Papers by pascal allemand
ABSTRACT This work describes a Rock Automated Detector algorithm developed for the analysis of Ex... more ABSTRACT This work describes a Rock Automated Detector algorithm developed for the analysis of ExoMars 2016 mission landing site, its validation, and performances.
Journal of the Virtual Explorer, 2001
ABSTRACT At the catchment scale water temperature is influenced by geographical factors, but at t... more ABSTRACT At the catchment scale water temperature is influenced by geographical factors, but at the reach scale superficial and groundwater hydrology and channel geometry strongly affect thermal patterns. During the last 30 years, studies have been pointed out the significance and complexity of water exchanges between the channel and the hyporheic and phreatic zones. These surface-subsurface water exchanges influence water temperature patterns. Braided rivers present particular thermal conditions with very high spatial water temperature variability. This high thermal variability is difficult to comprehend using only in situ measurements and so thermal infrared (TIR) remote sensing is particularly suited to assessing the thermal patterns associated with these rivers. The aims of this study are to evaluate temperature patterns of nine braided reaches at very high spatial resolution (~20 cm) and to link temperature and water-body types. We hypothesized that river type has an influence of the spatial patterns of water temperature and that the patterns change through the day. All reaches are located in France, in the Rhône catchment. The nine reaches were selected based on high aquatic habitat diversities and are located in three regional areas: the massif des Écrins, the Rhône valley, and south Alps. They are about 1 km long. We have three distinct temporal approaches. The first one is a multi-site approach which proposes one survey of each site during summers 2010 or 2011. Three reaches were selected for the second phase (a multi-annual analysis and were therefore imaged both in summers 2010 and 2011. The last phase is an intra-day survey of two reaches with several flights at different times of day. This presentation focuses on the last approach with two reaches of the Drôme and Drac Noir rivers. To observe the evolution of the thermal patterns of these two reaches through the day, four flights within a day were realized during summer 2011 for both sites. The Drôme reach (44°44' N, 4°56' E) is characterized by a nivo-pluvial regime while the Drac Noir (44°40' N, 6°18' E) is a glacial river. Very high spatial resolution thermal images are needed because braided rivers have multiple, often narrow, channels. Satellite and aircraft TIR do not have fine enough spatial resolutions and consequently we used a drone, a helicopter and a paraglider to acquire sets of images. The three vector types were equipped with a thermal camera (7.5-14 μm) which can detect noise equivalent temperature differences of ±0.08°C. Based on flight and camera parameter, we collected thermal images with very high spatial resolution (10-30 cm). At the same time as the thermal acquisitions, visible images were recorded and in situ measurements of water temperatures, velocities and discharges were taken.
Journal of Structural Geology, 2004
We have modelled the formation and the layer-parallel shortening of layered (stromatic) migmatite... more We have modelled the formation and the layer-parallel shortening of layered (stromatic) migmatites. The model consists of thin superposed layers of partially molten microcrystalline wax. The melt (30 vol.%) has a negative buoyancy and a high viscosity contrast with its solid matrix. As soon as the shortening begins, melt-filled veins with high aspect ratios open along foliation. The melt is segregated into the veins, forming a stromatic layering. During incipient folding, crescent-shaped saddle reefs open at the hinges of open sinusoidal folds. Further shortening and melt-enhanced shear displacements on interlayer interfaces cause chevron folds to develop and the saddle reefs to become triangular. In comparison, a melt-free experiment shows only a few layer-parallel openings and no saddle reefs in chevron folds. On the basis of our experimental results, we propose that in migmatites: (1) mesoscale melt migration is a combination of flow in immobile veins and movements of veins as a whole; (2) the changes in the geometry of the mesoscale melt-flow network create the pressure gradients that drive melt migration; (3) the melt-flow network does not need to be fully interconnected to allow local expulsion; (4) melt expulsion is episodic because the temporal evolution of the network combines with the spatial heterogeneity of the deformation. q
Journal of The Virtual Explorer, 2001
Tectonophysics, 1997
... TECTONOPHYSICS I Strain partitioning and metamorphism in a deformable orogenic wedge: Applica... more ... TECTONOPHYSICS I Strain partitioning and metamorphism in a deformable orogenic wedge: Application to the Alpine belt a* Pascal Allemand ' , Jean ... 2. The corner flow model The concept of corner flow circulation has been experimentally tested by Cowan and Schilling {1978 ...
