Holocene and modern sediments in the Seine estuary (France): a synthesis

Abstract

This synthesis of numerous studies on the Holocene and modern sediments in the macrotidal setting of the Seine estuary demonstrates their overall evolution. In common with a number of estuaries, the lower Seine was an incised valley during the Weichselian glacio-eustatic sea-level fall, and infilling occurred during the subsequent lowstand, the Holocene sea-level rise and the late Holocene stillstand. In the upper estuary, above the basal gravel bed, fluvial freshwater deposits filled the valley. Next, fine sand and silts invaded the estuary upstream to Rouen; the sequence ends in loam, resulting from an increase in the supply of sediment to the fluvial system. In the upper estuary, anthropogenic deepening of the modern channel results in erosion of the Holocene sediments; the only bedforms are thin and narrow sand sheets and some rare megaripples. In the lower estuary, above the Weichselian basal gravel, the Holocene wedge records the change from a transgressed fluvial setting (i.e. gravel beds) to an open estuarine environment (i.e. tidal delta). The modern Seine estuary has been progressively infilled by marine sands and silts. Now silts and clays supplied during high river flows accumulate at the outlet, and offshore sands and gravel of the eastern Bay of the Seine are temporarily covered with veneers of mud. These freshly deposited muds (i.e. mud patches) are periodically partly reworked by waves and strong tidal currents, but silting of the inner shelf is noticeable.

Discontinuités longitudinales des dynamiques sédimentaires holocènes dans les petites vallées de l'Ouest du Bassin Parisien, l'exemple de la Mue (Basse Normandie)

“…Cette séquence est donc attribuable à la fin du Préboréal et au début du Boréal. Elle est contemporaine des premières phases de remplissage sédimentaire observées dans la plupart des basses vallées normandes (Huault, 1972 ;Clet-Pellerin et al, 1977 ;Lesueur et al, 2003, CletPellerin et Verron, 2004. La remontée du niveau de base, l'érosion des limons loessiques weichséliens et leur mise en place dans le fond de vallée par déborde-ment sont sans doute à l'origine de cette sédimentation.…”

“…Cependant les données acquises reposent principalement sur des recherches conduites dans les parties centrales et septentrionales du bassin, la partie occidentale et plus particulièrement la Normandie sont globalement restées à l'écart des recherches sur les dynamiques holocènes des fonds de vallées. Dans cette région, seule la vallée de la Seine a fait l'objet d'études récentes et approfondies (Lesueur et al, 2003 ;Sebag, 2002). Pourtant les petites vallées plus sensibles aux transformations de l'environnement et aux conditions de mise en valeur des bassins versants apparaissent comme des milieux privilégiés pour saisir précisément les modalités des changements survenus à l'Holocène (Pastre et al, 1997 ;Orth et al, 2004).…”

Holocene sedimentary infilling of a tide-dominated estuarine mouth. The example of the macrotidal Seine estuary (NW France)

“…Swells propagate dominantly from west to northwest. Local winds, generating wave agitation, blow dominantly from west to southwest [in Lesueur et al, 2003]. Near Le Havre, the significant wave height exceeds 2.2 m for only 4-5% of the year [Le Hir et al, 2001].…”

“…Investigations focussing on the long-term evolution of the estuary are relatively rare in this context. The main studies have concentrated on the fluvial terrace organization and Holocene infill in the inner domain, and on the very general Pleistocene to Holocene stratigraphic organization recorded in the seaward part of the system [Lefebvre et al, 1974;Alduc et al, 1979;Lautridou et al, 1999;Lesueur et al, 2003;Frouin et al, 2007]. Very few studies have finally concentrated on the Holocene sedimentary infilling of the estuarine mouth located at the transition between the open marine outermost domain, and the inner estuary.…”

Fluvial system evolution and environmental changes during the Holocene in the Mue valley (Western France)

“…Various studies have documented the alluvial sedimentary sequences of the Paris Basin during the Lateglacial and the Holocene, determining the main changes experienced by the fluvial system in the northern (Antoine et al, 2003) and central parts (Pastre et al, 2001(Pastre et al, , 2003(Pastre et al, , 2006 of the basin. Therefore, although the Seine valley has recently been studied (Sebag, 2002;Lesueur et al, 2003), the western part of the basin is poorly known, making comparison with changes of western European rivers difficult. Based on a systematic hand and power auger survey, the aim of this geomorphological and palaeoecological research is to determine the longitudinal pattern of the alluvial filling in the Mue valley and define the role of climate, human activities and autogenic controls on Holocene fluvial dynamics.…”