Generation of correlated properties in heterogeneous porous media

The spatial distribution of rock properties in porous media, such as permeability and porosity, often is strongly variable. Therefore, these properties usefully may be considered as a random field. However, this variability is correlated frequently on length scales comparable to geological lengths (for example, scales of sand bodies or facies). To solve various engineering problems (for example, in the oil recovery process) numerical models of a porous medium often are used. A need exists then to understand correlated random fields and to generate them over discretized numerical grids. The paper describes the general mathematical methods required to do this, with one particular method (the nearest neighbor model) described in detail. How parameters of the mathematical model may be related to rock property statistics for the nearest neighbor model is shown. The method is described in detail in one, two, and three dimensions. Examples are given of how model parameters may be determined from real data.     

Research progress and prospect of snow avalanche disaster prevention and control北大核心CSCD

Snow avalanches are a major natural hazard in the cryosphere. It seriously threatens transportation corridors, energy transmission and communication lines, mining and touristic areas in the cold mountainous regions and often causes the destruction of infrastructure and human casualties, hindering the sustainable development of society and economy in mountainous areas. Under climate change and the expansion of human activities to alpine mountains, more population and infrastructure will expose to the risk of avalanches. In order to ensure the sustainable development in mountainous areas, the demand for the prevention and management of avalanche disasters is increasing. Based on the review of the main avalanche research progress in China since 1960 and the avalanche research results all over the world, this paper summarized the progress on the influencing factors and regional distribution of avalanche activities, avalanche formation and movement mechanism, avalanche monitoring and early warning, avalanche risk assessment and engineering prevention, as well as the frontier problems and scientific difficulties that need to be studied. In addition, the impact of climate change on avalanche activities and the interaction between human activities and avalanche activities are discussed. By looking forward to the future needs of avalanche disaster prevention and reduction, including the countermeasures, the research on avalanche in China is promoted. © 2022 by the Author(s).     

The Coolgardie Goldfied,Western Australia: district-scale controls on an Archaean gold camp in an amphibolite facies terrane

Archaean lode gold deposits in the Coolgardie Goldfield, Western Australia, occur in mafic and ultramafic rocks which have been metamorphosed to the amphibolite facies. Mineralisation was broadly synchronous with peak metamorphism, the main phase of granitoid emplacement, and regional deformation. Several different structural styles are represented by the deposits of the Coolgardie Goldfield. Mineralisation occurs along sheared felsic porphyry-ultramafic rock contacts, in gabbro-hosted quartz-vein sets, in fault-bounded quartzvein sets, and in laminated quartz reefs sited in brittleductile shear zones. The structures hosting mineralisation formed in response to a progressive deformation event, related to granitoid emplacement in an east-west compressional far-field stress régime, but with local heterogeneous stress orientations. This occurred after an earlier period of thrust-stacking, with probable north-south directed tectonic transport. Two contrasting styles of goldrelated wallrock alteration are associated with the auriferous lodes of the Coolgardie Goldfield. A high-temperature assemblage (formation temperature >500°C), characterised by the proximal alteration assemblage garnet+ hornblende + plagioclase + pyrrhotite, contrasts with a medium-temperature assemblage (formation temperature <500°C), consisting of calcic amphibole + biotite + plagioclase + calcite + arsenopyrite + pyrrhotite. The distribution of the two styles of gold-related alteration is controlled by distance from voluminous syntectonic granitoids located to the west of the Coolgardie Goldfield, with the high-temperature style of alteration more proximal to the granitoid-greenstone contact than the medium-temperature style. The occurrence of gold deposits that formed under amphibolite facies conditions throughout the Coolgardie Goldfield supports a crustal continuum model for Archaean lode-gold deposits, which proposes that gold is deposited in metamorphic environments that range from the sub-greenschist to granulite facies. In addition, the data from Coolgardie suggest that syntectonic, synmineralisation granitic plutons may play a significant role in controlling the style of gold associated wallrock-alteration at deep crustal levels.     

