Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

PALAEO-ENVIRONMENTAL STUDY AREA P15

WEST BANK OF THE GIRONDE ESTUARY, WEST COAST, FRANCE

Plate P15 West bank of the Gironde Estuary, France. The two morphological units of the marshes (‘Mattes’ in the foreground and ‘Palus’ in the background) separated by the Cordonde Richard Chemier Ridge which was a traditional trackway since its appearance around 2,500 years.

SUMMARY

Four holocene marshes were studied along the West and the East Banks of the Gironde Estuary, and these are described in Palaeo-environmental Study Areas P15 and P16:

Opened marsh: _ The "Saint Ciers-sur-Gironde" marsh (East Bank) Digitated marshes: _ The "Reysson" marsh (West Bank) _ The "Monards" marsh (East Bank) _ The "La Perge" marsh (West Bank)

Nb. The following report sections 1,2,3 and 7 to 14 provide the introduction and conclusions for both Study Area P15 (West Bank of the Gironde Estaury) and Study Area P16 (the East Bank of the Gironde Estuary), France; several figures below refer to Study Area P16.

THE GIRONDE ESTUARY

1. LOCATION

1.1 Geographical Description (Figure P16.1)

1 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

The Gironde Estuary is the largest estuary in Europe and is located on the Atlantic coast of the southwestern France. The estuary is defined as a region between the confluence of the Dordogne et Garonne rivers at the Bec d'Ambès and the Atlantic Ocean, and measures 76 km in lenght. It is a typical macro-tidal dominated estuary with a wide mouth of 18 kilometers narrowing to 3 kilometers at the confluence of the rivers.

The Gironde originated as an incised valley formed during the Weichselian glacio-eustatic fall (100 000-18 000 B.P.) and has acted as a sink for fine sediment troughout the Holocene sea- level rise (SLR) (18 000 B.P. onwards). The incised valley of the present Gironde was inundated by the sea approximately 10 000 B.P. At that time, the rate of SLR exceeded that of sediment supply, producing a large accomodation space in which transgressive tidal-estuarine muds and sands were deposited. As the rate of SLR decreased around 6000-4000 B.P., sedimentation became more pronounced and the available space began to decrease significantly. Landward-derived fluvial sediments began to prograde over the tidal muds and sands, and a first unit of salt marshes (locally called "palus") formed in the lateral valleys. Around 2800 B.P., a sandy chenier ridge (locally called "Cordon de Richard") formed at the edge of these salt marshes and wholly or partly separated them from the Gironde. On the eastern side of the ridge a second unit of marshes (locally called "mattes") ocurred. The saltmarshes units were reclaimed during the seventeenth and eighteenth centuries, respectively. On the estuarine side of the eighteenth century dyke the modern tidal flats and the salt marshes began to form after the eighteenth century. Sedimentation within the estuary decreased the accommodation space and led to the increased transport of sediment to the shelf after 2000 B.P. This process was also aided by climatic and anthropogenic factors. Future evolution of the Gironde Estuary is likely to consist of further marsh growth and chenier development. However, future increases in the rate of SLR, and the degree of storminess, may cause a shift to an erosion regime in parts of the lower estuary.

1.2 Coastal Description

The valley of the estuary is incised into Tertiary limestones. On the West Bank of the estuary, the calcareous hills are 10-30 m high, and decrease in altitude from the south to the north. In the Médoc peninsula (Figure P16.2), they are covered by gravel terraces which record the Pleistocene glacial regressions. The gravels of the last glaciation is contained within the channel of the present estuary, below the Holocene deposits constituting the low hills bordering the estuary. On the East Bank, the substrate is composed by Cretaceous limestones to the north and calcareous Eocene sands and clay to the southeast. Pleistocene fluvial sands and gravels accumulated on the Tertiary carbonate deposits during the Weichselain low-wtand. The lateral bays of the primitive flooded ria were filled by hohlocene fine grain deposits constituting along the estuary the differents unit of marshes.

The modern estuary can be divided into three zones based upon morphology and dynamic processes. The upper estuary is characterised by meandering channels, sands and mud point bars and back barrier marshes. The middle estuary has a complex morphology of anastomosing channels between longitudinal bars and is bounded by mudflats and saltmarshes. The outer estuary is a more simplified two channel system, a deeply scoured tidal inlet with sandy shoals and well developed mudflats and saltmarshes.

1.3 Regional Authority

Conseil Régional d' Aquitaine,Conseil Général de Gironde; Towncouncils of the East Bank of the Gironde Estuary: Barzan, Saint Ciers-sur-Gironde, Braud-et-Saint-Louis, Etauliers, Saint- Bonnet-sur-Gironde; Towncouncils of the West Bank of the Gironde Estuary: Talais, Saint- Vivien-de-Médoc, Queyrac, Vensac, Jau Dignac et Loirac, Saint-Seurin de Cadourne, Saint Germain d'Esteuil, Saint Estèphe, Vertheuil.

2 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

1.4 Designation (Protected Areas)

IGN map, 25 000e, 1433 EST, 1533 OUEST and 1534 OUEST. IGN map, 25 000e, 1433 EST, 1433 OUEST , 1434 EST and 1434 OUEST.

2. MODERN HUMAN GEOGRAPHY

Municipalities of the East Bank of the Gironde Estuary concerned by our study areas: 428 inhabitants (Barzan); 3 095 inhabitants (Saint Ciers-sur-Gironde); 1 305 inhabitants (Braud- et-Saint-Louis); 1.394 inhabitants (Etauliers); 838 inhabitants (Saint Bonnet-sur-Gironde).

Municipalities of the West Bank of the Gironde Estuary concerned by our study areas: 547 inhabitants (Talais); 1 365 inhabitants (Saint Vivien de Médoc); 694 inhabitants (Vensac); 1 164 inhabitants (Queyrac); 866 inhabitants (Jau Dignac et Loirac); 767 inhabitants (Saint Seurin de Cadourne); 1 087 inhabitants (Saint Germain d'Esteuil); 1 799 inhabitants (Saint Estèphe); 1 068 inhabitants (Vertheuil).

3. CONTEMPORARY COASTAL PROBLEMS (DUNE MOVEMENT, EROSION, ACCRETION, I.E. COASTAL CONTEXT)

3.1 General

The discharge of the Gironde varies between 2.5 and 3.5 x 1010 m3/yr from a catchment area of 74 000 Km² (Castaing, 1981; Lesueur, 1996; Nagy, 1993). The winter mean flood discharge is appromimately 1.4 x 103 m3/s, and exceptional floods attain 7.5 x 10 m3/s. The flow rate varies from 200 m3/s in summer, to more than 5 000 m3/s in periods of springs floods. Tides in the Gironde are semi-diurnal with amplitudes ranging from 2.5 m (neaps) to more than 5 m (springs) and the tidal currents penetrate further landwards (100-130 Km) than saline conditions (50-100 Km). On the open coast large waves cause a strong littoral drift which introduces large volumes of sand into the estuary mouth.

At present, the sand carried by the Garonne and the Dordogne rivers accumulates within the Gironde estuary, and none reaches the mouth and adjacent Atlantic coastline. Approximately 40% of the fluvially sourced suspended silt and clay is deposited within the estuary. The remaining 60% of this material reaches the sea, and approximatively one third of this is deposited on the shelf mud patches. The suspended sediment yield of the Gironde represents 70% of the total suspended matter delivered by the French rivers to the Atlantic shelf, and 20% of the total suspended sediment discharge originating from all the great European rivers. The present-day flux of suspended matter is estimated to be between 0.5 x 106 t/yr during droughts years, and 1.5 x 106 t/yr in the wet periods.

The marshes along the Gironde Estuary are submitted to erosion through channel migration. Whislt the marshes remain dry throughout the summer months, they are prone to flooding during the winter.

3.2 Modelling sedimentary processes in the Gironde Estuary

In estuaries, turbidity maximum is the main feature indicative of fine sediment transport. This is a zone generally located near the head of the salt intrusion where suspended sediment concentration is higher than that in the river or that further seaward in the estuary (Dyer, 1988). It depends on a complex combination of the residual estuarine circulation, the tidal dynamics, and the deposition and erosion of the sediment (Officer, 1981). The Gironde estuary is one of the largest European macrotidal estuaries, which is known for its well-developed turbidity maximum (Allen et al., 1980, Sottolichio et Castaing, 1999). The estuary is estimated to contain over 5 million tons of fine sediments which represent more than 2 years of riverine solid inputs. An investigation on dynamics of the turbidity maximum has been carried out in the Gironde estuary by the implementation of two numerical models (Sottolichio et al., 2000). The main

3 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

objective is to discriminate the role of tidal asymmetry and that of residual circulation in the formation of the maximum concentration zone.

Two-dimensional modelling and tidal effects

In both models, sedimentary processes have been extremely simplified, in order to highlight factors inherent to estuarine dynamics. Settling velocity was expressed by a constant but strong value (1 mm/s, i.e. representative of flocculated particles). Critical shear stress for erosion and deposition were chosen constant over the entire domain. By this way, mud deposition and erosion were not locally influenced by a favourable parameterization. Despite these simplifications, a two-dimensional (depth-averaged) model was satisfactory in reproducing the turbidity maximum under the tidal wave propagation effect only. The position of the simulated turbidity zone was consistent with the observed situations for different river flow conditions, considering either the semi-diurnal tidal cycle and the neap-spring tidal cycle (Figure P16.3). An equilibrium position of the turbidity maximum was observed for a constant river flow. However, long periods of simulation (over a month) showed an excessive escape of suspended sediment towards the ocean and a loss of mass of the turbidity maximum, suggesting that the tidal asymmetry is the main mechanism acting in the formation of the turbidity maximum, but it can not totally retain the sediment in the estuary.

Three-dimensional modelling

A three-dimensional model incorporated the vertical velocity currents gradients, the vertical suspended sediment gradients, and the density residual circulation effect subsequently. The turbidity maximum geometry was improved and the escape of suspended matter towards the ocean was reduced. The removal of salt (and therefore of the density circulation effect) caused an excessive seaward dispersion of sediment (Figure P16.4). These results suggest that the density residual circulation is necessary to maintain the stability of mass of the turbidity maximum in a seasonal timescale. So far, simulations with the 3D model have been too short to verify this hypothesis by the estimation of a reliable seasonal sediment balance. However, this feature seems consistent with the horizontal distribution of the maximum bottom shear stress calculated over a semi-diurnal tidal cyle (Figure P16.5). It shows a distinctive pattern for two main portions of the estuary. The maximum shear stress is flood-oriented in the upper estuary, while it is ebb-oriented in the lower estuary. Flood-oriented maximum shear stress is representative of an efficient tidal pumping, which is able to maintain suspensions within the estuary. It can be deduced that the tidal pumping is effective in the upper estuary only. In the lower estuary, ebb-oriented shear stress (coupled to a longer ebb phase) suggest the suppression of the tidal pumping effect, and the need for an additional mechanism, as the salt- induced density circulation.

WEST BANK OF THE GIRONDE ESTUARY

4. KNOWN HISTORICAL, ARCHAEOLOGICAL AND PALAEO-ENVIRONMENTAL SETTING OF THE COASTAL COMMUNITY

Due to relative rapid deposition rate and a high sensitivity to local environmental changes, the sedimentary archives of the holocene marshes of the West Bank of the Gironde Estuary provide some of the most detailed recordings of coastal change over the last hundreds to thousands of years. Study of such marshes can be used to bring greater understanding of how the coast evolves in reponse to changing conditions over this longer time periods. This study area allows to make reconstruction of holocene palaeoenvironments of marshes using sedimentological and faunal investigations coupled with 14C datations.

4 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

4.1 Sedimentological and palaeo-environmental data concerning the study area

Two different types of marshes were studied on the West Bank of the Gironde Estuary: the "Reysson" marsh situated 40 km upstream the mouth of the estuary and the "La Perge" marsh more ramified and located 20 km downstream the "Reysson" marsh.

The "Reysson" marsh

The Reysson Marsh (Figure P16.1) is a simple "digitated" marsh formed by the infilling of a small tributary valleys. It is situated 60 kilometres to the North of Bordeaux. It borders on the left bank of the Gironde Estuary and extends 7.5 km to the West. The area is generally low lying (1 to 3 m N.G.F.) with a slight rise around St-Corbian near the centre of the marsh. The marsh has a narrow entrance to the Gironde leading to a restricted environment.

