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Mechanical stratigraphy as a factor controlling the development of a sandbox transfer zone: a three-dimensional analysis.
No full textIn thrust belts, fold–fault terminations are common features of the structural architecture and can pose complicated problems to unravel, in
particular when two or more terminations are in close proximity. Such terminations usually reflect pre-existing attributes. Amongst the many
factors, lateral variations in the mechanical stratigraphy can control along-strike geometry and kinematics of fault-related folds.
A displacement transfer zone was produced in a compressional sandbox model by means of two adjacent, mechanically different
stratigraphic domains. The experiment allowed two discrete chains to develop in the different domains, so that a complex structural setting
occurred in the connecting area. Periclinal folds, oblique thrust fronts and oblique ramps developed in the resulting transfer zone. The
interaction between periclines in the transfer zone produced lateral culminations in the folded structures. The analysis of displacement across
the structural domains revealed that a significant loss of slip along the faults occurred in the relay zone. In this area, imbricate faulting was
partially replaced by layer-parallel shortening. A linear relationship appears to exist between the bed length of the thrust sheet and the related
fault slip
Influence of structural inheritance on foreland-foredeep system evolution: An example from the Po valley region (northern Italy)
Full text linkUnderstanding the development of foreland-foredeep systems and the influence exerted by pre-existing structures on their evolution is an important step for defining the key factors that control long-term basin and lithosphere dynamics, comprehending the associated seismic hazard and assessing their economic potential in the domain of hydrocarbon exploration. The Po Valley is a rather unique foreland basin for two major reasons: a) it developed intermittently at the front of two different mountain chains, the Northern Apennines and the Southern Alps, progressively converging one towards the other; b) the inherited structures, mainly derived from the Mesozoic extensional tectonics, are oriented at high angle to the advancing belts. The coexistence of these two factors and their various implications make the Po Valley basin a complex case study that deserves attention. Taking advantage of the recent building of a 3D structural model across the region, we reconstructed the possible geometry and migration pattern of the Tertiary basins that developed at the front of the Northern Apennines and the Southern Alps, as part of the Po Valley tectonic evolution. In addition, a number of sections sliced from the 3D model across selected domains have then been used to restore the present-day structural units to their pre-compressional setting, while highlighting the key stages of their geological history. Results from the model analysis show that the Mesozoic extension-related tectonics and the associated carbonate facies geometry and distribution localized and constrained the Alpine structures inside/around the basin. Their control on the Cenozoic deformation and sedimentation is evident during the Paleogene and the Miocene whereas it becomes more subtle during the Plio-Pleistocene when lithospheric-scale mechanisms need to be invoked. Notwithstanding the model uncertainties and its explicit regional significance, our results may be taken as reference for any foreland-foredeep setting worldwide, especially in complex systems where tectono-sedimentary inhomogeneity is spatially and temporally dominant
Fracturation associated to fault-related folds: 3D analogue models
No full text3D analogue models have been used to investigate the distribution pattern of fractures during the evolution of fault-related folds. In the upper part of the brittle crust, folds are often associated to fractures. The timing and distribution of these fractures may have significant implications for hydrocarbon exploration and production in folded and fractured reservoirs. Successful development of fractured reservoirs in anticlinal traps requires knowledge of the spatial variability of joint orientations throughout a fold, as the production may strongly depend on the permeability created by systematic joint sets. We present the results of two sets of sandbox experiments that reproduce geometry and kinematics of a fault- propagation fold and a fault-bend fold, in order to analyze the relationship between fracturing and evolution of folding. In both experiments, an initial 6 cm thick layer sand pack was constructed manually, trying to minimize local inhomogeneities and packing anisotropy. Coloured (but mechanically equivalent) layers were used as marker horizons within the sand-pack to facilitate identification of faults and displacement measurement in cross-section view. Finally, at the top of the multilayer, a thin layer of SI-CRYSTAL powder, 0.5 cm thick, has been added. The strong cohesion of this material allows fractures to open, without collapsing. As SI-CRYSTAL powder and dry sand have Mohr-Coulomb failure envelopes, they are both suitable for modelling the brittle upper crust. During the experiments, a moving piston caused horizontal progressive shortening within the multilayer. Two digital cameras continuously monitored in map and in section view the evolution of the models. Moreover, a topographic measurement device (a structured light 3D scanning system) allowed to acquire the topography in the different shortening steps movements. At the end of each experiment (21,4% shortening), the model was cut in order to obtain internal vertical sections. All these steps allowed to reconstruct in 3D and analyse the two fault-related folds, to highlight differences and analogies in the fracture development and distribution through time/shortening. The data show a main fracture pattern parallel to fold axes, but interesting and significant differences occur in the number of fractures, their average length, continuity and other parameters that have been automatically detected using the 3D models. 3D reconstruction of models and their quantitative analysis are therefore fundamental tools for hydrocarbon exploration and evaluation in folded reservoirs as it allows to predict the spatial distribution of fracture in the different types of folds, related to their amount of shortening
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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