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117 hlm.;18 c

Late Pleistocene glaciations in southern East Sayan and detection of MIS 2 terminal moraines based on beryllium ( 10 Be) dating of glacier complexes

International audienceAnalysis and summary of publications on southern East Sayan, eastern Tuva, and northern Mongolia have shown that the late Pleistocene glaciation covered a large area and had a complicated dynamics of glacier advance and retreat. Starting with MIS 5, the Todza Basin and, partly, the Oka Plateau, Azas Volcanic Plateau, Mondy Basin, and river valleys in southern East Sayan were periodically covered with ice. The thickness of ice in the eastern Todza Basin was 700 m, on the Azas Volcanic Plateau it reached 300–600 m, and in the valleys of southern East Sayan it is estimated as 700–800 m. The thickness of ice in the Mondy Basin was 300–350 m. Geological and geomorphological studies and isotope surface exposure dating (10 Be method) of boulders from terminal moraine complexes have provided evidence for extensive MIS 2 glacier advance in the Mondy Basin and in the Sentsa, Jombolok, and Sailag river valleys (southern East Sayan). The average age of exposure for three groups of samples is 14, 16, and 22 k

Carving mountains : aeolian erosion as a major factor controlling the topographic evolution in the Gobi region (Mongolia).

International audienceThe Tsagaan Els Basin in SE Mongolia is a 31 000 km2 endoreic depression submitted to active erosion and surface lowering. The present-day depression is superimposed to a complex pattern of Cretaceous grabens and semi-grabens separated by basement highs composed of Proterozoic to Paleozoic metamorphic and magmatic rocks (Johnson et al., 2001). The summits of those basement highs correspond to fragments of a very low relief planation surface that formed prior to the Cretaceous extension phase, most probably during the Early to middle Jurassic (Jolivet et al., 2007). The Late Cretaceous sediments largely seal the extension phase. Paleogene to Neogene sedimentation is extremely condensed, marked by numerous aeolian dune deposits and carbonated paleosols, both indicating a long-lasting arid to semi-arid climate. The Quaternary sediments are limited, mainly composed of aeolian dunes, thin alluvial deposits, patchy outcrops of shale corresponding to small ephemeral lakes, and grain-thick sheets of gravels to pebbles covering strongly winnowed surfaces. Mapping of the drainage system shows a first-order trend towards the lowest point of the basin, associated to a second-order highly complex river network associated to local base levels. Numerous river capture events are observed indicating a poorly stabilized, locally constrained drainage system. In the center of the Tsagaan Els Basin, the c.a. 55 km long, 20 km wide Dulan Ul hill corresponds to one of the basement horsts, cropping out of the Cretaceous series. This flat-topped mountain, culminating around 950 m a.s.l. and 200 m above the basin is bordered to the north by a large fan-like morphological structure carved within the Cretaceous series. Similar fan-shaped morphologies are observed on several locations within the Tsagaan Els Basin, that cannot be explained through alluvial deposits or river incisions.In this study, we performed a detailed mapping of the displacement of the sand (that largely corresponds to the mode of wind direction) over the central part of the Tsagaan Els Basin. We show that the fan-like morphology upwind of the Dulan Ul hill is effectively related to wind-erosion carving into the Cretaceous sediments in front of the basement high. This strong aeolian erosion, associated to the occurrence of large lithological contrasts between the basement and the sedimentary series explains the complex and extremely versatile drainage network

Erosion around a large-scale topographic high in a semi-arid sedimentary basin: Interactions between fluvial erosion, aeolian erosion and aeolian transport