A preliminary survey of the Reysson marsh conducted by the BRGM (Capdeville and Lapeyre,) shows that it fills an ancient basin formed from the erosion of the surrounding Tertiary limestones in two stages. The Upper Eocene limestone crops out around the marsh to the west of the hill at St-Corbian, as well as within the marsh near to Brion providing the site used by the Romans. The hill at St-Corbian and the area surrounding the marsh to the east of the hill is made up from colluvial deposits of fluvial origin and pebble and gravel terraces.

The two stages of erosion have created a ledge at a depth of -6 m NGF (Figure P15.1), and a maximum depth in the basin at -15 m NGF. The erosional events may have been linked to the two major sea level regressions of the Würm period. The bottom five meters of the basin are filled with a green clay, topped by a grey clay that constitutes the largest facies present in the marsh. The facies forms a large triangular wedge tapering towards the head of the marsh, with a thickness exceeding 10 m near the entrance to the marsh. Above the grey clay to the west of St-Corbian is a layer of peat which reaches a maximum thickness of 3m, whereas to the east of St-Corbian the top layer is a brown clay, the result of pedological changes to the grey clay.

The "La Perge" marsh

The "La Perge" "digitated" marsh formed by the divagation of the lateral channel of the estuary.marsh opening on the "opened" marsh of "Talais" (Figure P16.1). On the estuarine side of the peninsula there are two units of reclaimed marshes which have an elevation of around 2 m above present-day mean sea level, and are separated by a chenier sandy ridge type ("Cordon de Richard") 1-1.5 m high (Pontee et al, 1997). The two entities of marshes together with the present day mudflat form a low gradient coastal plain covering of several hundred square kilometers (Allan and Posamentier, 1993).

Diot et Tastet (1995) investigated the Holocene palaeoenvironments and chrono-climatic limits in two cores collected in the internal part of the "La Perge" marsh to the west of the "Cordon de Richard".

4.2 Archaeological data concerning the study area (Appendix P15.1, Figures P15.2 and P15.3)

The "Reysson" marsh (Figure P15.2)

The most important archaeological site is the Gallo-roman city of Brion, built around 2000 B.P. on a 18 ha hill of substrate lying a few meters above the marsh surface. The city is progressively abandoned during the IIIrd century. The last Gallo-Roman traces of occupation of Brion occured at the IVe century. After a complete desertion, a small fortificated castle is established during the XIVe century on the isle of Brion (Boudet, 1987). Then, at the beginning of the XVe century the site is definitively abandoned.

In the Reysson marsh, the other archaeological sites knew a similar historic evolution with, firstly, a Gallo-Roman occupation (villa, agricultural properties) and, secontly, an occupation by religious (Abbay of Vertheuil, hospital of Saint Jean-de-Jerusalem) and laic (castle of Vertheuil and of Saint Germain) communities.

5 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

The "La Perge" marsh (Figure P15.3)

The La Perge marsh has known an ancient human occupation, particularly during the Neolithic period. The Neo-Chalcolithic sites, and even some Bronze Age sites are generaly found in the humid parts of the marsh and show a high density of human occupation (Les Pargaux, Le Loc, Le Plancat, L'Angle, Lapartens,¼). The occupation became less clear since the Iron Age.

Earlier archaeological remains (from the Gallo-Roman to the Medieval period) show passage- way and circulation axes: possible antic way of the Médoc (Le Taste), medieval fortified buildings for checking of the roads (Mayan, Le Taste, Les Cercins etc.).

5. PALAEO-ENVIRONMENTAL AND ARCHAEOLOGICAL POTENTIAL: INVESTIGATIONS IN THE REYSSON MARSH

5.1 Holocene palaeo-environments of the Reysson marsh

The study of the processes that have contributed to the past coastal changes in the Reysson marsh include sea level variations, wind-wave climate changes and anthropogenic influences such as marsh reclamation or dredging. At the start of the Holocene there was a major sea level transgression with sea level rising at around 10-15 mm.yr -1 (Kidson, 1986) along the european coastline. There is some evidence that since this initial rate of rise dropped to 1-3 mm.yr -1 by 6,000 yrs B.P. (Kidson, 1986). It is thought that in the next century there may be an increase in sea level rise of between 3-6 mm.yr -1 (Warrick and Oerlemans, 1990).

The aim of this study is to reconstruct the holocene palaeoenvironments of the "Reysson" marsh on the western bank of the Gironde estuary using sedimentological, palynological and faunal investigations of the sedimentary archives coupled with 14C datations.

Data and methods

The seven cores used in this study (Table 1a) were collected from locations along the lines created by the BRGM survey (Figure P15.1). The cores were described and sampled for sedimentological analyses. Samples were dried and wet sieved using mesh sizes of 50 _m and 100 _m. The fraction greater than 100 _m was then dry sieved through a mesh of 250 _m to remove the larger particles and to allow for easier sedimentological analysis and the morphological study of the quartz in this fraction. The 100 and 250 _m fractions were examined for mineral and faunal composition. Particle size data was obtained on bulk sediment through the use of a Malvern 3600E laser granulometer. Additional peat samples were dated using carbon 14 radio-isotope methods; the results are given in Table 1b.

Palynological investigations were made on six of the seven cores. 2 cm3 blocks of sediment were collected in the muddy and organic layers. The samples were initially prepared through 200 µm sieves. They were then treated with HCl to remove all carbonate material, a 50% solution of HF to remove silicate material, HCl treatment to remove fluorosilicates, and a 10% KOH solution to remove the soluble organic matter. After this, the mineral fraction was separated from the particulate organic matter using a "liquid of Thoulet" with a density of 2, and the remaining material was then sieved through a 5 µm sieve. Samples were stained and mounted, and counts were made using a microscope (x 400 and x 1000). A minimum of 250 pollens were counted in each sample to give a statistically valid count. The study of palynofacies requires a concentration of organic matter (Diot, 1991) to allow observations of the plant micro-debris and dinoflaggellates which are useful salinity indicators. Other micro- organisms were also observed in the samples, especially the chitinous membranes of foraminifera, dinocysts, brackish water algae (Tasmanites and Platydicysta) and fresh water algae (Concentricytses and the family of Prasinophyceae).

The pollen zonation (zones NM1 to NM7) is the local scale (NM for North Medoc) defined by on the basis of ecological pollen groups similar to those found in the present day lakes and

6 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France littoral basins on a sandy substrate along the Atlantic coast (Bournerias et al., 1988). The age of the boundaries between each zone (Table 1c) was calculated in a peat section sampled 30 km to the northwest of Reysson (La Perge; Diot and Tastet, 1995), and where 6 14C dates were obtained. The ages were extrapolated assuming a constant peat accumulation rate between each dated sample. Given the uncertainty of the date itself and the thickness of the dated sample, the date of each boundary actually corresponds to an age range.

Results (Figure P15.4)

The head of the marsh: cores 9305 and 9306

These cores are located in the west of the marsh (Figure P15.1), where surficial sands occur above or below the peat layer (Figure P15.5).

Lithology

Core 9305 consists of alternating peat and sand layers above a basal mud level below 6.80 m depth. Core 9306 is simpler, with a basal mud unit below 3.40 m depth, a sand unit up to 0.90 m depth, and a surficial peat with a mud layer at 0.70 m depth.

Carbon Dating

There is only one date available for these two cores (Table 1b). It was obtained in a peat facies at 1.20 m depth in core 9305 and gives an age of 5040 ± 80 years B.P..

Palynology

The upper 2.85 m of core 9305 essentially correspond to zone NM4, with the end of NM5 at the base and NM1/2/3 above 0.35 m (Figure P15.6). Observations in the basal mud level below 6.80 m show some marine shells, dominant Pinus and abundant teriary pollens (determination G. Farjanel, BRGM Orleans) likely resulting from substrate reworking.

The top peat layer of core 9306 also belongs to NM4 (Figure P15.4). The basal mud unit shows dominant Pinus with high percentages of Primulaceae and Scrofulariaceae, probably resulting from the reworking of older deposits (pre-NM5).

Core 9306 is located near the small substrate hill of Le Peuilh (Figure P15.1), close to an important Neolithic site where a 2.5 m peat core was analysed for pollen content (Marambat, 1995). The base gave an age of 5580 ± 80 years B.P.(datation obtained on another core realised in the proximity for archaeological investigations). The whole section is very similar to the top of cores 9305 and 9306 and belongs to NM4.

The occurrence of tertiary pollens in the head of the marsh indicates that a part of the material is derived from substrate reworking to the west.

The central part of the marsh: cores 9302, 9303, and 9304:

Three cores were taken from the central part of the marsh, to the west of Saint-Corbian and to the east of Brion (Figure P15.1).

Lithology

The three cores located near the centre of the marsh all consist of a facies of grey to grey-green mud (up to 8 m thick) with abundant plant debris and gypsum, below a layer of peat (1.5 to 2 m thick). There is a thin layer of mud near the middle of the peat in cores 9302 and 9303 that may be contemporaneous with each other. In all three cores there is a distinct decrease in the amount of plant material present from the base of the mud facies to the top. The bottom two meters of core 9304 is filled by a medium sand

7 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

with some plant debris.

Carbon Dating

Dates exist for cores 9303 and 9304 (Table 1b) close to the base of the peat layer, giving ages of 6207 ± 148 and 5893 ± 151 years B.P., indicating that the peat began forming at about the time the rate of sea-level rise decreased.

The mud facies found around 1.00 m depth in core 9303 is dated from the peat above it at 0.85 m to 4571 ± 144 years B.P. and below it at 1151 cm to 4560 ± 80 years B.P., and was probably deposited during one or a few to a few periods of flooding.

Palynology

Core 9304 is characterized by irregular supply, especially in Quercus, Poaceae and Pteridophyteae. The correspondence with local zones is thus difficult to assess. While the lowest sample can be attributed to NM6, the bulk of the grey-green mud shows high percentages of Chenopodiaceae, indicating brackish waters, and belongs to NM5. The overlying peat corresponds to zones NM4 and NM1/2/3.

A very similar but clearer pattern appears in core 9303 (Figure P15.7), with the grey- green mud belonging to zones NM6 and NM5 and the peat corresponding to the top of NM5, NM4 and NM 1/2/3. Core 9302 which has strong lithologic similarities with 9303 was not analysed.

In all these cores, the transition from the mud to the peat marked by termination of estuarine supply as demonstrated by disappearance of dinocysts and chitineous foraminiferas.

Environmental implications

The grey mud facies sampled in the cores fills the greatest part of the depression of the Reysson marsh, as seen on Figure P15.5. The strong presence of gypsum within the cores gives evidence for the influence of saline waters in the deposition of the sediment. The overall homogeneous character of this grey mud unit indicates that no striking environmental change occurred during its deposition. There is an upward increase in the abundance of yellow and brown aluminosilicates, and a slight decrease in median grain size from 15 to 8 µm. This could indicate a gradual transition to a higher position in the intertidal zone, but is however inconsistent with the decreasing amount of plant debris. The marsh finally becomes isolated from estuarine influences and is occupied by a peat-bog as soon as 6,000 B.P. (before the end of NM5), indicating that the grey mud is contemporaneous with the flooding of the ria during early holocene sea- level rise. The thin mud layer deposited around 4570 years B.P. indicates a period of flooding of the marsh at that time, possibly due to a rise in sea-level or increased storminess.

The palaeochannel north of the Brion site: core 9402

This core was taken from just north of the archaeological site at Brion, in an infilled channel approximately 15 m wide (Figure P15.1).

Lithology

The channel is mostly infilled with peat within which are three very different mud facies (Figure P15.5):

- a sandy mud with quartz and plant debris below 7.20 m depth; - a beige mud with plant debris, calcite and shell fragments between 6.10 and 5.60 m

8 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

depth; - a grey mud very similar to that in the three previous cores between 5.35 and 3.30 m, with some plant debris and large amounts of gypsum.

Faunal Data

In the beige-grey mud facies were found some gastropods and ostracods (Potamocypris sp., Cypridopsis vidua and Candora gr. angulata). Although there were very few in the samples, they indicate calm shallow, fresh water conditions without any marine influence and rich in aquatic vegetation. The presence of some palustral species indicate the proximity of the bank of a river or lake.

Carbon Dating

The base of the lowest peat facies has been dated at 9970 ± 70 years B.P.. Two more dates were obtained from below and above the upper grey mud facies, and give ages of 6430 ± 100 and 5730 ± 80 years B.P. respectively. This means that the upper peat layer is contemporary with the peat that is found in the rest of the marsh.

Palynology

The whole section was analysed (Figure P15.8). The basal peat layer shows dominant Pinus sylvestris with a poor variety of trees, and dominant Cyperaceae and Poaceae among NAPs. This zone has been labelled NM7. Towards the top of the peat, Pinus decreases and Quercus increases rapidly; this corresponds to NM6. The grey- green mud is marked by high percentages of Chenopodiaceae, Quercus, Corylus, Alnus, Tilia and the occurrence of dinocysts and chitineous for aminifers; it corresponds to NM5. The top peat layer is very similar to that observed in the other parts of the marsh, with the top of NM5, NM4 and NM1/2/3.

