Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast,

PALAEO-ENVIRONMENTAL STUDY AREA P14

OLERON ISLAND, NEAR LA ROCHELLE, WEST COAST, FRANCE

Plate P14 View of the beach at ‘La Perroche’ marsh on Oléron Island, Atlantic coast, France, showing the peat layer exposed on the beach, evidence of changing coastal environments

1. LOCATION

1.1_ Geographical Description

Oleron Island, 175Km2, is located on the Atlantic coastline and belongs to the Département de Charente Maritime (Plate P14a and Figure P14.1). Situated North of the estuary, Oléron Island isolates the silty bay of Marennes-Oléron from the Atlantic Ocean. The Charente and the Seudre rivers, flowing into this bay, are bordered by vast saltmarshes. Marennes- Oléron bay is largely open to the ocean at its northern extremity. At the southern end Pertuis de Maumusson is a narrow inlet with strong tidal currents.

It is a low,flat, spindle-shaped island experiencing constant transformation due to erosion or sedimentation. Belonging to the , Oleron Island is composed of sedimentary rocks. The island is orientated NW-SE following the axis of an anticline (Anticline of Gémozac). On the south-western part of the island, stretches of sands, sandstones, clays and Cenomamian limestone develop parallel to the coast (Figure P14.2).

1.2 Coastal description

The western rocky coast of the island is punctuated by a succesion of small littoral marshes separated from the ocean by sandy dunes. Most of the marshes have become pasture but some of them are still swamps. Peat formation is found in most of these coastal marshes. Theses peat layers can extend under the dunes and appear at low tide on the beach.

1 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

A coastal dune system surrounds the whole island. The dunes were formed at the end of the Holocene transgression due to the erosion of the calcareous substrate or to the destruction of ancient sandy dunes. These sandy formations are more developed to the south (Massif de St Trojan), and to the east (Massif des Saumonards).

Marennes-Oléron bay, isolated from the open ocean by the island, is subject to a constant supply of sediment from the Charente and the Seudre rivers.

1.3 Regional Authority

Conseil Régional de Poitou-Charentes Conseil Général de Charente Maritime. Town councils of St Pierre d'Oléron, Dolus d'Oléron, St Georges d'Oléron, St Denis d'Oléron, La Brée-les- Bains, Le Château d'Oléron, Le Grand-Village-Plage, ST Trojan-les-Bains. UNIMA ( Union des marais de La Charente Maritime) group of cities (Syndicats Intercommunaux) or associations for the management of marshes.

1.4 Designation (protected areas)

IGN map, 25 000e, 1330 OT

2. MODERN HUMAN GEOGRAPHY

The main activity of the island, together with fishing and oyster-farming, is tourism. Its population is 19 000 during the winter.

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

The north of the island is a hard rocky coast of jurassic limestone. To the west the coast is composed of a narrow sandy foredune lying on a rocky cenomanian substrate which isolates the littoral marshes from the ocean. The southern oceanic side and the north-eastern bay side are characteristic dune accreting coasts (massif de saint trojan and massif des saumonards). Soft muddy coasts with wide intertidal mud flats are located on the south-eastern side of the island facing the Marennes Oléron bay.

The coastal cliffs of the northern part of the island experience a maximum erosion of 20 to 30cm/yr. The dune accreting coasts to the south-east and the north-west are generally eroding except the Massif des Saumonards and the Pointe de Gasteau which are in accretion. To the east the dune coast ,which isolates littoral swamps, has a rate of erosion of 60 to 70cm/yr. The soft muddy coast in the south-western part of the island is slowly accreting (a few centimeters per year). Only the sandy ridge of the Pointe de Bellevue is accreting south-eastwards involving erosion to the north and an infilling of the internal part of the bay.

2 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

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

4.1 Sedimentological and palaeo-environmental data concerning the study area

At the begining of the Holocene the sea invaded the river valleys formed by erosion during the last glaciation. A deep ria system developed. During the last stages of sea-level rise, the Pertuis de Maumusson channel (20m deep), separated the island from the continent.