ABSTRACT The study area is the western margin of the Mesozoic intracratonic basin of southeastern... more ABSTRACT The study area is the western margin of the Mesozoic intracratonic basin of southeastern France. The study interval is Rhaetian to Earliest Sinemurian in age, and is made up of siliciclasticcarbonate lithologies bearing sulphur-rich mineralizations. The deposits accumulated in marginal marine to marine shelf environments. Investigation sites were commercial exploratory wells plus scientific wells of the French Continental Scientific Drilling Programme — Géologie profonde cle la France. The stratigraphic cycles were investigated and correlated on the basis of current concepts of genetic stratigraphy. A variety of techniques were applied, including (1) sedimentological core analysis; (2) quantitative Computer Processed Interpretation of well-log data, qualitative calibration of well-log signatures; (3) spectral analysis through direct numerical processing of well-log data; (4) input of biostratigraphic data. Chronostratigraphic cross-sections were reconstructed through correlation of genetic sequences, and backstripping at each site further permitted real palaeogeometries to be obtained at any given time-step. Two transverse and longitudinal cross-sections at reservoir- and margin scales were drafted. Such transects provide a wide range of helpful insights for investigating (1) patterns of early fluid migrations; (2) basin geohistory at a resolution of about one million years; and (3) control on the development of stratigraphic cycles.
ABSTRACT The study area is the western margin of the Mesozoic intracratonic basin of southeastern... more ABSTRACT The study area is the western margin of the Mesozoic intracratonic basin of southeastern France. The study interval is Rhaetian to Earliest Sinemurian in age, and is made up of siliciclasticcarbonate lithologies bearing sulphur-rich mineralizations. The deposits accumulated in marginal marine to marine shelf environments. Investigation sites were commercial exploratory wells plus scientific wells of the French Continental Scientific Drilling Programme — Géologie profonde cle la France. The stratigraphic cycles were investigated and correlated on the basis of current concepts of genetic stratigraphy. A variety of techniques were applied, including (1) sedimentological core analysis; (2) quantitative Computer Processed Interpretation of well-log data, qualitative calibration of well-log signatures; (3) spectral analysis through direct numerical processing of well-log data; (4) input of biostratigraphic data. Chronostratigraphic cross-sections were reconstructed through correlation of genetic sequences, and backstripping at each site further permitted real palaeogeometries to be obtained at any given time-step. Two transverse and longitudinal cross-sections at reservoir- and margin scales were drafted. Such transects provide a wide range of helpful insights for investigating (1) patterns of early fluid migrations; (2) basin geohistory at a resolution of about one million years; and (3) control on the development of stratigraphic cycles.
Geodinamica Acta, 2000
3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by seque... more 3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad subsiding area in an extensional framework, with a larger size than the present-day basin. During the Aalenian time, the subsidence pattern changes drastically (early stage of the central Atlantic opening). Further steps of the opening of the Ligurian Tethys (base Hettangian, late Pliensbachian;...) and its evolution into an oceanic domain (passive margin, Callovian) are equally recorded in the tectono-sedimentary history. The Lower Cretaceous was characterized by NE–SW compressive medium wavelength unconformities (late Cimmerian–Jurassic/Cretaceous boundary and intra-Berriasian and late Aptian unconformities) coeval with opening of the Bay of Biscay. These unconformities are contemporaneous with a major decrease of the subsidence rate. After an extensional period of subsidence (Albian to Turonian), NE–SW compression started in late Turonian time with major folding during the Late Cretaceous. The Tertiary was a period of very low subsidence in a compressional framework. The second folding stage occurred from the Lutetian to the Lower Oligocene (N–S compression) partly coeval with the E–W extension of the Oligocene rifts. Further compression occurred in the early Burdigalian and the Late Miocene in response to NE–SW shortening. Overall uplift occurred, with erosion, around the Lower/Middle Pleistocene boundary.L'image stratigraphique 3D du Bassin de Paris, bassin intracratonique méso-cénozoïque a été obtenue par la corrélation d'environ 1 100 puits (diagraphies) selon les principes de la stratigraphie séquentielle. Il enregistre fidèlement les principaux évènements tectoniques affectant la partie occidentale de la plaque ouest-eurasiatique : l'ouverture et la fermeture de la Téthys et l'ouverture de l'Atlantique. De la base du Trias au Jurassique terminal, le Bassin de Paris est un domaine subsident, de superficie supérieure à l'actuel bassin, dans un contexte extensif avec un changement de mode de subsidence durant l'Aalénien (ouverture de l'Atlantique central). Il enregistre les différents stades de l'ouverture de la Téthys ligure (base de l'Hettangien; Pliensbachien terminal;...) et son passage à un domaine océanique (marge passive, Callovien). Le Cretacé inférieur est caractérisé par des discordances de moyenne longeur d'onde selon une compression NE–SW (néo-cimmérien - limite Jurassique/Crétacé et intra-Berriasien - et Aptien terminal) contemporaines de l'ouverture du Golfe de Gascogne. Ces discordances s'accompagnent d'une diminution importante de la vitesse de subsidence. Après une période de subsidence en contexte extensif (Albien à Turonien), un régime de compression NE–SW s'installe dès la fin du Turonien avec une « phase » de plissement majeur à la fin du Crétacé. Le Tertiaire est une période de très faible subsidence dans un contexte compressif. La seconde période de plissement se produit du Lutétien à l'Oligocène inférieur (compression N–S) en partie contemporaine de l'extension E–W associée aux rifts oligocènes. D'autres paroxysmes de compression se produisent à la base du Burdigalien et au Miocène terminal en réponse à une compression NE–SW. Une surrection généralisée du bassin, avec érosion, se produit aux alentours de la limite Pléistocène inférieur/moyen.