Environmental implications

The upper mud facies in this core is very similar to the grey mud in the central part of the marsh, and the date of the peat just above indicates that it is contemporaneous. It is probably a lateral equivalent, as confirmed by the occurrence of large amounts of gypsum and aluminosilicates. As in other places within the marsh, the communication with the estuary stopped after 6000 B.P., thus isolating the island of Brion more than 3000 years before the roman settlement.

The beige mud facies below is very distinct from all other deposits in the Reysson Marsh. It is dominated by plant and shell debris, and contains some calcite probably derived from the surrounding eocene substrate. Faunas indicate a freshwater depositional environment, clearly different from that of the overlying grey mud. The beige mud therefore indicates a phase of continental terrigenous deposition prior to 6400 B.P., at a time when the holocene transgression had not reached this site. The basal sandy mud has a similar continental, terrigenous origin.

The communication with the estuary: core HO 9301

The core is located close to the Gironde estuary (Figure P15.5), at the mouth of the marsh.

Lithology

The sedimentary column is predominately constituted by a grey mud becoming more yellow towards the top of the core. The mud shows signs of iron staining throughout, an indication of oxidation of the sediment. At the base of the core the sediment lacks the black and iron stainings, but contains some roots and plant debris that is possibly

9 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

analogous to the large grey mud facies present in cores 9302, 9303 and 9304. There is a gradual increase near the top of the core of aeolian quartz grains. This facies is lithologically distinct from the grey mud making up most of the cores in the central part of the marsh, and possibly corresponds to the brown clay shown on Figure P15.5.

Palynology (Figure P15.9)

The presence of Chenopodiaceae is constant throughout the core, although decreasing around 1.2 m depth. The variations of Tilia, Alnus and Quercus indicate the transition from NM5 to NM4 around 1.5 m, whereas the uppermost zones NM1/2/3 are absent. A small anthropogenic influence is marked by the appearance of Cerealia and Plantaginaceae above 1.5 m depth.

Environmental implications

The grey mud at the base of the core appears to be the equivalent of that observed in the central part of the marsh. The change from a grey mud to a yellowish grey mud at 2.60 m is also picked out clearly in the mineralogy by a disappearance of sulphurs and gypsum, indicating a reduced influence of saline waters.

Discussion

Holocene infill of the Reysson marsh

At the beginning of its history, the Reysson Marsh was an enclosed depression with a relatively flat bottom lying at - 5 to - 6 m NGF, with localised areas at - 10 m NGF, probably corresponding to channels and or palaeo-karst depressions (Figure P15.5). The first lithologic unit to be deposited is the green clay, sampled directly above the eocene limestone substrate. The formation of this clay is related to the first marine flooding at the beginning of the Holocene from 12000 to 5000 B.P.. All the available dates indicate that almost all of the marsh was already filled by 6000 B.P.. Thus, the green clay unit is probably much older. It is a remnant of either a previous high sea-level stand, or of the very first marine invasion at the beginning of the Holocene.

The sandy facies overlying the substrate in the western part of the marsh were sampled in cores 9305 and 9306, and at the base of core 9304. The distribution of these deposits clearly indicate their continental origin. The date at 1.20 m in core 9305 (5040 B.P.) indicates that their accumulation may have begun before the holocene flooding of the depression. After 5580 B.P. (the base of Le Peuilh peat section close to 9306) these sands appear to be restricted to the very head of the marsh (core 9305). In the channel to the north of the Brion site, a peat-bog had developed as soon as 10000 B.P.(basal peat), and short phases of fresh water flooding led to the deposition of muds interbedded in the peat.

The main facies evidenced in the Reysson depression is the grey-green mud wedge tapering towards the head of the marsh. This facies was sampled in five of the cores. The sedimentological and palynological investigations reveal the presence of gypsum, dinocysts and chitineous foraminifers indicating the influence of estuarine waters, and abundant Chenopodiaceae indicating brackish water conditions. The dates at the base of the overlying peat unit to the west of the St-Corbian hill clearly show that the deposition of this grey-green mud had stopped as soon as 5700 B.P., indicating a very rapid infill (few hundreds of year) of the main depression after the initial holocene flooding. Such a rapid deposition is easily explained by the enclosed character of the depression, probably acting as a decantation basin for estuarine waters with very restricted freshwater input and one or two small channels communicating with the estuary around the hill of St-corbian. By 6000 B.P., the Reysson depression probably looked like a very flat and poorly drained vegetated saltmarsh where peat began accumulating.

This situation remained unchanged throughout most of the Holocene, except for a very short phase of marine flooding occurring around 4600 - 4500 B.P. in the central part of the

10 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

depression. This event is marked by a thin mud layer with shell debris in cores 9303 and 9302.

There is no date available at the top of the cores, however palynological investigations suggest that the bulk of the peat unit was formed during zone NM4. The three uppermost zones are present at the top, but they are difficult to differentiate, suggesting that the deposition rate significantly decreased after 3000 B.P. The final reclamation of the Reysson marsh occurred later than elsewhere in the Medoc. It was finally planned in 1762 and further delayed by the french revolution until the middle of the XIXth century (Lacroix, 1998). At the beginning of the XVIIIth century, there is mention of a small and sinuous channel running across the marsh, but the depression was almost permanently flooded and impossible to cross in several places (Masse, 1707).

Archaeological implications

Evidence presented in this study indicates that the roman settlement on the site of Brion occurred at a time when the marsh was almost completely filled and occupied by a fresh water peat-bog. There is no evidence of a major estuarine flooding since then. The only remaining communication with the estuary probably was the small sinuous channel mentioned at the beginning of the XVIIIth century, but it was probably too small to allow boat circulation. Therefore, it is very unlikely that the city of Brion was a harbour.

Comparison with other areas

The evidence presented in this study clearly suggests that the infill of the Reysson Marsh took place earlier than in the northenmost part of the Medoc (Pontee et al., 1998; Massé et al., in prep.), where peat-bogs were restricted to the very head of the valleys (La Perge) and the bulk of the mud deposition occurred between 6000 and 2000 B.P.. Moreover, palynological investigations show that the three uppermost zones (NM1/2/3) are much more developed to the North, suggesting that peat accumulation stopped earlier in Reysson.

These differences can easily be explained by the contrasted geomorphological contexts (Figure P16.2). The enclosed character of the Reysson digitated depression can account for a very rapid infill, whereas the widely opened marsh areas of the northenmost part of Medoc stayed under estuarine influence for a significantly longer period. However, available data on the east bank of the Gironde estuary suggest that the geomorphological context plays a very limited role and that the infill of the lateral marshes occurred earlier in the internal parts of the estuary. The infill of the small, enclosed Monards marsh appears to be synchronous to that of the wide, opened North-Medoc marshes. On the other hand, the history of the small, digitated Reysson marsh appears to be very synchronous and similar to that of the wide opened Saint- Ciers marsh on the opposite side of the Gironde, where there is evidence for a rapid early holocene infill and extensive peat accumulation as soon as 5700 B.P. Moreover, a later phase of estuarine water penetration is documented between 5000 and 2600 B.P.. This event could be synchronous with the small flooding documented in Reysson around 4600 - 4500 B.P.

Conclusions

These results indicate that the infill of the Reysson Marsh occurred rapidly at the beginning of the Holocene. Before the main flooding around 6000 yr B.P., it was an enclosed depression with a relatively flat bottom lying at - 5 to - 6 m NGF.

While landward-derived sandy deposits occur in the western part of the marsh, the main facies present in the depression is a grey-green mud deposited under brackish conditions (presence of Chenopodiaceae) with a marked influence of estuarine waters (presence of gypsum and dinoflaggellates). Because of the enclosed character of the depression, this accumulation was very rapid and had stopped as soon as 5700 B.P., when a peat-bog developed in the central part of the marsh. The communication with the estuary remained very reduced, except for a very short phase of marine flooding around 4600 - 4500 B.P. The peat

11 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

accumulation significantly decreased after 3000 B.P.

Sedimentological and palynological evidence shows that the infill of the Reysson Marsh is contemporaneous to that of all other marsh areas in the middle/upper parts of the Gironde estuary. In contrast, the Holocene deposits found in the lower part close to the mouth are clearly younger.

5.2 Archaeological synthesis of the Reysson marsh (Figure P15.2)

Cette étude sommaire du marais de Reysson a pour but de synthétiser nos connaissances sur les témoins archéologiques de la présence humaine dans et autour de cette dépression marécageuse de la fin de la préhistoire au XVIIe siècle et d'évaluer les relations que l'homme a pu entretenir avec son environnement.

Ce marais de 8 km de long dans le sens est/ouest, pour une largeur ne dépassant pas 2 km dans le sens nord/sud, est aujourd'hui divisé entre quatre communes (Saint-Germain-d'Esteuil et Saint-Seurin-de-Cadourne au nord, Vertheuil et Saint-Estèphe au sud) et sert de limite aux cantons de Pauillac et de Lesparre. Il constitue pourtant une unité naturelle particulièrement homogène avec un certain nombre de spécificités. L'importante densité des sites archéologiques mis au jour dans ce secteur et leur grande diversité révèlent l'attrait du marais de Reysson sur l'homme depuis la préhistoire. C'est d'ailleurs l'un des secteurs le plus densément occupé du Médoc.

Le Néolithique

Les découvertes néolithiques, et en particulier à l'important site du Peuilh établi sur un îlot dans la partie occident.le du marais démontrent que l'occupation humaine était essentiellement tournée vers les zones basses et humides. Pratiquement tous les reliefs naturels autour et dans le marais, souvent de petits monticules d'à peine 2 à 3 m d'altitude, ont livré des silex et quelquefois de véritables habitats. Mais les découvertes se font souvent dans la moitié inférieure de ces reliefs, au contact direct avec le marais. Une partie de ces sites, c'est le cas au Peuilh, est même enfouie sous les sédiments du marais comme cela est également observé sur la rive droite de l'estuaire (secteur de Saint-Ciers-sur-Gironde). Dans le cas du Peuilh, l'habitat a pu être aménagé sur pilotis (?). La découverte de mobilier du Néolithique dans le marais, mais aussi de l'âge du Bronze, voire de l'âge du Fer, viendrait prouver qu'une partie du marais était alors partiellement comblée, hors d'eau et accessible à pied sec toute l'année ou une partie de l'année. Les études paléoenvironnementales viennent confirmer que le marais de Reysson était en grande partie comblé dès le Néolithique. Une végétation luxuriante semble alors s'étendre sur l'ensemble du secteur et favoriser l'occupation de l'homme. Du fait d'une possible phase régressive du niveau marin ou plus probablement d'un isolement du marais par rapport à l'estuaire, le marais de Reysson va progressivement se transformer en tourbière.

Ages du Bronze er du Fer

La localisation des sites archéologiques de l'âge du Bronze et du Fer est plus lâche qu'au Néolithique. Elle n'en reflète pas moins les mêmes aires de répartition ; la continuité de l'occupation des paléorivages et des îlots est remarquable. On observe, et c'est particulièrement net au Peuilh, que les sites sont plutôt établis sur les parties moyennes et hautes des reliefs. Ce phénomène est peut-être lié à un changement de comportement ou à une raison naturelle comme une possible remontée du niveau de l'eau, même si cette dernière n'a pas été observée dans les sondages géologiques. Les découvertes sporadiques d'objets de l'âge du Bronze ou du Fer dans le marais laissent croire que l'homme circule toujours dans le marais comme au Néolithique mais rien ne permet d'affirmer qu'il maîtrise pleinement ce secteur. L'état de nos connaissances ne permet pas non plus de saisir l'état de développement exact du marais (complètement comblé ou à nouveau envahi par l'eau?). Contrairement à d'autres secteurs de l'estuaire où les marais sont des hauts lieux de production du sel ou d'échanges commerciaux liés à l'estuaire ou à l'océan, celui de Reysson ne permet pas de saisir une activité clairement liée aux zones humides quelque soit leur nature. Faut-il voir dans

12 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France ce phénomène des conditions originales ? Le marais de Reysson était-il encore ouvert vers l'estuaire mais plus suffisamment pour en profiter pleinement ? La seule certitude vient de la formation continue de tourbières dans le marais de Reysson à des époques où elles sont ailleurs érodées.

