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Terrigenous Turbidites and Associated Facies |
Laboratoire de Sédimentologie et Géochimie Marines, Université de Perpignan, France
The methods we have used in this study of pelitic sediments are based on the concept of fine-grained particle populations, and include: the counting of grains in the >40 µm fraction (lithoclastic, biogenic, authigenic and aggregates); grain-size analysis of the pelitic fraction expressed as a bi-logarithmic frequency curve giving the ‘evolution index’ of three granulometric classes—silt, clayey-silt and clay; mineralogical indices based on the ratios between particles with different hydrodynamic behaviour—quartz, mica-illite and smectite; and geochemistry of Mn, Cu and Fe to characterize the biogenic nature of the sediment.
A succession of turbiditic (heterogeneous population), hemipelagic and pelagic (homogeneous population) sediments were examined from the NW Mediterranean margin. We identify three main sequences in the Pleistocene to Recent succession, each of which may be interrupted by episodic events: (1) a palaeoclimatic sequence (
5 m thick) of Pleistocene to Holocene age, marking the end of deep channelized lobe construction on the Rhone deep-sea fan; (2) a dynamic sequence (repeated intervals of 20–50 cm thick) of Würmian and Holocene age respectively, in the lower fan and in the central basin; and (3) a uniform sequence (without granulometric, mineralogical or geochemical grading) corresponding to a ponded unit filled with reworked sediments (contourites) and slumps.
