Stratigraphy and facies development of the pre-Cenozoic sediments in southern Egypt: a geodynamic approach

The study of the geology of southern Egypt, in-between the Red Sea and the Libyan borders, south of latitude 24°30′N reveals a succession of the Precambrian Arabo–Nubian Shield along the Red Sea coast overlain by Paleozoic–Mesozoic sediments. The Paleozoic section in the study area is well developed in three sub-basins, namely, Uweinat–Gilf, South Nile, and Etbai. Paleozoic sediments are well developed in the three sub-basins mostly sandstones of Cambrian overlain by glaciogene sediment conglomerates at base namely Gabgaba Formation and by the Naqus Sandstone at top. The tectonic events during the Early Paleozoic Caledonian Orogeny are marked by several unconformities and tectonic uplift and down faulting expressed in the many faults in the Uweinat–Gilf and South Nile sub-basins. The Carboniferous is well-developed sandstones in the three studied sub-basins. The glaciation at the Permian is reflected in sea-level fall, hence continental sediments are well developed in many parts of Egypt—a phase of the Hercynian Orogeny. Volcanics are very well common in the study areas ranging in age from 48 to 34 Ma at Uweinat and Gebel El-Asr. Vulcanicity continued during the Paleozoic and Mesozoic at the Triassic of Nasab El-Balgum and in the south Western Desert, the south Eastern Desert, and Etbai area. The highly seismic conditions in southern Egypt continued up to very recent times where tremors were noticed in the 80s and 90s of the last century pointing to very unstable area.     

Rejuvenation of dry paleochannels in arid regions in NE Africa: a geological and geomorphological study

Although the River Nile Basin receives annually ca. 1600 billion cubic meters of rainfall, yet some countries within the Basin are suffering much from lack of water. The great changes in the physiography of the Nile Basin are well displayed on its many high mountains, mostly basement rocks that are overlain by clastic sediments and capped by volcanics in eastern and western Sudan. The central part of the Nile Basin is nearly flat including volcanics in the Bayuda Mountains and volcanic cones and plateaus in southwestern Egypt. The high mountains bordering the Nile Basin range in elevation from 3300 to 4600 m.a.s.l. in the Ethiopian volcanic plateau in the east to ca. 3070 m.a.s.l. in the western Gebel Marra, and 1310 m.a.s.l. in the Ennedi Mountains in northwestern Sudan. In central Sudan, the Nile Valley rises approximately 200–300 m.a.s.l. In Egypt, the River Nile is bounded by the Red Sea Mountains in the east, assuming ca. 1000–2600 m.a.s.l., mostly of basement rocks, which are covered to the north of Aswan by Phanerozoic sediments sloping to the west, passing by the Nile Valley and continuing through the Western Desert. The Phanerozoic cover on both sides of the Nile is known as the Eastern and Western Limestone Plateaus. These plateaus assume elevations varying from 300 to 350 m.a.s.l. near the eastern bank of the Nile to 400–500 m.a.s.l. south Luxor at Esna and west of Aswan. The nearly flat Sahara west of the Nile Valley rises gradually westward until it reaches Gebel Uweinat in the triple junction between Egypt, Sudan, and Libya. Gebel Uweinat has an elevation of 1900 m.a.s.l. sloping northward towards the Gilf Kebir Plateau, which is 1100 m.a.s.l. The high mountains and plateaus in the southern and western Egypt slope gradually northward where the Qattara Depression is located near the Mediterranean coast. The depression is ?134 m.b.s.l., which is the lowest natural point in Africa. All these physiographic features in Sudan and Egypt are related to (i) the separation of South America from Africa, which started in the Late Paleozoic and continued up to the Cretaceous, giving rise to several generally E–W-oriented tectonic features inside Africa, (ii) the uplift of the Red Sea Mountains and their continuation inside Africa resulted in the East African Rift System (EARS), (iii) the Guinea–Nubia Lineament crossing Africa from the Atlantic to the Red Sea where many havoc trends, mostly E–W-trending faults, and uplifted basement features pierce the overlying sediments, (iv) parallel and longitudinal structures associated with volcanic plateaus and cones extend from west Sudan (Gebel Marra) to Ethiopian Plateau, passing by volcanics and plume features in between and the basins in east Africa were subjected to wrench related inversions, and (v) the Sudd linear E–W area stretching more than 1000 km between Gebel Marra in the west, passing by South Sudan and reaching southwestern Ethiopia. Here, fluviatile and subsurface waters led to ponds, lakes, and wet areas that are hard to exploit. The impact of these features led to the present south to north River Nile, but passing by many changes in the direction of its many tributaries and slope reversal of some of the major extinct rivers, either sectors of the main Nile or the rivers once flowed into the main river. The paleoclimatic changes during the Quaternary period: wet and dry have a great effect on the physiographic features and slope reversal of the Nile Basin drainage system.     