Tectonophysics, 1991
Allemand P. and Brun, J.-P., 1991. Width of continental rifts and rheological layering of the lit... more Allemand P. and Brun, J.-P., 1991. Width of continental rifts and rheological layering of the lithosphere. in: P.R. Cobbold (Editor), Experimental and Numerical Modelling of Continental Deformation. Tectonophysics, 188: 63-69.
We describe a new method to map intra-plot soil surface heterogeneities at a 5 cm spatial resolut... more We describe a new method to map intra-plot soil surface heterogeneities at a 5 cm spatial resolution. Our approach unites aerial image classification acquired at very high spatial resolution (VHSR) with local soil sampling. VHSR aerial image processing, based on image classification, allows precise mapping of the spatial distribution of soil surfaces; soil sampling defines soil typology by physical and chemical characteristics. This method has been applied to a plot area located on the hillslopes of Burgundy vineyards (Monthelie, France), where decennial erosion data were already available, in order to assess the effect of soil surface characteristics and slope angle on erosion intensity and localisation. From this method, four classes of radiance were distinguished and interpreted as four soil surface state classes (SSC), defining specific areas within the studied plot. These SSCs have been characterised by their grain-size distribution, their organic carbon, calcium carbonate, and total nitrogen contents. By allowing soil surface states to be mapped at five centimetre resolution, this approach provides novel insights into the characterisation of soil patterns and into erosion analysis on cultivated hillslopes. Our work shows that the spatial distribution of soil erosion is related to the local slope steepness but also to the spatial distribution of stoniness that results from water and tillage erosion processes.
Remote Sensing of Environment, 2016
Jgr Journal of Geophysical Research Planets, 1991
Using the width of concentric grabens formed during the relaxation of the Asgard basin on Callist... more Using the width of concentric grabens formed during the relaxation of the Asgard basin on Callisto, in combination with rheological flow laws of ice and laws conceming the variations in strain rate around a relaxing crater, the surface thermal gradient of Callisto at -4 b.y. is estimated to be near 0.5øK km-1. It is assumed that the graben width depends on the depth of the brittle/ductile transition zone. Around the Asgard basin, the depth of this brittle/ductile transition zone varies from 23 km (at 200 km from the crater rim) to 4 km (at 800 km from the crater rim). It is assumed that the thermal characteristics were constant over the extended zone and that the difference in the depth of the brittle/ductile transition zone is only due to differences in the strain rate around the basin during the relaxation of the initial cavity. Calculations show that NewtonJan flow law for ice gives a strain rate of extemal relaxation at the crater rim of about 10-14 s-1, while a power law gives a strain rate of about 10-6 s-l, assuming a surface temperature between 100 and 150øK. The order of magnitude of the calculated thermal gradient is independent of the chosen flow law. This calculated gradient is, however, one order of magnitude lower than those calculated theoretically with a chondritic abundance of radioactive elements in the silicate part of Callisto.
