The drainage of Lake Ojibway in glaciolacustrine sediments of northern Ontario and Quebec,Canada

Physical evidence for the drainage of glacial lakes remains relatively rare in depositional records, giving rise to much debate on the location of outlets and discharge pathways, as well as on the climate impact of the attendant meltwater forcing. Lake Ojibway developed following the withdrawal of the Laurentide Ice Sheet in northern Ontario and Quebec, Canada. The late‐stage evolution of this large ice‐dammed lake was influenced by the complex dynamics of the retreating ice margin, which highly complicates the identification of the termination of Lake Ojibway in glaciolacustrine sediment records. Here, we document the composition of sections of rhythmites that contain in their upper part an anomalously thick and whitish bed (10–15 cm) that is in turn overlain by ～1 m of faintly bedded rhythmites. Grain‐size analyses showed that the thick whitish bed consists primarily of fine to coarse silt (2–63 μm), contrasting with the lower and upper rhythmites that are largely dominated by clay (<2 μm). The detrital carbonate content of the thick silt bed is characterized by consistently high values (2.5 to 2.8%), whereas the bounding rhythmites show lower and highly variable values. Oxygen isotope measurements further show a marked change going from typical glacial meltwater values (～ ?29.6 to ?27.7‰; VSMOW) for the lower rhythmites and the silt bed to modern‐like meteoric values (?18.4 to ?14.6‰) for the uppermost rhythmites. These data suggest that this marker bed may be associated with a major drawdown event that possibly corresponds to the final drainage of Lake Ojibway. AMS radiocarbon dating of ostracods extracted from the drainage bed also documents an important hardwater effect within the Ojibway basin.     

Distribution and chronology of Pleistocene permafrost features in France: Database and first results

Numerous periglacial features (polygons, nets, soil stripes, ice‐wedge pseudomorphs and sand‐wedge casts, involutions) have been recorded in France by examining bibliographical sources and aerial photographs. These data show that a large part of France was affected by permafrost during the Pleistocene and only the southern Aquitaine Basin and Languedoc seem to have been beyond its maximum extent. The first OSL ages obtained from the aeolian infill of wedge structures indicate that at least two phases of thermal contraction cracking occurred in southwestern France between ～25 and 36 ka. Chronostratigraphical data from loess in northern France indicate that these episodes correspond to the formation of ice‐wedge networks associated with tundra gleys. In the latter region, two additional permafrost episodes probably occurred during the Last Glacial, the older one corresponding to the end of Marine Isotope Stage (MIS) 4 around 60 ka and the more recent one to MIS 2 around 19–16 ka. Although stratigraphical data indicate that these episodes were relatively short (about one millennium), relict permafrost may have existed for longer periods in northern France.     

Relationship between the fractal dimension of orthopyroxene distribution and the temperature in mantle xenoliths

As rock textures reflect the physical conditions and the mechanisms of formation of the rocks, new approaches are used for improving texture analyses, both qualitatively and quantitatively. Pioneer work has recently boosted interest in fractal analysis for quantifying and correlating patterns. Fractal‐like patterns relate to a degree of multiscale organization, and fractal dimensions (FD) and their potential variations can be used to infer the physical conditions of rock formation at various scales of observation. Here, we characterize quantitatively the shape and distribution of orthopyroxene grains in ultramafic xenoliths in terms of FD and their relation with temperature of equilibration. Fractal analysis has been applied to several populations of mantle xenoliths: 7 xenoliths collected in the vicinity of Pico Santa Isabel on Bioko Island, an alkaline basaltic volcano in oceanic domain (Gulf of Guinea, Equatorial Atlantic), 9 samples from Sangilen, in the Agardag alkaline lamprophyre dyke (Russia), and 11 samples form Śnieżnik (Lutynia, Poland), in the continental domain. Fractal analysis has been conducted to characterize the degree of complexity of the petrographic textures: it is indeed known that large values of FD are associated to more complex textures. The correlation here observed between the orthopyroxene fractal dimension and the temperature of equilibration suggests that FD captures a significant textural feature directly related to the temperature (i.e. generated by a temperature‐controlled process). The significant difference in the FD–T correlation observed for the continental and oceanic mantle domains suggests that the mechanical and rheological behaviour is distinct in the oceanic and continental lithospheres. These first promising results should be confirmed by analysing other mantle suites of rocks in different geodynamic settings. Copyright © 2015 John Wiley & Sons, Ltd.     

Otolith reading and multi-model inference for improved estimation of age and growth in the gilthead seabream Sparus aurata (L.)

Accurate knowledge of fish age and growth is crucial for species conservation and management of exploited marine stocks. In exploited species, age estimation based on otolith reading is routinely used for building growth curves that are used to implement fishery management models. However, the universal fit of the von Bertalanffy growth function (VBGF) on data from commercial landings can lead to uncertainty in growth parameter inference, preventing accurate comparison of growth-based history traits between fish populations. In the present paper, we used a comprehensive annual sample of wild gilthead seabream (Sparus aurata L.) in the Gulf of Lions (France, NW Mediterranean) to test a methodology improving growth modelling for exploited fish populations. After validating the timing for otolith annual increment formation for all life stages, a comprehensive set of growth models (including VBGF) were fitted to the obtained age–length data, used as a whole or sub-divided between group 0 individuals and those coming from commercial landings (ages 1–6). Comparisons in growth model accuracy based on Akaike Information Criterion allowed assessment of the best model for each dataset and, when no model correctly fitted the data, a multi-model inference (MMI) based on model averaging was carried out. The results provided evidence that growth parameters inferred with VBGF must be used with high caution. Hence, VBGF turned to be among the less accurate for growth prediction irrespective of the dataset and its fit to the whole population, the juvenile or the adult datasets provided different growth parameters. The best models for growth prediction were the Tanaka model, for group 0 juveniles, and the MMI, for the older fish, confirming that growth differs substantially between juveniles and adults. All asymptotic models failed to correctly describe the growth of adult S. aurata, probably because of the poor representation of old individuals in the dataset. Multi-model inference associated with separate analysis of juveniles and adult fish is then advised to obtain objective estimations of growth parameters when sampling cannot be corrected towards older fish.     

