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 390 毫秒
1.
Although it is a pelagic sediment, fine-grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units. Numerous occurrences of allochthonous chalk have been reported in recent years, having been recognized by large-scale bedding features seen in outcrop. Smaller-scale internal features, such as contorted laminae, and larger features, such as smeared burrows and imbricated flint nodules, attest to a significant amount of soft-sediment deformation and synsedimentary slumping in European chalk sections of Late Cretaceous age. Truly autochthonous chalks contain complex, tiered ichnofabrics and in some cases exhibit a diagenetic nodular fabric that is undisturbed by transport. In some situations, such as stagnant water conditions, autochthonous chalks may exhibit primary lamination, although this is very uncommon in European chalk sequences. Different types of redepositional processes produce an array of varied allochthonous fabrics. Glide and slump units, for example, contain internal deformational features produced during sliding. Ooze flow causes plastic deformation of chalk units, internally as well as externally. Resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric, such as a conglomerate composed of detrital chalk clasts. In this paper, typical macroscopic, sedimentary fabric types are illustrated, and the means of identifying them are discussed in terms of bioturbation features, in situ diagenetic nodules versus detrital clasts, physical deformation structures and development of flints.  相似文献   

2.
 During the Cenozoic, in the western Paris Basin, atmospheric weathering of the chalks with flints of the Upper Cretaceous led to the creation of clay with flints. A reconstitution of the chalks lost to dissolution is proposed and is based on the determination of the age of the parent chalks of the clay with flints and the quantification of the thickness of dissolved chalk. The chalks affected by weathering range in age from Turonian to Maastrichtian, thus confirming the deposition of calcareous sediments in the western Paris Basin up to the Maastrichtian. Chalk weathering took place in situ, as indicated by the preservation of the stratigraphic succession of the chalk in the clay with flints profiles. Weathering led to the dissolution of 20–200 m of chalk, with regional variations. The weathering rate varies between 2.1 and 14.5 m/Ma. Received: 20 July 1998 / Accepted: 1 July 1999  相似文献   

3.
Microtexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability.  相似文献   

4.
The Chalk is one of the most extensively distributed series in England. It is essentially a soft limestone principally consisting of the remains of marine organisms, deposited in shallow water.The Upper Chalk of Kent, in particular, is characterized by a high porosity and relatively low dry density. The porosity and dry density of the Lower Chalk of Yorkshire and the Middle Chalk of Norfolk are lower and higher respectively, because of the higher content of interstitial secondary calcite. Porosity is not a significant factor as far as the gross permeability of the Chalk is concerned.The Upper Chalk of Kent is moderately weak, when tested in unconfined compression, whilst the Lower and Middle Chalk are moderately strong. All three groups of Chalk suffer a substantial reduction in strength when saturated, in the case of the Upper Chalk the loss in strength is dramatic. The indirect tensile strength is usually less than one twentieth that of the unconfined compressive strength. When subjected to undrained triaxial tests the Upper Chalk first underwent brittle failure at lower confining pressures but above 4.9 MN/m2 significant plastic deformation occurred leading to barrel-shaped failures.Young's modulus is not a simple constant but varies with stress, increasing somewhat with increasing stress in the Chalk from Yorkshire and Norfolk. This did not happen in the Upper Chalk since plastic deformation began much earlier.  相似文献   

5.
Diagenetic history of a North Sea chalk   总被引：1，自引：0，他引：1  
A study of the petrofabrics of Danian and uppermost Maastrichtian chalk from the North Sea was undertaken to investigate its particulate components and diagenetic history. Danian and Maastrichtian chalks are intensely mottled and burrowed globi-gerinid lime mudstones. The Danian chalk matrix is composed of coccolith and thoracosphaerid debris, whereas the Maastrichtian chalk matrix contains mainly coccoliths. The lower part of the Danian is often argillaceous. Three modes of lithification are evident—a spot-welding of adjacent grains (important in Danian chalk), selective overgrowths (prolific in Maastrichtian chalk), and a sparry calcite pore filling associated with Maastrichtian stylolitization. Not only does the scant cementation of chalk stem from an inadequate source of metastable calcium carbonate in the form of aragonite, but also indirectly in that extensive pressure-solution is impeded by certain pore fluid compositions. Pressure-solution can occur only at point contacts where a threshold linear pressure is exceeded and so allows an increase in calcite solubility. It is proposed that through the formation of spot-welds an initial rigid intergranular framework is constructed in chalk relatively early during diagenesis. Subsequent increases in overburden eventually permit extensive stylolitization and the late diagenetic reprecipitation of a sparry calcite pore filling adjacent to stylolites. The time and genesis of selective overgrowths is less clear.  相似文献   