Since 6000 years B.P., constant coastal changes have occurred: the western rocky, wave dominated coast underwent intensive erosion . The Atlantic south-western coast, supplied by littoral drift, accreted to constitute the Saint-Trojan dune system. On the less dynamic bay coasts, the wide mudflats were supplied with fluvio-marine sediments from the Charente and the Seudre rivers. Another important accreting dune system lies on the eastern coast (massif des Saumonards). 50% of the island is situated below the altitude of 5m NGF.

4.2 Archaeological data concerning the study area (see Appendix P14.1 and Figure P14.3)

The island was continuously occupied from the Palaeolithic to the Modern ages. 33 sites are known on the island but 18 of them are particularly representative. The Neolithic period is the most well representated. The Gallo-Roman, Medieval and Modern sites are found everywhere except in the south probably due to the presence of sandy dune systems. The study of 4 Neolithic sites (La Perroche , Ponthezière L'Ecuissière and Ors) located on Oléron Island were used to specify micro-scale coastal changes.

5. THE PALAEO-ENVIRONMENTAL AND ARCHAEOLOGICAL POTENTIAL

5.1 Interpretation of the sedimentary archives of the La Perroche marsh

We focused our investigations on a small marsh called La Perroche (Plate P14 and P14a) located on the south-western coast of Oleron Island to try to reconstruct coastal changes. This marsh is separated from the ocean by a narrow foredune and a dam and is surrounded by outcrops of Cenomanian limestone, forming the substrate of the Holocene deposits.The marsh has a flat surface lying around 1m NGF.

In order to determine the succession of Holocene palaeo-environments, more than 10 percussion corings were made. The study of the sedimentary sequences allowed a reconstruction of a succession of palaeo-environments which were characterised by their faunal (ostracods) assemblages. Using 14C dating a determination was made of the chronology of this evolution and the infilling of the marsh since the sea reached its present level around 6000 years ago.

Data and methods

Cores were collected over the whole marsh area (Figure P14.4, Table 1) and on the La Perroche beach from peat formations outcropping at low tide. 8 cores particularly representative of the sedimentary sequences were selected for this study : H 9602, H 9603, L 9818, L 9908 in the western part, L 9909 to the east, L 9817 to the south, L 9906 to the north and L 9910 on the beach.

The sedimentological study, based on lithological and grain-size analysis, allowed the definition of palaeo-environments in terms of dynamic processes and marine influences. Ostracods were counted and classified according to species. They were gathered in 4 associations belonging to 2 different environments (Yassini, 1969):

3 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

· Continental with fresh water and brackish water ostracods (Figure P14.5). · Marine s.l. composed of coastal and marine s.c.species (Figure P14.6). · Benthic foraminifera were mentionned in terms of presence/absence. · Charophytes, mainly consisting of gyrogonites, were semi-quantitatively evaluated.

These cores will be successively analysed, explaining the sedimentological and the microfauna data as well as the chronological information obtained by 14C dating. Each study will end with a brief summary of their characteristics in terms of palaeo-environments.

Macrofauna analysis was made on the core L 9906 giving more information on palaeo- environments. The variations in shell density and in the quantity of species observed gives us some understanding of the coastal changes which have occurred in the La Perroche marsh (Dupont 2000).

Geophysical analysis took place in the marsh to localise the sedimentary units observed in the cores and to measure the depth and the morphology of the calcareous substrate. Two methods were used in this study. The method of "pseudo-sections de résistivité" was used along 3 transects through the marsh and the method of "sondage électromagnétique en domaine temporel" (TDEM method) at 7 points in La Perroche marsh (Figure P14.7).

