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61.
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
62.
鄂尔多斯北部大牛地地区钻井施工中钻杆偏磨、耐磨环失效现象很普遍。通过对比分析研究,认为造成钻杆耐磨环失效的主要原因有:地层研磨性、钻杆的井下工况、耐磨材料选择与敷焊工艺的影响。 相似文献
63.
Early Permian ammonoids from the Kaeng Krachan Group of the Phatthalung-Hat Yai area, southern peninsular Thailand 总被引:1,自引:1,他引:1
Masayuki Fujikawa Katsumi Ueno Apsorn Sardsud Wirote Saengsrichan Yoshihito Kamata Ken-ichiro Hisada 《Journal of Asian Earth Sciences》2005,24(6):739
An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Böse, Agathiceras? sp., and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand. The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clastic-dominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoid fauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Böse, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting. 相似文献
64.
Said Ettazarini 《Environmental Geology》2005,49(2):293-299
Possible water–rock interaction processes, in the Moroccan basin of Oum Er-Rabia, were discussed by a geochemical study of groundwater from the Turonian limestone aquifer, the most important water resource in the region. Different types of water according to the classification of Piper were defined. Waters have shown an evolution from dominant CHO3–Ca–Mg type through mixed to SO4–Cl–Ca–Mg type. The use of geochemical diagrams and chemical speciation modeling method has shown that water–rock interaction is mainly controlled by carbonate and anhydrite dissolution, ion exchange and reverse ion exchange processes. Water–rock equilibrium conditions are favorable for the precipitation of calcite, dolomite, kaolinite and magnesian smectite. 相似文献
65.
The early Mesoproterozoic Rohtas Limestone in the Son valley area of central India represents an overall shallowing-upward
carbonate succession. Detailed facies analysis of the limestone reveals outer- to inner-shelf deposition in an open marine
setting. Wave-ripples, hummocky cross stratifications and edgewise conglomerates argue against a deep marine depositional
model for the Rohtas Limestone proposed earlier. Stable isotope analysis of the limestone shows that δ13C and δ18O values are compatible with the early Mesoproterozoic open seawater composition. The ribbon limestone facies in the Rohtas
Limestone is characterized by micritic beds, each decoupled in a lower band enriched and an upper band depleted in dissolution
seams. Band-wise isotopic analysis reveals systematic short-term variations. Comparative enrichment of the heavier isotopes
in the upper bands is attributed to early cementation from sea water and water derived from the lower band undergoing dissolution
because of lowering of pH at depth. The short-term positive shifts in isotopic compositions in almost every upward gradational
transition from a seamed band to a non-seamed band support the contention that dissolution seams here are of early diagenetic
origin, although their formation was accentuated under overburden pressure. 相似文献
66.
Naser A. Al-Shayea 《Engineering Geology》2005,81(1):84-97
Propagation of a crack in engineering materials including rocks can cause failure. Knowledge of the stress state under which a crack can propagate, and the trajectory it may follow during its growth are thus very important for the stability of rock masses/materials and for the safe design of structures in/on rocks. In this paper, the crack initiation angle and subsequent crack propagation path are experimentally investigated for limestone rock specimens. This investigation was conducted under various mixed mode I-II loading conditions, including pure mode-I and pure mode-II.This study includes conducting diametrical compression tests on notched Brazilian disk specimens. Moreover, the effect of confining pressure and temperature on crack initiation and propagation were also studied. The experimental results were compared with theoretical predictions of crack initiation angle. The results showed that limestone behaves in brittle fashion, and the effects of confining pressure and temperature on failure trajectories were not significant. Generally, the crack initiation angle can be predicted by the maximum tangential stress criterion. However, for notched Brazilian disk with high value of crack orientation with respect to loading direction, crack does not propagate from the tip of the crack. This important observation indicated that the tensile-strength failure can become more critical than the fracture-toughness failure. 相似文献
67.
A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. Yet, the particular mechanisms through which fluids and associated parameters influence the stress regime and thus the seismicity of a particular area are not well understood.We carry out a study of the spatio-temporal behavior of earthquakes, fluid-related parameters (groundwater levels) and meteorological observables (precipitation) in the swarm earthquake area of Bad Reichenhall, southeastern Germany. The small volume in which the earthquakes take place, almost yearly occurring earthquake swarms and a permanent, seismo-meteorological monitoring network, provide nearly controlled experimental conditions to study the physics of earthquake swarms and to infer characteristic properties of the seismogenic crust.In this paper we (1) describe this fairly unique study area in terms of geology, seismicity and atmospheric conditions; (2) present two cases of earthquake swarms that seem to follow above-average rainfall events; and (3) examine the observed migration of hypocenters with a simple pore pressure diffusion model.We find significant correlation of seismicity with rainfall and groundwater level increase, and estimate an average hydraulic diffusivity of D = 0.75 ± 0.35 m2/s for Mt. Hochstaufen in 2002. 相似文献
68.
