Anne Gervais

Present morphology and depositional architecture of a sandy confined submarine system: the Golo turbidite system (eastern margin of Corsica)

Abstract The modern sandy Golo turbidite system (500 km2) is located in a confined basin on the eastern margin of Corsica. The Golo turbidite system is fed by a single river, which supplies coarse sand derived from active weathering of the neighbouring mountains. The late Quaternary deposits have been imaged using a closely spaced grid of 1000 km of sparker seismic-reflection profiles (line spacing close to 1.6 km, vertical resolution of 2m). The turbidite system is composed of four non-coalescent fans that were at times active simultaneously and of two small deposits onto the slope. The resulting sedimentation pattern is characterized by stacked turbidite deposits. At a regional scale, there is a continuum of fan morphologies and geometries from south to north. The use of both seismic and sedimentary facies, together with mapped seismic geometry of sedimentary bodies, allowed definition of four architectural elements: (1) submarine valley (canyon and gully), (2) sandy channel, (3) muddy levee, and (4) sandy lobe. Some of these architectural elements can be recognized at a scale that is comparable to outcrop examples. Features such as progressive lateral migration and avulsion, or complex longitudinal evolution (progradation and retrogradation), can also be accurately described. Despite the active tectonics along the studied margin, the main variations in sedimentation appear to be controlled by eustatic changes, pre-existing seafloor topography, and sediment source characteristics. The general pattern of sedimentation is controlled by the influence of a confining slope, leading to the predominance of aggradation and to specific morphology and architecture of sedimentary bodies.

Foraminifères benthiques et paléoproductivité: réflexions sur une carotte de l'upwelling (NW africain)

Two different paleoproductivity proxies, both based on benthic foraminiferal frequency data, are tested in a sediment core from the NW African upwelling area. A first proxy, the BFAR, enables us to estimate the total amount of organic matter introduced into the benthic ecosystem. The second one, the sample scores on the first axis of a P.C.A., enables us to estimate export-paleoproductivity when the oxygen concentration does not exceed 4.4 mL/L. The comparison of these micropaleontological proxies also allows us to evaluate the quality of the organic matter, and thus, to estimate what part of the organic matter introduced in the benthic ecosystem has been remineralized, and what part has ultimately been stored in the sediment.