Epoque Gallo-Romaine

L’époque gallo-romaine est marquée par une forte concentration de découvertes antiques autour du marais de Reysson, sur ses rivages ou sur ses îlots. Cette occupation reste dans la lignée de celle observée depuis le Néolithique. L'îlot du Peuilh est toujours occupé, comme celui de Cassan plus au nord. La présence de l'homme prend cependant un aspect tout particulier avec l'établissement de l'agglomération gallo-romaine de Brion à partir du Ier siècle ap. J.-C. sur les marges septentrionales du marais (trame urbaine avec un théâtre, une zone cultuelle et de possibles thermes). Elle fait du marais de Reysson un haut lieu de l'occupation antique en Médoc. Quel lien faut-il y voir avec le marais lui même et avec l’estuaire? Il semble difficile de ne pas trouver un rapport entre l'aspect du paysage et cette très forte présence gallo-romaine, car outre l'agglomération, les coteaux étaient occupés par diverses autres constructions : habitats et établissements agricoles du type villa. Des phénomènes similaires de conquête apparaissent à la même époque en d'autres lieux autour de l'estuaire : marais du Monard, marais de Saint-Ciers, etc. Mais dans ces cas, la présence humaine et les activités sont clairement liées aux marais, aux paléorivages et aux cours d'eau : exploitations du sel, zones de fret avec fortes activités portuaires tournées vers la circulation à grande échelle de marchandises, etc. Il est tentant d'imaginer une situation assez comparable dans les marais de Reysson. Un port a ainsi été envisagé à Brion, ce qui permettait de justifier l'établissement d'une agglomération à cet endroit. Des articles récents envisagent même la culture de l'huître médocaine à cette époque dans ce marais ! Pourtant les campagnes de fouilles réalisés à Brion depuis une quarantaine d'années et les découvertes anciennes faites sur le pourtour du marais, si elles confirment la forte densité de l'occupation, ne démontrent pas pour autant l'existence d'activités portuaires, du moins pas dans les proportions observées sur la rive droite de l’estuaire. Des canaux en eau devaient permettre la circulation de petites embarcations, mais il est plus difficile d'envisager un trafic commercial comme à Barzan, par exemple.

Ce qui caractérise l'époque gallo-romaine, ce sont les activités agricoles et la "ville de Brion" ressemble bien plus à un "bourg agricole" qu'à une "ville de marins". L'importance des domaines agricoles dans ce secteur du Médoc, va aussi en ce sens : villa de Cassan, de Vertheuil, etc. et les contacts qu'entretenaient tous ces sites avec l'estuaire ne semblent pas plus importants que pour d'autres campagnes girondines. Alors pourquoi une telle concentration de la présence de l'homme autour de cette dépression marécageuse si le rapport entre les deux semble secondaire ? Cela tient sans doute à la nature des terrains autour de Reysson : des sols argilo-calcaires à argilo-graveleux de qualité qui intéressent particulièrement les Gallo-romains. Nous sommes sans doute assez loin de l'importance que l'on prête aujourd'hui aux graves médocaines. Ce sont des formations calcaires et argileuses de l'Éocène supérieur, couronnées vers l'ouest par des marnes et des calcaires de l'Oligocène. Le site de Brion en matérialise assez bien le centre géographique et le marais de Reysson divise ces terroirs en deux zones : celle de Cissac au sud et celle de Blaignan au nord. En fait la vision que l'on a traditionnellement de l'organisation de l'occupation antique sur les marges du marais, tournée vers le marais et l'estuaire, est sans doute à inverser. L'habitat et les activités humaines seraient plutôt à envisager tournés vers la terre et sur les marges de ces terres agricoles de qualité pour en conserver le maximum d'espace disponible en raison de leur faible superficie en Médoc. Cela laisse penser que ce secteur était densément exploité et occupé à l'époque antique ce que confirmerait les découvertes.

Le marais de Reysson n'était certainement pas complètement délaissé mais l'importance que lui prêtent les historiens de ces dernières décennies est sans doute à minimiser. Le marais devait offrir des activités d'appoint aux productions agricoles locales : chasse, pêche, exploitation des plantes de marais tels que le jonc et le roseau. Cette vision d'une occupation humaine tournant en partie le dos à l'estuaire et surtout à ces marges marécageuses va à

13 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

l'encontre des idées reçues jusqu'à présent mais permet de proposer des hypothèses nouvelles tout aussi recevables.

Epoque Medieval

L'approche historique de ce secteur reste difficile faute de d'éléments archéologiques ou de textes anciens, cependant, les rares éléments recueillis permettent d'affirmer que les rivages du marais de Reysson sont toujours occupés au cours du haut Moyen âge. L'apparition d'un réseau paroissial dense et l'établissement de communautés humaines importantes au Moyen âge (villages, châteaux, abbaye et prieurés) confortent la place prépondérante des activités agricoles toujours riches. Les activités liées à l'estuaire, quand elles apparaissent dans les textes anciens, sont généralement rejetées directement sur les rivages estuariens : ports de Mapon, de Calon, de Notre-Dame-de-l'Entre-deux-Arcs, de la Maréchale, etc. Elles n'apparaissent pas plus qu'à l'époque antique dans le marais de Reysson et s’il arrive que celui-ci soit inondé au point de permettre à des embarcations d'y circuler, comme le révèlent quelques documents d'époque moderne (XVIIe-XVIIIe siècle), il n'en demeure pas moins une zone isolée, coupée des influences estuariennes. Ce type d'accidents, fréquents lors d'hivers pluvieux comme en bien d'autres marais de la Gironde, sont plus souvent liés à des apports des cours d'eau de l'intérieur qu'à un débordement de l'estuaire même si ce scénario n'est pas à écarter.

Toute l'histoire de la présence humaine dans et autour du marais de Reysson depuis la préhistoire jusqu'à son drainage au XVIIe siècle, en fait un secteur original assez différent des marais du Nord-Médoc ou des la rive droite de l'estuaire.

Il semble que l’activité humaine étaient tournée vers l’agriculture autour du marais plutôt que vers l’exploitation du marais lui-même.

6. PALAEO-ENVIRONMENTAL AND ARCHAEOLOGICAL POTENTIAL: INVESTIGATIONS IN THE “LA PERGE” MARSH

6.1 Holocene palaeo-environments of the La Perge marsh

We focussed our studies on palynological analysis based on cores realised in the «La Perge» marsh. We use and refine the chronoclimatic scale based on pollen diagram constructed by Diot and Tastet (1995) to established correlations in a transect of five cores collected from the head of the valley of La Perge marsh.

The aims of this study were, fristly, to compare the evolution of ecological pollen groups to distinguish between local and regional vegetation and climatic signals, and, secondly, to precise the conclusions of Pontee et al (1997) on the history of the two morphological units of marshes define in the Médoc Peninsula.

Dating Methods

Guided by the results of approximatively 360 bore holes made by the BRGM (Bureau de Recherche Géologiques et Minières, French Geological Survey), around 25 cores were obtained from the Médoc peninsula using a vibrocorer. We will present the results of 5 cores which were studied in detail and whose location is shown in Figure P15.10 and Table 2a. Cores HOREST 9202, 9203, 92.4, 9205 and 9206 were collected in the first unit of marshes, whilst core HOREST 9201 was situated 20-30 m to the north of the "Cordon de Richard" in the second unit of marshes. All the cores were located between 2 and 3 m N.G.F.

The methods are described above (see the paragraph of the palaeo-environmental study of the "Reysson" marsh).

Dates were obtained using the 14C technique on 6 peat samples in core 9206, and on one sample of Scrobicularia shells at the base of core 9204 (Table 2b).

14 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

Results

Sedimentological characteristics:

All the cores studied are composed mainly of silty-clayey muds, although some contain layers of peat and sand. The lithology of the cores is depicted in Figure P15.11. Each schematic log was constructed after a detailed sedimentological and lithological examination of the cores.

Core 9206 shows shelly sands which grade into alternating sand and mud. From 3.05 to 0.89 m the sediment is peat and is highly organic, homogenous and black in colour. Sands reappear then between 0.80 and 0.20 m and these become soily to the top of the core.

Core 9204 is comprised of mud which is generally rich in organic matter. From 5.60 to 4.30 m a dark grey green silty mud shows numerous Scrobucularia shells and shell debris. From 4.30 to 0.95 m the mud is grey, homogenous, shell-less and contains numerous organic debris which becomes more abundant above 2.10 m. Above 0.95 m the mud becomes beige to brown, and is rich in organic debris and roots.

Core 9205 is composed of fine sand with micas and shell debris from 7.60 to 4.30 m, which is overlain by predominantly yellowish-grey mud. Plant debris are present between 1.90 and 3.00, and iron stains are present from 1.90 to 1.10 m. From 1.10 to 0.80 m the mud is dark grey.

Core 9202 is composed mainly of mud, with a layer of black coloured sands and pebbles between 3.00 and 2.40 m. Below this the mud has a yellowish taint and calcareous pebbles are present. Above this there is light grey mud which again becomes yellowish in the upper 0.80 m.

Core 9201 is composed solely of mud except for thin beds of small shell debris which occur from 0.60 to 0.90 m. From 3.60 to 1.50 m the sediment is composed of a grey mud with iron stains. From 1.50 to 0.90 cm the mud has a grey green colour. Above the shell beds the sediment becomes browner and oxidised plant debris is visible.

Palynological results

The palynological results are presented in a depth diagram of ecological pollen groups for each core (Figures P15.12, P15.13, P15.14, P15.15 and P15.16). In each core, we have identified a number of pollen zones (NM1 to NM6) adapted from Diot and Tastet (1995). Theses zones are mainly based on variations of tree pollens and were defined on the total pollen diagrams.

Pollen counts

The percentages of each taxon were initially expressed as percentages of the total pollen counts. This count excludes fern spores, except for those of Osmunda, which is an indicator of a particular plant group for the lagoons on the Atlantic coast. Non- differentiated fern spores are presented (as a percentage of the total pollen count) because they indicate estuarine water supply (Turon, 1973). The spores and pollens deposited in the continental marsh have a number of input routes: (i) atmospheric-both regional and local (ii) waterbourne from freshwater streams and tidal water (Turon, 1984), on marine waters (Bernard and Pons, 1985) or on the modern sediments on the Arcachon basin (Marambat, 1992) show that pollens and spores have a representative regional signal along with a local signal which is of variable importance. Local influences include the pollens of the Chenopodiaceae, Cyperceae and Pteridophyteae spores. Dinoflaggellates were counted separately, and are presented as percentages of the total pollen counts.

Ecological pollen groups

To illustrate the plant evolution, the taxa were gathered in ecological pollen groups similar to the present day ones. These groups correspond to botanic associations

15 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

described in lakes or littoral basins on a sandy substrate on the Atlantic coast (Bournerias et al, 1998). The following plant associations were identified from the most continental one to the centre of the lake (Figure P15.17):

(i) pine forest (ii) oak forest (iii) alder wood (iv) marsh or Osmunda marsh (v) humid meadow (with Cyperaceae) (vi) sedge community (vii) water community

The other pollen associations include Poaceae, which are ubiquist in maedows, anthropogenic association (ruderals and cereals), and Pteridophyteae. Each group contains a number of different pollens and these are given in Table 3.

Pollen zones

As mentioned earlier, the pollen zones presented on the diagrams of ecological pollen groups were adapted from those defined by Diot and Tastet (1995) on the total pollen diagrams. We have relabelled them NM1 to NM6, NM standing for North Médoc.

Zone NM1 is characterised by the dominance of thermophilous oak forest composed of deciduous oaks (Quercus type pedunculata-pubescens) accompanied by Quercus ilex (holm-oak), Tilia, Corylus, Ulmus and Carpinus.

Zone NM2 is characterised by (i) the start of a decrease in Quercus pollens, (ii) a constant occurrence of Tilia, (iii) the highest percentages of Ulmus and Fagus in the whole sequence, and (iv) the appearance of the first traces of anthropogenisation, noticeably the appearance of Cerealia.

Zone NM3 is characterised by (i) the continuation in the decrease of Quercus, (ii) Fagus and Tilia still being present, (iii) a decrease in Corylus, and (iv) an increase in Pinus pinaster to the extent that it becomes more important than Pinus sylvestris. In core 9204, zone NM3 was divided in sub-zones NM3a and NM3b, the boundary corresponding to an important increase in the percentage of the marsh association.

Zone NM4 is characterised by (i) a very reducted oak forest signature, (ii) the continued presence of Carpinus and Fagus, (iii) the disappearance of Tilia, and (iv) the appearance of Ericaceae and Poaceae which indicate a moor robust heath type environment.