Results

The core H 9602 (Figure P14.8) is composed, from 4.5 to 3.6m depth, by coarse sands with pebbles, overlain from 3.6 to 2.2m by clays containing plant debris and silty laminations. The fauna appears at 3.1m in a layer of organic matter.. It is a very poor and varied fauna, composed successively by polyhaline waters species (Loxoconcha rhomboïdea) brackish and marine waters species (Cyprideis, Callistocythere), all calibrated and then probably displaced.

From 2.3 to 1.9m, silty sands with shell laminations appear containing predominantly brackish (Cyprideis torosa and Loxoconcha elliptica) and coastal water species while some marine species are also able to subsist.The brackish water fauna seem complete and are not displaced. Lots of foraminifera were observed in these sands showing a marine influence.

From 1.9 to 1.7m, clays with plant and shell debris develop. In this sequence, ostracods reach their maximum level (more than 1000 individuals), 50 % of them become freshwater species (Limnocythere inopinata, Candona sp.).

A peat layer without fauna is observed from 1.7 to 0.55m. It is overlain by 30cm of clay, 10cm of peat and 5cm of organic soil. In clay at around 40cm depth, a rich freshwater fauna (Limnocythere and Cypris bispinosa) develops.

14C dating (Table 2) gave the base of the peat layer as 4870+/-50 years B.P. (1.6m) and the top of the peat layer as 3740+/-50 years B.P. (55cm).

In conclusion, the core H 9602 shows, at the base, an erosion of calcareous substrate due to a high level of energy. Then, there is a first period of infilling: the link with the sea allowed the intrusion of marine to brackish fauna. Next, peat deposits indicate swamp formation in which the acidity of the water does not allow the preservation of calcareous fauna. Finally, at the top of the core, the swamp is submerged again by continental water indicating that communication with the sea is cut off.

The core H 9603 (Figure O8) shows successively, from the base, at 3m depth, 80cm of calcareous substrate, 10cm of clay, 10cm of coarse sands and 10cm of clay with silty-sandy laminations. Then, between 1.9 and 1.2m, azoïc silty sands with a bed of gravel at the base are

4 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France observed. Between 1.2m and 0.7cm, medium silty sand is found with a level of shell debris at around 90cm. This sand contains few ostracods (less than 10 individuals) indicating brackish to coastal influences. Foraminifera are present in this core until a depth of 40cm. From 70 to 30cm, clay with roots was found overlain at the top by a sandy soil. Around 30cm, a second period of ostracods development appears. It is composed principally by freshwater species (80 %) with around 40 individuals.

This core confirms that, after the erosion of the cenomanian substrate, the infilling of the La Perroche depression by a succession of clay and sand layers occurred with the presence of some displaced coastal fauna indicating a "marine" invasion. Peat bogs are not well developed here impling that the swamp formation, in this part of the marsh, was very fleeting. At the top, the aeolian silty-sandy deposits, in which the marine and coastal fauna disappeared, show the disconnection with the ocean.

The core L 9818 (Figure P14.9) is 4.4m in length and is composed, from the base, of 20cm of cenomanian calcareous deposits, covered by 40cm of fine sands then by 1.2m of coarse sands with pebbles in a silty matrix. Above, is 70cm of clay containing mollusc debris at the top. In this clay, an abundant fauna is observed (reaching 2300 individuals at 1.8m) composed of brackish water organisms dominated by Cyprideis torosa species. A few freshwater ostracods, foraminifera and charophytes are also present.

From 1.8 to 1.5m, shelly sand without microfauna is observed. This is overlain by 1.3m of peat with charophytes. From 1.4 to 1.2m, freshwater species (Limnocythere inopinata, Cypridopsis vidua, Candona sp.div.) increase until they represent 70% of the total fauna against 30% of brackish water species. A quantity of 4000 individuals is reached at 1.35m. Foraminifera are present from 1.4 to 1.2m. In comparaison with the last sedimentological sequence, the composition of the brackish water fauna has not changed but there is a reduction in their quantity.

