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21.
Hummocky cross-stratification-like structures in deep-sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France) 总被引：1，自引：0，他引：1
Hummocky cross-stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf. Sedimentary structures named hummocky cross-stratification-like structures, similar to true hummocky cross-stratification, have been observed in the Turonian–Senonian Basque Flysch Basin (south-west France). The bathymetry (1000 to 1500 m) suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf. The morphology of these three-dimensional structures shares similarities with the morphology of hummocky cross-stratification despite a smaller size. The lateral extent of these structures ranges from a few decimetres to many decimetres; they consist of convex-up domes (hummock) and concave-up swales with a non-erosive base. Four types of hummocky cross-stratification-like geometries are described; they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations. In the Basque Flysch, hummocky cross-stratification-like structures are only found in the Tc interval of the Bouma sequence. Hummocky cross-stratification-like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages. This observation suggests that hummocky cross-stratification-like structures are linked genetically to the turbidity current but form under a very restricted range of parameters. These structures sometimes show an up-current (upslope) migration trend (antidunes). In the described examples, they could result from standing waves forming at the upper flow interface because of Kelvin–Helmholtz instability. 相似文献
22.
新疆西昆仑库地复理石源区性质及构造背景分析 总被引：3，自引：3，他引：3
出露于库地北一些克沟中的复理石作为西昆仑库地蛇绿岩的基本组成单元之一，其本身具有重要的大地构造位置，但长期以来，有关其形成的构造环境分析却尚属空间。笔者等在对该套复理石沉积序列详细分析的基础上，本文从沉积大地构造学的角度，利用岩石矿物，主量元素，微量元素及稀土元素等地球化学数据对其母源区性质及构造背景进行了一系列分析判别，确定其形成的构造环境为大洋岛弧的弧前盆地。 相似文献
23.
A Late Archean foreland fold and thrust belt in the North China Craton: Implications for early collisional tectonics 总被引：10，自引：0，他引：10
The Archean North China craton is divided into the Western and Eastern blocks along the Central Orogenic belt. A 1600 km long Archean foreland basin and thrust belt fringes the eastern side of the Central Orogenic belt. Rocks in the orogen form tectonically-stacked east-vergent fold and thrust sheets including foreland basin sediments, 2.50 Ga ophiolitic mélange, and an island arc complex. Foreland basin sediments overlie a passive margin sequence, and include a 2.50 Ga deep-water turbidite sequence that grades upward and westward into shallow-water molasse, now disposed in structurally imbricated east-verging thrusts and asymmetric folds that gradually migrated craton-ward with deformation, uplift, and erosion of the orogen. There is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the North China craton along the Central Orogenic belt at 2.50 Ga. The Qinglong foreland basin and Central Orogenic belt of the North China craton represents one of the best-preserved Archean orogen-to-craton transitions in the world. Its classic internal to external zonation, and flexural response to loading, demonstrate that convergent tectonics in the Archean were broadly similar to Phanerozoic convergent margin processes. 相似文献
24.
造山带研究中有关复理石和磨拉石的几个问题 总被引：1，自引：0，他引：1
在造山带研究中,碰撞方式和时限的争议是全球造山带研究中的一个共同现状或面临的难题。利用复理石和磨拉石时代来限定碰撞时限是造山带研究的一项重要内容。本文首先综述了复理石和磨拉石从提出到广泛应用以及不同历史时期被赋予的构造含义;其次,根据其可能发育的构造环境,指出复理石和磨拉石纪录造山带的相关信息及其演变过程。被动陆缘复理石可能纪录了参与碰撞拼贴块体的亲缘性,而且被动陆缘、活动陆缘或者岛弧环境的复理石均形成于碰撞作用之前,因此最年轻的复理石时代可提供碰撞时间的下限;(周缘)前陆盆地的磨拉石形成于碰撞造山作用过程中,因此其最早的磨拉石沉积时代可用于限定碰撞时间的上限。从复理石到磨拉石地层的渐变过程(连续沉积)指示了碰撞构造事件的发生、以及之后的碰撞造山作用是均变过程,会发育不同尺度规模的不整合。因此,造山带中的不整合未必代表有重大构造事件的发生,而连续沉积并不表明没有大的构造事件。 相似文献
25.