Geodinamica Acta, 2000
3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by seque... more 3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad subsiding area in an extensional framework, with a larger size than the present-day basin. During the Aalenian time, the subsidence pattern changes drastically (early stage of the central Atlantic opening). Further steps of the opening of the Ligurian Tethys (base Hettangian, late Pliensbachian;...) and its evolution into an oceanic domain (passive margin, Callovian) are equally recorded in the tectono-sedimentary history. The Lower Cretaceous was characterized by NE–SW compressive medium wavelength unconformities (late Cimmerian–Jurassic/Cretaceous boundary and intra-Berriasian and late Aptian unconformities) coeval with opening of the Bay of Biscay. These unconformities are contemporaneous with a major decrease of the subsidence rate. After an extensional period of subsidence (Albian to Turonian), NE–SW compression started in late Turonian time with major folding during the Late Cretaceous. The Tertiary was a period of very low subsidence in a compressional framework. The second folding stage occurred from the Lutetian to the Lower Oligocene (N–S compression) partly coeval with the E–W extension of the Oligocene rifts. Further compression occurred in the early Burdigalian and the Late Miocene in response to NE–SW shortening. Overall uplift occurred, with erosion, around the Lower/Middle Pleistocene boundary.L'image stratigraphique 3D du Bassin de Paris, bassin intracratonique méso-cénozoïque a été obtenue par la corrélation d'environ 1 100 puits (diagraphies) selon les principes de la stratigraphie séquentielle. Il enregistre fidèlement les principaux évènements tectoniques affectant la partie occidentale de la plaque ouest-eurasiatique : l'ouverture et la fermeture de la Téthys et l'ouverture de l'Atlantique. De la base du Trias au Jurassique terminal, le Bassin de Paris est un domaine subsident, de superficie supérieure à l'actuel bassin, dans un contexte extensif avec un changement de mode de subsidence durant l'Aalénien (ouverture de l'Atlantique central). Il enregistre les différents stades de l'ouverture de la Téthys ligure (base de l'Hettangien; Pliensbachien terminal;...) et son passage à un domaine océanique (marge passive, Callovien). Le Cretacé inférieur est caractérisé par des discordances de moyenne longeur d'onde selon une compression NE–SW (néo-cimmérien - limite Jurassique/Crétacé et intra-Berriasien - et Aptien terminal) contemporaines de l'ouverture du Golfe de Gascogne. Ces discordances s'accompagnent d'une diminution importante de la vitesse de subsidence. Après une période de subsidence en contexte extensif (Albien à Turonien), un régime de compression NE–SW s'installe dès la fin du Turonien avec une « phase » de plissement majeur à la fin du Crétacé. Le Tertiaire est une période de très faible subsidence dans un contexte compressif. La seconde période de plissement se produit du Lutétien à l'Oligocène inférieur (compression N–S) en partie contemporaine de l'extension E–W associée aux rifts oligocènes. D'autres paroxysmes de compression se produisent à la base du Burdigalien et au Miocène terminal en réponse à une compression NE–SW. Une surrection généralisée du bassin, avec érosion, se produit aux alentours de la limite Pléistocène inférieur/moyen.
Geochim Cosmochim Acta, 1999
It is often argued that the δ18O value of oceanic water was maintained close to 0‰ for hundreds o... more It is often argued that the δ18O value of oceanic water was maintained close to 0‰ for hundreds of millions of years, as a consequence of oxygen isotope exchange between oceanic crust and seawater. However, for several decades, the interpretation of the biosedimentary oxygen isotope record has conflicted with the igneous record because, with increasing age, a general trend of decreasing δ18O values (about 6‰) is observed in most carbonates, cherts and phosphates, especially for the Paleozoic and early Mesozoic. We developed a dynamical model of seawater-crust interaction that computes the δ18O value in these two reservoirs as function of time. This model takes into account the continuous production of crust at oceanic ridges, its expansion rate, the permeability profile with space and time, the mineralogical mode of the crust, and the kinetics of oxygen isotope exchange between rock-forming minerals and seawater. The model indicates that the δ18O value of seawater may vary by ±2‰ with a time response ranging from 5 to 50 Ma for expansion rates of 1 to 10 cm.a−1. The variation of ±2‰ is fixed by both integrated water-rock ratio and closure time of the seawater-crust system by sediments. Variations in the oxygen isotope ratio of seawater through time have important implications for the interpretation of the systematically low δ18O values of pre-Jurassic marine sediments. According to our model, marine paleotemperatures could be up to 10°C lower than those expected when applying the classical hypothesis of an ice-free ocean with a δ18O value of −1‰.
Lunar and Planetary Science Conference, Mar 1, 2001
The sinuosity of lobate martian craters is analysed using image analysis techniques. From dimensi... more The sinuosity of lobate martian craters is analysed using image analysis techniques. From dimensional analysis, we demonstrate that the wave length of the lobes allow us to obtain some quantitative results on the rheology of the megaregolith during the impact event.
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Papers by pascal allemand