International audienceLarge-scale aeolian erosion features such as pans usually develop upon a relatively homogeneous erodible sedimentary rock substratum and show simple concave morphologies. However, some erosional depressions in semi-arid to arid settings develop in more complex geological contexts, associating sedimentary basins and outcrops of non-erodible basement. In semi-arid basins, the geomorphic evolution is controlled by interplay between the processes of fluvial erosion and deposition (especially of the finer sediment fraction in ephemeral lakes) and the processes of aeolian erosion and deflation. The occurrence of non-erodible basement outcrops within a region of overall deflation complicates drainage systems and wind-flow patterns. Both are liable to evolve rapidly through time and their interactions remain poorly understood. In this study, we use a detailed geomorphological analysis, including mapping of the aeolian sand-motion direction within the 16,300 km2 Tsagaan Els depression (Gobi Desert, Mongolia) as well as in situ-produced cosmogenic 10Be and 26Al based quantitative constraints, to propose a conceptual model for the morphologic evolution of geologically complex semi-arid basins. Based on theoretical studies of wind-flow patterns around obstacles, we demonstrate that the occurrence of erosion-resistant basement highs inside the basin induces the localization of preferential deflation zones and aeolian and fluvial carving of large-scale relief. The enhanced deflation zones form sub-depocenters controlling local drainage systems that mobilize clastic material and transport it to the deflation zone. These river systems are frequently captured by neighboring streams, which creates unstable conditions of erosion and deposition. Such rapid modifications of the topography through time affect the hydrogeologic structure of the basin and may impact potential sediment-hosted mineral deposits

Geomorphic Mesozoic and Cenozoic evolution in the Oka-Jombolok region (East Sayan ranges, Siberia)

International audienceThe East Sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far-field effects of the India-Asia collision and the extension linked to the opening of the Baikal Rift System. The active deformation that affects this range is very recent (around 5 Ma) but occurs in a very complex morphotectonic setting and the understanding of the Tertiary deformation relies entirely on a detailed knowledge of the pre-deformation situation. Using apatite fission track thermochronology, cosmogenic 10Be and morphological study on Tertiary lava flows we demonstrate that prior to the Oligocene the morphology of the East Sayan area was characterized by a wide, constantly rejuvenated erosion surface. Apatite fission track thermal modelling indicates that this surface started to form at least in Late Jurassic-Early Cretaceous (140-120 Ma). The long-term exhumation rates (several tens of million years) derived from apatite fission track data (17.5 m/Ma) and the short-term erosion rates (over a few hundred thousand years) derived from cosmogenic 10Be data (12-20 m/Ma) are coherent implying a near constant mean erosion rate since Late Jurassic. This constant, slow erosion prevented the formation of a lateritic-kaolinic weathering crust on the planation surface. By Oligocene-early Miocene times a long wavelength uplift that remains to be explained, induced incision that created shallow valleys later filled by basaltic lava flows. Finally, the present short-wavelength topography initiated during the Pliocene

Morphotectonic analysis and 10 Be dating of the Kyngarga river terraces (southwestern flank of the Baikal rift system, South Siberia)

International audienceThe formation of the Baikal rift system basins is controlled by active faults separating each basin from the adjacent horsts. The kinematics of these faults is mainly explored through investigation of complex sequences of the fault-intersecting river terraces that record both tectonic and climatic events. This study focuses on the northern margin of the major Tunka basin that develops south-west of Lake Baikal. The development of the basin is controlled by the segmented Tunka fault. We performed a detailed mapping of the Kyngarga river terraces, the best preserved terraces staircase in Baikal rift system, at their intersection with the Tunka fault. In order to decipher the chronology of seismic events and the slip rates along that segment of the fault, key terraces were dated using in situ produced cosmogenic 10Be. We demonstrate that the formation of the terrace staircase occurred entirely during MIS1–MIS2. The obtained data allowed us to estimate the rate of incision at different stages of the terrace staircase formation and the relationship between the vertical and horizontal slip rates along this sub-latitudinal segment of the Tunka fault making respectively 0.8 and 1.12 mm yr− 1 over the past ~ 12.5 ka. Analysis of the paleoseismology and paleoclimate data together with terrace dating provided the possibility to estimate the influence of tectonic and climatic factors on the terrace formation. Our proposed model of the Kyngarga river terrace development shows that the incisions into terraces T3 and T6 were induced by the abrupt climatic warming episodes GI-1 and GI-2, respectively, whereas terraces T5, T4 and T2 were abandoned due to the vertical tectonic displacement along the Tunka fault caused by coseismic ruptures

History of late Pleistocene glaciations in the central Sayan-Tuva Upland (southern Siberia)

