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The wide continental shelf of the Gulf of Lion (up to 70 km) has been the object of numerous investigations since the early days of oceanography. Yet, the question of sequences duration, the mechanisms of deposition and factors implied remained unanswered. A study of a very dense grid of Very High Resolution (VHR) seismic reflection (Sparker) data associated with surficial cores both, collected by IFREMER between 1992 and 2001 on the outer shelf and upper slope offshore of Sète in the Languedoc region gives a new insight into these issues. Analysis of the 3D geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms. Prism PI with low angle clinoforms (<1°) lies on the upper part of the shelf and is interpreted to be prodeltaic-offshore deposits. Prism PII with steeply dipping clinoforms (4°) lies on the outer shelf between 40 and 70 km from the present day coastline and is interpreted to be littoral deposits. Results obtained from integrating lithology, palynology, micropaleontology, seismic stratigraphy, stratigraphic simulation, support the hypothesis that the basic depositional pattern records a 100 000-years glacioeustatic (interglacial/glacial) cycle. As previously suggested by Aloïsi [Aloïsi, J.C., 1986. Sur un modèle de sédimentation deltaïque: contribution à la connaissance des marges passive, Thèse de Doctorat d'Etat. Université de Perpignan, 162 pp], prisms PI corresponds to deposition at high sea level and prisms PII to deposition during low sea level at glacial maxima. Five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles (the last five cycles at least) are recorded on the shelf of the western part of the Gulf of Lio

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International audienc

The Pliocene-Pleistocene icehouse stratigraphic record is characterized by distinct sediment distribution patterns and chronostratigraphic relationships resulting from high-frequency, high-amplitude changes in sea level. These modern relationships are often used as a template for sequence stratigraphic interpretation and for predicting sediment distribution in ancient greenhouse systems, deposited at times when sea-level fl uctuations are known to have been different from the most recent period of geologic time. Numerical modeling suggests that the depth of the shelf rollover, and thereby also shelf accommodation, rapidly adapts to changes in eustatic amplitude along passive, constructional sedimentary margins. Lower amplitudes and perhaps also lower frequencies during greenhouse periods would allow across-shelf delta progradation and sediment delivery to the slope and basin fl oor during both third-and fourth-order highstands. Care should therefore be taken when extrapolating stratigraphic models between icehouse and greenhouse systems.