Holocene story of
the Palavas – Aresquiers barrier beach

Introduction

The Palavas – Aresquiers shore extends along the northern coast of the Gulf of Lions, West of the Rhône Delta and East of high-gradient coastal streams that have provided most of the clastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km-wide area is constituted by a small coastal watershed (15 km long) in low-lying carbonate hills, a kilometre-wide marsh, a sandy beach barrier and a shoreface experiencing local low sedimentation rates. This onshore–offshore transition zone is a key area to understand universal relationships between erosion, by-pass, deposition and preservation processes.

What was done ?

Unlike the neighbouring Rhône deposits that display numerous thick deltaic sequences related to a continuous sediment flux, the Palavas – Aresquiers domain exhibits peculiar sedimentary bodies. The analysis of about 250 km of new VHR seismic profiles acquired over the study area, 9 short cores and outcrops data allowed us to determine the three-dimensional high-resolution geometry of the coastal system tracts from Quaternary to present-day. This revealed dominant denudation processes in the upstream catchments associated with the formation of incised valleys during Quaternary lowstands. In addition, we evidenced erosion and deposition mechanisms controlled by littoral hydrodynamics that have taken place on this shore since the last transgression. In particular, metre-high and hundreds of metre-long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is striking!

Main results

The Maguelone shore can be used as an experimental study to analyze generic onshore/ offshore dynamics under the influence of microtidal wave/current hydrodynamics and very low river-derived sediment flux during a eustatic cycle. Indeed, the geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea-level changes, and is successfully analyzed with 2D sequence stratigraphy cross-shore models. In areas like the Maguelone shore, where clastic fluxes are limited, we demonstrate that traditional sequence stratigraphy methods are not fully relevant and need to integrate alongshore hydrodynamical processes. Thus we show