Post-glacial persistence of turbiditic activity within the Rhône deep-sea turbidite system (Gulf of Lions, Western Mediterranean): Linking the outer shelf and the basin sedimentary records

Abstract

Emplacement of post-glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity. On the continental rise of the Gulf of Lions (Western Mediterranean), an aseismic area, we identified turbiditic beds deposited during the rising stage and highstand of sea level. Swath bathymetry, sediment cores, in situ Cone Penetrating Tests (CPTU), heavy mineral associations and radiocarbon dating determined the source, composition, distribution and age of the turbiditic beds. Turbidites are composed of homogeneous to positively graded silts to medium sand with quartz (up to 90%), shell debris and shelfal benthic faunas. Their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms. Their source is found in relict regressive sands at the outershelf. Their deposition occurred just after the onset of the post-glacial sea level rise and the concomitant sediment starvation of the Rhône deep sea turbiditic system until recently. Whilst canyons are fed with sand by strong seasonal hydro-sedimentary dynamics on the outershelf, the emplacement of post-glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons. Our study revealed that this low energy aseismic margin undergoes significant transport of sand, down to the base of slope, during the sea-level rise and the Holocene highstand.

Sea-level control on turbidite activity in the Rhone canyon and the upper fan during the Last Glacial Maximum and Early deglacial

“…In its upper part (between 500 and 1350 water depths) the canyon has a U-shape with a stepped structure and well-developed internal terraces (Droz, 1983;Dennielou et al, 2009). Similar welldeveloped terraces have been already described in canyons feeding turbidite systems like the Cap Breton canyon (Cirac et al, 2001), the Cap Timiris Canyon (Antobreh and Krastel, 2006), and the Zaire/Congo canyon (Babonneau et al, 2002).…”

“…On the Rhone Turbidite System the post-glacial period is recorded by the end of the turbiditic activity and dated at 15,510 ± 50 14 C years (~18 cal. ka BP) (Bonnel et al, 2005;Dennielou et al, 2009). Pollen and dynocist assemblages determined in the turbiditic facies allowed to assign a maximum age of ca.…”

“…In addition, the general anti-clockwise circulation in the Gulf of Lions has contributed to the westwards development of an elongated mud belt on the mid-shelf (Berné et al, 2007;Fanget et al, 2013). Along the shelf edge, modern hydrodynamic processes are dominated by wind-driven circulation (Ulses et al, 2008) and dense water cascades ) that rework relict sand bodies at the shelf edge and contribute to the export of sediment through the canyon and onto the base of slope Canals et al, 2006;Gaudin et al, 2006a;Palanques et al, 2006;Dennielou et al, 2009).…”

Impact of open-ocean convection on particle fluxes and sediment dynamics in the deep margin of the Gulf of Lions

“…It has been pointed out that the floor of the giant scours is devoid of Holocene deposits, while a Holocene drape is well developed on the adjacent seabed ( Fig. 10 in Dennielou et al, 2009). This can be interpreted as a possible imprint of the interaction of the deep OOC with the seabed.…”

External controls on turbidite sedimentation on the glacially-influenced Armorican margin (Bay of Biscay, western European margin)

“…9). The sediment input ceased rapidly after 15 ka while the sea-level rose dramatically at that time (Bard et al, 1996;Bard et al, 2010), suggesting that sediment storage increased during the deglacial sea-level rise and the subsequent highstand conditions (Dennielou et al, 2009;Zaragosi et al, 2000). This is corroborated by the significant increase in sediment particle size and thickness of the overspill deposits after the deglacial Fleuve Manche discharge (Figs 7 and 8), the sediment source for sedimentary flows evolving from direct fine river sediment to remobilisation of winnowed material from the continental shelf.…”