International audienceThis work describes the history of late Pleistocene glaciations in the central Sayan-Tuva Upland (southern Siberia). Geological and geomorphological analysis as well as 10Be surface-exposure dating revealed the glacier fluctuations in this continental area. The available published data show that the glaciers were formed in the MIS 6 and probably survived in the MIS 5. Data are also available concerning glacial advances in different periods of MIS 4, MIS 3 and MIS 2. ELAs were 2030-2230 m. Two distinct 10Be exposure ages groups are highlighted reflecting the time of formation of glacial deposits in the MIS 2 associated to the Big Sayan Ridge outlet glaciers. The Sentsa - Sailag group (terminal moraine) has a mean exposure age of 16.44 ± 0.38 ka. The Jombolok (terminal moraine) - Jombolok (outwash plain) group has a mean exposure age of 22.80 ± 0.56 ka. The last glaciation that occurred at MIS 2 is characterized by the absence of ice cap on the Azas volcanic Plateau and of ice field in the Todza Basin. The thickness of the valley glacier was 300-400 m. At MIS 2, the terminal moraines were ∼1300-1400 m a.s.l. in the Tissa, Sentsa, Jombolok and Sailag river valleys

Uplift age and rates of the Gurvan Bogd system (Gobi-Altay) by apatite fission track analysis

International audienceThe dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower-Middle Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift phase probably started at 5 ± 3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

Validation of an instrument for measuring psychosocial and organisational work constraints detrimental to health among hospital workers: The NWI-EO questionnaire.

International audienceBackgroundQuality of care, job satisfaction and the health of registered nurses (RNs) are associated with their exposure to psychosocial and organisational work factors (POWFs).ObjectivesTo develop and validate an extended version of the Revised Nursing Work Index (NWI-R), the NWI-EO (Extended Organisation) tool specifically designed for occupational physicians and those involved in prevention programmes in healthcare institutions to assess the perception of POWFs, and then to determine priorities for preventive action to improve work organisation at the hospital staff level.MethodsThe tool was validated in the ORSOSA study, a multicentre French cohort of RNs and NAs (n = 4085) recruited in 214 work units of 7 French university hospitals. A total of 34 items (19 candidate items developed by a focus group and 15 items from the NWI-R) were analysed using principal component analysis (PCA) based on a randomised split-half of the data. In addition, construct validity, test–retest reliability, internal consistency and concurrent validity were assessed.ResultsResponse rate was 91%. Twenty-two items were selected (9 of the 15 NWI-R items and 13 of the 19 candidate items) by PCA, resulting in an 8-factor solution that explained 53% of the common variance. The stability of the factorial structure of this 22-item NWI-EO questionnaire was confirmed by PCA on the other half-sample as well as by PCA on subgroups (age, gender, occupational group, specialty area, hospital). Reliability, assessed by internal consistency and test–retest, was satisfactory. Concurrent validity with two external measurements of organisational characteristics of work units was also observed.ConclusionThe NWI-EO was found to have good psychometric properties. Several POWFs accessible to prevention programmes can be evaluated with this tool: poor communication in the work unit, lack of support from senior nurses, inadequate staffing to perform duties, poor relationships between workers, frequency of interruptions during tasks, low level of shared values within the team with regard to work, lack of support from the administration, and changes in planned vacations and time off. We believe the NWI-EO is a useful tool for assessing POWFs among RNs and NAs in order to determine priorities for preventive action to improve work organisation at the unit level

Silicon Nanowires Based Resistors for Bacteria Detection

Silicon nanowires (SiNWs) based resistors used as bacteria sensors are fabricated using the classical silicon technologies. SiNWs are grown by vapor liquid solid (VLS) method using gold as catalyst. Electrodes of the device are made of heavily in-situ doped polycristalline silicon. Results show potential use of the corresponding resistors, with SiNWs as sensitive units, for bacteria detection. Bacteria are preferentially hanged into SiNWs array and electrical resistance of the device decreases due to the presence of bacteria. Such resistors are promising bacteria sensors to monitor contamination in controlled environment for hygiene, fabricated in a simple and low-cost fabrication technology