量增加,气温降低。各种气候指标指示吐鲁番盆地古新世和始新世气候比较温暖湿润,而渐新世气候干旱温凉。  相似文献   

18.
Neogene strata of the northern part of the Pegu (Bago) Yoma Range, Central Myanmar, contain a series of shallow marine clastic sediments with stratigraphic ages ranging from the Early to Late Miocene. The studied succession (around 750 m thick) is composed of three major stratigraphic units deposited during a major regression and four major transgressive cycles in the Early to Late Miocene. The transgressive deposits consist of elongate sand-bars and broad sand-sheets that pass headward into mixed-flats of tidal environments. Marine flooding in transgressive deposits is associated with coquina beds and allochthonous coral-bearing sandy limestone bands. Major marine regressions are associated with lowstand progradation of thick estuary point-bars passing up into upper sand-flat sand bodies encased within the tidal flat sequences and lower shoreface deposits with local unconformities. The succession initially formed in a large scale incised-valley system, and was later interrupted by two major marine transgressions in the generally regressive or basinward-stepping stratigraphic sequences. Successive sandbodies were formed during a sea-level lowstand and early stage of the subsequent relative rise of sea level in a tide-dominated estuary system in the eastern part of the Central Myanmar Tertiary Basin during Early to Late Miocene times.  相似文献   

19.
The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (“molassa”). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.  相似文献   

20.
Himalayan orogeny in relation to Global Tectonics is a hotly debated subject. Orogeny can result either from collision of continental plates or by an endogenic process of mantle upwelling along pre-existing fracture zones in the crust. This paper describes a new technique of frequency analysis of radiometric ages of crystalline rocks in the mountain ranges straddling the Indus-Tsangpo Suture Zone (ITSZ), the supposed line of collision between India and Asia, and shows that all the ranges from Karakoram to Lesser Himalaya across the ITSZ got uplifted simultaneously in a particular sequence. This contradicts the concept of suturing, places the ITSZ in the category of one of the intracrustal thrusts of the Himalayan orogenic system and establishes the family affinity between the Karakoram and the Himalaya. Analysis of stratigraphic and structural data points out that this family affinity is not confined to the ranges only but extends beyond into the foreland and oceanic basins as well. This paper also explains a number of apparent contradictions in terrain geomorphology, ophiolites in suture zones, thickness anomaly of Himalaya-derived sediments in eastern and western wings of terrestrial and oceanic basins to the south of the ranges, the status of Mid-oceanic Ridges in global tectonics, convergence aspect between Himalaya and India, nature of Foothills Fault and metamorphism of early Tertiary sediments in the Himalayan foreland basin.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号