以岩石学与构造研究相结合为基础，宏观与微观观察为主，地球化学为辅的综合研究方法论证了本区太古代地质体由三套变质建造组成。其中花岗质岩石占７１％，原地深熔紫苏花岗岩为１１．８％，浅色麻粒岩是１．２％，浅粒岩、含砾麻粒岩质浅粒岩（底砾岩）３６．７％和原地深熔花岗岩２０％。高角闪岩相以浅位岩为主原地深熔花岗岩的原岩建造为类磨拉石建造系列，低角闪岩似绿岩建造的原岩建造为镁铁质泥灰岩粉砂岩型复理石建造。其地质体是由６１．２％的层状变质岩系和３１．８％的原地深熔花岗岩组成。根据各建造的地层缺生，底砾岩及低、高角闪岩相矿物共生组合区域性叠加和变辉绿岩群的分布规律，确定三套变质建造为不整合接触，据此提出新的划分方案并与华北地台北部太古界分布区作了对比，事实证明岩石地层学的方法，在太古代地质与成矿研究中仍是有效的。 相似文献
26.
La fabrique magnétique du flysch dauphinois (Alpes francaises) : origine et application quantitative
RésuméLes propriétés magnétiques des schistes, grès et calcaires du flysch eocène de la zone dauphinoise ont été étudiées en relation avec la minéralogie et la structure de ces roches. La susceptibilité magnétique en champ faible est principalement due au paramagnétisme des phyllosilicates (illite et chlorite).L’anisotropie de susceptibilité correspond à un ellipsoïde aplati qui présente les caractéristiques suivantes : un axe minimal perpendiculaire à la schistosité et un axe maximal parallèle soit à une linéation d’intersection soit à la direction d’étirement maximal.On présente un modèle mathématique simple permettant d’utiliser le taux d’anisotropie magnétique pour quantifier l’orientation préférentielle des phyllosilicates. Ce modèle testé sur les niveaux les plus phylliteux du flysch donne des résultats en bon accord avec ceux de la goniometrie de texture. Les possibilités et les avantages de cette méthode structure-logique quantitative sont discutés. 相似文献
27.
Shallow high-resolution seismics and reprocessing of industry profiles in southern Bavaria: The Molasse and the northern Alpine front 总被引：1，自引：0，他引：1
The purpose of this seismic investigation in the Upper Bavarian Miesbach area, as part of the international TRANSALP project, was to study the tectonic contact between the autochthonous Foreland Molasse and the allochthonous Folded Molasse marking the tectonic front of the Alpine orogen. Another specific target was the dip of the frontal emerging main thrust of the tectonic units Helveticum/Ultrahelveticum and Rhenodanubian Flysch overriding the Folded Molasse. Twelve seismic profiles obtained from the hydrocarbon industry were reprocessed. From the Foreland Molasse southward to the Autochthonous Molasse in the subsurface of the overthrust Folded Molasse conspicuous features such as steep normal faults at the Molasse base, S-directed thickening of Molasse sediments or sedimentary discordant base of Upper Marine Molasse can be recognized.Shallow high-resolution seismic measurements were conducted along two profiles across the tectonic contact between Foreland Molasse and Folded Molasse, as well as along a profile across the frontal emerging main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch. Geological structures could be identified in the top 300–500 ms two-way traveltime interval, which is hardly possible with the usual deep-seismic method. The method thus provides a bridge between deep-reflection seismics and surface geology.In contrast to the western Bavarian Molasse zone, the tectonic boundary between the Foreland Molasse and the Folded Molasse in the investigated area is not characterized by a large blind-thrust triangle zone but by a simple south-dipping thrust plane. Adjacent to the S follow several steeply south-dipping inverse Molasse thrust slices and the Miesbach syncline. The inverse thrust slices are interpreted as the overturned and sheared northern limb of a fault propagation fold, which linked the Folded Molasse to the Foreland Molasse during a final orogenic phase.The main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch are well imaged in the near-surface interval of the high-resolution reflection seismic data. In contrast to previously published results, these thrust planes show a gentle dip to the S from the surface down to at least 500–1000 m depth. 相似文献
28.
