Cleats and their relation to geologic lineaments and coalbed methane potential in Pennsylvanian coals in Indiana

Cleats and fractures in Pennsylvanian coals in southwestern Indiana were described, statistically analyzed, and subsequently interpreted in terms of their origin, relation to geologic lineaments, and significance for coal permeability and coalbed gas generation and storage. These cleats can be interpreted as the result of superimposed endogenic and exogenic processes. Endogenic processes are associated with coalification (i.e., matrix dehydration and shrinkage), while exogenic processes are mainly associated with larger-scale phenomena, such as tectonic stress.At least two distinct generations of cleats were identified on the basis of field reconnaissance and microscopic study: a first generation of cleats that developed early on during coalification and a second generation that cuts through the previous one at an angle that mimics the orientation of the present-day stress field. The observed parallelism between early-formed cleats and mapped lineaments suggests a well-established tectonic control during early cleat formation. Authigenic minerals filling early cleats represent the vestiges of once open hydrologic regimes. The second generation of cleats is characterized by less prominent features (i.e., smaller apertures) with a much less pronounced occurrence of authigenic mineralization. Our findings suggest a multistage development of cleats that resulted from tectonic stress regimes that changed orientation during coalification and basin evolution.The coals studied are characterized by a macrocleat distribution similar to that of well-developed coalbed methane basins (e.g., Black Warrior Basin, Alabama). Scatter plots and regression analyses of meso- and microcleats reveal a power-law distribution between spacing and cleat aperture. The same distribution was observed for fractures at microscopic scale. Our observations suggest that microcleats enhance permeability by providing additional paths for migration of gas out of the coal matrix, in addition to providing access for methanogenic bacteria.The abundance, distribution, and orientation of cleats control coal fabric and are crucial features in all stages of coalbed gas operations (i.e., exploration and production). Understanding coal fabric is important for coal gas exploration as it may be related to groundwater migration and the occurrence of methanogenic bacteria, prerequisite to biogenic gas accumulations. Likewise, the distribution of cleats in coal also determines pathways for migration and accumulation of thermogenic gas generated during coalification.     

The correlation between the macroseismic attenuation trend and the geo-structural framework; The calabropeloritan arc as an example

After describing attempts at perfecting a methodology for studying isotropic and anisotropic macroseismic fields in previous works, the authors here try to identify the causes of anisotropy in the context of the “new basement tectonics”.The seismic data are taken both from reconstructions of the macroseismic fields of historic events, by means of a critical analysis of the data, and from macroseismic fields of recent events surveyed by the authors. These data are correlated to the structural framework obtained through recent neotectonic studies and the lineament distribution traced on satellite images and using the “shadow” method. Generally the direction of elongation of the mesoseismic area is closely dependent on the source parameters and can be associated with recent and present-day systems outlined by the latest neotectonic studies.The best correlation is observed, however, with the lineament pattern obtained using the “shadow” method: the domains of the lineaments associated with the preferential trend of the macroseismic field show, in the rose diagram of cumulative number, values of prevalence and kurtosis higher than average; in the cumulative lengths diagram, on the other hand, they show prevalence maxima and, in particular, kurtosis maxima which are all the higher the more the anisotropic trend of field is accentuated. Using the “Giant Griffith Cracks” model for the lineaments, it can be deduced that the swarms refer to fracture systems with greater vertical development generated during the most recent tectonic phases.Finally, from a study of the dynamic characteristics of the elastic waves, that are the main agents responsible for macroseismic effects, it can observed that the wavelength order of magnitude is comparable with that of the linear parameters in the “warp” formed by the “Giant Cracks”. It can, thus, be deduced that the strong absorption of energy can be determined by the fracture swarm when the wave propagation occurs orthogonally to the swarm.     

The principle of antagonism in the earth's evolution

It is shown that for a complete geological interpretation of the evolution of the Earth, the principle of antagonism between endogenic and exogenic forces must be consistently applied. Inasmuch as the nature of the endogenic forces is random, it is possible to distinguish between effects of the two types of forces by a statistical test for nonrandomness (or randomness). Examples are given. Thus it is, e.g., shown that the orientation of valley trends in Switzerland is non-random; therefore the pre-design of the Swiss valleys is of tectonic, not erosive origin.     