The top of this core is formed by 15cm of clay covered by 5cm of organic matter. Freshwater and brackish water fauna are found at the top: around 35 individuals, 30% of which are freshwater species. Foraminifera and charophytes are also observed.

The top and the base of the peat layer were 14C dated (Table 2): 5290+/-50 years B.P.(1.45m on peat) and 3630+/-50 years B.P. (20cm on peat). AMS 14C dating on ostracods at 1.85m gave an age of 5850+/-40 years B.P.

In conclusion, L 9818 shows, after the erosion of the cenomanian limestone, a flooding period due to the establishment of communication with the ocean and water accumulated from hinterland drainage. This led to the development of essentially a brackish water fauna. The progressive building of a coastal sandy dune, which decreases the marine input, is marked by a change in the composition of fauna which begins to show a freshwater influence. Then, a swamp without fauna develops. The end of the sequence is characterized by a new invasion of "melting" waters which can be linked to episodic opening of the sandy dune system.

The core L 9908 (Figure P14.9) is the longest core taken from the marsh (around 5m). At the base, 50cm of calcareous pebbles are overlain by clay and then by alternating layers of coarse sand with gravel and silty sand (from 4.4 to 3.8m, from 3.7 to 3.2m, from 2.9 to 2.6m) or a sandy clay (from 3.8 to 3.7m, from 3.2 to 2.9m, from 2.6 to 1.6m). Mollusc debris appears from 2.3 to 1.6m. At around 2.3m, brackish water ostracods develop in clay, progressively becoming freshwater species until 2.15m. At this depth, the quantity of ostracods is low: a maximum of 50 individuals is reached around 2.25m. An azoïc peat level develops in clay from 2.06 to 1.97m. From 1.6 to 0.85m, a thick peat layer without fauna appears. Then, from 85cm to the top 60cm of sand, 13cm of clay and 12cm of organic soil are observed. From 85 to 60cm, ostracods, essentially brackish water forms, are present in fine sand. Progressively coastal water ostracods appear at the top of this level. This coastal fauna, generaly represented by juvenile

5 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France forms and then probably displaced, characterize a marine invasion and could here underline a chenalisation effect as presently observed in the Gironde Estuary (Carbonel 1980).Finally, few fresh and brackish water species are observed in clay at the top of the core. Foraminifera appear at the same time as ostracods from 2.5 to 2.1m and from 80 to 40cm. Few charophytes are present between 90 and 75cm.

14C dating (Table 2) on the peat layer, gave the following results : 5270+/-70 years B.P. (197.5- 200cm), 4880+/-70 years B.P. (157.5-162.5cm) and 4140+/-70 years B.P. (92.5-95cm).

In conclusion, the core L 9908 shows, at its base, high energy conditions particularly marked by detritus deposits in which some episodes of clay sedimentation occurred. Next, the dynamic of the environment decreases allowing the development of fresh and brackish water species. Then, follows swamp formation where the acid conditions do not permit the development of microfauna. Then, a second, probably very short, period of marine invasion occurs bringing displaced coastal fauna.

The core L 9909 (Figure P14.10) shows from its base at 4.2m until 2.2m, a succesion of clay and calcareous pebbles in a silty matrix with some sandy laminations corresponding to a reworking of the substrate.

From 2.2m to the top, an accumulation of coarse sands with pebbles is observed. No fauna or flora were found in the sediments of this core.

The deposits of L 9909 are different from the others. They demonstrate the presence of a high level of energy permitting rapid and early infilling of this site, preventing later deposition.

