No abstract

Several marine geophysical data and piston-coring surveys acquired during the last decade allow one to better understand the close dynamic interactions between the sand-rich Orinoco turbidite system and the compressional structures of the Barbados prism. These interactions have been active since Eocene time as illustrated by the study of outcrops onshore Barbados Island. Because of strong morphologic and tectonic control in the east-Caribbean active margin, the present-day Orinoco turbiditic pattern system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the South-American margin induces the convergence of the turbidite channels toward the abyssal plain, at the front of the accretionary prism. Also, whereas in most passive margins the turbidite systems are organized upstream to downstream as canyon, channel-levee and lobes, here, due to the tectonic control, the sedimentary system is organized upstream to downstream as channel-levee, canyons and channelized lobes. Indeed, at the edge of the Orinoco platform, the system has multiple sources with several distributaries and downstream the channel courses are complex with frequent convergences or divergences that are emphasized by the effects of the undulating seafloor tectonic morphologies associated with active thrust tectonics and mud volcanism. On top of the accretionary prism, turbidite sediments are filling transported piggy-back basins whose timing of sedimentation vs. deformation is complex. While erosion processes are almost absent on the highly subsiding Orinoco platform and in the upper part of the turbidite system, they develop mostly between 2000 and 4000 m of water depth, above the compressional structures of the Barbados prism (canyons up to 3 km wide and 300 m deep). In the abyssal plain, the main turbiditic channel develops toward the east and connects with the Vidal mid-Atlantic channel. The sediments transported in this channel are filling several elongated basins linked with fracture zones (notably the Barracuda Basin), and finally end their course in the Puerto-Rico trench, the deepest morphologic depression of the region. Piston-cores have demonstrated that turbidite sediments above the Highlights ► An overview of the nature and architecture of the Orinoco turbidite system is proposed. ► We discuss how the active margin tectonic processes control the turbidite system. ► We discuss the specificity compared with turbidite systems in passive margins. ► Deep-marine erosion processes and sediments transport are described. ► A numerical model is proposed and compared with the actual sedimentary system.

During Eocene-Oligocene times, the Gr~s d'Annot turbidite system (French Alps) was deposited in several tectonically controlled sub-basins, which were mainly fed from a southern major sediment source: the Corsica-Sardinia Massif. In order to establish regional correlations in the southern part of the basin, four kilometre-scale outcrop areas were studied in detail. From south to north these are: the St Antonin, Annot, Grand Coyer and Chalufy areas. The results are: (1) an updated chronostratigraphic framework, (2) a major SE-NW correlation panel, approximately 400m thick and 50km long, parallel to palaeocurrent directions, within which all stratigraphic units are defined in terms of sedimentology and micropalaeontology and (3) some correlation panels at outcrop scale (around 5 km long and several hundred metres thick), within which all stratigraphic units are defined as before, but with the addition of a direct visual control on correlations, which enables the reconstruction of higher resolution geometry. Seven time-equivalent stratigraphic packages have been correlated from upstream to downstream, making use of micropalaeontologic constraints, and their geometric and facies evolution have been reconstructed through times. This evolution may be related to different stages in the basin deformation, induced by the east to west development of the Alpine foreland basin.

No abstract