A. Tu
rul 《Engineering Geology》1998,50(3-4):337-345
The Atatürk dam was built across the Firat River on clayey limestone. A grout curtain, providing impermeability in the left and right abutments, was done in grouting galleries. The well known rock mass classification systems for tunneling purposes [rock structure rating (RSR), rock mass rating (RMR) and rock mass quality index (Q)] were used to classify the rock mass along these galleries. Based on RSR, RMR and Q values, the rock masses in the galleries have been classified into three different classes. Correlation between the three classification systems is discussed and suggestions are made for using rockbolt, shotcrete with wiremesh and steel ribs for supporting the rock mass. 相似文献
69.
In the Neoarchaean intracratonic basin of the Kaapvaal craton, between approximately 2640 Ma and 2516 Ma, two successive
stromatolitic carbonate platforms developed. Deposition started with the Schmidtsdrif Subgroup, which is probably oldest in
the southwestern part of the basin, and which contains stromatolitic carbonates, siliciclastic sediments and minor lava flows.
Subsequently, the Nauga formation carbonates were deposited on peritidal flats located to the southwest and were drowned during
a transgression of the Transvaal Supergroup epeiric sea, around 2550 Ma ago. This transgression led to the development of
a carbonate platform in the areas of the preserved Transvaal and Griqualand West basins, which persisted for 30–50 Ma. During
this time, shales were deposited over the Nauga Formation carbonates in the southwestern portion of the epeiric sea. A subsequent
period of basin subsidence led to drowning of the stromatolitic platform and to sedimentation of chemical, iron-rich silica
precipitates of the banded iron formations (BIF) over the entire basin. Carbonate precipitation in the Archaean was largely
due to chemical and lesser biogenic processes, with stromatolites and ocean water composition playing an important role. The
stromatolitic carbonates in the preserved Griqualand West and Transvaal basins are subdivided into several formations, based
on the depositional facies, reflected by stromatolite morphology, and on intraformational unconformities; interbedded tuffs
and available radiometric age data do not yet permit detailed correlation of units from the two basins. Thorough dolomitisation
of most formations took place at different post-depositional stages, but mainly during early diagenesis. Partial silicification
was the result of diagenetic and weathering processes. Karstification of the carbonate rocks was related to periods of exposure
to subaerial conditions and to percolation of groundwater. Such periods occurred locally at the time of carbonate and BIF
deposition. Main karstification, however, probably took place during an erosional period between approximately 2430 Ma and
2320 Ma.
Received: 15 September 1996 · Accepted: 12 May 1998 相似文献
70.
This paper analyzes – chemically, mineralogically, and petrolographically – the patinas developed on several Mediterranean
monuments made with different stones (siliceous and carbonatic) in order to establish their origin and their evolution under
the present environmental conditions, and to evaluate the environmental parameters controling their development. Most of the
patinas show a common sequence of layers, which, from the outer to the inner zone, are: (1) present bioactivity and/or biological
remains, (2) gypsum-rich patina, and (3) calcitic brown to orange patina. Each one may exhibit different fabrics (from micritic
to stromatolitic) and may be more or less continuous and homogeneous. The main mineral components are calcite and gypsum,
but Ca-oxalates and Ca-phosphates have also been found associated to biological structures, as well as quartz and clays. The
different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem
to be related to the biological activity, facilitating the growth of different organisms and leading to the development of
a deposit with distinct characteristics (fabric, texture, porosity, etc.). The gypsum-rich patina has been interpreted as
a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the
atmospheric dust. The mineralogy and texture of the patina is independent of the nature of the underlying rock and only in
few cases a micritization process has been observed as interaction between patina and rock. Recently, the penetration of endolithic
microflora produced drillings and the development of a fissuration system parallel to the surface, and thus the detachment
of the crust from the rock and even flackening of the rock itself has been observed. Consequently, under the present climatic
conditions in the Mediterranean basin, erosion is a more active process than deposition, and the crusts and patinas show a
tendency to disappear from the surface of the monuments.
Received: 3 November 1996 · Accepted: 10 September 1997 相似文献