新疆蛇绿岩带的分布、特征及研究新进展

新疆位于亚洲大陆的北部,构造上跨越了古亚洲和特提斯两大构造域,现今主要由中新生代盆地和其间的古生代造山带组成。古生代造山带主要由陆缘岩系和岩浆岩组成,其中夹有洋壳残片和前寒武结晶基底的碎块;洋壳残片从北向南大致分布12条,其中出露较集中的约30多处。这些蛇绿岩,以塔里木盆地为界,北部主要为古亚洲洋的洋壳残片,南部主要为特提斯洋的洋壳残片。在介绍其基本特征的同时,本文侧重报道了近年来新疆区域地质调查的一些成果。     

西藏羌塘盆地的构造沉积特征及演化

西藏羌塘盆地是特提斯构造域内晚古生代—中生代海相复合盆地。经历了晚古生代板块构造演化阶段、中生代板块构造演化阶段和新生代抬升剥蚀阶段 ,形成了晚古生代大陆边缘盆地、中生代南羌塘被动大陆边缘和北羌塘弧后盆地以及晚侏罗世之后的构造地貌盆地。受多期构造运动作用 ,盆地从北向南形成了北缘冲褶带、北羌塘变形带、中央碰撞隆起带、南羌塘变形带和南缘冲断带五个构造单元。变形由坳陷边缘到中心逐渐减弱 ,侏罗山式褶皱样式 ,反映出盖层浅层滑脱的变形特征     

漠河盆地中侏罗世沉积源区分析及地质意义

漠河盆地位于额尔古纳地块北缘,其北为蒙古-鄂霍茨克造山带,与紧邻的俄罗斯上阿穆尔盆地在中生代时期同属一个盆地。漠河盆地中侏罗统包括绣峰组、二十二站组、额木尔河组和开库康组。根据盆地碎屑岩中的砾石、岩屑和重矿物的组合特征,确定母岩类型以变质岩和中酸性火成岩为主,少量沉积岩和基性火成岩;结合古水流方向,确定盆地沉积物源主要来自南侧。沉积物源具有多源性:其一为陆块抬升基底,其二为切割的岩浆弧。与区域岩石对比分析表明,陆块抬升基底可能来自古元古界兴华渡口群和寒武系兴隆群,切割的岩浆弧与古生代同碰撞和后碰撞花岗质岩石及早中生代中酸性火成岩有关。根据母岩供给特点,认为中侏罗世沉积时期漠河盆地不是典型的前陆盆地,而应是挤压背景下形成的挤压挠曲盆地或山间盆地。     

Pseudotachylytes in the southern border fault of the Cenozoic intracontinental Teletsk basin (Altai, Russia)