The core L 9817 (Figure P14.10) was taken near the sandy dune system. From the base, at a depth of 3.7m to 1.2m, a clay layer overlays a bed of pebbles corresponding to the remains of the calcareous substrate. From 3.2 to 2.9m, a layer of micaceous sands is observed. Microfauna analysis showed homogeneous fauna composed of more than 90 % freshwater species. The other 10% corresponds to brackish water ostracods with some coastal water forms. At 2.9m, numerous brackish (Loxoconcha elliptica) and coastal water (Aurila convexa) ostracods are present with shells debris. From 2.8 to 1.7m, the freshwater forms are dominant with the species Cypridopsis vidua, Limocythere inopinata and Candona sp.div.. 1000 individuals were recorded around 1.7m. From 1.7m to 1.2m, the number of freshwater ostracods reaches 5000 individuals around 1.3m. An increase in the quantity of Cypridopsis and of Limocythere occurs while the quantity of Candona decreases. Ostracods disappear then around 1.2m. Few foraminifera are observed from 2.9 to 1.2m. Some rare charophytes appear at 2.5m and then disappear. They were found again in low quantities from 1.65m, then they increased between 1.4 and 1m to disappear at this point.

The top of the core is composed of a peat layer between 1.1 and 0.82m, azoïc fine sand between 80 and 35cm, and finally an accumulation of 30cm of black organic matter without fauna.

Three 14C dates (Table 2) were obtained. The first one gives an age of 2070+/-70 years B.P for the base of the peat level (1.1m). The other dates (AMS) in clay give respectively at 1.6m: 2710+/-40 years B.P.(on ostracods) and at 2.9 m : 3080+/-40 years B.P.(on shell debris).

Despite its geographical location near the sandy dune system, the core L 9817 is less exposed to marine influences than the others. This core shows a relatively homogeneous sedimentary sequence composed almost exclusively of clay. Early in the core, the majority of the species are brackish water forms with a few marine s.l. individuals demonstrating here an invasion from two different origin. Firstly, the marsh is connected with the sea and the penetration of marine water permitted the development of marine water ostracods. Secondly, the presence of freshwater fauna indicate the beginning of a cutting off from the sea and the penetration of

6 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France freshwater from rain and hinterland drainage. Then, 14C dating indicates a more recent sedimentation than those in the other cores in which brackish to marine water faunas were observed.

The core L 9906 (Figure P14.11) shows at its base (4.2m), 30cm of calcareous pebbles coming from the erosion of the cenomanian substrate. They are overlain by alternating coarse sandy layers and pebbles (from 3.85 to 2.7m, from 2.33 to 1.2m, from 96 to 65cm) and clay (from 2.7 to 2.33m, from 1.2 to 0.96m, from 65 to 35cm). Shell debris is present in the core from 1.2 to 0.65m. The top is formed by an accumulation of organic debris of 35cm. Few foraminifera are observed from 1.3 to 0.9m and from 35 to 10cm. Charophytes are found from 50cm to the top. Ostracods appear from 1.3 to 0.65m in clay and fine, silty, shelly sand and from 40 to 10cm in clay and in organic matter at the top. From a depth of 1.3 to 0.95m, a majority of brackish water fauna (Loxoconcha elliptica) is observed with only a few freshwater species and rarely any coastal water species. A peak of 400 individuals is reached around 1.05m. Coastal ostracods are juvenile, calibrated, and then may be displaced. From 95 to 60cm, the number of brackish water species increase in ratio with the freshwater ones. The coastal species appear around 95cm and disappear around 65cm. The quantity of juvenile, displaced, coastal fauna is here more important (380 individuals at 90cm). Proportionally, the flux of the displaced fauna is higher during this period. From 1.3 to 0.95m, a brackish environnment develops with short and repeated marine influences. At 60cm, we observe a return to brackish conditions. From 40 to 10cm, freshwater ostracods (Candona, Cypridopsis), which represent the total fauna at 40cm, are progressively replaced from 35cm by brackish waters ostracods (Cyprideis).

14C dating (Table 2) at 97 cm (AMS on Ostracods) gave an age of 3170+/-40 years B.P..

The core L 9906, which is near the landward extremity of the marsh, has no peat layer. The period of fauna development correlates with those observed in core H 9602, except at the top where the presence of brackish fauna can be explained by an opening of the coastal dune allowing the penetration of a small quantity of marine water to this site which is at the north of the marsh.

