Monitoring water flow in a clay-shale hillslope from geophysical data fusion based on a fuzzy logic approach

Seismic and electrical resistivity tomography allow subsurface characterization from acoustic P-waves (Vp), shear S-waves (Vs) velocities, and electrical resistivity (ρ). Both geophysical methods were used to monitor water flow during a controlled rainfall experiment on a clay-shale hillslope located in the Laval catchment at Draix (Alpes-de-Haute-Provence, France). The objectives of the rainfall experiment were to analyse the water infiltration processes and identify possible water pathways by combining multi-method observations. The seismic data provide information on fissure density and the electrical resistivity data provide information on soil water content within the hillslope. Changes of the Vp and electrical resistivity fields with time show some similar pattern. To go further in the analysis of the water flow a geophysical data fusion strategy based on fuzzy set theory is applied. The computed fuzzy cross-sections based on expert hypotheses show the possibility for the material to be saturated during the rainfall experiment. The data fusion process is repeated in time for each acquisition set. The relative difference between the obtained fuzzy cross-sections is calculated and reveals possible locations where water may be transferred within the hillslope.     

Petrological evidence for stepwise accretion of metamorphic soles during subduction infancy (Semail ophiolite,Oman and UAE)

Metamorphic soles are tectonic slices welded beneath most large‐scale ophiolites. These slivers of oceanic crust metamorphosed up to granulite facies conditions are interpreted as forming during the first million years of intraoceanic subduction following heat transfer from the incipient mantle wedge towards the top of the subducting plate. This study reappraises the formation of metamorphic soles through detailed field and petrological work on three key sections from the Semail ophiolite (Oman and United Arab Emirates). Based on thermobarometry and thermodynamic modelling, it is shown that metamorphic soles do not record a continuous temperature gradient, as expected from simple heating by the upper plate or by shear heating as proposed in previous studies. The upper, high‐T metamorphic sole is subdivided in at least two units, testifying to the stepwise formation, detachment and accretion of successive slices from the down‐going slab to the mylonitic base of the ophiolite. Estimated peak pressure–temperature conditions through the metamorphic sole, from top to bottom, are 850°C and 1 GPa, 725°C and 0.8 GPa and 530°C and 0.5 GPa. These estimates appear constant within each unit but differing between units by 100–200°C and ~0.2 GPa. Despite being separated by hundreds of kilometres below the Semail ophiolite and having contrasting locations with respect to the ridge axis position, metamorphic soles show no evidence for significant petrological variations along strike. These constraints allow us to refine the tectonic–petrological model for the genesis of metamorphic soles, formed via the stepwise stacking of several homogeneous slivers of oceanic crust and its sedimentary cover. Metamorphic soles result not so much from downward heat transfer (ironing effect) as from progressive metamorphism during strain localization and cooling of the plate interface. The successive thrusts originate from rheological contrasts between the sole, initially the top of the subducting slab, and the peridotite above as the plate interface progressively cools. These findings have implications for the thickness, the scale and the coupling state at the plate interface during the early history of subduction/obduction systems.     

Tunable diode laser measurements of trace gases during the 1988 Polarstern cruise and intercomparisons with other methods

Measurements of NO₂, HCHO, and H₂O₂ were made by the highly specific method of mid infra-red absorption spectroscopy using tunable diode lasers (TDLAS) during the 1988 Polarstern expedition. The TDLAS data are compared to those obtained during the cruise using less direct methods. Southern Hemisphere NO₂ levels suggest nett photochemical destruction of O₃ in the boundary layer. Northern Hemisphere HCHO averaged 0.47±0.2 ppbv; the HCHO measurements are used in a simple calculation to estimate OH noontime maxima of 3–6×10⁶ cm^-3.     

Genetic differentiation ofNiphargus rhenorhodanensis (Amphipoda) from interstitial and karst environments

Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus.     

Lacustrine wave-dominated clastic shorelines: modern to ancient littoral landforms and deposits from the Lake Turkana Basin (East African Rift System,Kenya)

This paper presents an overview of some of the most significant, recent to ancient, littoral morpho-sedimentary structures and deposits from the Lake Turkana Basin. We highlight the importance of wave-related sedimentary processes in lakes, and more specifically in rift lakes. In the published literature, references to wave-dominated shorelines are mainly in regards to coastal marine environments. However, numerous modern lakes exhibit typical wave-dominated littoral landforms, and related sedimentary deposits are known from several paleolake successions in the geological record. Wave-related processes are often of relatively minor importance in depositional models for lacustrine environments. Classical models emphasize clastics transported by rivers, which are then distributed by fan-deltas and/or deltas into a water body of fluctuating depth, where reworking of clastics is limited in the littoral domain, and episodic in deep waters. Modern processes in Lake Turkana and the exposed paleolake deposits of the Turkana Basin demonstrate that this view is incomplete. Wave-dominated shorelines are evident (1) for modern Lake Turkana based on prominent and active littoral landforms (e.g., beach ridges, sand spits, washover fans, and arcuate-cuspate deltas); (2) for the Holocene (African Humid Period) climate-driven highstand of Megalake Turkana and its subsequent forced regression based on conspicuous raised beach ridges and spits; and (3) for the Pliocene–Pleistocene (Omo Group, Nachukui Formation) from typical nearshore sedimentary facies and stratigraphic architectures associated with paleolake Turkana. These examples from the Turkana Basin coupled with examples from other lacustrine settings, suggest that wave-dominated clastic shorelines represent significant portions of existing and ancient lake-shores. As this view contrasts with classic depositional models for lakes, notably for those found in rift setting, we also present examples of wave-influenced littoral landforms from other lakes of the East African Rift System. Identifying lacustrine paleoshorelines from typical clastic landforms and deposits is the key to the spatial reconstruction of lakes over time, and to determine transgressive–regressive cycles. Waves action is an important agent in lakes for the erosion, transport, and deposition of clastics at the basin-scale, an aspect that needs to be integrated in sedimentary models.     