The Cenozoic intracontinental Teletsk basin in the Central Asian Altai Mountains is composed of a complexly structured northern and a more simple southern sub-basin. These sub-basins formed in two distinct kinematic stages when first the NNW-striking Teletsk- and then the NE-striking West-Sayan shear zones became reactivated in the Cenozoic under dominant NS-oriented horizontal compression. Although the entire Teletsk basin strikes roughly NS, the southern sub-basin is parallel to the NNW-trending, amphibolite facies Teletsk ductile shear zone, while the northern sub-basin is NS-striking and flanked by differently structured, greenschist facies basement. Basement reactivation closely controlled the southern sub-basin formation, but this is less clear for the northern sub-basin. Contrasts between northern and southern basement and the exclusive occurrence of pseudotachylytes along the margins of the southern basin are explored for their contribution to the formation of the Teletsk basin with two distinct sub-basins.In the ductile shear fabric of the basement flanking the southern sub-basin, concordantly interleaved pseudotachylytes and isolated breccia lenses reflect local brittle deformation along the ductile fabric. The genetic link between breccia lenses and pseudotachylyte occurrences was defined by microstructural investigation. It allows to explore their possible development in a dextral strike–slip zone. These rocks occur in a large fault-bounded segment of the basement. The geometry of the structures in the segment is comparable with a dextral strike–slip sidewall-ripout structure along the Teletsk shear zone. Seismic slip related to pseudotachylytes is attributed to the sudden stress release on the NNW-striking Teletsk shear zone, when the latter became unconstrained by reactivation of the NE-trending West-Sayan fault zone at its northern boundary. The boundary of the sidewall-ripout structure was reactivated as a large listric fault in a later stage. The northern sub-basins roughly develop along an NS strike and are assumed to reflect reactivation of the ductile shear zone underneath the variably structured greenschist facies basement outcropping along the flanks of the sub-basin.     

新疆博格达山北缘晚古生代-中生代古水流样式转折及其构造意义

新疆准噶尔盆地南缘博格达山北缘地区古水流方向在晚古生代到中生代期间发生过三次重要的转变。晚石炭世晚期以前指向南,晚石炭世晚期到二叠纪期间指向东、南东东向,三叠纪—侏罗纪指向南,白垩纪及其以后指向北。结合盆地物源和沉积环境分析,博格达山北缘自晚古生代以来可划分为四个构造演化阶段,古流向转折期为盆地各期构造演化的分界线,它们是盆地对周缘造山带构造演化沉积响应的重要记录。另一方面,古水流转折时间资料的获得,对准噶尔盆地周缘不同构造带的隆升时代是一个非常重要的限定。晚石炭世晚期至二叠纪,古水流资料指示沉积物主要来自准噶尔盆地西部,准噶尔盆地西—西北缘强烈隆升,自三叠纪早期开始到侏罗纪晚期,准噶尔盆地北缘抬升,博格达山北缘沉积物主要来自北方;侏罗纪晚期到白垩纪,古水流指示沉积物主要来自盆地南部,博格达山隆起并遭受剥蚀。然而,什么原因造成石炭纪末以来,准噶尔盆地周缘几个造山带顺时针方向依次隆起,有待进一步研究。     

Pre-Cenozoic geology of the Latrobe Valley Area—onshore Gippsland Basin,S.E. Australia

In 2010–2011, a well on the uplifted northern edge of the Latrobe Valley (Yallourn North-1A) cored a 550 m section of mostly arenaceous sediments from the Lower Cretaceous Tyers River Subgroup. A follow-up core-hole (Yallourn Power-1) aimed at extending the Tyers River Subgroup section some 5 km south into the Latrobe Valley instead encountered Paleozoic basement rocks immediately below Cenozoic coal measures. From a re-examination of earlier coal and groundwater bore results, and new interpretations from gravity, seismic and magneto-telluric (MT) surveys, there is a significant area of Paleozoic basement rock that may underlie the whole northern Latrobe Valley area. The uplifted Yallourn North Lower Cretaceous sediments are a separate basin entity herein named the Monash trough. It appears they are separate from the main Lower Cretaceous Strzelecki Group Basin sediments on the southern side of the Latrobe Valley. Attributes of the Monash trough may underlie the main Strzelecki Basin, but this remains to be substantiated by further drilling. The intervening subcrop of Paleozoic basement rocks is herein named the Glengarry basement block. It shows characteristic gravity, MT and seismic features covering some 200 km² of the northern Latrobe Valley area. The boundary between the Glengarry basement block and Strzelecki Basin approximates to the Princes Highway. It is uncertain whether structural separation of the Monash trough from the main Strzelecki Basin always existed, or whether uplift and stripping of Cretaceous rocks over the Glengarry basement block occurred in post-Cretaceous but pre-Cenozoic times. Comparative rank and maturity indices indicate a greater depth of burial of the Glengarry basement block than what exists today, whereas less stripping and loss of section have occurred to the Monash trough. Cretaceous sediments of the Tyers River Subgroup (Rintouls Creek Formation, Tyers Conglomerate) in the Monash trough are dominated by mudstones, siltstones with lesser quartzose sandstones, conglomerates and thin coals. The sediments are over 300 m thick and are conformably overlain by 100 m of volcaniclastic sediments typical of the main Strzelecki Group, in turn overlain by nearly 100 m of Cenozoic coal measures. New detailed spore–pollen dating of Yallourn North-1A cores indicates that all Cretaceous sediments in the Monash trough are Barremian in age. This revises the traditional Neocomian age assigned to the formation. High total organic carbon levels in the 100 m-thick mudstones of the Locmany Member in the Rintouls Creek Formation constitute a mature petroleum source rock worthy of future hydrocarbon exploration.     