6.
Chalk deformation and large-scale migration of calcium carbonate   总被引：2，自引：0，他引：2  
Y. MIMRAN 《Sedimentology》1977,24(3):333-360
Sixty Upper Cretaceous chalk exposures were examined and sampled in Dorset, the Isle of Wight and Guildford, South England, in order to investigate the effects of tectonic deformation on the chalk fabric. Light and scanning-electron microscopes were used extensively, and chemical, mineralogical and isotopic analyses ware carried out. Two types of fabric modification were distinguished. The first type involves more than 90% volume loss by mechanical compaction at the early stages of deformation followed by dissolution and removal of calcium carbonate in the advanced stages of deformation. Chalks which have undergone this type of fabric modification are dense and consist of well rounded 0.5–3 μ calcite crystals with well developed pressure-solution contacts. These chalks contain a high proportion of calcispheres (many of which are plastically deformed) but very few well preserved planktonic foraminifera and coccoliths. They are relatively enriched in insoluble constituents and depleted in strontium. The second type of fabric modification involves introduction of calcium carbonate into the pore spaces. Chalks which have undergone this type of modification are dense and contain a high proportion of 3–5 μ polygonal interlocking calcite crystals. Fossils are virtually never deformed, and delicate foraminifera and coccoliths are well preserved. Insoluble constituents similar to those found in the unmodified chalks occur in low concentrations. Removal of calcium carbonate at crystal contacts has taken place in chalks which have been subjected to high effective tectonic stresses and at crystal peripheries in chalks which have been subjected to high pore fluid pressure. Dissolution at crystal peripheries is responsible for the extensive calcium carbonate losses, and it is termed herein ‘confining pressure solution’. Introduction of calcium carbonate occurs in rocks which were under low tectonic stresses. During deformation calcium carbonate migrates from chalks under high stresses towards those under tow stresses, while some goes into solution in sea water. Well developed joints and high pore fluid pressure might increase the rate of calcium carbonate removal by three orders of magnitude. Petrographic and isotopic data suggest-that all fabric modifications studied took place in meteoric water.  相似文献   

7.
Ground investigations for the A303 Stonehenge Tunnels revealed a unique and complex Chalk geology including the presence of the thickest (>20 m thick), and previously unknown phosphatic chalks in England, partly filling fault controlled erosional channels. The use of natural gamma-ray borehole logs to determine the presence and thickness of the phosphatic deposits is of particular value and combined with the lithostratigraphy, macrofossil and nannofossil biostratigraphy from cores has, for the first time, accurately constrained the Coniacian to Santonian age and the lenticular geometry of such deposits. Four phosphatic chalk events between 88.5–86.5 Ma are recognised associated with synsedimentary faulting. We suggest a causal link between tectonics, subsidence and channel-formation, phosphatisation events, pulses of oceanic upwelling on a frequency of about 0.5 million years to mantle-controlled plate tectonic episodes. The implications of this geology for construction of the A303 and the archaeology of the area are discussed.  相似文献   

8.
Chalks originate as Cretaceous to Recent pelagic or hemipelagic calcareous ooze, which indurate via burial diagenesis to chalk and limestone. Because they accumulate in pelagic settings with high environmental continuity, chalks may form thick formations and even groups. For this reason, and because chalks have a simple mineralogy (low magnesium calcite, silica and clays), they are ideal for the study of diagenetic processes including the depth-related decrease of porosity. It is the aim of this study to illustrate how the evaluation of in situ elastic strain can help in understanding these processes including the interplay between stress-controlled diagenetic processes and processes furthered by thermal energy. Petrophysical core and well data can be used for analyses of how porosity reduction via pore collapse and pressure dissolution is related to in situ elastic strain. The data in question are: depth, density of overburden, pore pressure, ultrasonic P-wave velocity and dry density/porosity. The analysis reveals that the transition from ooze to chalk is associated with high elastic strain and consequent pressure dissolution at calcite–particle contacts causing contact cementation. The transition from chalk to limestone is also associated with high elastic strain, especially at clay–calcite interphases causing development of stylolites via pressure dissolution, and consequent pore-filling cementation. Following each transformation the elastic strain drops rapidly. The observation of this diagenesis-related pattern in elastic strain of the sedimentary rock is novel and should not only be helpful in understanding the porosity development in sedimentary basins, but also add basic scientific insight.  相似文献   

