The 100‐ka and rapid sea level changes recorded by prograding shelf sand bodies in the Gulf of Lions (western Mediterranean Sea)

Abstract

[1] Thick forced regressive units on the wide continental shelf of the Gulf of Lions (western Mediterranean) recorded the composite effect of sea level changes during the Quaternary. They are mostly composed of coastal siliciclastic and bioclastic wedges showing clinoform geometry. These deposits have been intensively explored through high-resolution seismic investigations, but only recently it was possible to ground truth seismic interpretations, based on a long (100 m) borehole that crossed the succession and recovered a large part of the mainly sandy deposits ($84% recovery). A multiproxy analysis of the sedimentary succession shows that (1) the stratal architecture of the shelf margin is defined by major bounding surfaces that are polygenic erosion surfaces associated with coarse-grained material incorporating abundant and diverse shells, including cold-water fauna (presently absent from the Mediterranean Sea). Between each surface, coarsening upward units with steep (up to 5°) foresets are made of massive (more than 20 m thick) sands with possible swaley and hummocky cross-stratification, passing seaward to sands with muddy intervals and, further offshore, alternating highly boiturbated sands and silts. Each prograding wedge corresponds to a forced-regressive shoreface (or delta front/prodelta), deposited during the overall sea level falls occurring at (relatively slow) interglacial/glacial transition and therefore represents the record of 100 ka cyclicity. Higher-frequency Milankovitch cyclicities are also probably represented by distinct shoreface/delta front wedges; (2) detailed examination of the architecture and chronostratigraphy of the most recent sequence shows that minor bounding surfaces, corresponding to abrupt shallowing of sedimentary facies, separate downward stepping parasequences within the last 100 ka sequence. These events are in phase with millennial-scale glacial climatic and sea level variability, the downward shift surfaces corresponding to the falls during the coldest stadials. These deposits provide a comprehensive and well-constrained Pleistocene analog to the numerous shoreface deposits attributed to falling-stage systems tracts recognized in ancient stratigraphic records, studied at the outcrop scale.

Simulating Non-Stationary Seismic Facies Distribution in a Prograding Shelf Environment

“…(Tesson, 1996;Tesson et al, 2000). These results can be compared with the findings by Rabineau et al (2005Rabineau et al ( , 2006 who used very high resolution seismic data and shallow cores, and by the new deep core (100 m) presented very recently by Bassetti et al (2008). Although their study site is located further south-west and is related to the Bourcart and Hérault canyons, and not to the Rhone delta, profile P_1052 of Rabineau (Fig.…”

“…2). It is possible to relate our Unit U5 to Sequence S2 and Unit U60 of Rabineau et al (2006); in Bassetti et al (2008), the extent of our Unit U5 is very limited and corresponds to their unit U57 limited by discontinuities D45 and D30 (~5 m) (Rabineau's and Bassetti's notations are identical). Their findings are that the seismic facies are entirely consistent with the observed core data.…”

“…We therefore decided to limit the data set to the seismic profiles to test the applicability of this methodology to the initial geophysical survey of a potential reservoir. Very recently, Bassetti et al (2008) reported on a 100 m long core in this area, with sediment dating, which will be used for comparison in the results of simulation section.…”

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).…”

A 500 kyr record of global sea-level oscillations in the Gulf of Lion, Mediterranean Sea: new insights into MIS 3 sea-level variability

“…There five major RPUs were identified and interpreted to correspond to the last five 100-kyr cycle sea level falls (Fig. 1b) (Bassetti et al, 2008;Rabineau et al, 1998Rabineau et al, , 2005. However, precise dating of RPUs sequence boundaries was still needed to constrain better the imprint of sea-level oscillations on the GoL margin and to determine the leading cyclicity of the deposition of those units, i.e., if they originated during sea-level lowerings of 20 kyr or 100 kyr cycles (Lobo et al, 2004).…”