A traverse through the western Kunlun (Xinjiang,China): tentative geodynamic implications for the Paleozoic and Mesozoic

The northern part of the western Kunlun (southern margin of the Tarim basin) represents a Sinian rifted margin. To the south of this margin, the Sinian to Paleozoic Proto-Tethys Ocean formed. South-directed subduction of this ocean, beneath the continental southern Kunlun block during the Paleozoic, resulted in the collision between the northern and southern Kunlun blocks during the Devonian. The northern part of the Paleo-Tethys Ocean, located to the south of the southern Kunlun, was subducted to the north beneath the southern Kunlun during the Late Paleozoic to Early Mesozoic. This caused the formation of a subduction-accretion complex, including a sizeable accretionary wedge to the south of the southern Kunlun. A microcontinent (or oceanic plateau?), which we refer to as “Uygur terrane,” collided with the subduction complex during the Late Triassic. Both elements together represent the Kara-Kunlun. Final closure of the Paleo-Tethys Ocean took place during the Early Jurassic when the next southerly located continental block collided with the Kara-Kunlun area. From at least the Late Paleozoic to the Early Jurassic, the Tarim basin must be considered a back-arc region. The Kengxiwar lineament, which “connects” the Karakorum fault in the west and the Ruogiang-Xingxingxia/Altyn-Tagh fault zone in the east, shows signs of a polyphase strike-slip fault along which dextral and sinistral shearing occurred.     

南祁连南缘弧形逆冲推覆构造

南祁连南缘弧形逆冲推覆构造是一个具有双重叠置结构的推覆系统。原地系统主要为侏罗—白垩纪的含煤岩系和磨拉石建造,外来系统由元古界、古生界和三叠系组成。推覆体滑动的总体方向为ＳＳＷ,最大推移距离在１０ｋｍ以上。该推覆构造形成于燕山晚期,是在地幔底辟影响下盆地内产生伸展作用和特提斯地体碰撞过程中与板内应力复合作用的结果。     

班公湖—怒江构造带西段三叠纪—侏罗纪构造—沉积演化

班公湖－怒江构造带西段在大地构造位置上处于特提斯构造域东端，横跨班公湖－怒江断裂带。三叠纪－株罗纪期间，其构造－沉积演化经历了大陆初始裂谷（T）、原洋裂谷（J1）、残余弧后盆地（J2－J3）阶段。初始裂谷阶段的拉张是呈南断北超的半地堑式由东向西进行的，逐渐形成地堑式原洋裂谷盆地。中晚侏罗世，南部新特提斯洋壳开始北各俯冲,产生的区域挤压应力使原洋裂谷逐渐封闭，裂谷盆地的小洋壳表现出以南向俯冲为主的双向式腑冲，同时伴生区域热沉降，盆地具残余弧后盆地的性质。该阶段,羌南地区发育碳酸盐岩为主的稳定陆缘沉积，冈度斯－念青唐古拉板片北部则形成广泛南超的近源碎屑沉积。     