Zone NM5 is characterised by (i) the continued presence of Quercus, Fagus and Carpinus, (ii) the first appearance of Juglans, (iii) the dominance of Pinus pinaster, (iv) the clear indication of anthropogenic activity shown by the presence of Cerealia and the development of Poacea grasslands and moors or heaths.

An additional sample at the top of the core 9206 was analysed. It is not included in the diagrams because of the lack of continuity with the underlying peat sequence. This sample is very similar to the top sample in core 9201, and clearly different from the rest of the sequences, with a very high Pinus pinaster content and abundant Poacea. This association could degine a sixth zone (NM6) corresponding with the last century pine plantations, however the boundary with zone NM5 is impossible to locate on the diagram.

Dating

The age of the boundaries between each zone was calculated in core 9206, where six 14C dates were obtained. The ages were extrapolated assuming a constant peat accumulation rate between each dated sample. Given the uncertainty on the date itself and the thickness of the dated sample, the date of each boundary presently corresponds to an age range. The results

16 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France are present in Table 2c. For a better readability, only the mean ages are represented on the diagrams.

Because the cores are separated by a maximum of 12 Km only, it is reasonable to suppose that the ecological changes represented by palynological data are contemporaneous. Thus relative dates were assigned to the pollen zones in all the cores in addition to the one absolute date from the base of core 9204 (Table 2c). By assuming a steady sedimentation rate between these dates it is possible to calculate the amount of time that each cm of core represents. This in turn allows dates to be assigned to each pollen sample within the core, and hence the evolution of ecological pollen groups can be plotted against time. Because no date is available in the lower parts of cores 9201, 9202 and 9205, this has only been done for the two westernmost cores (9204 and 9206, Figure P15.18 and P15.19). On the mean ages of the zone boundaries were used in this calculation.

Discussion

Previous palynological studies on the French Atlantic coast and especially on the Médoc area (Diot and Tastet, 1995) have referred to the classical zonation of Godwin (1956), based on the variations of the trees pollens in mountainous areas. But in lowmands in general, and more especially in the Aquiatine, the recognition of the Atlantic, Subboreal and Subatlantic climatic zones is difficult. In the Médoc area, the abundance of trees pollens is > 2 %, the making taxa (Abies, Ulmus, Picea,¼) show very small percentages, and their variations are not significant. The oceanic climate attenuates seasonal temperature variations compared to the mountainous areas and continental lowlands. This is particularly true for the Médoc peninsula, located between the Gironde estuary and the Atlantic ocean. For these reasons, the local/regional pollen zonation (NM1 to NM6) is mainly based on the variations of Quercus, which is the only significant marker there. For the moment, we do not attempt to make it correspond with other zonations in France (Visset, 1979; Voeltzel, 1987; Marambat, 1992; Marguerie, 1992; Bernard, 1996; Sanchez-Goni, 1996).

Evolution of vegetation landscapes in the North Medoc area

During zone NM1 (prior to 5300 B.P.), the head of the valley of La Perge is almost filled, and the site of core 9206 is occupied by a peat-bog, receiving pollen supply from the surrounding oak forests and humid grasslands. To the west, the site of core 9204 is located in a channel largely open to marine water supply from the estuary, as revealed by abundant dinoflaggellates and pollens of Chenopodiaceae, usually growing on schorres. The other sites are located on open tidal flats accreting on the western bank of the estuary.

During zone NM2 (5300 to 3100 B.P.), the peat-bog at the head of the valley is receiving supply from an alder wood and a marsh with Osmunda, probably indicating a change in the position of the tidal channel. To the west, cores 9201, 9202 and 9205 are still located on open tidal flats, as revealed by abundant estuarine supply. The only noticeable change is a sligh reduction of estuarine dinoflaggellates, foraminifera and ostracods in core 9204, which can be interpreted as a narrowing of a channel as a result of progressive infill.

During zone NM3 (3100 to 2100 B.P.), the peat-bog at the head of the valley records the disappearance of the marsh with Osmunda and the decrease of the alder wood. To the west, the site of core 9204 evolves from a tidal channel with dinoflaggellates and Pteridophyteae spores suppied by the disappearance of dinoflaggellates and the dominance of Chenopodiaceae. To the west, estuarine supply is still present, especially in core 9201 still located on an open tidal flat. The zone NM3 is divided in NM3a and NM3b.

During zone NM4 (2100 to 1300 B.P.), the peat-bog at the head of the valley records the disappearance of the alder forest, and the development of humid grassland with Cyperaceae and moors with Ericaceae. A sticking change occurs at the site of core 9204, with the complete disappearance of estuarine supply and the development of a continental marsh. Sedimentation

17 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France apparently stops at the site of core 9205, whereas cores 9202 and 9201 are still located on an open tidal flat or in a wide tidal channel.

During zone NM 5 (after 1300 B.P.), the peat-bog at the head of the valley is surrounded by humid grasslands with small lakes as indicated by the presence of the sedge community. The continental marsh at the site of core 9204 is surrounded by pine forests and grasslands with Poaceae. Anthropogenic influence is clear. Sedimentation still goes on at the sites of cores 9202 and 9201, in a tidal channel surrounded by humid grasslands.

The most striking change in vegetation landscapes occurs near the NM3/NM4 (2100 B.P.) boundary. It is marked by (i) the apparent ending of sedimentation at the site of core 9205, (ii) the transition from a brackish water to a continental marsh at the site of core 9204 and (iii) the disappearance of the alder wood at the head of the valley (core 9206). These changes indicate a sudden decrease in estuarine supply in the first generation of marshes, and may be contemporaneous with the establishment of the "Cordon de Richard", for which 14C dates obtained on shell samples indicate an age comprised around 2575+/-162 B.P (Pontee et al, 1997). After that date, estuarine water penetration in the first generation of marshes is apparently restricted to the site of core 9202, i.e on the estuarine channels.

Comparison with other areas

These regional climatic changes are relatively discrete in the diagrams compared with the striking change at the boundary between zones NM3/NM4, linked to a local factor.

As mentioned before, we did not attempt to precisely match the North Médoc pollen zones with the climatozones of Godwin (1956). However, previous work in Europe has always referred to the Atlantic/Subboreal/Subatlantic zonation, and a rough parallel has to be established for comparaison with other areas.

Zone NM1 is marked by the highest Quercus and Corylus percentages and low Tilia amounts. It may thus be correlated with the end of the Atlantic period. Zone NM2 is marked by a slight decrease in Quercus and the strongest Ulmus occurrence, and roughly correlates with the Subboreal zone. Finally, zones NM3, NM4 and NM5 are characterised by (i) a general decrease in trees pollens, (ii) a clear decrease in oak forest (especially during zone NM3), (iii) the occurrence of Fagus and (iv) a clear anthropogenic influence.

The North Médoc pollen zones are approximatively the same as those determined elsewhere in the Médoc (Marambat, 1992). The difference is that here amounts of Pinus maritima and Tilia in the Atlantic pariod (zone NM1) are lower. In the Subboreal period, the decline of Fagus is hardly seen with percentages below 1%. In the marshes of the Bordeaux area (Paquereau, 1964), the subboreal is considered as a richer phase with Ulmus, Tilia and hygrophytes, and anthropogenisation is already present which is not the case in the Médoc.

In the Loire estuary (Visset, 1979; Voeltzel, 1987) the criterion are the same except for Tilia which is present since the Atlantic and non characteristic of the Sbboreal. The Subboreal is characterised by a sparse oak forest in wet ground with Quercus, Alnus and Corylus which is present at the base and then declines.

On the Atlantic coast of Spain, in the peat marsh of Buelna which is close to the coast and at 230 m in altitude, similar events were described (Menendez-Amor and Florschutz, 1961). After mud deposition the peat forms during the second half of the Subboreal (extrapolated date). High percentages of Cyperaceae and Poaceae date to the first century of our era, 2260+/-45 B.P. and 1775+/-60 B.P.. This event is considered by the authors as indicating a regional man induced deforestation.

Climatozones in the North Médoc during the Holocene are similar to those defined on the Atlantic coast (Brittany, Loire and Gironde estuaries). In particular, the Subboreal/Subatlantic

18 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France transition (NM2/NM3) approximately dates to 3100 B.P., which is older than the age of 2500 B.P. commonly admitted in the rest of Europe (Mangerud et al, 1974).

The Holocene accretion of the North Médoc marshes

The diagram on Figure P15.20 presents a correlation between five cores based on pollen zones. It gives further information on the accretion of the North Médoc marshes, and especially on the impact of the formation of the "Cordon de Richard". The diagram has been plotted against altitude (NGF height), and consequently the lines representing the pollen zones boundaries may be considered as an indication of palaeotopographies. The inferences are nevertheless limited by compaction processes which were not taken into account.

It is obvious that the lower parts of cores 9206 and 9205 are much older than the rest of the sections, and at the end of zone NM1 (5300 B.P.), both sites were high points. This is easily explained for core 9206 by the location at the head of the valley of La Perge, and a peat-bog appeared there when sea-level reached its present-day level. The base of the core is mostly a mixture of sand, gravels and clay with shell debris. These deposits probably represent a basal transgressive unit which was not sampled at the other sites because the base of the Holocene deepens eastward (Pontee et al, 1997). The early infill at the site of core 9205 may be explained by very restrained communication with the estuary, making this a preferential accumulation zone. The fine sand facies at the base of the core was not described anywhere else, and could represent the top of the basal transgressive unit mentionned above.

During zones NM2 and NM3a (5300 to 2500 B.P.), the three other sites are largely open to estuarine influences, and the palaeotopography in the La Perge channel at the end of zone NM2, from core 9204 to core 9201, appears the almost flat, with a very low decreasing gradient towards the estuary. The sandy facies occuring in core 9202 is probably due to a local factor; making it an isolated feature in an overall muddy tidal flat. By the same time, sedimentation at the site of core 9205 has slowed down. During zone NM3a, the last estuarine influences at the site of core 9204 are marked by a sligh increase in accumulation rate, leading to a more steep topography from there towards the estuary.

Available dates indicate that the "Cordon de Richard" began forming around 2500 B.P., i.e. at the NM3a/NM3b boundary, clearly marked at the site of core 9204 by the disappearance of estuarine influences and the establishment of a continental marsh environment. This shelly ridge appeared between cores 9202 and 9201 (Figure P15.20). It is still unclear which factor is responsible for the appearance of this feature, however it is obvious that the "Cordon de Richard" began accumulating on an almost flat surface, and that the distinction bteween the first and the second unit of marshes was inexistant until then.

After the beginning of the "Cordon de Richard" formation, sedimentation accelerates in the first generation of marshes as a result of hindered estuarine water penetration. Sedimentation rapidly stops at the site of core 9205, probably because the communication with the estuary between the Jau-Dignac and Valeyrac terraces is almost completely obstructed. To the North, the wide communication between the Jau-Dignac and Saint-Vivien terraces (Figure P16.2) still functions. The "Cordon de Richard" is probably less developed or more discontinuous there, however the sedimentation rate increases in the channel of La Perge. This is particularly obvious in core 9202 and results in the appearance of a steep topographic gradient between the first and the second generation of marshes. By the same time, the site of core 9204 rapidly accretes to reach the same altitude as the head of the valley. On both sites, sedimentation goes on until after the NM4/NM5 boundary (1300 B.P.) and probably stops very late when definitive reclamation occured during the 17th century. In contrast, the sedimenattion rate in core 9201 seems to be unaffected by the "Cordon de Richard" formation and remains constant until reclamation during the 18th century. Conclusions

The sedimentary archives of the palaeochannel of La Perge have recorded palaeo- environmental changes since more than 6,000 years. Pollens and spores variations in six cores

19 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

were used to define five pollen zones for the North Medoc area (NM1 to NM5). The age of the zone boundaries was extrapolated on the basis of seven 14C dates, and the results are compared with other zonations on the Atlantic coast.

To illustrate the local vegetation evolution, pollen taxa where then gathered in ecological groups similar to present-day botanical groups on the Atlantic coast: pine forest, oak forest, alder wood, marsh, humid meadow, sedge and water communities. Prior to 5,300 B.P., the head of the valley of La Perge (core 9206) is almost completely filled and occupied by a peat-bog until after 500 B.P. To the west, the other cores are located in a channel largely opened on the estuary. The site of core 9204 evolves to a brackish water marsh after 2,100 B.P. This last change is also marked by the disappearance of the alder wood at the head of the valley (core 9206). It is contemporaneous with the formation of the "Cordon de Richard", between 2,500 and 1,500 B.P. The first and second unit of marshes presently seen in the Medoc were first individualised in consequence of hindered estuarine water penetration behind this ridge. Accretion stops rapidly in protected areas (core 9205), and the sedimentation rate increases in the tidal channels (cores 9204 and 9202). Definitive reclamation occured during the 17th century.