Integrated 3D forward stratigraphic and petroleum system modeling of the Levant Basin,Eastern Mediterranean

The Eastern Mediterranean Levant Basin is a proven hydrocarbon province with recent major gas discoveries. To date, no exploration wells targeted its northern part, in particular the Lebanese offshore. The present study assesses the tectono‐stratigraphic evolution and related petroleum systems of the northern Levant Basin via an integrated approach that combines stratigraphic forward modeling and petroleum systems/basin modeling based on the previous published work. Stratigraphic modeling results provide a best‐fit realisation of the basin‐scale sedimentary filling, from the post‐rift Upper Jurassic until the Pliocene. Simulation results suggest dominant eastern marginal and Arabian Plate sources for Cenozoic siliciclastic sediments and a significant contribution from the southern Nilotic source mostly from Lower Oligocene to Lower Miocene. Basin modeling results suggest the presence of a working thermogenic petroleum system with mature source rocks localised in the deeper offshore. The generated hydrocarbons migrated through the deep basin within Jurassic and Cretaceous permeable layers towards the Latakia Ridge in the north and the Levant margin and offshore topographic highs. Furthermore, the basin model indicates a possibly significant influence of salt deposition during Messinian salinity crisis on formation fluids. Ultimately, the proposed integrated workflow provides a powerful tool for the assessment of petroleum systems in underexplored areas.     

Maps of Titan's surface from 1 to 2.5 μm

We have acquired resolved images of Titan with the adaptive optics systems PUEO/KIR at the CFHT (Hawaii) and NAOS/CONICA at the VLT (Chile). We report here on images and maps (when data at several orbital phases are available) of Titan's surface from observations taken during the last 4 years (2001-2004) in all the methane windows between 1 and 2.5 μm (namely, at 1.08, 1.28, 1.6, and 2 μm). We present the only complete maps of Titan currently available at 1.3 μm, a spectral window where Titan appears particularly bright in spectroscopy, with a resolution of about 200 km at best on the ground. Our surface maps show the bright and dark regions sharing Titan's landscape with as much detail as possible from the ground and with high contrast in most cases. From the information gathered by comparing the maps at different wavelengths we derive constraints on the ground's composition. Our results could complete/optimize the return of the Cassini-Huygens mission.     

GAUGE: the GrAnd Unification and Gravity Explorer

The GAUGE (GrAnd Unification and Gravity Explorer) mission proposes to use a drag-free spacecraft platform onto which a number of experiments are attached. They are designed to address a number of key issues at the interface between gravity and unification with the other forces of nature. The equivalence principle is to be probed with both a high-precision test using classical macroscopic test bodies, and, to lower precision, using microscopic test bodies via cold-atom interferometry. These two equivalence principle tests will explore string-dilaton theories and the effect of space–time fluctuations respectively. The macroscopic test bodies will also be used for intermediate-range inverse-square law and an axion-like spin-coupling search. The microscopic test bodies offer the prospect of extending the range of tests to also include short-range inverse-square law and spin-coupling measurements as well as looking for evidence of quantum decoherence due to space–time fluctuations at the Planck scale.     

Nonuniform cratering of the terrestrial planets

We estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets [Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.-M., Levison, H.F., Michel, P., Metcalfe, T.S., 2002. Icarus 156, 399-433]. After determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination, the impact positions are calculated analytically, assuming the projectiles follow hyperbolic paths during the encounter phase. As the source of projectiles is not isotropic, latitudinal variations of the impact flux are predicted: the calculated ratio between the pole and equator is 1.05 for Mercury, 1.00 for Venus, 0.96 for the Earth, 0.90 for the Moon, and 1.14 for Mars over its long-term obliquity variation history. By taking into account the latitudinal dependence of the impact velocity and impact angle, and by using a crater scaling law that depends on the vertical component of the impact velocity, the latitudinal variations of the cratering rate (the number of craters with a given size formed per unit time and unit area) is in general enhanced. With respect to the equator, the polar cratering rate is about 30% larger on Mars and 10% on Mercury, whereas it is 10% less on the Earth and 20% less on the Moon. The cratering rate is found to be uniform on Venus. The relative global impact fluxes on Mercury, Venus, the Earth and Mars are calculated with respect to the Moon, and we find values of 1.9, 1.8, 1.6, and 2.8, respectively. Our results show that the relative shape of the crater size-frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study. Nevertheless, by neglecting the expected latitudinal variations of the cratering rate, systematic errors of 20-30% in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method.