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The origin of third-order depositional sequences remains debatable, and in many cases it is not clear whether they were controlled by tectonic activity and/or by eustatic sea-level changes. In Oxfordian and Berriasian–Valanginian carbonate-dominated sections of Switzerland, France, Germany and Spain, high-resolution sequence-stratigraphic and cyclostratigraphic analyses show that the sedimentary record reflects Milankovitch cyclicity. Orbitally induced insolation changes translated into sea-level fluctuations, which in turn controlled accommodation changes. Beds and bedsets formed in rhythm with the precession and 100-kyr eccentricity cycles, whereas the 400-kyr eccentricity cycle contributed to the creation of major depositional sequences. Biostratigraphical data allow the correlation of many of the 400-kyr sequence boundaries with third-order sequence boundaries recognized in European basins. This implies that climatically controlled sea-level changes contributed to the formation of third-order sequences. Furthermore, this cyclostratigraphical approach improves the relative dating of stratigraphic intervals. 相似文献
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Avoiding high concentrations of arsenic, manganese and salinity in deep tubewells in Munshiganj District, Bangladesh 总被引：1，自引：0，他引：1
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Laurent Picot Damien Becker Fréderic Lapaire Kamil Ustaszewski Wolfgang A. Hug et Jean-Pierre Berger 《Eclogae Geologicae Helvetiae》2005,98(2):281-296
Resume. Situés dans la partie la plus distale du bassin molassique suisse et dans le prolongement sud du fossé rhénan, les dép?ts
conglomératiques appartenant au groupe stratigraphique des Gompholithes & Conglomérats ont fait l’objet d’une étude sédimentologique
et paléontologique détaillée. La multitude des affleurements réalisés lors des travaux de construction de l’autoroute Transjurane
dans la région de Porrentruy (Jura), permet d’appréhender ces paléoenvironnements rupéliens (Oligocène inférieur).
Les études sédimentologiques et paléontologiques révèlent l’existence d’environnements c?tiers avec des falaises de calcaires
mésozo?ques entaillées par des canyons où se trouvent des rivières au régime torrentiel. Ces rivières qui érodent les couches
du Mésozo?que créent des galets qui sont déposés sous la forme de deltas marins progradant vers le nord. A l’abri des exutoires
des canyons se développent quelques environnements lacustres.
Ces dép?ts conglomératiques sont fortement liés à l’activité tectonique rupélienne. La distension rhénane et l’activité de
la faille transformante située entre le fossé rhénan et le bassin de la Bresse subdivisent les différents blocs mésozo?ques
en horsts et grabens, permettant ainsi l’érosion des sédiments dans les parties hautes (horst) et leur transport dans les
zones basses (graben).
La découverte de rares galets de roches endogènes et effusives dans les dép?ts conglomératiques montre un transport du socle
des Vosges vers le sud dans la région de Porrentruy par l’intermédiaire sans doute d’une dérive littorale. Bien que la surrection
des Vosges et de la Forêt-Noire et leur mise à l’érosion soient connues dès la base du Miocène, la présence de ces galets
atteste l’existence de failles dès le début du Rupélien qui mettent à l’érosion le socle du massif des Vosges.
Located in the distal part of the Swiss Molasse Basin and in the southern extension of the Rhine Graben, the conglomeratic deposits belonging to the Gompholithes & Conglomérats stratigraphic group have been the object of detailed sedimentological and paleontological studies. The great number of outcrops that came into sight during the building works of the Transjurane highway in the vicinity of Porrentruy (Swiss Jura) lead to a better understanding of Rupelian paleoenvironments (Early Oligocene). The sedimentological and paleontological studies reveal the existence of coastal environments with Mesozoic limestone cliffs notched by canyons with torrential rivers. Those rivers eroding the Mesozoic series create pebbles deposits forming marine deltas prograding towards North. In protected areas, some lacustrine environments can develop. These conglomeratic deposits are strongly bound to the Rupelian tectonic activity. The rhenish distension and the activity of the transform faults located between the Rhine Graben and the Bresse basin divide the Mesozoic blocks in horst and graben structures, thus allowing the erosion of sediments in higher regions (horst) and their transport in lower zones (graben). The discovery of rare pebbles made of endogene and effusive rocks in those conglomeratic deposits shows a transport coming from the Vosges massifs towards south to the Porrentruy region, probably with the support of a littoral drift. Although the surrection of the Vosges and Schwarzwald massifs (and the beginning of their erosion) is normally attributed to the base of the Miocene, the presence of those pebbles attests the existence of faults putting the basement of the Vosges massif to erosion since the base of Rupelian.
Manuscrit re?u le 4 février 2003 Révision acceptée le 30 mars 2005 相似文献
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Interpretation of Core Extrusion Measurements When Tunnelling Through Squeezing Ground 总被引：1，自引：0，他引：1
Squeezing intensity in tunnelling often varies over short distances, even where there is no change in the excavation method
or lithology. Reliable predictions of the ground conditions ahead of the face are thus essential to avoid project setbacks.