The chronoclimatic zonation and holocene palaeo-environmental reconstruction in the Gironde estuary area should be precised by additional investigations in other locations (Centre Medoc and Eastern bank).

6.2 Archaeological synthesis of the La Perge marsh: Les témoins de la présence humaine dans le marais de La Perge de la fin de la Préhistoire au Moyen âge (Figure P15.3).

Le marais de La Perge est sans doute l'un des plus étendu du Médoc puisqu'il traverse pratiquement toute la péninsule médulienne dans un sens est-ouest, et trouve dans les marais de Lesparre et Saint-Vivien un prolongement vers l'estuaire.

Seules les époques préhistorique et protohistorique sont bien représentées. Pour le Néolithique, mais aussi pour les sites de l'âge du Bronze, les découvertes sont matérialisées par des séries lithiques abondantes associées traditionnellement à des éléments domestiques comme de la céramique. De nombreuses trouvailles faites autour du marais de La Perge sont anciennes (XIXe siècle). Elles furent décrites comme de simples "sites à silex" ou "ateliers de taille" (L'Estremeyre, Gargassan, Panissas, La Séougue, Les Pargaux, etc.), mais il ne fait pas de doute que certains de ces sites sont des habitats. Tous ces sites ont livré d'importantes séries d'outils en silex (haches polies et taillées, pointes de flèche, grattoirs, lames, percuteurs, perçoirs, racloirs, etc.). Des prospections minutieuses, comme celles menées par Julia Roussot-Larroque à Queyrac dans les années 1990, auraient sans doute permis de mettre au jour de la céramique et d'en préciser la datation. Une forte concentration de ce type de découvertes s'observe sur les rivages ou paléorivages en aval du marais de La Perge, dans sa partie orientale: Queyrac, Vensac, Jau-Dignac-Loirac. Les découvertes sont plus rares en amont dans le marais de La Perge proprement dit. Des transformations postérieures du paysage, comme les mouvements dunaires, n'y sont peut-être pas étrangers. Les découvertes isolées sont aussi nombreuses dans ce secteur mais elles doivent être considérées avec prudence, surtout les haches polies en raison de la facilité avec laquelle elles ont pu circuler jusqu'à des dates récentes.

Le Néolithique

La localisation géographique des sites du Néolithique dans ce secteur semble directement liée à la nature du sol et à son orientation. Les fortes concentrations de Vensac et plus encore de Queyrac et Saint-Vivien (L'Angle, La Grande-Rivière, Le Guadet, Le Plancat) correspondent traditionnellement aux terrasses fluviatiles du Pléistocène. Mais la localisation précise des sites révèle que l'homme a des préférences pour les marges humides de ces terrasses au contact

20 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France avec le marais. Les sites en arrière plan ne sont pas rares mais ne sont jamais éloignés des rivages ou paléorivages de plus de 3 à 4 km. Comme cela a pu être observé dans le marais de Reysson plus au sud ou celui de Saint-Ciers sur la rive droite de l'estuaire, l'activité humaine au Néolithique était essentiellement tournée vers les zones basses et humides. Là aussi pratiquement tous les reliefs autour et dans le marais ont livré des silex. Les découvertes se font souvent dans la moitié inférieure de ces reliefs au contact avec le marais, mais les conditions de vie et le niveau de l'eau devait être différents de ceux que nous connaissons aujourd'hui. La découverte de mobilier dans le marais, comme c'est le cas à l'Oustau Neuf, au large de l'île de Jau, tendrait cependant à prouver que certaines parcelles étaient déjà comblées et donc accessibles, voire habitables. La remonté du niveau marin, même modeste, après le Néolithique a contribué à l'enfouissement de certains de ces sites.

L’Age du Bronze

Les découvertes de l'âge du Bronze sont déjà moins nombreuses. Peu d'habitats sont connus dans le secteur de La Perge à l'exception de ceux de Queyrac (L'Angle, Le Plancat) et surtout de Lapartens à Vendays. Dans ce dernier cas, les fouilles récentes de Julia Roussot-Larroque ont mis au jour des structures bâties faites d'un assemblage de pièces de bois qu'une datation au C14 a permis d'attribuer à la transition du Bronze ancien et du Bronze moyen (environ 1500 av. J.-C.). Les autres sites, comme ceux de Queyrac n'ont souvent livré que de la céramique associée à des outils en silex encore courants à cette époque. Les objets métalliques y sont rares, voire inexistants. Enfin les autres découvertes de l'âge du Bronze se résument uniquement à la mise au jour de dépôts de haches en bronze comme ceux de Mayan à Vendays, du Temple à Saint-Vivien, de Cassanac à Vensac ou de Méric à Jau-Dignac-Loirac ; ou à des objets en bronze isolés, généralement des haches comme celle des Arrestieux à Vensac. Ces trouvailles sont souvent anciennes et le contexte de leur découverte mal connu.

Bien que plus lâche, la localisation des sites de l'âge du Bronze rejoint d'assez près celle du Néolithique. Les terrains de prédilection des établissements humains sont encore les terrasses fluviatiles du Pléistocène (Vensac, Queyrac, Saint-Vivien) et la continuité de l'occupation des marges du marais est particulièrement évidente. Le site de Lapartens par exemple devait être primitivement établi sur les berges d'une lagune ou d'un ancien marais aujourd'hui colmaté. Les populations de l'âge du Bronze avaient une préférence pour les rivages ou paléorivages, mais elles semblent prendre un peu de recul à partir du Bronze moyen ou final. Les sites sont plus volontiers établis sur des terrains un peu plus hauts qu'à l'époque précédente, sans être trop éloigné non plus du rivage. La monté du niveau marin au cours de la protohistoire en est peut- être responsable.

L’Age du Fer

La situation est plus difficile à cerner pendant l'âge du Fer à cause de la rareté des traces archéologiques. Ces dernières sont même inexistantes pour le premier âge du Fer. Pour le marais de La Perge, les découvertes se résument à une fosse du deuxième âge du Fer à Merlazac, aux limites de Vensac et de Vendays et à une monnaie celte en électrum trouvée à au Taste à Vensac, à quelques centaines de mètres du même site de Merlazac. Il reste cependant impossible de tirer des conclusions avec seulement deux sites. Malgré ce faible nombre de découvertes, il faut pourtant constater leur très forte proximité du marais. Cette localisation annonce peut-être un état de fait nouveau plus nettement marqué au tournant de notre ère et qui est le problème du franchissement du marais : pont, passage à gué, route aménagée ? Il est dans l'immédiat impossible de définir l'état de comblement et de conquête de ce marais. Les résultats exposés plus haut permettent d'affirmer que le marais de La Perge était en partie colmaté dans sa partie amont au moins depuis la fin du Néolithique. Son exutoire vers l'estuaire, entre Queyrac, Saint-Vivien et l'île de Jau a pu être encore influencé par la remonté du niveau marin à la fin de la Protohistoire ou aux débuts de l'époque historique.

L’Epoque Gallo-Romaine

21 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

Les traces de l'occupation humaine dans et autour du marais de La Perge sont peu nombreuses, voire inexistantes, pour l'époque gallo-romaine, alors qu'elles sont en général abondantes sur les autres secteurs de l'estuaire. De plus, les quelques sites signalés anciennement sont hypothétiques, ou les structures dégagées laissent indécis quant à leur nature (Les Cercins, Mayan, Le Taste, L'Argenteyre, Le Plancat, Noaillac, etc.). Les rares habitats clairement identifiés sont modestes (Vendays) et le type de la villa luxueuse, si courant sur les rivages de l'estuaire, est absent de ce secteur, sauf peut-être sous le bourg de Queyrac. S'ajoute à cela des problèmes de chronologie et de datation pour tous ces sites que seule une étude plus développée permettrait de résoudre. A l'évidence, si les terrasses graveleuses du Pléistocène étaient le domaine de prédilection des hommes de la fin de la Préhistoire, elles semblent plutôt délaissées par les Gallo-romains qui leur préfèrent les formations argilo- calcaires de la région de Blaignan et de Cissac. Mais dans tous les cas, l'installation humaine, même modeste, se fait désormais plutôt sur des terrains à l'abri des inondations. Il semble également que les conditions à l'origine du peuplement gallo-romain ne soient plus exclusivement liées à la nature des terrains. Les traces antiques de ce secteur sont peut-être liées au trajet des routes qui de Lesparre joignent la pointe du Nord-Médoc, ou du moins, à des points de passage de ces routes terrestres au travers du marais. Le site de Taste à Vensac se trouve probablement au bord de l'un de ces chemins d'axe nord-sud qui traverse la marais de La Perge dans sa partie la plus étroite. Ces dépressions marécageuses, qui barrent la Médoc en de multiples endroits depuis Bordeaux jusqu'à Soulac, ont dû poser de nombreux problèmes dans l'organisation du réseau viaire antique. Les ingénieurs romains y ont répondu dans la mesure du possible et la principale voie romaine du Médoc (la Levade) a dû être adaptée aux conditions difficiles du terrain. Un tronçon repéré au sud de La Perge, à Lesparre, aurait d'ailleurs été construit sur pilotis selon la technique des "longs ponts" caractéristique de cette époque.

Epoque Medievale

Si les informations sont inexistantes pour le haut Moyen âge (entre le IVe et le XIe siècle), l'organisation des communautés humaines médiévales autour du marais de La Perge après cette lacune apparaît particulièrement développée. Le plus surprenant est la forte concentration d'établissements fortifiés directement sur les marges de cette zone marécageuse (Les Cercins, Le Taste, Mayan, Carcanieux). L'avantage des marais était d'alimenter facilement en eau les fossés de ces petits châteaux, mais au delà de cet aspect technique et défensif, ces fortifications commandaient et gardaient des points de passage dans le marais. Cet important dispositif de contrôle rappelle l'impossibilité qu'avaient les routes terrestres d'éviter ces marécages. En fait, les seuls véritables efforts de maîtrise de ce milieu contraignant perceptibles au Moyen âge paraissent être d'assurer des passages à travers le marais de La Perge.

Si le marais entre Queyrac (Germain, 1973), l'île de Jau et Saint-Vivien est aujourd'hui poldérisé, tout comme l'embouchure proprement dite du marais de La Perge, entre Queyrac et Vensac, la partie amont est en revanche une immense zone sauvage difficile à mettre en valeur où seules quelques routes arrivent à se frayer un passage. Cet état de fait résume assez bien toutes les facettes de l'histoire du marais de La Perge depuis la fin de la Préhistoire.

7. CURRENT APPROACH TO THE ARCHAEOLOGICAL RESULTS OF THE GIRONDE ESTUARY MARSHES

Nb. See also P16, East Bank Gironde: the following section provides dicussion and conclusions for both study areas.

Many prospections are still in progress in the marshes of the Gironde Estuary to precise the present conceptual model to have a better understanding how the estuary evolved in the past and how people reacted to these coastal changes.

22 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

8. CURRENT APPROACH TO THE PALAEO-ENVIRONMENTAL RESULTS OF THE GIRONDE ESTUARY MARSHES

New cores will be realised on the East and West Banks of the Gironde Estuary. The last campaign of sampling will occur in the central part of the Sait Ciers-sur-Gironde" marsh and on the "Ordonnac" marsh.

9. SUCCESSES AND PROBLEMS IDENTIFIED BY THE LIFE PROJECT

Archaeological evidence has proved to be a useful tool in the reconstruction of coastal wetland changes in the past. Site distributions are better suited to palaeogeographical, rather than sea- level, modelling as it is frequently difficult to relate an archaeological structure/feature to contemporary sea-level with any degree of precision.

10. COMMUNITY INVOLVEMENT ISSUES AND SOCIAL INCLUSION

10.1 Funding Agency

The "Conseil Régional Poitou-Charente" (for the Southern part of the marshes of the East Bank), the "Conseil Général de la Charente Maritime" (for the Northern part of the marshes of the East Bank), the "Conseil Régional d'Aquitaine" (marshes of the West Bank) and the "Conseil Général de la Gironde"(marshes of the West Bank) can, with or without the State, subsidize research or managment studies on the coastal zone, upon request of a city council or of a group of cities.

The "Service Régional de l'Archéologie d'Aquitaine" for the Southern, and the "Service Régional de l' Archéologie de Poitou-Charente" for the Northern, depending on the Culture Ministry, is the authority delivering the excavation authorizations and supporting, at least partially, archaeological research.

