Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science最新文献

In spite of their suitability, waterlogged Bronze Age settlements of the Alpine area are actually under-investigated for archaeobotany. New investigations in Grésine (Bourget Lake, Savoie) bring new data on farming economy. Food plants include different cereals, oil plants, pulses, and many collected fruits. Various farming practices are documented. The fields seem to be long-term cultivated, autumn and spring sowings probably taking turns with short fallow phases. Grassland communities were exploited and could in part have grown during fallow phases on the cultivated land.

An example, from South India, shows the potentialities offered by the study of high altitude non-allophanic andisols to reconstitute the local palaeoenvironmental history. In this type of soils, organic matter is stabilised in the form of organometallic complexes that migrate downwards very slowly. Compared to the broad signal recorded by peat bogs, the soil organic matter signal appears to be more site-specific, which enables precise palaeoenvironmental studies. This application comes just when precise palaeoclimatic reconstitutions are necessary to build reliable climatic models.

The north–south structural evolution in the Subandean zone (eastern side of the Central Andes) reflects the complexity of the orogenic front that propagates on an heterogeneous substratum inherited from pre-Andean palaeogeographies. The construction of balanced cross-sections shows that this north–south evolution corresponds to a progressive transformation from thick-skin transpressive deformation to thin-skin compressive deformation. The thrust front propagation is controlled, in the north, by NNE–SSW to north–south rift systems Permo-Triassic to Jurassic in age, oblique to the chain, and in the south, by the relatively isopach series of the preserved Palaeozoic silico-clastic platform.

Characterization of the genetic relations between magma suites and associated gold/base metal hydrothermal deposits is imperative to our understanding of the role of magmas in the mineralization process. Melt inclusions trapped in igneous phenocrysts were used to characterize calc–alkaline magmas associated with Valea Morii porphyry–copper deposit, Romania. A comparative study of mineralized intrusion versus barren intrusion reveals parameters that may influence the magmatic–hydrothermal connection. The present results emphasize the importance of the chemistry of residual melts (trapped in magmatic inclusions) rather than bulk magma compositions (derived from whole rock analysis) in determining the metal concentration in released magmatic fluid.

This paper considers the relations between the North Atlantic Oscillation, reflecting the climate variation patterns on the North Atlantic region, and mass balance variations of Alpine and Scandinavian glaciers. This study first enhances the mass balance representativeness of climate variations on the massif scale. However, dealing with glaciers in the North and the South of Europe, the mass balance variations are inversely correlated. Analyses comparing the mass balance variations and the NAO index show that annual trends between these two components are really poor, but at the decadal scale, the two signals are well correlated.

This paper determines the isotopic signature of monthly precipitation in Tunisia and highlights the main influence of air mass origin and temperature. On an event basis, this impact is confirmed and two groups can be distinguished at Sfax: (i) rain coming from Atlantic air masses that circulate in northern Africa (group I), (ii) precipitation due to atmospheric circulation on the Mediterranean Sea (group II). Mediterranean rains are enriched in oxygen-18 (−4.1 ‰), whereas the Atlantic ones show a more depleted value (−6.7 ‰). These specific signatures will be useful for groundwater tracing.

This paper deals with the study of Lake Massoko (9°20′00S–33°45′20E, Tanzania), a maar lake of the East-African Rift. Although some water flux of the hydrologic balance of this lake are easily quantified, only the net flux between the Lake and groundwater can be appreciated. Overpassing this limit requires the establishment of stable isotopic (¹⁸O and ²H) budgets. This approach is discussed with a special attention on the atmospheric vapour estimation. Results allow to estimate the underground outflow at 60 % and underground inflow at 25 %, with regard of the total water input. This confirms the importance of the groundwater circulation in volcanic lakes of the East African Rift.

In spodosols of Gascony (France), conversion of maritime pine stands into maize cropping leads to an incorporation of maize organic matter, which changed the isotopic (δ¹³C) and phenolic signature in A and L horizons of soil. Hydrolysis of phenol lignin in forests and cultivated soils showed the predominance of vanillic units under forest and the early but moderate incorporation of cinnamic acids. Incorporation of syringic units appeared higher, related to a large maize production of stable syringic phenols. Syringic units represented a long-term marker of maize inputs in soils, whereas vanillic units revealed the degradation of forest organic matter.

In order to study the wave impact on beach profile morphological changes, we have developed a numerical ‘deterministic’ model. We focus on the sensitivity analysis of various modelling approaches in order to explain their limitations. Validating the model with experimental measurements, we put forward the poor estimation of the bed sediment concentration given by classical formula. We propose a new parameterization relying on a Shields parameter based on the breaking-induced shear-stress.

The eastwards motion of the Caribbean plate is supposed to be related to a Cretaceous flip of subduction from eastwards to westwards vergence. However, we do not observe on the seismic profiles recorded during the CASIS 2 cruise any evidence of subduction beneath the Aves Ridge and Nicaragua Rise. Aves volcanic arc has been probably formed after the collision of the Caribbean volcanic plateau as shown by a wedge of volcanic-clastic sediments imaged by the seismic cruise CASIS 2. A recent left-lateral transtensional tectonics is observed in the lower Nicaragua Rise; the Colombia basin might have a motion towards the northeast relative to the rise.