Ratio between erosion and tectonic processes in platforms and mountainous regions

The paper discusses changes in the structure of river valleys under action of Coriolis forces, directed migration of river channels toward the right-side banks regardless of river orientation, dimensions, and water abundance. The values of lateral and bottom erosion in river valleys are compared with the rates of modern deformations in platforms and mountainous regions. This phenomenon is to be taken into consideration when interpreting lineaments and other topographic features as tectonic elements.     

Sedimentogenesis in the Mesozoic-Cenozoic continental rifts of Central Asia

An analysis of continental sedimentogenesis in Mesozoic rifts of the Transbaikal region and Mongolia, as well as in the Cenozoic Baikal rift zone, revealed a succession of volcanic-sedimentary formations, which constitute the sedimentary cover. The peculiar sedimentation features reflect exogenic processes that are characteristic of rift structures and the influence of deep-seated (exogenic and catagenic) sources. It is proposed to define a specific, rift, type of sedimentogenesis.     

Granulites and related rocks in variscan median Europe: A dualistic interpretation

On the basis of differences in structural, petrological and radiometric features, two main clear-cut groups can be distinguished for the granulites of the Variscan median Europe.Group I comprises lenses of eclogite-granulite scattered in the internal zones of the Hercynian belt, whereas Group II includes granulitic slices related to deep-seated Alpine lineaments and xenoliths scavenged by recent volcanoes.Group I granulites belong to early thrust nappes of the Variscan orogen; they display high-pressure assemblages and are commonly associated with eclogites and garnet-peridotites. From radiometric data, this HP granulitic-eclogitic metamorphism happened around 450-400 Ma throughout median Europe. A subduction context is suggested by the low T/P gradient, the occurrence of eclogites and the contemporaneity with some blueschist-facies rocks.Group II granulites are characterized by massive occurrences, intermediate-pressure granulite-facies parageneses and the absence of eclogites. Granulitic paragneisses often display a pronounced depletion in granitophile elements and may appear as degranitized restites. Numerous basic-ultrabasic complexes occur and are interpreted as deep-seated, layered igneous intrusions emplaced during the granulitic metamorphism. Radiometric dating indicates a late Hercynian (ca. 300 Ma) age. The high T/P gradient, the occurrence of synchronous basic intrusions and the post-collision context suggest a granulitic event due to a major thermal anomaly.The Variscan cycle is thus characterized by two granulite-forming episodes. “Older granulites” of the HP type result from an early compressive stage in a crustal subduction context and “younger granulites”, from a major thermal event which originated in the upper mantle and annealed the deepest parts of the Variscan belt. A broadly similar duality in the genesis of granulitic rocks may be anticipated in other collisional belts.     

藏北长江源地区河流地貌特征及其对新构造运动的响应

对藏北长江源地区河谷地貌和新构造变形调查发现,该区具有平行式水系格局,河谷地貌以形态不同的窄谷和宽谷为特点,新近纪以来该区主要经历了早期挤压和晚期伸展构造演化过程,产生了褶皱-逆冲、走滑剪切、正断层和地堑构造3种构造变形样式。长江源区河谷地貌的形成演化明显受新构造运动的影响,新构造运动不仅控制了河谷地貌形态与水系格局,而且影响了河流阶地分布以及洪(冲)积扇的形态、结构。长江源地区主要水系至少自全新世以来是沿新构造运动产生的不同性质断裂构造溯源侵蚀发育而成。     

辽宁、吉林、黑龙江地区流水成因的砂金矿

该区具有重要工业意义的砂金矿床,几乎皆是流水成因的。研究其矿质来源、含金地质体的风化剥蚀作用、砂金矿在河谷中的搬运方式和距离、砂金矿的成矿作用及矿床特征,不但可以扩大砂金矿的找矿前景,还能为在砂金矿分布区寻找岩金矿提供依据。     