10.2 Investigation and Monitoring

Since December the 27th 1999 storms, embankment and breakwater (East Bank) are currently being reinforced and hightened around the nuclear power station of the EDF (the French electricity Company).

In 1994, a study concerning the renewal of the embankment and breakwater of the village of Valeyrac (West Bank) was undertaken by the DDE and the PAB (Bordeaux harbour authority), without any result. A hydraulic study of the Reysson marsh, funded by the "Conseil Régional d'Aquitaine" and the "Conseil Général de la Gironde", is in progress under the "Syndicat mixte du Pays Médoc", a new association of cities.

10.3 Current Status and Approach

The renewal of the small haven of Port-des-Callonges (East Bank) for fishing and leisure boats is underway. The project is funded by the cities of Braud and Saint-Ciers (60%), the remaining (40%) is shared between the Conseil Régional d'Aquitaine and the Conseil Général de la Gironde.

Some tourism circuits are maintained by city councils (West Bank) in relation to the archaeological sites. The councils of the villages along the estuary wish the "Conseil Régional d'Aquitaine" and the "Conseil Général de la Gironde" to take responsability for coastal defences.

10.4 Public Awareness

The presence, along the estuary since 1978, of a nuclear power station of Braud-et-Saint-Louis (East Bank) led to a sensible public awareness. Since the December 27th 1999 storms, this

23 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

awareness increased considerably because of the flood following upon the breaking of the estuarian defences. The consequence of this event led the French Authority for Nuclear Safety (ASN) to classify this incident at the level 2 of the International Nuclear Event Scale (INES). The city of Saint-Ciers has a small Archaeological Museum organised and maintained by volunteers.

Small public awareness concerning coastal problems on the West Bank of the Gironde Estuary. Informations are given by the media (especially after the December, 27th 1999 storm), and by occasional thin booklets or by the elect in episodic city reviews. From the archaeological point of view the city of Saint-Germain-d'Esteuil organize, during summertime, guided visits of the site of Brion.

10.5 Experiences, successes and problems with the current approach

The major experience on the East and West Banks of the Gironde estuary is derived from the past, and especially from the December 27th 1999 storm with the deficiency of the embankment to prevent submersion of the marshes in case of exceptional events .The maintenance of estuary defences is not sustainable by the city councils without external funding.

11. CONCLUSIONS

11.1 Threats

The St Ciers-sur-Gironde marsh is bounded on its western estuarine margin by sea defences which was first built during the 17th century. Bank, embankment erosion and danger of submersion of the saltmarshes are the principal threat, especially for the St Ciers marsh where was built, in 1978, a nuclear power station. The marsh is used for intensive corn growth and intensive watering could bring about a salinisation of the groundwater.

The danger of submersion and the bank and embankment erosion are the most important threats in the area of the West Bank of the Gironde. Intensive corn growth alters the estuarine marshes.

11.2 Management Needs

In the framework of the "Syndicat du Grand Marais", grouping together the cities of Braud-et- Saint-Louis and Saint-Ciers-sur-Gironde (East Bank), the problems of the embankments of the Gironde estuary will be tackled and proposed to the future State/Region plan for funding.

There is a project of creating a "Syndicat intercommunal", who would gather the cities along the West Bank of the Gironde Estuary for the touristic and economic management of the estuarian marshes, for the exploitation of their natural and archaeological or cultural sites, as well as for their defence against flooding. The problems of the embankments of the Gironde estuary could be tackled by the future State/Region plan for funding.

12. KEY ISSUES

Palaeo-environmental studies of sedimentary archives from numerous boreholes and manual gouge augers of the marshes of the Gironde Estuary allowed the interpretation of the coastal changes and their chronology. On the East Bank, the current known archaeological sites distribution has also been integrated with stratigraphic data to reconstruct the spatial extent of marsh development during specific chronological periods. A minimum occupiable datum (MOD) has been defined for successive archaeological periods to provide indication of the maximum upper limit of past sea-levels (MHWST). Where evidence for a fluctuation in relative sea-level rise does occur, greater emphasis is placed upon the timing of the event that the inferred height sea-level had reached. Cartographic evidence has been used to determine the nature of marsh

24 Palaeo-environmental Study Area P15 West Bank of the Gironde Estuary, west coast, France

development over the past 300 years. Lastly a palaeogeographic evolution for the last 6000 years of the Saint-Ciers marsh is proposed.

The analysis of the sedimentary archives of the marshes of the West Bank of the Gironde Estuary, the interpretation of the archaeological sites and the dendrochronological data allowed the reconstruction of the Holocene coastal changes and their chronology. Throughout the Holocene SLR and post-Holocene high/still stand, the lateral bays of the original Gironde ria have acted as a long-term sediment sink leading to a marked reduction in capacity. The evidence of this evolution are two morphologic units of marshes separated by a sandy chenier ridge. Today the estuary continues to evolve as it has since 6000 years B.P. For example the middle of the mudflat in Verdon bay, showed by the satellite "Spot" image, may represent a precursor for a new chenier ridge formation. Further ridge development may lead to the isolation of an area of mudflat that may them become colonised by marsh vegetation creating a new marsh morphological unit.

13. BIBLIOGRAPHY

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Ters, M. (1973). Les variations du niveau marin depuis 10 000 ans, le long du littoral Atlantique Francais. Le Quaternaire: Travaux français récents; 9eme congrès International INQUA, Christchurch, New Zealand, pp 114-135. Tooley, M.J. (1992). Recent sea-level changes. In: J.R.L. Allen and K. Pye (Editors), Saltmarshes, Morphodynamics, Conservation, and Engineering Significance, Press Syndicate of the University of Cambridge, Cambridge: 19-40. Turon, J.L.,(1973). Apports des ensembles sporopolliniques à la reconnaissance du Quaternaire récent du Golfe de Gascogne. Thèse d'Etat, Univ. BordeauxI, 107 p. Turon, J.L.,(1984). Le palynoplancton dans l'environnement actuel de l'Atlantique nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire., Mém. Inst. Géol. Bassin Aquitain, 17, Université Bordeaux I, 313 pp. Verger, F. (1968). Marais et wadden du littoral français. Biscaye Frères Ed., Bordeaux, 548 pp. Visset, L., (1979). Recherches palynologiques sur la végétation pléistocène et holocène de quelques sites du district phytogéographique de Basse Loire. Thèse d'Etat, Soc. Sc. Nat. Ouest France, Nantes, suppl. h. s. au bull., 282 p. Voeltzel, D., (1987). Recherches pollenanalytiques sur la végétation holocène de la plaine alluviale de l'estuaire de la Loire et des coteaux environnants., Thèse Univ. Nantes, Spéc. Paléoécologie, 178 p. Wang, J., Massé, L. and Tastet, J.P. (in prep). Vertical accretion of the Holocene infill of the Monards Marsh (Barzan, Gironde Estuary, France). Warrick, R. and Oerlemans, J., (1990). Sea-level rise. In: J.T. Houghton, G.J. Jenkins and J.J. Ephram (Editors), Climate change - the IPCC scientific assessment, Cambridge University Press, Cambridge. White, W.A. (1961). Colloid phenomena in sedimentation of argillaceous rocks. Journal of Sedimentary Petrology, 31, 560-570. Williams, H.F.L. (1994). Intertidal benthic foraminiferal biofacies on the central Gulf Coast of Texas: modern distribution and application to sea level reconstruction. Micropaleontology, 40, 169-183. Wilkinson, T. J. and Murphy, P. (1986). Archaeological survey of an inter-tidal zone: the submerged landscape of the Essex coast, England. Journal of Field Archaeology, 13, 177-194. Wilkinson, T. J. (1989). The archaeological survey of coastal and estuarine wetlands. In: Coles, J. M. and Coles, B. J. (eds.). The Archaeology of Rural Wetlands. W.A.R.P. Occasional Paper No. 2. University of Exeter. Pp 23 - 26. Van de Plassche, O. (1991). Coastal submergence of the Netherlands, northwest Brittany (France), Delmarva Peninsula (VA, USA), and Connecticut (USA) during the last 5500 to 7500 sidereal years. In: Sabadini et al. (eds.). Glacial Isostacy, Sea-Level and Mantle Rheology. Kluwer: Dordrecht. Pp 285-300. Vos, P. C. and De Wolf, H. (1993). Diatoms as a tool for reconstructing sedimentary environments in coastal wetlands; methodological aspects. Hydrobiologia, 269/270, 285- 296. Zwolsman, J.J.G., Berger, G.W. and Van Eck, G.T.M. (1993). Sediment accumulation rates, historical input, postdepositional mobility and retention of elements and trace metals in salt marsh sediments of the Scheldt estuary, SW Netherlands. Marine Chemistry, 44, 73- 94.

14. ACKNOWLEDGEMENTS

We thank all the Municipalities of the East and West Banks of the Gironde Estuary for their active participation in the LIFE project and towards the prerapation of this report.

31

CORE NUMBER LAMBERT III GRID REFERENCE ALTITUDE X Y m N.G.F.* HOREST 9301 356.55 335.40 2.5 HOREST 9302 352.90 335.55 1 HOREST 9303 353.40 335.00 1 HOREST 9304 351.42 335.80 2 HOREST 9305 349.57 334.45 2 HOREST 9306 349.85 334.93 1 HOREST 9402 351.11 336.25 2 * Nivellement Général de la France (a) Location of cores.

Core Depth Age (years Cal. age Sample Ref. labo Meas. number (cm) B.P.) (years B.C.) type type HOREST 35-37 3380 ± 80 1885 - 1490 Peat Beta 95384 T HOREST 81-85 4571 ± 144 3647 - 2891 Peat UQ 2082 T HOREST 110-112 4560 ± 80 3510 - 3025 Peat Beta 95385 T HOREST 170-175 6210 ± 150 5436 - 4787 Peat UQ 2083 T HOREST 180-182 2410 ± 80 791 - 263 Peat Beta 95386 TE HOREST 47-51 3490 ± 60 1945 - 1675 Peat TO 4725 AMS HOREST 70-75 4920 ± 70 3625 - 3810 Peat Beta 95387 T HOREST 148-152 5893 ± 151 5204 - 4402 Peat UQ 2085 T HOREST 118-123 5040 ± 80 3985 - 3660 Sandy peat Beta 95388 T HOREST 318-323 5730 ± 80 4780 - 4375 Peat Beta 95389 T HOREST 545-550 6430 ± 100 5566 - 5146 Peat Beta 95390 TE HOREST 710-715 9970 ± 70 9905 - 9044 Peat Beta 95391 T

(b) 14C dates obtained on samples from the Reysson marsh, (T: traditional; TE: traditional extended cutting).

Zone boundary Age (years B.P.) Cal. age (years) NM1 / NM2 1299 ± 142 549 - 912 A.D. NM2 / NM3 2122 ± 112 253 B.C. - 7 A.D. NM3 / NM4 3132 ± 129 1574 - 1157 B.C. NM4 / NM5 5302 ± 293 4525 - 3618 B.C.

(c) Age of pollen zone boundaries in the North Médoc area.

