Stratigraphic organization of late Pleistocene deposits of the western part of the Golfe du Lion shelf (Languedoc shelf), western Mediterranean sea, using high-resolution seismic and core data

Detailed analysis of shallow penetration single-channel seismic data, integ rated with piston core data, reveals that the stratigraphic architecture on the Rhone shelf of the western Mediterranean Sea is characterized by a com plex stratigraphy comprising both the regressive and transgressive parts of late Pleistocene depositional sequences. Several cycles of deposition are observed and are interpreted to be associated with fourth- or possibly fift h-order cycles of relative change of sea level. The regressive parts of the sequence are inferred to have been deposited either during late highstand or during periods of relative fall of sea level. These deposits are charact erized, in some instances, by discrete downstepping wedges and internal dow nward shift surfaces; however, in other instances this evidence is not pres ent, The transgressive parts of the depositional sequences are characterize d by backstepping wedges and isolated sand bars. In general, these types of deposits are more common on the western part of the Rhone shelf and are la rgely absent on the extreme eastern part of the shelf. The transgressive de posits seem to be preferentially preserved at both inner and outer shelf lo cations and less so in the middle shelf. The exception to this is the area near the Rhone Delta depocenter, where transgressive deposits are observed across the entire shelf. Key surfaces separating stratigraphic units includ e ravinement surfaces, down-lap surfaces, and subaerially formed erosional surfaces. These stratal discontinuity surfaces constitute the basis for ana lysis of the stratigraphic architecture. This area is dominated by seismic reflection geometries suggesting a high-e nergy depositional environment. Relatively steeply dipping seismic reflecti ons bounded by horizontal to irregular erosional surfaces characterize most of the upper Pleistocene section in this area. The high-energy seismic fac ies correspond to three types of deposits: (1) thick regressive sands of lo bate delta-front origin, (2) retrogradational beach barriers overlying the regressive wedge on the outer to middle shelf, and (3) late transgressive b each sands and ridges observed at the inner shelf. The stratigraphic comple xity illustrated here is likely analogous to similar, although commonly und etected, complexity that characterizes petroleum fields in shallow-shelf se ttings, A variety of geomorphic elements have been interpreted here, These include transgressive sand bars, wave-dominated distributary mouth bars, recurved s pits, isolated shelf edge shoreface/beaches, and distributary channels. The se elements are consistent with an interpretation of a depositional environ ment characterized by wave-dominated delta deposition. The morphology of th e delta in the eastern part of the shelf (i.e., near the depocenter) seems to be consistent from the outer to inner shelf location, suggesting that th e position of the shoreline relative to the shelf edge and the presence of submerged shelf outboard of the shoreline had only minor impact on deltaic deposition; moreover, climatic change and changes of fluvial discharge that likely characterized this area during the late Pleistocene similarly had o nly minor effect on delta morphology.