西昆仑山前晚三叠世古构造特征及对侏罗-白垩纪沉积的控制

造山带和盆地是在时空发展和形成机制上具有密切联系的构造系统。青藏高原内部晚三叠世古特提斯造山带的形成,对北缘的塔里木盆地产生了重要的影响,导致了盆地内部西昆仑山前地区发生了强烈的冲断构造变形,而这一冲断构造变形所形成的古构造-古地貌对后期侏罗-白垩纪的沉积具有重要的控制作用,同时也决定了该地区的油气分布。本文基于对西昆仑山前露头区中生代地层分布详细的野外考察和盆地覆盖区钻井资料的整理,结合对盆-山结合带清晰地震剖面的详细解释,开展西昆仑山前的晚三叠世古构造特征及侏罗-白垩纪沉积充填过程研究,以期揭示晚三叠世的古构造-古地貌特征及对沉积的控制作用。通过研究发现,西昆仑山前地区发育晚三叠世前陆褶皱冲断带,冲断带根部发育基底卷入构造,锋带发育叠瓦状构造;古生界受逆冲断裂控制,形成一系列的北陡南缓的背斜隆起,冲断带前锋位置与新生代构造前锋位置相近。三叠纪末古地貌形态由于特提斯造山带的强烈隆升,总体呈南高北低的地貌形态,但是褶皱冲断构造带受地表风化剥蚀作用,背斜核部形成南缓北陡的古隆起,而断层破碎带形成南陡北缓的洼地,是侏罗系发育前的基本地貌格架。早侏罗世受特提斯造山带造山后伸展的影响,西昆仑山前发育4个箕状断陷,控陷断层发育于古造山带一侧;受大型控陷断层的影响,在断陷内部呈北高南低的地形特点,断陷内侏罗系逐渐向北部斜坡超覆。晚三叠世形成的古构造-古地貌与早侏罗世断陷叠加形成的古地理格架一直控制了侏罗纪-早白垩世的沉积,直到晚白垩世沉积时才没有起到控制作用。     

Decoding Provenance and Tectonothermal Events by Detrital Zircon Fission‐Track and U‐Pb Double Dating: A Case of the Southern Ordos Basin

Multi-dating on the same detrital grains allows for determining multiple different geo-thermochronological ages simultaneously and thus could provide more details about regional tectonics. In this paper, we carried out detrital zircon fission-track and U-Pb double dating on the Permian-Middle Triassic sediments from the southern Ordos Basin to decipher the tectonic information archived in the sediments of intracratonic basins. The detrital zircon U-Pb ages and fission-track ages, together with lag time analyses, indicate that the Permian-Middle Triassic sediments in the southern Ordos Basin are characterized by multiple provenances. The crystalline basement of the North China Craton (NCC) and recycled materials from pre-Permian sediments that were ultimately sourced from the basement of the NCC are the primary provenance, while the Permian magmatites in the northern margin of NCC and Early Paleozoic crystalline rocks in Qinling Orogenic Collage act as minor provenance. In addition, the detrital zircon fission-track age peaks reveal four major tectonothermal events, including the Late Triassic-Early Jurassic post-depositional tectonothermal event and three other tectonothermal events associated with source terrains. The Late Triassic-Early Jurassic (225–179 Ma) tectonothermal event was closely related to the upwelling of deep material and energy beneath the southwestern Ordos Basin due to the coeval northward subduction of the Yangze Block and the following collision of the Yangze Block and the NCC. The Mid-Late Permian (275–263 Ma) tectonothermal event was associated with coeval denudation in the northern part of the NCC and North Qinling terrane, resulting from the subduction of the Paleo-Asian Ocean and Tethys Ocean toward the NCC. The Late Devonian-early Late Carboniferous (348±33 Ma) tectonothermal event corresponded the long-term denudation in the hinterland and periphery of the NCC because of the arc-continent collisions in the northern and southern margins of the NCC. The Late Neoproterozoic (813–565 Ma) tectonothermal event was associated with formation of the Great Unconformity within the NCC and may be causally related to the Rodinia supercontinent breakup driven by a large-scale mantle upwelling.     