To study the global evolution of the palaeo-environments using malacofauna analysis, the shells of core L 9906 were gathered in five groups (Gruet et al, 2000):

N°1: an open marine environment (open intertidal zone). N°2: a marine environment subject to tides with the beginning of isolation from the marsh (estuarine zone). N°3: shells showing an environment subject to tides with a more isolated marsh (lagoonal zone) N°4: a brackish water environment (marshly zone with ditches and channels). N°5: a freshwater environment (terrestrial zone).

The malacofauna analysis at the base of core L9906 showed an environment open to the sea, but no major variation can be described from the observation of the specific associations (Figure P14.12). The only variations observed are the presence of some remains from group N°1 and the rocky environment at the base of the core. This seems to indicate the presence of a rocky coast in the vicinity. Then, after a hiatus in the malacofauna, the environment seems to have fundamentally changed with inputs of both marine and fresh waters. Had there been anthropogenic influences in the marsh at that time, or had the seasonal variations caused the fresh and marine water species to succeed each other? The environment is largely enclosed and the water becomes stagnant and brackish . Only a light marine water influence can be noted from 35 to 27.5cm. Then, the marine influence disapears progressively, giving place to molluscs living in stagnant, fresh water rich in vegetable matter (group N°4).

As for marine molluscs, the continental ones are subject to numerous factors affecting their distribution. If the degree of humidity and the temperature are the principal factors other factors, such as the nature of the soil, o the underground, and the vegetation on the surface,

7 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France can act also. According to the characteristics of an environment, we obtain associations of species or ecological groups. A classification was developed by Puissegur (1976) dividing the continental molluscs into groups of ten going from the most woody environment to the most marine and humid environment. A similar classification has been applied to continental samples of core L 9906. With the exception of Cochlicella ventricosa living near the ocean and on the dunes, all the other species belong to group 10 defined by Puissegur. Valvata cristata belongs to A1 sub-group: "stagnant water rich in plants: marsh"; Anisus leucostomus, to A2 sub-group: "periodic marsh" and Acroloxus lacustris, Anisus crista, Radix peregra, Stagnicola palustris to A3 sub-group: "calm waters (ditches,lakes,¼), but not many aquatic plants". The freshwater species are all typically from stagnant waters : the peat is established.

The core L 9910 (Figure P14.11) was taken in a peat layer outcropping on the beach of La Perroche at low tide. From the base to a thickness of 70cm silty clay is overlain, to the top, by a peat layer of 40cm. A unique episode of fauna development is found from 30 to 20cm depth. It is only composed of freshwater ostracods (Candona sp.div., Cypridopsis vidua) with a maximum of 160 individuals at 20cm. No foraminifera were observed. Few charophytes are present from 30 to 20cm.

The sedimentary record of this core demonstrate low energy conditions. Fauna appear only at the base of the peat and correspond to a freshwater environnment without a marine influence (no brackish fauna, no foraminifera, but some freshwater molluscs). The top of the peat is azoïc and perforated by actual molluscs.

The "speudo-sections de résistivité" method allows an image to be obtained of the morphology of the substrate and of the superficial formations.

· Transect 1: (Figure P14.13) along this transect, oriented NE-SW, perpendicular to the La Perroche-Bussac way, the resistivities are generaly low. The "speudo-section inversée" allows the definition of three different layers from the base to the top: a layer with a high resistivity > than 22 ohm.m (purple to yellow layers), a layer with a resistivity between 6 and 20 ohm.m (green layers) and then local areas with a resistivity lower than 5 ohm.m (blue layers).

· Transect 2: (Figure P14.14) in this transect, located at 500m to the N-E of transect 1, we observe two of the three units previously observed in transect 1: the first one comprises a layer with high resistivity > than 22 ohm.m at the base and at the top of the profile (red to yellow layers), and the second one comprises a layer in the middle part of the profile with a resistivity between 6 and 20 ohm.m (green layers).

