Grain Deformation Processes in Porous Quartz Sandstones – Insight from the Clusters of Cataclastic Deformation Bands

Presented at: Powders and Grains 2017 – 8th International Conference on Micromechanics on Granular MediaPorous sandstones represent classical reservoirs for water or hydrocarbons. Deformation in such granular material is due to tectonic events and occurs through the process of cataclasis, implying the crushing of the grains to a diversity of smaller clasts. Cataclasis is generally accompanied by porosity and permeability decrease. Although it is known that cataclastic deformation localizes to form individual bands and clusters of bands, the parameters controlling the distribution of this deformation were not well understood until recently. We used scanline measurements to show a favoured localization and clustering of the deformation on the case of normal-fault stress regime and potentially in strike-slip fault regime. The reverse regime favours the formation of distributed networks of conjugate deformation bands. At the scale of a cluster, field data reveals that the minimum modal grain size value of the host sandstone(s) controls the band density. Finally, microscopic cathodoluminescence analysis reveals enhanced quartz cementation for high degree of cataclasis. Hence, because band clustering, high degree of cataclasis and band cementation are favoured in normal-fault stress regime, tectonic extension appears to be favourable conditions for the formation of efficient barriers to fluid-flow in porous sandstone reservoirs.publishedVersio

Moving the financial accounting research front forward: the UK contribution

The purpose of this paper is to review the recent UK contribution to the field of financial accounting research, set against the backdrop of the global (mainly US) research effort. A systematic overview of recent research in the field is presented, based upon an analysis of 261 articles published between 1998 and 2002 in seven general, non-US journals. These are the journals that UK academics publish in most frequently and 115 of the articles are UK-authored. It is found that the research areas of MBAR and disclosure currently dominate conventional financial accounting research. The comparison of findings across institutional settings offers fruitful lines of inquiry for research within these main areas (i.e. studies of value relevance, analysts' forecasts, voluntary disclosure and earnings management). While most research is seen to follow the highly quantitative, economics-based US tradition, a significant amount of UK research adopts a more qualitative approach, and distinctive UK contributions are evident in a number of areas (in particular, the disclosure process and corporate social reporting). There are signs that UK researchers are helping researchers in other countries contribute to the global body of scholarly knowledge

Neuronal MeCP2 is expressed at near histone-octamer levels and globally alters the chromatin state

MeCP2 is a nuclear protein with an affinity for methylated DNA that can recruit histone deacetylases. Deficiency or excess of MeCP2 causes severe neurological problems, suggesting that the number of molecules per cell must be precisely regulated. We quantified MeCP2 in neuronal nuclei and found that it is nearly as abundant as the histone octamer. Despite this high abundance, MeCP2 associates preferentially with methylated regions and high-throughput sequencing showed that its genome-wide binding tracks methyl-CpG density. MeCP2 deficiency results in global changes in neuronal chromatin structure, including elevated histone acetylation and a doubling of histone H1. Neither change is detectable in glia, where MeCP2 occurs at lower levels. The mutant brain also shows elevated transcription of repetitive elements. Our data argue that MeCP2 may not act as a gene-specific transcriptional repressor in neurons, but might instead dampen transcriptional noise genome-wide in a DNA methylation-dependent manner

Regulation of MicroRNA Biogenesis: A miRiad of mechanisms

microRNAs are small, non-coding RNAs that influence diverse biological functions through the repression of target genes during normal development and pathological responses. Widespread use of microRNA arrays to profile microRNA expression has indicated that the levels of many microRNAs are altered during development and disease. These findings have prompted a great deal of investigation into the mechanism and function of microRNA-mediated repression. However, the mechanisms which govern the regulation of microRNA biogenesis and activity are just beginning to be uncovered. Following transcription, mature microRNA are generated through a series of coordinated processing events mediated by large protein complexes. It is increasingly clear that microRNA biogenesis does not proceed in a 'one-size-fits-all' manner. Rather, individual classes of microRNAs are differentially regulated through the association of regulatory factors with the core microRNA biogenesis machinery. Here, we review the regulation of microRNA biogenesis and activity, with particular focus on mechanisms of post-transcriptional control. Further understanding of the regulation of microRNA biogenesis and activity will undoubtedly provide important insights into normal development as well as pathological conditions such as cardiovascular disease and cancer

Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors

Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe

Factors controlling permeability of cataclastic deformation bands and faults in porous sandstone reservoirs

International audienceImproving the prediction of sub-seismic structures and their petrophysical properties is essential for realistic characterization of deformed sandstone reservoirs. In the present paper, we describe permeability contrasts induced by cataclastic deformation bands and faults in porous sandstones (766 data synthesized from field examples and the literature). We also discuss the influence of several factors, including tectonic regime, presence of a fault, burial depth, host sandstone porosity, and grain size and sorting for their initiation and permeability. This analysis confirms that permeability decrease is as a function of grain-crushing intensity in bands. Permeability reduction ranges from very limited in crush-microbreccia of compaction bands to high permeability reduction in cataclasites and ultracataclasites of shear-dominated bands, band clusters and faults. Tectonic regime, and especially normal-fault regime, with its tendency to localize strain and generate faults, is identified as the most important factor, leading to the formation of cataclastic bands with high permeability contrasts. Moreover, moderate burial depth (1–3 km) favors cataclastic bands with high permeability contrasts with respect to the host sandstone. High porosity, coarse-grain size and good grain sorting can slightly amplify the permeability reductions recorded in bands

Analyse de la déformation sur carottes et diagraphies dans un réservoir karstique côtier de la marge proximale du Golfe du Lion

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Tectonic regime controls clustering of deformation bands in porous sandstone

International audiencePorous sandstones tend to deform by the formation of low-permeability deformation bands that influence fluid flow in reservoir settings. The bands may be distributed or localized into clusters, and limited recent data suggest that tectonic regime may exert control on their distribution and clustering. In order to explore this suggestion, we performed a synthetic analysis based of 73 sets of bands, including 22 new sets measured for a reverse Andersonian regime that fill the important gap in data for this context. We find a surprisingly strong correlation between clustering and tectonic regime, where bands clearly are more distributed in the reverse regime compared to the normal regime. Together with the observed band distributions, capillary pressure data show evidence that efficient membrane seals are expected for extension, whereas pervasive permeability anisotropy is expected for contraction. Such a basic new rule concerning tectonic regime is very useful for assessment of reservoir properties where deformation bands are common but below seismic resolution