Distribution of the energy release, b-values and seismic hazard in Egypt

A review of the seismicity and seismic history of Egypt indicates areas of high activity concentrated along Oligocene-Miocene faults. This supports the idea of recent activation of the Oligocene-Miocene stress cycle. There are similarities in the spatial distribution of recent and historical epicenters. Destructive earthquakes in Egypt are mostly concentrated in the highly populated areas of the Nile Valley and Nile Delta. Some big earthquakes located near the plate boundary as far away as Turkey and Crete were strongly felt in Egypt. The distribution of the energy release shows a possible tectonic connection between active zones in Egypt and the complicated tectonic zones in Turkey and Crete through geologically verified fault systems. The distribution of intensity shows a strong directivity along the Nile Valley. This is due to the presence of a thick layer of loose sediments on top of the hard rock in the Nile Valley graben. The distribution of b-values indicates two different zones, comparable with stable and unstable shelf areas. Stress loads in the northern Red Sea and northern Egypt are similar. Geologically, northern Egypt is a part of the Unstable Shelf area. The probability to have an earthquake with intensity V or larger within 94 years is more than 80% in the Nile Valley and Nile Delta areas, Egypt-Mediterranean coastal area, Aswan High Dam area, Gulf of Aqaba-Levant Fault zone and in the oil fields of the Gulf of Suez. The maximum expected intensity in these areas and within the same period is V–VI for a 80% probability and VII–VIII+ for a 10% probability. Intensity VIII–IX has been reported for several earthquakes in both historical and recent time.     

Basement of the South China Sea Area: Tracing the Tethyan Realm

The basement of the South China Sea (SCS) and adjacent areas can be divided into six divisions (regions) – Paleozoic Erathem graben-faulted basement division in Beibu Gulf, Paleozoic Erathem strike-slip pull-apart in Yinggehai waters, Paleozoic Erathem faulted-depression in eastern Hainan, Paleozoic Erathem rifted in northern Xisha (Paracel), Paleozoic Erathem strike-slip extending in southern Xisha, and Paleozoic-Mesozoic Erathem extending in Nansha Islands (Spratly) waters. The Pre-Cenozoic basement in the SCS and Yunkai continental area are coeval within the Tethyan tectonic domain in the Pre-Cenozoic Period. They are formed on the background of the Paleo-Tethyan tectonic domain, and are important components of the Eastern Tethyan multi-island-ocean system. Three branches of the Eastern Paleo-Tethys tectonic domain, North Yunkai, North Hainan, and South Hainan sea basins, have evolved into the North Yunkai, North Hainan, and South Hainan suture zones, respectively. This shows a distinctive feature of localization for the Pre-Cenozoic basement. The Qiongnan (i.e. South Hainan) Suture Zone on the northern margin of the South China Sea can be considered the vestige of the principal ocean basin of Paleo-Tethys, and connected with the suture zone of the Longmucuo-Shuanghu belt–Bitu belt –Changning-Menglian-Bentong-Raub belt, the south extension of Bitu-Changning-Menglian–Ching Mai belt–Chanthaburi-Raub-Bentong belt on the west of South China Sea, and with the Lianhua-Taidong suture zone (a fault along the east side of Longitudinal Valley in Taiwan)–Hida LP/HT (low pressure-high temperature) metamorphic belt–Hida-marginal HP/LT metamorphic belt in southwestern Honshu of Japan, on the east of the South China Sea. The Qiongbei (North Hainan) suture zone may eastwards extended along the Wangwu-Wenjiao fault zone, and connects with the Lufeng-Dapu-Zhenghe-Shangyu (Lianhuashan) deep fault zone through the Pearl River Mouth Basin. The Meso-Tethys developed on the south of the South China Sea. The Nansha Trough may be considered the vestige of the northern shelf of the Meso-Tethys. The oceanic crust of the Meso-Tethys has southwards subducted along the subduction-collision-thrust southern margin of the Nansha Trough with a subduction-pole opposite to those of the Yarlung Zangbo-Mytkyina-Bago zone on the west of the South China Sea, and the Meso-Tethyan (e.g. Northern Chichibu Ocean of the Meso-Tethys) suture zone “Butsozo tectonic line” in the outer belt of the Jurassic-Early Cretaceous terrene group in southwest Japan, on the east of the South China Sea.     

