Evidence for pre-Messinian submarine canyons on the Gulf of Lions slope (Western Mediterranean)

On the Gulf of Lions margin, the Messinian Salinity Crisis (MSC) event led to a significant and widespread erosion of the Miocene shelf and slope. It is thus difficult nowadays to restore the morphology of the margin at the beginning of the crisis, and to study the Middle-Upper Miocene series rarely preserved from erosion. In this study, thanks to the use of multichannel seismic reflection data from the Gulf of Lions western slope, it has been possible to image the Miocene slope deposits. Interpretation of the data reveals several diachronic sediment bodies just beneath the Miocene/Pliocene boundary. These bodies are related to slope erosional–depositional complexes, underlain by erosional unconformities outlined by seismic reflector truncations. They are V- or U-shaped in cross section. Over their mapped extent, these bodies are typically 8–12 km wide and incise up to 600 ms TWTT into the Miocene slope deposits. In plan view, they are roughly elongated NW–SE, perpendicularly to the present day shelf break, and they progressively migrate towards the South-East. We interpret these seismic bodies as buried Miocene submarine canyons pre-dating the dramatic drawdown related to the MSC. In this study we try to constrain their age, and we discuss the events that may be at their origin. We also discuss the long-term impact of these slope canyons on the evolution of the margin.