This paper presents a case study of the instability mechanisms, and the excavation sequence, re-qualification and reinforcement methods adopted to pass through a short segment of a nearly 2-km tunnel built as part of a new 55-km state highway in northern Turkey. The instability problems were encountered during tunnel excavation due to the failure to recognize the fact that alteration in stress field and resulting deformation could cause dilation and increase in the permeability of claystone-shale layers and local fault gouge zones, and in turn significant reduction in shear strength. Change in natural drainage pattern and capillarity exacerbated saturation and the consequent strength reduction. The 92-m3 loose material flowed into the tunnel due to the collapse and caused 2.5 months of delay in completion of the tunnel. Longitudinal and oblique cracks observed in shotcrete were attributed to the reduction in modulus upon saturation, which caused a large cumulative deformation of approximately 110 mm at a section about 30 m behind the collapse face.
It is concluded that early detection or prediction of potentially problematic zones (via probe drilling and monitoring) in tunnelling is of paramount importance, especially through mixed or difficult ground conditions characterized by alternating layers, folding, faulting and localized zones of high water pressure. Because mechanical detection methods cannot be fully relied upon, availability of experienced personnel to predict and deal with such instability problems effectively and promptly is the best insurance for successful completion of tunnelling contracts. 相似文献
29.
Complex flow-like landslides (CFLLs) are important geomorphic agents of Late Quaternary mountain evolution in the Flysch Belt of the Outer Western Carpathians. The CFLLs are characterised by the upper section of deep-seated, retrogressive landslide of structurally unfavourably oriented rocks and lower sections composed of earthflows originated due to liquefaction of material accumulated from the upper slopes. Radiocarbon dating of organic matter incorporated into landslide debris or related deposits suggests that most of the CFLLs collapsed repeatedly throughout the Holocene with typical recurrence intervals of approximately 1–2 ka. Catastrophic landslides that occurred during extreme hydrometeorological events in recent decades displayed evidence of Holocene activity. Most of the CFLLs dammed and steepened adjacent valleys. Our chronological dataset is biased by erosion of older landforms, but most of the dated reactivations correlate to regional increases in humidity identified by previous paleoenvironmetal studies. 相似文献
30.
Rita Catanzariti Alessandro Ellero Mehmet Cemal Göncüoglu Michele Marroni Giuseppe Ottria Luca Pandolfi 《Comptes Rendus Geoscience》2013,345(11-12):454-461
In the Boyal? area, northern Turkey, the tectonic units of the ?stanbul–Zonguldak Terrane and the IntraPontide suture zone are thrust over the deposits at the top of the Sakarya Terrane, known as Tarakl? Flysch. It consists of Early Maastrichtian–Middle Paleocene turbidite and mass-gravity deposits, whose source mainly corresponds to the ?stanbul–Zonguldak Terrane, and, with a lesser extent, to the IntraPontide suture zone. These deposits were sedimented in a foredeep basin developed during the convergence between Sakarya and Eurasian continental microplates. In the Late Paleocene–Early Eocene time span, the Tarakl? Flysch was deformed (D1 phase) during the closure of the foredeep basin. In the Miocene time, the strike-slip tectonics (D2 phase) related to the North-Anatolian fault produced further deformations of the Tarakl? Flysch. 相似文献