Evolution of taphrogenic lineaments in continental platforms

The Rift System of eastern Africa is taken as a basis for an enquiry into the nature and age of taphrogenic lineaments in continental platforms. Special emphasis is placed on those segments in which the early Precambrian infrastructure has been exposed by continued uplift and deep erosion, and the evidence points to a genetic association of the Neogene graben faults with dislocation zones originating in the Precambrian and affecting the deep lithosphere. These proto-rift dislocations were repeatedly rejuvenated during successive tectonothermal cycles, showing blasto-mylonites, flaser gneisses and migmatites according to tectonic depth, and culminating in brittle surface faulting. A fundamental difference between taphrogenic and orogenic processes is emphasized by the oblique crossing of younger fold belts by the lineaments. Geophysical and other evidence from Africa confirms data from the Rhinegraben and Lake Baikal showing that continental rift systems are underlain by zones of high heat flow and intrusions of anomalous low density mantle rock (penetrative convection), producing structures comparable with those beneath mid-ocean ridges. Geological mapping, however, proves that dilation is minimal and that rift volcanism is of continental type and, with small exceptions, is limited to a sector extending south from the Afar triangle in Ethiopia through Kenya. It is suggested that sea-floor spreading in the African rifts was prevented by their geotectonic position, and that the continent was under pressure from the active mid-ocean ridges surrounding it on three sides. Evidence is described from East Africa, and from the West African and Guiana Shields, indicating that continental lineaments extended into the ancestral rifts of sea-floor spreading. It is concluded that in the lithosphere, above the mantle lowvelocity zone, deep criss-crossing lineaments of ancient origin exist, of which some served in Precambrian times as dislocation zones and channels for penetrative convection and were thus pre-conditioned for periodic tectonothermal rejuvenation. Certain segments of these channels have been selected by the powerful rising mantle dorsals associated with sea-floor spreading, and thus play a part in plate tectonics.     

岩溶地下水富集的地貌组合形态

岩溶地貌组合形态是地质背景条件、地壳隆升、断裂和褶皱等构造运动及溶蚀、侵蚀作用等内外动力地质作用的综合表象。特定的岩溶地貌组合形态,能够反映地下岩溶发育的过程和特征,表现地下水的运动及赋存状态,因而可作为寻找和圈定地下水富集区段的标志。文章通过总结区域水文地质调查实践的成果及经验,列出了8种能够有效反映地下水富集区段的岩溶地貌组合形态,分别是:岩溶山间平坝区、谷地及洼地古地表干流遗迹线、沟口洼地孤峰下、溶蚀沟谷交汇处、岩溶陡崖下、岩溶谷中湾对湾段、缓坡及浅洼地边缘、垄岗台地丘陵区。并逐一描述各个地貌形态特征,通过典型实例剖析,分析了它们的赋水机制。实践证明这些地貌组合形态可作为寻找地下水富集区段的标志。      

Distribution, geometry, age and origin of overdeepened valleys and basins in the Alps and their foreland

Overdeepened valleys and basins are commonly found below the present landscape surface in areas that were affected by Quaternary glaciations. Overdeepened troughs and their sedimentary fillings are important in applied geology, for example, for geotechnics of deep foundations and tunnelling, groundwater resource management, and radioactive waste disposal. This publication is an overview of the areal distribution and the geometry of overdeepened troughs in the Alps and their foreland, and summarises the present knowledge of the age and potential processes that may have caused deep erosion. It is shown that overdeepened features within the Alps concur mainly with tectonic structures and/or weak lithologies as well as with Pleistocene ice confluence and partly also diffluence situations. In the foreland, overdeepening is found as elongated buried valleys, mainly oriented in the direction of former ice flow, and glacially scoured basins in the ablation area of glaciers. Some buried deeply incised valleys were generated by fluvial down-cutting during the Messinian crisis but this mechanism of formation applies only for the southern side of the Alps. Lithostratigraphic records and dating evidence reveal that overdeepened valleys were repeatedly occupied and excavated by glaciers during past glaciations. However, the age of the original formation of (non-Messinian) overdeepened structures remains unknown. The mechanisms causing overdeepening also remain unidentified and it can only be speculated that pressurised meltwater played an important role in this context.     

The role of karst in the genesis of sulfur deposits, Pre-Carpathian region, Ukraine

