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While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability. • Transport rates can be ten times greater on medium-sized beach than coarse one. • Offshore wind generate a grain size sorting, the finest sands are exported seaward. • Topographic variations of the beach depends on its grain size and sand supply. • The return of fine sediments depends on marine storms occurrence and intensities. [ABSTRACT FROM AUTHOR]

Marine mud belts represent potential continuous high-resolution climatic, environmental and anthropogenic archives. In this study, a geochemical record of the Gulf of Lions mud belt, which receives sediments from the Rhône watershed and to a lesser extent from the Languedoc region, is reported from Core KSGC-31. The effects of natural climatic changes and possible anthropogenic disturbances on Holocene sedimentation were ascertained by analysing sedimentation rates, chemical weathering (Al2O3/K2O) and sediment-source shifts (neodymium isotopic ratios; εNd). Measurements of elemental and isotopic lead were used to trace the source and determine the potential vectors of anthropogenic contaminations over the Holocene. High εNd values, recorded from 9000 to 3000 calibrated annum before present (cal. a BP) and around 1500 and 600 cal. a BP, are interpreted as an increase in sediment transport from the Alpine crystalline massifs to the sea induced by enhanced hydro-sedimentary conditions upstream. During the early and middle Holocene, low and stable weathering conditions were persistent, while the late Holocene was characterized by higher and more fluctuating weathering conditions. Sudden changes in the 206Pb/207Pb ratio observed during the Roman and Medieval periods suggest clear shifts in lead source from a natural Holocene background to late Holocene anthropogenic contaminations. Even though those shifts are coeval with atmospheric lead contaminations from Spain and Germany recorded in several sediment and ice archives, the local origin (the Cévennes) and the fluvial contamination is more likely in these cases. Those findings are contemporaneous with historical mining records in the Cévennes and point to an intensification of the merchant shipping. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strong interannual variability of the sediment dynamics in the Gulf of Lion. • Massive sediment accumulation near the Rhone River mouth (∼56 % of the river inputs) • Sediment deficit on the inner shelf due to the long-term reduction of the Rhone inputs. • Storm-induced sediment accumulation in the southwestern Gulf of Lion. • Cold winters mainly impact the southwestern and outer shelf and the submarine canyons. A simulation based on a hydro-sedimentary model was conducted for the period between summer 2010 and spring 2012 in the Gulf of Lion (northwestern Mediterranean Sea) to understand the spatial and temporal variability of sediment transport, erosion and deposition on the continental shelf and slope. Datasets of both simulated and observed current, temperature and suspended matter from the shelf and the Cap de Creus Canyon which is the main export route towards the continental slope, were first compared to assess the reliability of the simulation. The simulation shows the massive sediment accumulation near the Rhone River mouth (∼56 % of the inputs), the accretion along the mid-shelf mud belt, and the impact of dense shelf water cascading on sediment resuspension and erosion inside the Cap de Creus Canyon. The two studied autumn–winter periods were strongly contrasted in terms of meteorological conditions and subsequent impacts on the sediment dynamics. During the first period (2010–2011) dominated by marine storms, the shelf sediment underwent strong changes, the Rhone River sediment load accumulated in a relatively small area, stock of littoral sands moved to the inner shelf (20–40 m) while inner shelf fine particles fed the mid-shelf mud belt and the upper Cap de Creus Canyon. During the second period (2011–2012) with very little marine wind and a particularly cold winter, sediment on the shelf underwent little change except for a southwestward growth of the Rhone River prodeltaic deposit. Sediment from the southwestern end of the shelf as well as from the upper Cap de Creus Canyon was flushed toward deeper reaches by dense shelf water cascading. Cascading also had a more moderate impact in the various canyons incising the continental shelf. Our work supports the view of an unbalanced sedimentary system, with a deficit mainly over the inner shelf, whose main driver is probably the strong and fast reduction of particulate matter inputs from the Rhone River (by a factor of 4 in less than one century). [ABSTRACT FROM AUTHOR]

In the classic Wilson plate-tectonic cycle, plate convergence and orogenesis follow plate divergence. This results in an asymmetric doubly vergent collisional orogen with pro- and retro-wedge/foreland basin systems (lower and upper plate, respectively). Conceptual models propose that an orogen evolves as a single dynamic system from an early, non-equilibrated, growth stage to a late, mature, steady-state stage. Yet, early convergence processes and mechanisms responsible for the transition from rift to collision are, as yet, little known and quantified. In particular, most of our understanding of wedge/foreland dynamics comes from the pro-wedge, where mainly late orogenesis is well preserved. In contrast, the retro-foreland basin is believed to preserve the full orogen history due to lower shortening and translation values. This is the case in the NE Pyrenean retro-wedge, where recent studies suggest that during early orogenesis the Pyrenees never reached a steady-state configuration.Our work aims to constrain the timing and rates of orogenic episodes as well as timescales for sediment transport from source to sink in the Eastern Pyrenees. We apply coordinated U-Pb and (U-Th)/He dating methods on detrital zircon to ten samples through the syn-orogenic Upper Cretaceous to Eocene succession. We use the recently developed in situ double dating approach to address firstly, a two-fold shortcoming in quantifying syn-orogenic denudation and secondly, an issue with recognising the signature of early Pyrenean convergence in source-to-sink processes. Firstly, most previous regional exhumation studies have focused on reconstructing thermal histories for currently exposed bedrock, which has led to sparse constraints on the initiation and early phase of convergence. Moreover, regional detrital double dating has until recent years been performed either on distinct batches of grains or statistically non-representative numbers of grains or samples. Secondly, in the Pyrenees, the delay between the end of rifting (and associated HT metamorphism, early Cenomanian) and the onset of convergence (end Santonian) is short, leading to difficulties in recognising a clear thermal signature of early orogenesis.Our results show that lag times (the difference between the age of apparent cooling and deposition, assuming instantaneous transport) sharply decrease during the Maastrichtian, passing from >50 Myrs to <20 Myrs. This indicates a significant increase in denudation rates. Around this time we also note a marked increase in the proportion of Early Cretaceous rifting and Hercynian source signals, indicating a change in source area(s) and/or progressive unroofing of thermally reset rifted Pyrenean crust. All these changes are recorded over <2 Myrs and are synchronous with changes in paleo-current directions. We interpret these results as recording the sedimentary response to the onset of Pyrenean orogenesis. Our data suggest that the early orogen and the Early Cretaceous rift extended further east, in an area which has since been destroyed by the Oligo-Miocene opening of the Gulf of Lion. Our work clarifies early growth in the Pyrenees, providing new evidence for dynamic coupling between range and foreland basin(s), and contributing to the debate on the role of rift inheritance into early orogenic processes. [ABSTRACT FROM AUTHOR]