9.
The Upper Cretaceous chalks of southern England are a thick sequence of rhythmically bedded, bioturbated coccolith micrites, deposited in an outer shelf environment in water depths which varied between 50 and 200–300 m. The products of sea floor cementation are widely represented in the sequence, and a series of stages of progressive lithification can be recognized. These began with a pause in sedimentation and the formation of an omission surface, followed by (a) growth of discrete nodules below the sediment-water interface to form a nodular chalk, erosion of which produced intraformational conglomerates. (b) Further growth and fusion of nodules into continuous or semicontinuous layers: incipient hardgrounds. (c) Scour, which exposed the layer as a true hardground. At this stage, the exposed lithified chalk bottom was subject to boring and encrustation by a variety of organisms, whilst calcium carbonate was frequently replaced by glauconite and phosphate to produce superficial mineralized zones. In many cases, the processes of sedimentation, cementation, exposure and mineralization were repeated several times, producing composite hardgrounds built up of a series of layers of cemented and mineralized chalk, indicating a long and complex diagenetic history. Petrographic study of early cemented chalks indicates lithification was the result of the precipitation of small crystals on and between coccoliths and coccolith fragments. By analogy with known occurrences of early lithification in Recent deeper water carbonates, the cement is believed to have been either high magnesian calcite or aragonite, and more probably the former. The vast scale of operations involved in the cementation process precludes carbonate in expelled pore fluids as the source of cement, whilst quantities of aragonite incorporated in sediment are also inadequate. This, plus the observed association of horizons of early lithification with pauses in sedimentation associated with omission surfaces suggests seawater as a source of cementing materials. Stratigraphic studies indicate that processes of early lithification leading to hardground formation proceeded to completion in intervals to be measured in tens or hundreds of years. Regional studies suggest that early lithification characterized relatively shallow water phases associated with regional regression over the whole of the area, whilst in detail, the distribution of mature mineralized hardground complexes is strongly correlated with sedimentary thinning and condensation over small areas and the buried flanks of massifs. Early cementation in more basinal areas is typically in the form of nodular developments and incipient hardgrounds, whilst day contents in excess of a few percent appear to have inhibited early lithification. The striking rhythmicity of hardgrounds and nodular chalks is no more than a particular expression of the overall rhythmicity of chalk sequences. The stage of early lithification reached in any instance is dependent on sediment type, the time interval represented by the associated omission surface and the degree of associated scour and erosion (if any). Chalk hardgrounds differ from most others described in the geological literature in their widespread distribution (individual hardgrounds may cover up to 1500 km2), the presence of striking glauconite and phosphate replacements of lithified carbonate matrices, their frequently sparse epifaunas, and boring infaunas dominated by clionid sponges. These differences reflect the deeper water shelf setting of the chalk, and the more open marine, oceanic circulatory system, both strikingly different from the setting of other, shallower water hardgrounds. Litho- and biostratigraphic variation in the chalk sequences of the area studied are summarized in an appendix.  相似文献   

10.
In 140 metres of Maastrichtian White Chalk (nannofossil chalk) exposed near Hemmoor, NW Germany, values of 87Sr/86Sr increase from 0.707760 in the Belemnella sumensis Zone (Lower Maastrichtian) at the base of the section (-54.5 m; referred to 0 m at a prominent marl, M900) to 0.707821 in the Belemnella baltica/danica Zone (Upper Maastrichtian) at the top of the section (+84.5 m). A plateau in 87Sr/86Sr occurs between -5m and +50m in the section, probably as a result of a very high rate of sedimentation in this interval. A belemnite and associated nannofossil chalk have similar 87Sr/86Sr values, suggesting that there has been little diagenetic alteration of the 87Sr/86Sr ratios in the chalk, which therefore preserves its original 87Sr/86Sr. Comparison of 87Sr/86Sr and nannofossil zonations for sequences at Bidart, France, and DSDP Sites reveals discordance and so possible diachronism of the basal boundaries of nannofossil Zones CC25B and CC25C.  相似文献   

