Multiscale spatio-temporal variability of sedimentary deposits in the Var turbidite system (North-Western Mediterranean Sea)

The Var turbidite system is a small sandy system located in the Ligurian Basin (Mediterranean Sea). It is active during present sea-level highstand and shows four types of sediment transfer processes: (1) low-density turbidity surges generated by small-scale failures (2) low-magnitude, high-frequency (yearly) hyperpycnal turbid plumes, (3) high-magnitude, less-frequent, hyperpycnal currents and (4) high-magnitude flows generated by large slope failures. These processes have different imprints on the morphology of the system. Inversely, the topography plays a role on the behaviour of these flows. The depositional and erosional architecture of the system has been investigated in detail on the basis of SAR imagery and a set of cores using an interface corer collected repetitively from a dense group of sites. The inner terraces located in the upper part of the turbidite system are generally depositional and thus provide a detailed record of recent sediment transfer processes. But the lower the elevation, the more terraces are affected by turbulent flow erosion. Downward, the channel-floor is a complex area where flows mainly by-pass but locally erode or deposit. The levee is dominantly depositional, but only records high-magnitude events, able to spill over. Low-magnitude, high-frequency events, such as yearly hyperpycnal currents are confined in the upper part of the system and thus have little control on system architecture. Moreover, they provide only thin deposits that can be misinterpreted in terms of involved process, and will probably be erased from the geological record. High-magnitude events have strong control on the system architecture as they erode the channel-floor and participate in the construction of the Var Sedimentary Ridge.