Holocene development of the east bank of the Gironde Estuary: geoarchaeological investigation of the Saint Ciers-sur-Gironde marsh

Abstract

The nature of postglacial sea-level change and sediment infilling of the Gironde Estuary, SW France, has previously been reconstructed using a sequence stratigraphic model. This paper examines specifically the development of the St Ciers-sur-Gironde marsh during the late Holocene. The study area forms the largest expanse of coastal wetlands on the east bank of the Gironde. A geoarchaeological approach is used incorporating borehole survey, sedimentological and diatom analysis, radiocarbon dating, archaeological, documentary and cartographic evidence, which aims to test and refine the previous model of estuarine development.The later Holocene sequence is characterized by alternating clay-silt and peat facies. Diatom evidence indicates that clay-silt units represent sedimentation under marinebrackish estuarine conditions in intertidal mudflat, and potentially saltmarsh, environments. The palaeoenvironmental conditions represented by the main upper peat unit, dated to 5600-2600 BP, are currently unknown due to the absence of diatom evidence from these levels. Within an overlying trend of rising relative sea-level over the past 6000 years, 3 negative sea-level tendencies appear to have occurred. There is insufficient resolution in the present data set to determine the exact nature of each or their duration.

Morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005: The Seine estuary (France)

“…Thus, Whitehouse and Mitchener (1998) underline the impact of the seasonal variations which include the evolution of the flows river (Christie et al, 1999;Dyer et al, 2000;Prandle et al, 2006), the swell and storms (Stevenson et al, 1988;Green et al, 1997;Roman et al, 1997;Ryan and Cooper, 1998;Anthony, 2000;Bassoullet et al, 2000;Verney, 2006). In addition, estuarine systems act as a 'hub' acting as a linkage point between the inland river and the ocean and thus are prone to construction, both in historical and modern times (Davis and Barnard, 2000;Mellalieu et al, 2000). Also, for these natural parameters, it is necessary to add the impact of the anthropogenic activities which modify the hydrodynamic conditions on the surface of the mud flat (Lafite and Romaña, 2001;van der Wal and Pye, 2004;Kim et al, 2006;Jaffe et al, 2007).…”

Holocene coastal changes and infilling of the La Perroche marsh (French Atlantic coast)

“…The first phase of peat development may be interpreted as the result of a high water table and stable sea-level around 5300-4900 years BP. Similar peat layers developed at around the same time or slightly earlier in the internal/median zones of the Gironde estuary (5600-5000 years BP on the east bank, Mellalieu et al, 2000; 6200-5700 years BP on the west bank, Massé et al, in press b). These peat beds did not extend towards the estuary mouth due to a slower deposition rate/deeper substrate at that time (Massé et al, in press c).…”

“…Recent work on the Holocene evolution of the coastal areas of south-western France (Bay of Biscay) has focused on the marshes of the Gironde estuary (figure 1) (Diot and Tastet, 1995;Pontee et al, 1998;Mellalieu et al, 2000;Massé et al, in press a, b, c) and shelf mud patches (Lesueur et al, 1989(Lesueur et al, , 1994(Lesueur et al, , 1996. It is starting to provide a better overall picture of the Holocene infill of the Gironde estuary since 6000 years BP Massé et al, unpubl.…”

Salt Marshes as Potential Indicators of Global Climate Change

“…2000; Lespez et al. 2010; Mellalieu et al. 2000), indicators of environmental change like pollen composition (e.g.…”

“…The analysis of salt marsh formations in terms of age and climate also benefit from archeological findings (e.g. Gonzalez et al 2000;Lespez et al 2010;Mellalieu et al 2000), indicators of environmental change like pollen composition (e.g. Goman et al 2008;González and Dupont 2009;Long et al 1999;Ward et al 2008), and the C ⁄ N-ratio which has the potential to provide information as to the origin of organic material preserved in coastal environments (see review by Lamp et al 2006).…”