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.     

Source(s) and cycling of the nonhydrolyzable organic fraction of oceanic particles

A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using ¹³C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. ¹³C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments.     

Couplage des équations de transfert de masse et des lois d''interactions solution-solide par l''utilisation des lanthanides comme traceurs — Approche expérimentale

In underground flow tracing studies, the estimation of the nature and the importance of interactions undergone by the substance used very often constitutes an obstacle to good modeling of mass-transfer processes in solution.

We propose a method to quantify these phenomena by the use of lanthanides as tracers.

For this study, we set up an analytical methodology adapted to routine measurements. The quality of five lanthanides as indicators has been examined. We have demonstrated the formation, by substitution, of a carbonate complex which is extremely stable in the natural environment. The field experiments carried out demonstrated the efficiency of those tracers and confirmed their great stability.

Tracer recovery graphs show that, in accord with our hypothesis, convection and dispersion are identical for all the lanthanide elements. Moreover, we have established a direct relation between their fixing rate on earth materials and the value of their stability constants.

Thus, we demonstrate the possibility of correlative multitracing, with known and quantifiable interelement relations.

Résumé

Dans les études de circulations souterraines par traceur, l'estimation de la nature et de l'importance des interactions subies par la substance utilisée constitue, bien souvent, un obstacle à une bonne modélisation des processus de transfert de masse en solution.

Nous proposons une méthode de quantification de ces phénomènes par l'utilisation des lanthanides comme traceurs.

Pour cette étude, nous avons mis au point une méthodologie analytique adaptée aux mesures de routine. Les qualités, en tant qu'indicateurs, de cinq lanthanides ont été examinées. Nous avons démontré la formation, par substitution, d'un complexe carbonaté extrèment stable en milieu naturel. Les expériences de terrain réalisées ont prouvé l'efficacité de ces traceurs et confirmé leur grande stabilité.

Les courbes de restitution obtenues ont montré que, conformément à nos hypothèses, la convection et la dispersion sont identiques pour l'ensemble de ces éléments. De plus, il a été établi une relation directe entre leurs taux de fixation sur le terrain et la valeur de leurs constantes de stabilité.

On dispose ainsi d'une possibilité de multitraçage corrélatif, avec des relations interélémentaires connues et quantifiables.     

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

The course of the active North Anatolian Fault system from Lake Abant to Lake Sapanca was traced by its high micro-earthquake activity. If approaching from the east this section includes a broad south to north overstep (fault offset) of the main fault. Local seismicity has been recorded in this area by a semi-permanent network of 8 stations since 1985 within the frame of the Turkish–German Joint Project for Earthquake Research. The effect of the overstep and its complex fracture kinematics are reflected by the seismicity distribution, the variations of composite fault-plane solutions, and by the spatial coda-Q distribution. Areas of different stress orientation can be distinguished and assigned to different groups of faults. The stresses and the tectonic pattern only in part correspond to a simple model of an extensional overstep and its correlative pull-apart basin. Other types of deformation involved are characterized by normal faulting on faults parallel to the general course of the main strike-slip fault and by synthetic strike-slip faults oriented similar to Riedel shears. Shear deformation by this fault group widely distributed in an area north and east of the main fault line may play an important role in the evolution of the overstep. The development of a pull-apart basin is inhibited along the eastern half of the overstep and compatibility of both strands of the main fault (Bolu–Lake Abant and Lake Sapanca– Izmit–Marmara Sea) seems to be achieved with the aid of the fault systems mentioned. The extension of the missing part of the pull-apart basin seems to be displaced to positions remote from the Lake Abant–Lake Sapanca main fault line, i.e. to the Akyaz?–Düzce basin tract. Highest Q-values (lowest attenuation of seismic waves) were found in the zone of highest seismicity north and west of the overstep which is the zone of strongest horizontal tension. If high coda-Q is an indicator for strong scattering of seismic waves it might be related to extensional opening of fractures.