Sedimentary sequences in the Gulf of Lion: A record of 100,000 years climatic cycles

Abstract

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

Radial gravitacional gliding indicated by subsalt relief and salt-related structures: the example of the gulf of lions, western mediterranean

“…Bessis (1986) and Burrus et al (1987) estimated small subsidence rates for the Gulf of Lions during the Plio-Quaternary. However, a recent study indicates that crustal tilting seems to have been quite significant offshore the Gulf of Lions during the Late Quaternary (Rabineau et al, 2005). This study, based on stratigraphic models applied to the shelf break area, estimates some 25 m of subsidence per 100 kyr for the last 540 kyr only, due to the margin tilting, which resulted in the creation of large amount of accommodation space for sediments during the period.…”

Understanding shallow gas occurrences in the Gulf of Lions

“…EuroSTRATAFORM scientists examining the Gulf of Lions took advantage of a significant amount of previous work that had been conducted in the area, including the acquisition of high resolution seismic data (Aloïsi, 1986;Baztan et al, 2005;Rabineau et al, 2005). Sub-bottom data in the area had identified regions of anomalous to occluded sub-surface reflectivity, which had been interpreted as being due to the presence of shallow gas (Aloïsi, 1986).…”

La huella de las oscilaciones globales del nivel del mar durante los últimos 530 000 años en el Golfo de León y su variabilidad durante el estadio isotópico marino 3

“…Estas secuencias, predominantemente regresivas, se conocen con el nombre de Unidades Regresivas Progradantes (Regressive Progradational Units, RPU) y confieren al margen un carácter regresivo forzado (Tesson et al, 1990(Tesson et al, , 2000Posamentier et al, 1992). Trabajos previos, basados principalmente en la interpretación de perfiles de sísmica de reflexión y de registros sedimentarios cortos, permitieron en una primera interpretación identificar cinco RPUs que fueron consideradas el resultado de las oscilaciones del nivel del mar de 100 ka de ciclicidad (Rabineau et al, 1998(Rabineau et al, , 2005Bassetti et al, 2008). Sin embargo, para establecer con mayor certeza el origen de tales secuencias, y en concreto la contribución de las oscilaciones del nivel del mar de los ciclos de 100 ka y/o de 23 ka, faltaba datar con mayor precisión los límites de secuencia de las RPUs (Lobo et al, 2004).…”