Fingerprinting stress: stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding-the case of the Monte Nero anticline in the Apennines, Italy

In this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold-and-thrust belt. First, we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion. Second, we use our new approach to present a high-resolution deformation and stress history that affected Meso-Cenozoic limestone strata in the Monte Nero Anticline during its late Miocene-Pliocene growth in the Umbria-Marche Arcuate Ridge (northern Apennines, Italy). In this area an extensive stylolite-joint/vein network developed during layer-parallel shortening (LPS), as well as during and after folding. Stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during LPS. The stress regime oscillated between strike slip and compressional during LPS before ultimately becoming strike slip again during late stage fold tightening. Our case study shows that high-resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses. Beyond regional implications, this study validates our approach as a new powerful toolbox to high-resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

Semantic Consistency in Boundary Extension

Two experiments explored the effect of semantic consistency on boundary extension by presenting images depicting scenes with either a semantically consistent or inconsistent object-background relation; Experiment 1 presented these images for brief durations and Experiment 2 presented these images for long durations. The results of these experiments revealed no difference in boundary extension for brief image durations in Experiment 1 and a significant difference in boundary extension for long image durations in Experiment 2, with semantically inconsistent scenes eliciting less boundary extension than semantically consistent scenes. These findings are interpreted as evidence for boundary extension being context-independent early in scene perception and context-dependent late in scene perception. I suggest that spatial computation initially operates on object-background spatial relations alone and does not include semantic information, whereas spatial computation later operates on both object-background spatial relations as well as semantic information about the scene. For semantically inconsistent scenes, the competing semantic information from the context depicted in the background and the context implied by the object interfere with further spatial computation later in scene perception

Vécu et contraintes lors de l'application d'une nouvelle approche pédagogique: Une étude de cas québécoise en comptabilité.

This paper presents the experience of faculty members of the accounting department at Université Laval in designing and implementing a new curriculum. These changes have resulted from the new requirements of the profession as well as the growing gap between employers' expectations and skills and professional attitudes of graduating accounting students. In addition to presenting the context of these changes, the paper discusses some of the difficulties faced during the implementation of the new curriculum and, more importantly, those faced when introducing a new teaching approach. The new curriculum is focused on a collaborative approach whereby student participation is solicited. However, several difficulties have been met during the implementation. For instance, faculty members face a higher level of uncertainty in the classroom and must devote more time in developing teaching material. Students' perceptions, obtained through focus groups, were that the new program did not prepare them properly and that some courses were not useful. Throughout the paper, we offer some strategies that can be used to minimize the impact of the difficulties faced when implementing a new teaching approach that can overturn previously firmly held beliefs about appropriate pedagogical methods.Cet article présente l'expérience vécue au Département des sciences comptables de l'Université Laval lors de la réforme des cours du baccalauréat. Cette réforme s'explique par les changements importants qui bouleversent la profession comptable et par l'écart grandissant entre les besoins des employeurs et les compétences et les attitudes professionnelles des finissants en comptabilité. En plus de présenter le contexte dans lequel s'est effectué la réforme, l'article fait état des obstacles rencontrés tout au long des modifications apportées au contenu des cours et, surtout, de l'implantation d'une nouvelle approche pédagogique. Le nouveau programme est centré sur une approche collaborative par problèmes où la participation de l'étudiant est fortement sollicitée. Un tel changement ne s'est pas fait sans rencontrer de nombreux obstacles. Par exemple, l'approche choisie a créé un niveau d'incertitude élevé chez les professeurs et a exigé, de leur part, d'allouer une partie importante de leur allouée au développement de matériel didactique. La perception des étudiants, obtenue à l'aide d'entrevues de groupe, était que les cours ne les préparaient pas adéquatement et que parfois, ils étaient inutiles. Nous proposons certains éléments de solution qui peuvent réduire l'impact des problèmes rencontrés lors de l'implantation d'une nouvelle approche pédagogique qui bouleverse certaines conceptions fortement ancrées

Paleostress magnitudes in folded sedimentary rocks

International audienceUsing Sheep Mountain Anticline (Wyoming, USA) as a case study, we propose a new approach to quantify effective paleo-principal stress magnitudes in the uppermost crust. The proposed mechanical scenario relies on a well-documented kinematic and chronological sequence of development of faults, fractures and microstructures in the folded strata. Paleostress orientations and regimes as well as differential stress magnitudes based on calcite twinning paleopiezometry are combined with rock mechanics data in a Mohr construction to derive principal stress magnitudes related to the successive steps of layer-parallel shortening and to late stage fold tightening. Such quantification also provides original insights into the evolution of the fluid (over)pressure and amount of syn-folding erosion

Stress and strain patterns, kinematics and deformation mechanisms in a basement-cored anticline: Sheep Mountain Anticline, Wyoming

International audienceIn order to characterize and compare the stress-strain record prior to, during, and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks, we investigate the relationship between the stress-strain distribution in folded strata derived from fractures, striated microfaults, and calcite twins and the development of the Laramide, basement-cored Sheep Mountain Anticline, Wyoming. Tectonic data were mainly collected in Lower Carboniferous to Permian carbonates and sandstones. In both rock matrix and veins, calcite twins recorded three different tectonic stages: the first stage is a pre-Laramide (Sevier) layer-parallel shortening (LPS) parallel to fold axis, the second one is a Laramide LPS perpendicular to the fold axis, and the third stage corresponds to Laramide late fold tightening with compression also perpendicular to the fold axis. Stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults, testifying for the homogeneity of stress record at different scales through time. Calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs. Our results especially point to an increase of differential stress magnitudes related to Laramide LPS from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip. This result is confirmed by a simple numerical model. Beyond regional implications, this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding

U-Pb dating of calcite veins reveals complex stress evolution and thrust sequence in the Bighorn Basin, Wyoming, USA: REPLY

International audienceThacker and Karlstrom (2019) commented on the paper of Beaudoin et al. (2018) by presenting a summary of the published data about exhumation of Laramide arches in Montana, northern Wyoming and western South Dakota. We thank the authors for this comment and wish to reply.Beaudoin et al. (2018) present U-Pb absolute ages of calcite cements that in-fill tectonic veins developed in the Bighorn basin during the Sevier and Laramide contractional events. At the scale of the basin, we report two trends: (1) an eastward, forelandward propagation of Sevier layer-parallel shortening vein development; and (2) a westward, hinterlandward propagation of Laramide layer-parallel shortening and folding-related vein development. We discuss the consistency between the latter Laramide sequence, valid in the sedimentary cover at the scale of the Bighorn basin, and the published exhumation sequence of the basement arches bounding the basin, i.e. Beartooth arch (West), Wind River range (South) and Bighorn arch (East) (Peyton et al., 2012, Crowley et al., 2002, Fan and Carrapa, 2014, Stevens et al., 2016)