11.
徐积刚  董世明  华文 《岩土力学》2015,36(7):1959-1965
为了研究围压对巴西裂纹圆盘应力强度因子的影响,使用权函数方法得到了围压作用下巴西裂纹圆盘的应力强度因子,进而得到径向集中荷载与围压共同作用下的应力强度因子的计算公式。在此基础上,从理论上分析了围压对巴西裂纹圆盘应力强度因子的影响,分析结果表明：围压对II型应力强度因子无影响,纯围压作用下裂纹趋于闭合;围压和集中力共同作用下,I型应力强度因子随着围压的增大而减小。对比分析了数值分析与理论结果,分析表明,理论与数值结果吻合良好,从而表明了理论分析的正确性。此外,还研究了围压对纯II型裂纹加载条件的影响,结果表明,纯II型裂纹的临界加载角随着围压增大而减小,直至为0。因此,当围压较大时,加载角为0°左右所发生的断裂不一定全是纯I型断裂。  相似文献   

12.
Metre-scale lithologic cycles, visible in core and on logs from Maastrichtian chalks of the Dan Field, were examined to determine their mechanisms of deposition and relation to hydrocarbon production. The lower parts of cycles consist of porous, cream-coloured, largely non-stylolitic, commonly laminated chalk with limited bioturbation (mainly escape burrows). Cycles are capped by thinner intervals of white to grey, hard, stylolitic chalk with concentrations of bioclastic material, intense burrowing and few preserved primary sedimentary structures. The cycle caps contain nearly twice as much Mg as compared to the more porous parts of cycles and also have slightly larger δ18O values (?4·1‰ for the caps; ?4·4‰ for porous zones). There is a significant reduction of average cycle thickness, as well as total thickness of the Maastrichtian chalk section, from SW to NE across the Dan Field. The cycle thinning largely results from a reduced thickness of porous chalks from the lower parts of cycles and thus is reflected in lower average porosity and permeability on the NE side of the field. These data indicate that episodic winnowing removed fine-grained constituents from highstanding northeastern areas. Porous cycle bases were deposited at relatively high rates that precluded complete bioturbation; preserved laminae, coupled with escape burrows, reflect episodic sediment influx in areas that flank the seafloor highs. Cycle tops apparently accumulated more slowly (throughout the region, but especially on seafloor highs), perhaps because of reduced productivity of planktic organisms. Slower sedimentation allowed more complete bioturbation and destruction of sedimentary structures, and also led to incipient high-magnesium calcite seafloor cementation (sufficient to yield firmer sediment and enhanced burrow preservation, but not to form true hardgrounds). Thus, the elevated magnesium contents and reduced porosity of the cycle caps reflect very early diagenetic processes that were only partially modified by burial diagenesis. Rates of chalk deposition, as inferred from physical and geochemical evidence, appear to be a significant control on reservoir characteristics in North Sea chalks. The highest average porosities and permeabilities are found in areas with the highest sediment accumulation rates where seafloor diagenesis is minimized. Topographic depressions at the time of sedimentation can thus be expected to have the best production characteristics, and synsedimentary topographic highs should have the thinnest sections and the poorest petrophysical properties.  相似文献   

13.
The Upper Turonian Chalk Rock occurs within a nodular unit within the otherwise generally soft, white chalk that dominates the English Upper Cretaceous. The nodular unit is condensed, and contains a number of hardgrounds that are designated here as the Chalk Rock Formation. The Chalk Rock contains some seven or eight hardgrounds, most of which are lithologically distinctive and can be traced over distances of up to 250 km. Nine beds within the Chalk Rock are named, comprising six hardgrounds and three marl seams. The lowermost widespread hardground appears to be more or less equivalent to the “Spurious Chalk Rock” of the south coast of England. In two areas the thickness of the Chalk Rock is greatly diminished. The most marked area, in west Wiltshire, is located close to the Palaeozoic Mendip Hills and indicates that the Mendip structure has influenced Turonian sedimentation. The other region of thinning is a platform-like area in the eastern Chiltern Hills WNW of London.  相似文献   