 Most of exogeneous epigenetic sulfur deposits are clearly associated with intensely karstified carbonate and sulfate rocks. This paper demonstrates, using the Pre-Carpathian region as an example, that karstification is one of the most important processes controlling the formation of sulfur deposits. This is determined by a coincidence of some major prerequisites of these two processes. In the Podol'sky and Bukovinsky regions the Miocene aquifer system is well drained by erosion valleys; the giant network caves known here in gypsum formed under past artesian conditions. In the region of sulfur deposits, associated with the same karstified gypsum strata, true artesian conditions still prevail. Hydrogeologic data show that abundant cavities detected in the vicinity of sulfur deposits can be interpreted as having the same origin as the fossil caves of the Podol'sky and Bukovinsky regions. The current widespread belief that the gypsum/anhydrite stratum in the region is aquifuge separating the Miocene aguifers is inadequate. This belief caused much controversy with regard to the genetic interpretations of sulfur deposits in the region. Caves formed by the upward water flow through the gypsum/anhydrite stratum govern the water exchange between the aquifers within the aquifer system. A new karst model for the formation of sulfur deposits is suggested. It agrees well with the hydrogeological features of the Miocene sequence and with biogeochemical mechanisms of sulfur origin in low-temperature diagenetic environments. Received: 16 February 1995 · Accepted: 4 June 1996     

中国云台山世界地质公园的新构造运动特征

云台山是一处以崖墙、瀑布为主体的山水地貌型世界级地质公园,其多层分布的崖墙、深邃幽静的峡谷和谷中谷现象等对研究云台山地区的新构造运动,具有重要的指示意义。云台山地区的新构造运动,不仅具有间歇性抬升特征,而且具有差异性、掀斜性抬升特征。形成了黄河南移、河流同步弯曲等现象和复杂的地貌景观。     

月球线性构造分类体系研究

月球线性构造是月球科学研究中的重要组成部分,建立月球线性构造分类体系是月球地质图编研的关键。前人对月球线性构造的分类研究主要基于月表的形貌特征,划分的线性构造类型参差不齐,尚未形成一个公认的、规范的、具有普适性的线性构造分类体系,以至于分类结果的可对比性差、参考性和易操作性较低,不利于月球线性构造纲要图的编制。并且月球线性构造的概念混乱、术语不统一,存在"同物异名、同词异义、异词同义、涵义不明"的现象,不利于全球性的统一制图和成果的展示及使用。鉴于此,本文采用多指标组合的分类方法,以成因机制和形貌特征作为主要指标,兼顾物质组成,再结合线性构造形成的动力学机制,建立了符合月球动力学演化背景的、统一规范的线性构造类型划分的新方案,避免了单以形貌特征为依据来分类出现的混乱状态,具有较好的科学性和可操作性。将月球的线性构造类型划分为:内动力地质作用形成的线性构造,包括皱脊、月溪、地堑、断裂;外动力地质作用形成的线性构造,包括坑缘断裂和坑底断裂,以及多成因机制、多动力来源作用形成的特殊类型如坑链等。在此基础上,并利用多源遥感数据建立了易于判别且具有代表性的线性构造识别标志,可为全月球线性构造的统一制图提供识别依据。     

Formation mechanism of eco-geo-environmental hazards in the agro-pastoral interlocking zone of northern China

 High sensitivity and distinct degradation characterize the eco-geo-environment in the agro-pastoral interlocking zone in northern China. Because of its specific natural conditions and human activities, this zone is easy to change and transfer between typical agricultural and pastoral environments. Several kinds of eco-geo-environmental hazards exist in the zone, such as land desertification, climatic disasters, endemic disasters, etc. The mechanisms of these eco-geo-environmental hazards include geotectonic processes in the Earth's history, and exogenic causes, such as the East Asia monsoon and irrational human activities. Both tectonic processes and exogenic causes act on the ecologically vulnerable environment, which makes the potential eco-geo-environmental vulnerabilities real hazards. Received: 9 July 1999 · Accepted: 18 April 2000     

Landforms and Neotectonics in the Equatorial Passive Margin of Brazil

Neotectonic movements have been proposed in the literature in order to explain some landforms of the equatorial passive margin of northeastern Brazil. Its seismo-tectonic activity is concentrated in a few sectors located on or near the coast. Active or recently active structures are mainly identified in Neogene deposits. Identifying a contribution of neotectonics to the morphogeny is difficult in a context where most major morphostructural patterns are explained by Cretaceous tectonics related to oceanic opening and by differential erosion induced by Tertiary epeirogenic uplift. We aim to assess the nature of features considered as possibly neotectonic in origin. Seismogenic faults are not related to significant topographic breaks, except on the coast, where they usually reach only a few meters in height. A study of landforms located near zones of seismo-tectonic activity indicates a possible, probably weak, contribution of neotectonics to the formation of a few high scarps. These scarps occur along or near fault zones reactivated in Cretaceous times. We conclude that neotectonic movements are the result of ongoing deformation along predominantly strike-slip fault zones, with long term deformation rates similar to those recorded by dated landmarks (0.01 mm.yr ^-1). Despite reported deformation rates that can amount in places to 0.4 mm.yr ^-1, neotectonic rates are lower than erosion rates. The consequence is that major structural landforms in the region mainly originated in Cretaceous to early Tertiary events.     

