Deformation related to Miocene westward translation in the core of the Betic zone Implications on the tectonic interpretation of the Betic orogen (Spain)

Abstract

The Cenozoic westward motion of the Betic-Rif internal zone (“Alboran block”) between Iberia and Africa is constrained by paleogeographic considerations and by wrench faulting which affects both sides of the external zones. However, in the Alboran domain itself there was so far no evidence of significant internal deformation related to this westward displacement which was consequently consider as an en bloc” motion. Our work, in Eastern Andalucia, demonstrates that the main tectonic units building up the Betic zone should be regarded as large-scale tectonic sheets with a typical duplex style. The direction of the tectonic transport is to the West. At meso-scale, the major structures exhibit a combination of hindward and foreward dipping imbricates on the respective east and west sides of antiformal stacks or “rigid cores”. On a broader scale, the same geometric framework appears on both east and west sides of the Sierra Nevada window which we interpret as a tectonic culmination on the hangingwall of a Subbetic décollement zone. The development of this tectonics, in retrogressive metamorphic conditions, postdates the ductile deformation of the internal complexes. The morpho-tectonic relationships between the culmination of the metamorphic cores and the Neogene basins give a way to date the westward motion of the “Alboran System of Nappes” of the middle and upper Miocene.     

Gradual diversions of the Rio Pastaza in the Ecuadorian piedmont of the Andes from 1906 to 2008: role of tectonics, alluvial fan aggradation, and ENSO events

The successive courses of the Rio Pastaza in the upper Amazonian Puyo plateau (Ecuador) during the past century have been followed using historical maps, aerial photographs, satellite imagery, topographic and river long profiles, and field studies. The abrupt change in direction of the Rio Pastaza from transverse to longitudinal was a result of two avulsions occurred between 1906 and 1976 at the braided-meandering transition of the former alluvial plain. These avulsions are related to aggradation at the toe of a braided piedmont fan prograding on to a hinterland-dipping topographic slope formed by ongoing tectonic backtilting. The main avulsion proceeded by annexation of a south-dipping depression created in front of the cordillera by backtilting of the plateau. A partial and gradual avulsion having occurred upstream of the former site between 1976 and 2008 is marked by the progressive predominance of a newly formed inner branch. Tectonic backtilting enhanced aggradation upstream of the initial site while it offered the newly avulsed channel a still more favorable way along the cordillera by creating a westward lateral slope. The correlation between ENSO events and the occurrence of the 1976–2008 avulsions strongly suggests that the triggers of the avulsions were the floods caused by the high water and sediment discharges associated with ENSO (La Ni?a) events contrasting with the regular monthly discharge and the lack of actual ‘normal’ floods during the inter-ENSO periods.     

Isostasy of the Northern Bay of Biscay Continental Margin

Summary. Spectral analysis of eight marine gravity profiles and seven SEASAT profiles, combined with corresponding bathymetric data over the Northern Bay of Biscay origin, yield identical admittance functions for wavelengths greater than 120 km. the resulting admittance function has been interpreted in terms of an Airy model of compensation for wavelengths greater than 250 km and in terms of an elastic plate model of compensation for shorter wavelengths. the Airy model corresponds to a crustal thickness variation across the margin. the plate model with an elastic thickness of 8 km is associated with the regional compensation of a sedimentary load which was probably emplaced during and just after rifting.     