14.
The aim of this paper is to evaluate the role of groundwater and sea weathering on the strength of the chalk rocks exposed on the coastline of the English Channel in Normandy, NW France. We present a study of the rock strength variations of three representative chalk units (Lewes Chalk, Seaford Chalk and Newhaven Chalk) exposed at various locations on the coastal chalk cliffs. The combination of UCS tests and SEM observations have been used (1) on dry natural chalk samples, (2) on chalk samples at various moisture contents, (3) on dry chalk samples submitted to a 10-day cycle of alternating wetting and drying by distilled water and by sea water. Dry chalk samples show low UCS strength (3.46–4 MPa) indicative of very weak rocks. When chalk samples are submitted to progressive water wetting, they present a decrease of UCS strength and Young's modulus of 40% to 50%. This behaviour begins at low values of water content within the chalk, i.e., for a degree of water saturation ranging between 10% and 17%. When chalk samples are submitted to an artificial weathering cycle with distilled water, a decrease in strength is observed, whereas the Young's modulus increases. SEM observations indicate the occurrence of microcracks and particle aggregates in the sample. When chalk samples are submitted to an artificial weathering with sea water, the decrease of UCS strength and Young's modulus achieves a minimum. SEM observations indicate salt crystals within the chalk. On the coastal cliffs of NW France, weathering processes depend both on chalk lithology, which show a range of sensitivity to weathering and on the location of the chalk in the coastal area. Processes allied to the degree of weathering (e.g., salt crystallisation or fresh water disaggregation) differ in the chalk massif, on the cliff face and on the shore platform.  相似文献   

15.
The Ulster White Limestone Formation is an unusual chalk because it underwent a period of post-depositional emergence and erosion, followed by burial under 1·5–2·0 km of Tertiary basalts. A high degree of pressure solution and cementation produced a well-lithified limestone with low porosities (2·3–10·4%). The Ulster White Limestone shows no evidence of thermally induced textural alteration, except for thin (<0·5 m) pseudospar contact recrystallization zones adjoining basalt dykes. Whole-rock δ18O values of samples not associated with basalt dykes range from - 3·26%o to - 6·50%o (PDB). The δ18O values of macropore cements range from - 4·96%o to - 11·52%o (mean=-8·27%o). Modelling of the diagenesis of the Ulster White Limestone using trace element concentrations and carbon, oxygen and strontium isotopic ratios of whole rock and cement samples suggests a low water-rock ratio and either marine or mixed marine-meteoric pore water environment during the main episode of recrystallization. The maximum possible burial temperature was modelled to be ? 105°C. The diagenetic history of the Ulster White Limestone is similar to that of North Sea chalks that are at comparable burial depths as the Ulster White Limestone after basalt deposition. The geochemical data show no indication of hydrothermal alteration associated with the overlying basalts. The degree of alteration of fine-grained limestones composed predominantly of low-magnesium calcite, such as the Cretaceous/Tertiary chalks, appears to be controlled largely by the burial (effective stress) history of the limestone.  相似文献   

16.
循环加载时围压对岩石动力特性的影响   总被引：1，自引：0，他引：1  
刘恩龙  黄润秋  何思明 《岩土力学》2011,32(10):3009-3013
针对砂岩岩样,探讨了在不同围压作用下和轴向循环加载时岩样的动力力学性质,研究围压对砂岩岩样的动力力学性质的影响。采用的试验设备是MTS－815岩石和混凝土试验系统,5组围压分别为10、20、30、40、50 MPa。岩样为汶川地区的干砂岩,轴向荷载施加的频率为1 Hz。结果表明,（1）随着围压的逐渐增加,试样的残余轴向应变和体变逐渐增加,且剪胀发生时的残余体变也逐渐增加;（2）动力荷载作用时岩样在高围压比低围压下的初始刚度和强度高;（3）不同围压作用下,当应力比Rs较大时,岩样在较小的循环次数下发生破坏;（4）试样的破坏模式为剪切破坏,动力荷载作用下试样形成的局部化破坏带更宽。  相似文献   