Spectroscopic investigation and theoretical modeling of kaolinite-group minerals and other low-temperature phases

This article summarizes some recent results obtained on the physical properties of environmental minerals, mostly kaolinite-group minerals and Fe- and Al-(hydr)oxides occurring in lateritic soils. The defective structure of these minerals, including impurities, stacking faults and radiation-induced defects, is probed using infrared spectroscopy and electron paramagnetic resonance. Resulting information bears on models of soil formation and transformation mechanisms of minerals in low-temperature environments. We underline the increasing impact of quantum chemical modeling in this field, providing straightforward interpretations of spectroscopic signals and overcoming the limits of fingerprint approaches. Importantly, the first-principles modeling of isotopic fractionation factors provides new links between mineralogical and geochemical investigations of secondary minerals.     

Structural context of meso-scale and cartographical duplex structure genesis in thrusting tectonics: role of tear faults. Zaghouan thrust belt. Case of Bir M'Cherga-Ain Asker area

Bir M'Cherga-Ain Asker area, situated in the hinterland of Zaghouan thrust (Tunisian dorsal), was the land example treated with metric and cartographic scale in order to identify duplex genesis criteria and to include thrusting tectonics associated with tear faults, which are in fact the directory response generating duplex structures identified in outcrop for the first time through Tunisia in this case. Given its geological location between the "dôme" and the "dorsal" zone of Tunisia, this area was the most exposed to a highly paleostress history expressed by a huge fault system remobilization and reactivation through several tectonic events from NE–SW middle Cretaceous distension to a NW–SE and NNW–SSE Paleogene compression. Regarding fault planes generated analysis, they show numerous streak generation of normal, strike-slip, and reverse faults that go with geodynamic and paleostress evolution of the studied area; we note that each streak generation is perfectly matching with one of the tectonic event (mentioned before) affecting the area. In this paper, we analyze duplex structure elaboration scenarios to assess the involved kinematics and their geometrical recognition criterious. We propose to discuss the causes of duplex structures installation in a thrust belt system and the predictable geometrical styles after its installation on foreland or backland. Using the geometrical criteria acquired through this analysis, we will show that such, however, exceptionable structures exist on the land, and that they record the mechanisms of their genesis linked to the tear faults acting in this case. We describe "tear faults" as the sliding breaks which disunite two compartments during deformation, allowing them to undergo different independent deformations in their drawing and their width (for example more or less stretched folds). These types of faults differ from that of the true stick-slip faults, which slice and shift preformed structures (it's even this shift which makes it possible to highlight them); here, there are no shift but dissimilarity of the structures on both sides of the fault; therefore, deformations are the direct results of displacements; they are expressed in thrust belts by ramp folds, intense internal deformations, and even by complex duplex structures. A duplex feature that is not mainly studied is made up by tilted imbricate sedimentary sequences (or horses), separated by link thrusts and underlined respectively at their tops and bottoms by roof and floor thrusts. Imbrications cause a shortening, a thickening, or a thinning of stratigraphic columns and even its crushing and inverting. In thrust belts, duplexes are usually set up following two or even more deformational events; those structures start typically with decollement and imbricate sedimentary unit ones which are made cover by a roof thrust sometimes visible at outcrop. Through this paper, we suggest to discuss geometrical duplex criteria, and we will try a zooming through different scales, from regional to local one in order to show how the shape (expression) of the deformation differs.     

A homogenization approach for evaluating the longitudinal shear stiffness of reinforced soils: column versus cross trench configuration

The macroscopic linear elastic behaviour of inclusion‐reinforced soils, regarded as periodic composite media, is investigated by means of the homogenization theory. Special attention is given here to the determination of their longitudinal shear stiffness properties, which strongly govern the reinforced ground response under lateral loading. Combining the use of analytical, variational and numerical methods, we thoroughly examined three particular engineering‐relevant configurations: single trench, column and cross trench reinforcements. Fairly accurate closed‐form expressions are thus obtained, giving the value of the reinforced soil longitudinal shear stiffness as a function of the individual components shear moduli and reinforcement volume fraction. It is shown in particular that adopting a cross trench reinforcement layout instead of the classical column configuration results in a much higher improvement of the longitudinal shear stiffness. The results are then applied to assessing the reduction of soil liquefaction risk, which can be attributed to the presence of the reinforcing inclusions. Again, they clearly demonstrate the excellent performance of the cross trench configuration as compared with the complete inefficiency of the column reinforcement technique. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of solar corona conditions on flare particle propagation

Data on high energy electrons and protons in different energy windows are analyzed and compared for two solar flares which occurred at 37 W solar longitude on the 25th February 1969 and the 29th March 1970. While the data for the first of these flares can be interpreted in the framework of a diffusion model with suitable values of the parallel diffusion coefficient, in order to explain the time behaviour of the different particles after the second event, we are led to suppose that the coronal magnetic fields are such that particles of different rigidity are ejected at different longitudes and that there is no good magnetic connection of the Earth with the flare region.