南海新生代沉积基底性质和盆地类型

根据新的重磁、地震及钻井资料,结合大地构造性质和新生代主要构造变形特征,将南海新生代沉积盆地基底划分为三个基底区,即北部古生界断陷基底区、西部中—古生界走滑拉分基底区以及南部复杂基底区。北部基底区以古生界变质基底为主,同时含有中生界残留断陷,它由北部湾断陷基底区、珠江口中—古生界断陷基底区以及西沙古生界断陷基底区三个次级区构成;西部基底区以走滑伸展为特征,分为莺歌海古生界、中建南中生界以及万安中生界等三个次级走滑拉分基底区;南部基底区较复杂,划分为曾母新生代早期褶皱基底区和南沙中—古生界复杂基底区。这八个次级基底区之间主要以俯冲—碰撞缝合带、蛇绿岩带、深海放射虫沉积岩带、洋中脊火成岩带以及深大走滑转换断裂带等分隔,各自有着不同的演化历史,控制了南海新生代多种类型次级沉积盆地的地质特征。     

新疆焉耆盆地中生代原始面貌探讨

新疆焉耆盆地是一中新生代盆地,通过对盆地残留中生代地层岩石特征分析,物源区位于盆地北部,碎屑由北向南搬运,在北部为粗碎屑堆积,南部为细碎屑堆积;盆地北部为辫状河相沉积,南部为滨浅湖相—辫状河相沉积;在盆地北部南天山山前和南部库鲁克塔格山上,现今仍残留有侏罗纪地层;这些都显示盆地原始沉积面貌比现今盆地要广。磷灰石裂变径迹数据显示焉耆盆地周邻山体于早白垩世中期隆升,早白垩世中期之前焉耆盆地与尤尔都斯、库车和库米什盆地在中生代是相连通的,为塔里木大型盆地的北部,晚白垩世大型盆地开始解体,焉耆盆地与这三个地区被分隔成彼此独立的盆地。     

加蓬海岸盆地南、北次盆成藏特征对比

加蓬海岸盆地属于被动大陆边缘盆地。盆地沉积盖层主要由白垩系、古近系和新近系组成,沉积地层组合具有明显的三分性,包括早白垩世盐下层系、早白垩世晚期阿普特期盐膏层和晚白垩世至新近纪盐上层系。根据目前的油气发现,北加蓬主要富集盐上油气资源,南加蓬主要富集盐下油气资源。从构造沉积背景、油气地质条件、油气发现规模、油气平面分布、油气勘探潜力5方面对南、北次盆进行对比,分析南、北次盆的油气聚集差异,结合勘探现状分析其勘探潜力,并指出南加蓬次盆勘探难点为圈闭识别,北加蓬次盆的勘探难点是砂体预测。     

Sr chemostratigrphy, δ<Superscript>13</Superscript>C,and δ<Superscript>18</Superscript>O of rocks in the Crimean carbonate platform (Late Jurassic,northern Peri-Tethys)

The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The ⁸⁷Sr/⁸⁶Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ¹⁸O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in ¹⁸O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ¹³C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ¹³C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.     

关于雅鲁藏布江缝合带(东段)的新认识

国内外不少地质学家大都将雅鲁藏布江蛇绿岩带视为印度板块与亚洲板块之间的缝合带。但是,笔者等在喜玛拉雅造山带的东段即仁布-康马一线以东地区的研究却发现,在雅鲁藏布江蛇绿岩带的南侧发育着一个宽大的增生杂岩体,它与雅江蛇绿岩是同一大洋即特提斯喜玛拉雅洋俯冲消减的产物,前者代表着特提斯喜玛拉雅洋消亡遗迹的主体,是印度板块与拉萨地块之间缝合带的主要组成部分;而后者代表的是俯冲带与拉萨地块之间的残余洋壳,它由北向南仰冲,构成日喀则-桑日弧前盆地前缘脊和南部基底,因而其不代表主缝合带。北喜玛拉雅增生杂岩体的发现改变了以Gansser(1964)为代表提出的喜玛拉雅造山带的构造模式,为重新审视印度板块与拉萨地块缝合作用过程提供了一个重要的地质制约和新的研究途径。