地球内外动力耦合作用与重大地质灾害的成因初探

提出了用以解释若干重大地质灾害的成因的地球内外动力耦合作用理论。在以往的自然灾害分类及研究中 ,常将内动力地质灾害和外动力地质灾害区分为两种类型 ,而注意两者的联系显然不够。本文则论证了在我国大部分地壳运动活跃地区内外动力耦合作用常是重大地质灾害的总体成因。     

福建泰宁丹霞地貌中的洞穴类型及成因浅析

福建泰宁白垩纪红层盆地出露晚白垩世沙县组紫红色中一薄层粉砂岩、粉砂质泥岩和崇安组紫红色厚层砾岩、砂砾岩。红层发育北东,北北东向等多组不同走向断裂及节理。经外动力地质作用形成青年期丹霞地貌,崖壁上千姿百态的丹霞洞穴构成独特的微地貌景观。丹霞洞穴发育受岩性及节理、裂隙控制,崇安组粉砂岩、砂岩及含砾砂岩夹层是形成洞穴的主要层位,岩层的厚度及节理、裂隙控制洞穴产出的规模,风化剥蚀、流水侧蚀、大气降水及其水流侵蚀、重力崩塌是形成不同形态洞穴的主要外动力作用,洞穴的形成以一种外动力作用为主,或在发展过程中叠加了其它外动力作用,因而常为多种外动力综合作用的结果。     

Interplay between tectonic, fluvial and erosional processes along the Western Border Fault of the northern Upper Rhine Graben, Germany

The northern Upper Rhine Graben, situated in the central part of the European Cenozoic rift system, is currently characterized by low intra-plate seismicity. Historical earthquakes have not been large enough to produce surface rupturing. Moreover, the records of Quaternary surface processes and human modifications are presumably better preserved than the record of the relatively slow tectonic deformation.In order to gain information on the neotectonic activity and paleoseismicity in this setting, the geological and geomorphological records of fault movements along a segment of the Western Border Fault (WBF) were studied using an integration of techniques in paleoseismology, structural analysis and shallow geophysics. The WBF segment investigated follows a 20 km long linear scarp of unclear origin. A series of geophysical measurements were performed and the results suggested that near-surface deformation structures are present at the segments' southern end. Several trenches opened at this location revealed fault structures with consistent extensional style and a maximum vertical displacement of 0.5 m. In one trench, the deformation structures were dated between 19 and 8 ka. Assuming the deformation has been caused by an earthquake, a M_w 6.5 earthquake would be implied. Aseismic deformation would point to a fault creep rate ≥ 0.04 mm/yr.A reconstruction of the sequence of events at the trench site, from Middle Pleistocene to Present, demonstrates that the morphology at the base of the scarp is the result of interplay between tectonic activity and fluvial and erosional processes. At the regional scale, a mixed origin for the WBF scarp is proposed, combining the effects of fluvial dynamics, erosion, regional uplift and localized tectonic activity on the WBF.     

Engineering geomorphological characterisation of the Vajont Slide,Italy, and a new interpretation of the chronology and evolution of the landslide

Although the 1963 Vajont Slide in Italy has been extensively studied for over 50 years, its regional geological and geomorphological context has been neglected. In this paper, we use field observations and remote sensing data to elucidate the interaction between endogenic and exogenic processes that brought the north slope of Monte Toc to failure. We present the first detailed pre- and post-failure engineering geomorphology maps of the slide area. The maps delineate two main landslide blocks, several sub-blocks, compressional and extensional zones, and secondary failures in the deposit. The maps provide new insights into the kinematics, dynamics and evolution of the slide. Finally, we discuss the origin of Vajont Gorge and a prehistoric failure that occurred at the same location as the 1963 slide. We propose, as part of a newly developed multi-stage landscape evolution sequence, that the prehistoric failure was a deep-seated gravitational slope deformation (sackung) that initiated during deglaciation and continued to slowly move until the catastrophic failure in 1963. We argue that the gorge was created by these deep-seated slow movements.