Such predictions would enable adjustments to be made during construction to the temporary support, to the excavation diameter
and also to the final lining. The assessment of the behaviour of the core ahead of the face, as observed by means of extrusion
measurements, provides some indications as to the mechanical characteristics of the ground. If the ground exhibits a moderate
time-dependent behaviour and the effects of the support measures are taken into account, the prediction of convergence is
feasible. If the ground behaviour is pronouncedly time-dependent, however, convergence predictions become very difficult,
because core extrusion is governed by the short-term characteristics of the ground, which may be different from the long-term
properties that govern final convergence. The case histories of the Gotthard Base Tunnel and of the Vasto tunnel show that
there is a weak correlation between the axial extrusions and the convergences of the tunnel. By means of the case histories
of the Tartaiguille tunnel and Raticosa tunnel, it is shown that to identify potentially weak zones on the basis of the extrusion
measurements, careful processing of the monitoring data is essential: the analysis of the data has to take account of the
effects of tunnel support and time, and has to eliminate errors caused by the monitoring process. 相似文献
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We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)-phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (∼0.1-0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic. 相似文献
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Microbially induced cementation of carbonate sands: are micritic meniscus cements good indicators of vadose diagenesis? 总被引：4，自引：0，他引：4
Characteristic fabrics such as micrite envelopes, calcified filaments and micritic grain-to-grain bridges are observed in a modern subtidal firmground (Wood Cay, Bahamas) and in a variety of firm- and hardgrounds of Lower Cretaceous and Upper Jurassic platform carbonates (Swiss and French Jura Mountains). Their similarity to microbial fabrics described in grapestones and in intertidal to continental vadose environments suggests that microbial activity played an important role in the initial stabilization and cementation of carbonate sands. 'Meniscus-type cements' (to distinguish them from vadose meniscus cements), which clearly formed in subtidal environments, are related to filament calcification, trapping of percolating micrite and microbially induced carbonate formation. Such meniscus-type cements are commonly micritic, but meniscus-shaped precipitation of fibrous aragonite or sparitic calcite around organic filaments is also observed. Therefore, an interpretation of vadose early diagenesis should not be based on meniscus cements alone. Similarly, subtidally formed filamentous structures can strongly resemble alveolar septal structures and be interpreted incorrectly as related to subaerial exposure. 相似文献
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The adsorption of two model siderophores, desferrioxamine B (DFOB) and aerobactin, to lepidocrocite (γ-FeOOH) was investigated by attenuated total reflection infrared spectroscopy (ATR-FTIR). The adsorption of DFOB was investigated between pH 4.0 and 10.6. The spectra of adsorbed DFOB indicated that two to three hydroxamic acid groups of adsorbed DFOB were deprotonated in the pH range 4.0-8.2. Deprotonation of hydroxamic acid groups of adsorbed DFOB at pH values well below the first acid dissociation constant of solution DFOB species (pKa = 8.3) and well below the point of zero charge of lepidocrocite (pHPZC = 7.4) suggested that the surface speciation at the lower end of this pH range (pH 4) is dominated by a surface DFOB species with inner-sphere coordination of two to three hydroxamic acids groups to the surface. Maximum adsorption of DFOB occurred at approximately pH 8.6, close to the first pKa value of the hydroxamic acid groups, and decreased at lower and higher pH values.The spectra of adsorbed aerobactin in the pH range 3-9 indicated at least three different surface species. Due to the small spectral contributions of the hydroxamic acid groups of aerobactin, the interactions of these functional groups with the surface could not be resolved. At high pH, the spectral similarity of adsorbed aerobactin with free aerobactin deprotonated at the carboxylic acid groups indicated outer-sphere complexation of the carboxylate groups. With decreasing pH, a significant peak shift of the asymmetric carboxylate stretch vibration was observed. This finding suggested that the (lateral) carboxylic acid groups are coordinated to the surface either as inner-sphere complexes or as outer-sphere complexes that are strongly stabilized at the surface by hydrogen bonding at low pH. 相似文献
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Batch adsorption and dissolution experiments with lepidocrocite (γ-FeOOH) and two siderophores, desferrioxamine B (DFOB) and aerobactin, were performed between pH 3 and 8 in the dark and under irradiation with UV-visible light. The increase in surface concentrations of adsorbed DFOB with increasing pH was explained in terms of electrostatic interactions between the protonated and charged terminal amine group of DFOB surface complexes and the charged lepidocrocite surface. The adsorption of aerobactin was consistent with the typical anion-like adsorption behavior of low molecular weight organic acids and indicated that the adsorption properties are strongly determined by the carboxylic acid groups. The adsorption experiments revealed furthermore that the Fe(III)-DFOB solution complex has a very low affinity for the surface, in contrast to Fe(III)-aerobactin solution complexes. In accordance with a surface-controlled mechanism of ligand-promoted dissolution, we found a linear correlation between dissolution rates of lepidocrocite and the surface concentrations of adsorbed DFOB. In the dark, 6- to 8-fold lower dissolution rate coefficients were determined for aerobactin in comparison to DFOB. These results suggested that aerobactin forms surface complexes that are less dissolution-active, characterized by a higher degree of multinuclear surface complexation and/or by less dissolution-active coordination modes of the involved iron-binding groups. For both DFOB and aerobactin, dissolution rate coefficients increased significantly under irradiation with UV-visible light. This increase was interpreted in terms of light-induced reduction of surface Fe(III), primarily by intrinsic photochemical processes of the lepidocrocite bulk phase, based on the observed photoreductive dissolution in the absence of organic ligands between pH 3 and 6. We hypothesize that the α-hydroxycarboxylate group of aerobactin may form a surface complex that additionally promotes photoreductive dissolution by a ligand-to-metal charge-transfer (LMCT) reaction, similar to citrate. However, LMCT reactions involving the α-hydroxycarboxylate group of aerobactin are rather ineffective, based on the comparison of light-induced dissolution rate coefficients determined in the presence of aerobactin and citrate. 相似文献