Table 1 West Bank of the Gironde Estuary:

Figure P15.1 Geological map of the Reysson marsh area and location of the cores and survey lines presented in this study. Figure P15.2 & Figure P15.3 Maps of the archaeological sites on the West Bank of the Gironde Estuary. Figure P15.4 Core lithology, 14C dates and tentative correlations based on pollen data. Figure P15.5 Vertical facies distribution along the survey lines presented on Figure P15.1. Figure P15.6 Vertical distribution of pollen groups, 14C dates (bold) and pollen zones in core HOREST 9305. Extrapolated ages of pollen zone boundaries are in italics. Figure P15.7 Vertical distribution of pollen groups, 14C dates (bold) and pollen zones in core HOREST 9303. Extrapolated ages of pollen zone boundaries are in italics. Figure P15.8 Vertical distribution of pollen groups, 14C dates (bold) and pollen zones in core HOREST 9402. Extrapolated ages of pollen zone boundaries are in italics. Figure P15.9 Vertical distribution of pollen groups, 14C dates (bold) and pollen zones in core HOREST 9301. Extrapolated ages of pollen zone boundaries are in italics. Figure P15.10 Location of the cores in the «La Perge» marsh. Figure P15.11 Core lithology. Figure P15.12 Depth diagram of ecological pollen groups in core 9206, 14C ages in bold characters, mean ages of the pollen zone boundaries in italics. Figure P15.13 Depth diagram of ecological pollen groups in core 9204, 14C ages in bold characters, mean ages of the pollen zone boundaries in italics. Figure P15.14 Depth diagram of ecological pollen groups in core 9205, 14C ages in bold characters, mean ages of the pollen zone boundaries in italics. Figure P15.15 Depth diagram of ecological pollen groups in core 9202, 14C ages in bold characters, mean ages of the pollen zone boundaries in italics. Figure P15.16 Depth diagram of ecological pollen groups in core 9201, 14C ages in bold characters, mean ages of the pollen zone boundaries in italics. Figure P15.17 Schematic distribution of ecological pollen groups on the Aquitaine coast. Figure P15.18 Age diagram of ecological pollen groups in core 9206. Figure P15.19 Age diagram of ecological pollen groups in core 9204. Figure P15.20 Correlation of pollen zones between the five cores. The shaded area represents the time interval during which the «Cordon de Richard» is supposed to have formed. Archaeological Inventory: West Bank of the Gironde Estuary Cultural Visible Coastal Sea-level Environment Climatic Running Unvalidated Coastal Unit Coastal Altitude Name Classification1 Classification 2 Source 1 Source 2 Description X Lamb2ext Y Lamb2ext Amenity Amenity Fragility Managment Change al Change Change Chronology Code Risk Context Value Bonus

Neolithic settlement with flints discovered between 1876 and 336.964 to 2055.791 to 3 m Cabanieux Neolithic settlement flints WB1 / 4 2 2 0 1 2 0 0 I F 6 1916. 337.100 2055.723

335.969 to 2055.285 to 3 to 4 m La Séougue Neolithic settlement flints WB2 6614 Neolithic settlement with flints discovered around 1876 4 2 2 0 1 2 0 0 I F 3 and 6 336.116 2055.200

Fence (aerial photographs), protohistoric enclosure inside 2 m La Hutte Protohistoric enclosure ditches WB3 2222 337.953 2055.268 4 3 3 1 1 2 0 0 I F 6 the marsh

Neolithic settlement with flints discovered between 1876 and 336.461 to 2054.308 to 2 to 3 m Gargassan Neolithic settlement flints WB4 / 4 2 2 0 1 2 0 0 I F 6 1916 336.639 2054.197

Settlement of a medieval hospital from the XII , XV and XVI 6 m Le Temple II Medieval church (prieuré) buildings (church and cemetery) WB5 1021 335.998 2052.194 4 0 0 0 1 2 0 0 D-I F 3 centuries

bronze axes, depository axes from Depository of 23 pieces from the Middle Bronze Age, and 336.290 to 2052.224 to 5 to 6 m Le Temple I Bronze Age artefacts WB6 6616 4 0 0 0 1 2 0 0 I F 3 the Bronze Age other isolated artefacts in 1880 and around 1893. 336.183 2052.103

Lithic tools (with axes), possible neolithic settlement 3 to 5 m Panissas Neolithic settlement flints, axes WB7 / 337.169 2051.292 4 1 2 0 1 2 0 1 I F 3 discovered around 1887.

Neolithic settlement with abundant flints, first references at the 339.432 to 2051.274 to 5 to 6 m Méric II Neolithic settlement flints WB8 / end of the XIX century, and during agricultural works around 4 0 1 0 1 2 0 1 D-I F 3 339.515 2051.318 1895.

flints depository of axes from the Depository of 24 axes from the Middle Bronze Age during 338.907 to 2051.098 to 4 to 5 m Méric I Bronze Age artefacts WB9 / 4 1 1 0 1 2 0 0 I F 3 Bronze Age agricultural works around 1891. 338.951 2051.057

Possible neolithic settlement with lithic tools and ceramics 339.500 to 2049.616 to 2 m L'Oustau neuf Neolithic settlement flints, ceramics WB10 / during the prospecting during the second half of the XIX 4 3 2 0 1 2 0 1 I F 6 339.617 2049.730 century

An isolated neolithic axe discovered at the end of the XIX 331.354 to 2049.852 to 5 m Taste-Soule Neolithic artefacts Axes WB11 / 4 0 0 0 1 2 0 0 R-I F 3 century (1876-1884) 331.452 2049.777

Depository from the Bronze Age discovered around 1882, Bronze Age furnitures,Gallo-Roman settlement, buldings, ditches (fortified structures 332.329 to 2049.369 to 3 to 4 m Les Cercins WB12 / gallo-roman settlement discovered around 1991, medieval 4 0 2 0 2 2 2 2 D-I-M F 3 and 6 medieval fortifications in the ground), bronze furnitures 332.392 2049.235 fortified settlement (fortified castle with moats)

Neolithic settlement with numerous flints discovered around 330.182 to 2049.049 to 3 to 5 m L'Estremeyre Neolithic settlement flints WB13 / 4 1 2 0 1 2 0 0 I F 3 and 6 1882. 330.325 2048.968

Depository of the Middle or Late Bronze Age discovered bronze axes, fortified structures in the between 1876 and 1882, (uncertain location), medieval 331.948 to 2048.363 to 4 to 5 m Mayan Bronze Age furnitures, medieval fortifications WB14 / 4 0 2 0 2 2 1 0 I F 3 ground (ditches) fortified site from the XIII century with stuctures in the ground 332.279 2048.080 (ditches)

Possible neolithic settlement with scattered flints, coins from 336.085 to 2048.799 to 3 to 5 m Le Taste I Possible neolithic settlement, Gallo-Roman building buldings, coins, flints, ford point (river) WB15 / the I century B.C., gallo-roman settlement or ford point on "La 4 2 1 0 2 2 0 1 I F 3 336.167 2048.709 Perge" discovered during agriculturale works around 1983 Archaeological Inventory: West Bank of the Gironde Estuary fortified structures in the ground Important medieval fortified settlement with structures in the 2 to 3 m Le Taste II Medieval fortifications WB16 6561 336.491 2048.691 4 2 2 0 1 2 2 3 D-I-M F 6 (ditches) groung and ditches

Discovery of a Mesolitic settlement with pits from the Second 3 m Merlanzac Mesolithic settlement from the Second Iron Age pits WB17 3082 6058 336.150 2048.398 4 2 2 0 3 2 0 1 I F 3 and 6 Iron Age

Neolithic settlement with abundant lithic tools, discovered 337.443 to 2047.902 to 3 m Les Pargaux Neolithic settlement flints WB18 / 4 2 2 0 1 2 0 0 I F 6 during the XIX century (before 1876). 337.667 2047.758

Settlement in border of the marsh from the Early or Late 339.651 to 2047.561 to 3 m Le Loc Neolithic settlement flints, ceramics WB19 10255 Neolithic (Peu-Richard period), discovered during 4 2 2 0 1 2 0 0 I F 6 339.703 2047.497 prospections in 1993

Neo-chalcolithic settlement in border of the marsh, late or 338.658 to 2047.111 to 3 to 4 m Le Plancat Neolithic, Bronze Age and Gallo-Roman settlement flints, ceramics WB20 10226 middle (?) bronze age settlement, gallo-roman settlement 4 2 2 0 3 2 0 1 I F 3 and 6 338.699 2047.150 discovered during the prospecting in 1993.

Settlement in border of the marsh from the Late Neolithic, 338.351 to 2047.030 to 5 m L'Angle Neolithic and Bronze Age settlement flints, ceramics WB21 10221 4 1 2 0 2 2 0 1 I F 3 discovered during surface prospections in 1993 338.434 2046.932

Discovery and excavations between 1997 and 1999, 8 m Lapartens Neolithic and Bronze Age settlement wooden structures, flints, ceramics WB22 / 333.384 2039.977 4 0 3 1 2 2 0 1 I F 6 wooden structures with flints and ceramics sherds

Important gallo-roman settlement located on a hill on the marsh 35.204 to 2036.396 to 4 to 5 m Cassan Gallo-Roman settlement buldings, ceramics WB23 / 4 1 2 0 1 2 0 2 I F 3 discovered during agricultur works around 1980. 350.318 2036.310

Neolithic settlement with flints and ceramics. Numerous artefacts (bronze axes) from the Middle and the Late Bronze Age. Settlement from the Iron Age (III and II centuries B.C.), then 14862 new settlement during the I century B.C.. Antique town with Settlements from the Neolithic and the Iron Age periods, building (theater, temple,houses), 14857 theater, temple, streets, probably therms,... occupied from the I 350.584 to 2036.017 to 2 to 6 m Brion Gallo-Roman town, fortified castle from the Medieval roads, metallurgy, flints, tools, WB24 4 3 3 1 3 3 2 3 I-M F 3 14860 to the III centuries A.D., then abandonned from the III to the IV 351.017 2036.478 period ceramics, paintings,… 14858 centuries A.D.Using of the place of the theater for a small fortified castle during the XIV century. First references in the XVIII century, first study in 1865, sounding from 1966 to 1984, excavation from 1985 to 1990.

Neolithic artefacts with flints discovered during agricultural 352.874 to 2035.842 to 2 to 5 m Le Trale Neolithic settlement flints WB25 / works and prospections discovered at the end of the XIX 4 1 2 0 1 2 0 1 I F 3 and 4 352.977 2035.987 century (between 1876 and 1916)

Discovery of an isolated axe discovered at the end of the XIX 356.142 to 2036.000 to 3 to 5 m Pey de Mapon Neolithic artefacts Axes WB26 / 4 0 0 0 1 2 0 0 R F 3 century before 1910. 356.298 2036.142

La Motte Late bronze age artefacts comprising an iron sword 2 m Artefacts Iron artefacts (iron sword) WB27 / 350.367 2035.367 4 1 1 0 1 2 0 0 I F 6 Blanque discovered around 1900.

Settlement located on a hill inside the marshes and on his borders, possible wooden building with piling, settlement from wooden structures,building, flints, the Early, Middle and Late Neolithic, from the Early and Middle 2 to 3 m Le Peuilh Settlement, fortifications WB28 657 349.771 2035.088 4 3 3 3 3 2 1 3 D-I F 3 and 6 pottery, ceramics, pyres Bronze Age, from the Gallo-Roman period, possible fortifications from the Medieval period, discovered around 1860. Excavation in 1913, 1981 and from 1983 to 1986

Enclosure (as protohistoric enclosure discovered in the 1 m Loumède Protohistoric enclosure ditches WB29 / Saintonge-Bronze or Iron Age?). Aerial photograph done in 353.74 2035.201 4 3 2 1 1 2 0 1 I F 6 1992. Archaeological Inventory: West Bank of the Gironde Estuary

La Palus de Neolithic settlement with flints, possible settlement from the Iron 350.958 to 2034.757 to 1 to 3 m Neolihtic settlement flints WB30 1011 4 2 2 0 1 2 0 1 I F 3 and 6 Reysson Age, discovered around 1880 351.053 2034.818

Fortification (medieval type with lumps) in border of the marsh, fortified structures in the ground 351.054 to 2034.689 to 3 to 4 m Juillan Medieval fortifications WB31 / structures in the ground with ditches. First references in the 4 1 2 0 1 2 1 2 D-I F 3 (ditches) 351.088 2034.741 XIX century.

Neolithic settlement with flints discovered during the 351.696 to 2034.397 to 4 to 5 m Lille Neolihtic settlement flints WB32 / 4 1 2 0 1 2 0 1 I F 3 agricultural works around 1880. 351.812 2034.390

fortified structures in the ground 352.230 to 2034.154 to 3 to 5 m Beyzac Medieval fortifications WB33 / Medieval fortified site with structures in the ground and ditches 4 1 2 0 1 2 1 2 D-I F 3 (ditches) 352.351 2034.305

Important gallo-roman villa with agricultural structures 352.686 to 2033.898 to 7 to 11 m Le Peyrat Roman villa ditches WB34 1010 4 0 0 0 1 2 1 1 D-I F 2 discovered during agricultural works around 1817. 352.830 2033.884

Discovery of a lancepoint from the Late Bronze Age around 354.048 to 2034.000 to 3 to 4 m Paluda Late Bronze Age artefacts Lancepoint WB35 / 4 1 1 0 1 2 0 0 R-I F 3 1933. 354.166 2033.828

2 to 5 m CalonSégur Fortified castle buildings WB36 / Fortified castle in border of the marsh (XIV, XVII, XVIII centuries). 355.553 2034.469 4 1 2 0 1 2 2 0 M F 3 Archaeological Inventory: West Bank of the Gironde Estuary Coastline Type

soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

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soft estuarine coast Archaeological Inventory: West Bank of the Gironde Estuary soft estuarine coast soft estuarine coast soft estuarine coast soft estuarine coast

soft estuarine coast

soft estuarine coast soft estuarine coast

soft estuarine coast

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soft estuarine coast

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soft estuarine coast Archaeological Inventory: West Bank of the Gironde Estuary soft estuarine coast

soft estuarine coast

soft estuarine coast

soft estuarine coast

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soft estuarine coast soft estuarine coast