17.
根据不同围压下板岩三轴试验的结果,研究不同围压下板岩的能量变化规律和损伤分析。研究结果表明,不同变形阶段板岩的弹性应变能、耗散能的变化情况不同,弹性应变能先增加后减小,耗散能加载初期几乎为零,进入屈服段急剧增加。根据弹性应变能与总吸收能之比将岩石压缩过程中裂隙发展划分为3个阶段:裂隙稳定发展阶段、裂隙加速发展阶段和裂隙贯通阶段。岩样破坏后总吸收能、耗散能与围压的关系表明,从开始加载到屈服段,畸变比能和体变比能之和Ue'大体等于弹性应变能Ue;从屈服段到峰值强度,Ue'小于Ue且差值越来越大。从能量角度定义损伤变量,认为:低围压状态对应较低的耗散能、较高的损伤值;高围压状态对应较高的耗散能、较低的损伤值。   相似文献   

18.
较低和较高围压下煤岩三轴试验及其塑性特征新表述   总被引：1，自引：1，他引：0  
李小春  白冰  唐礼忠  郭群 《岩土力学》2010,31(3):677-682
对煤岩进行了较低和较高多个围压下的常规三轴加卸载试验研究,给出了系统的试验成果。试验表明,较低围压下,卸载路径和加载路径几乎完全重合,煤岩应力-应变特性呈现明显的线弹性特征,并表现出一定的脆性破坏特性;而较高围压下,应力-应变呈现明显的非线性特征,卸载路径不再原路返回,呈明显的塑性变形特征。为了定量刻画煤岩的塑性硬化特性,提出了根据硬化参量的几何意义计算其值的方法,并选择累积塑性应变作为塑性硬化参量,计算了27 MPa围压下试验曲线的硬化参量,作为对比还计算了采用直接卸载法计算的该试验曲线的累积塑性应变值。结果发现,随着轴向变形逐渐增加,煤岩的塑性硬化逐渐增长,并且用该方法计算出的塑性硬化参量远大于用直接卸载法计算的结果。由于该方法完全符合路径积分的限制条件,因此,更加合理。  相似文献   

19.
An almost continuous layer of Upper Cretaceous deposits up to 1000 m thick was probably deposited across much of SW England. Phases of uplift in the late Cretaceous and early Cenozoic, each of which was followed by extensive erosion and dissolution, resulted in the removal of all except a few outliers of Chalk Group that crop out in east Devon and south Somerset. Those on the Devon coast between Sidmouth and Lyme Regis are some of the best exposed Cenomanian to early Coniacian successions in NW Europe and include the most westerly chalks preserved onshore in England. They form an integral part of the Dorset and East Devon World Heritage Site. In contrast to the Chalk of much of southern England, the older formations in Devon, the Beer Head Limestone, Holywell Nodular Chalk and New Pit Chalk, show marked lateral lithological variations that result from a combination of penecontemporaneous movements on local faults and relatively shallow-water environments close to the western edge of the Chalk depositional basin. The younger parts of the succession, the Lewes Nodular Chalk and Seaford Chalk Formations, comprise chalks that do not appear to have been greatly affected by penecontemporaneous fault movements. These formations include lithological marker beds that have been correlated with marker beds in the Sussex type area. The principal sedimentary breaks in the Devon succession cannot be correlated with confidence with eustatic changes in sea level.  相似文献   

20.
张希巍  王刚  蔡明  徐荃 《岩土力学》2018,39(10):3515-3524
以凌海花岗岩为研究对象,进行了一系列常规三轴高压试验,研究了花岗岩的变形特点及脆性演化规律。基于试验结果,分析了不同围压下的全应力-应变曲线,探讨了静态应变采集试验中花岗岩表面变形特点、峰前损伤规律及其与裂隙扩展的关系,总结了动态采集试验中典型的裂纹扩展模式,并基于改进的峰后能量平衡法评价岩石的脆性。研究结果表明：多应变片静态采集三轴试验中岩样不同位置变形规律差异明显,压缩应变较大的区域往往是裂隙产生、扩展的位置;动态应变采集三轴试验中识别了3种典型的裂隙扩展模式,且与应力加载方式存在一定联系;在70 MPa围压范围内,岩样都表现出明显的脆性破坏特征,其脆性指数随围压增加呈现出先减小后增加再减小的变化趋势。该研究成果对进一步开展其他硬岩的变形破坏机制研究和地下工程的稳定性分析具有一定参考价值。  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