Flocculation Potential of Estuarine Particles: The Importance of Environmental Factors and of the Spatial and Seasonal Variability of Suspended Particulate Matter

Estuarine systems are complex environments where seasonal and spatial variations occur in concentrations of suspended particulate matter, in primary constituents, and in organic matter content. This study investigated in the laboratory the flocculation potential of estuarine-suspended particulate matter throughout the year in order to better identify the controlling factors and their hierarchy. Kinetic experiments were performed in the lab with a “video in lab” device, based on a jar test technique, using suspended sediments sampled every 2 months over a 14-month period at three stations in the Seine estuary (France). These sampling stations are representative of (1) the upper estuary, dominated by freshwater, and (2) the middle estuary, characterized by a strong salinity gradient and the presence of an estuarine turbidity maximum. Experiments were performed at a constant low turbulent shear stress characteristic of slack water periods (i.e., a Kolmogorov microscale >1,000 μm). Flocculation processes were estimated using three parameters: flocculation efficiency, flocculation speed, and flocculation time. Results showed that the flocculation that occurred at the three stations was mainly influenced by the concentration of the suspended particulate matter: maximum floc size was observed for concentrations above 0.1 g l⁻¹ while no flocculation was observed for concentrations below 0.004 g l⁻¹. Diatom blooms strongly enhanced flocculation speed and, to a lesser extent, flocculation efficiency. During this period, the maximum flocculation speed of 6 μm min⁻¹ corresponded to a flocculation time of less than 20 min. Salinity did not appear to automatically enhance flocculation, which depended on the constituents of suspended sediments and on the content and concentration of organic matter. Examination of the variability of 2D fractal dimension during flocculation experiments revealed restructuring of flocs during aggregation. This was observed as a rapid decrease in the floc fractal dimension from 2 to 1.4 during the first minutes of the flocculation stage, followed by a slight increase up to 1.8. Deflocculation experiments enabled determination of the influence of turbulent structures on flocculation processes and confirmed that turbulent intensity is one of the main determining factors of maximum floc size.     

On the similarity functions A and B as determined from the ‘VOVES’ experiment

Data collected during the french VOVES-1977 experiment are used for the determination of the functionsA() andB() of the stability parameter . It is found that, although pertaining to different geographic conditions, they lead to the same kind of dependency ofA andB upon as found previously considered data. The influence of baroclinicity onA andB is also studied and it is found in that, statistically, consideration of this parameter does not lead either to a decrease of the large scatter of experimental points or to a significant improvement of the similarity theory. It is also shown that a satisfactory estimation of the surface geostrophic wind can be made from the network of meteorological stations, to compute such functions.     

Modeling the suction- and deviator stress-dependent resilient modulus of unsaturated fine/coarse soil mixture by considering soil–water retention curve

Experimental observations have shown that the resilient modulus M_r of fine/coarse soil mixture can be significantly affected by the coarse grain content f_v, deviator stress σ_d and suction \(\psi\). In this study, a constitutive model incorporating the soil–water retention curve (SWRC) was proposed to describe the effects of \(\psi\) and \(\sigma_{{\text{d}}}\) on M_r. This model was then extended to the effect of f_v. The proposed model implied the resilient modulus at saturation condition (M_r-sat), the resilient modulus at optimum moisture content (OMC) condition (M_r-opt), the suction at OMC (\(\psi_{{{\text{opt}}}}\)) and the parameters related to SWRC. The model was validated using experimental data from five studies reported in the literature. Comparisons with three representative existing models showed that the proposed model was capable to well describe the suction-dependent effect of deviator stress in the full range of suction, while the existing models gave satisfactory simulation results only in the low suction range. Indeed, experimental studies revealed that there was a threshold suction \(\psi_{{{\text{th}}}}\), and with increasing \(\sigma_{{\text{d}}}\), the M_r decreased when \(\psi < \psi_{{{\text{th}}}}\), but increased when \(\psi > \psi_{{{\text{th}}}}\). When \(\psi < \psi_{{{\text{th}}}}\), all models gave good simulations. On the contrary, when \(\psi > \psi_{{{\text{th}}}}\), only the proposed model gave good simulations, in particular when \(\psi_{{{\text{th}}}} > \psi_{{{\text{opt}}}}\). This showed the performance of the proposed model in describing the variation in resilient modulus of unsaturated fine/coarse soil mixtures with changes in coarse grain content, deviator stress and suction.