· Transect 3: (Figure P14.15) in the last transect, located at the border of the departmental road, we observe the same three resistivity units described in transect 1: layers with high resistivities > than 22 ohm.m (purple to yellow layers) are located at the base and at the top of the profile. The layers with a resistivity of between 6 and 20 ohm.m (green layers) are mainly located in the middle of the profile. Low resistivity (< than 6 ohm.m) is observed near the surface up to a depth of 8 meters.

The "sondage TDEM" method uses induction to create an electric field in the ground. Seven "sondage TDEM" (Figure P14.16) were taken with different scales. We found at the top a layer with a thickness less than 1 meter and a very low resistivity. Below this layer, we have two different types of layer. The stations 2, 4, 5, 6 and 7 show a layer of 3 to 10m with very high resistivity (more than 1000 ohm.m). The stations 1, 2 and 9 show a layer with high conductivity (less than 50 ohm.m). Then below, we define a deep layer with a resistivity of between 5 and 15 ohm.m.

8 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Discussion

Previously, no detailed study has been undertaken in the La Perroche marsh. Only peat layers discovered at low tide on the beach and located just behind the coastal dune, have been described (Pineau 1891, Welsch 1969). In 1972, Gabet undertook three corings in these peat layers. The deepest reached 1.7m showing shelly sand with quartz under a peat layer of 1.3m thick. Two peat samples at 30cm depth (to avoid surface contamination from pholads and annelids) and at 1.3m were 14C dated. The results were respectively 3600+/-100 years B.P. and 4920+/-110 years B.P..

To complete the results of the core analysis and to reconstruct the chronology of coastal changes, we gathered the 8 cores in two transects through the marsh, the first one is orientated S-N (transect A, Figure P14.17 : L 9910, L9817, H 9603, L 9818, L 9906), the second NW-E (transect B, Figure P14.18 : L 9908, H 9603, H 9602, L 9909).

On transect A (Figure O17), we observed an important sandy-gravely unit in the northern part of the marsh. It corresponds to the erosion of the calcareous substrate and was deposited by a high fluviatile dynamic linked to deglaciation (André 1986).

A comparison of the ages of the peat layers indicates two episodes of peat development. The first appears between 5000 and 3500 years B.P. These dates correlate with those obtained by Gabet (1973). This episode corresponds to a major period of swamp formation, the evidence of which outcrops on the beach and in the western part of the marsh.

A second period of peat development occurs after 2100 years B.P. It is only recorded at site L 9817 and indicates a more recent period of marsh isolation. This site is located on a high point of the substrate. Due to the nature of the sediment and the 14C ages obtained, the core L 9817 can be interpreted as a tidal channel formed in more ancient deposits during the second period of invasion in the marsh (since 3500 B.P).

The cores of transect B (Figure P14.18) show only the first episode of swamp development observed in transect A (5000-3500 years B.P.). The sandy-gravely unit observed previously at the head of the marsh, also develops on its eastern side where gravel is quarried (at site L 9909).

These two peat layers indicate the development of a swamp during the period of marsh isolation. Detailed observations of these peat levels show that they are eroded at the top. The 14C dating undertaken at the top of these peat layers does not allow an accurate determination of when their development stopped.

In consequence, the transgression period following the end of the first generation of swamp formation can be estimated between 3500 and 2100 years B.P., when the second generation appears. This break in swamp development estimated at around 2800 years B.P. can be interpreted as a positive sea-level tendency (Shennan, 1986). In this period, in the Gironde Estuary, many indicators of a high sea level were found. Around 2800 years B.P., in the estuary, the shelly chenier ridge of Richard develops, indicating a period of high dynamic (Pontee et al. 1998). Moreover, in other estuarine marshes, near the mouth of the Gironde, sediments dated to this period show a positive sea-level tendency.

The quantity and the well preserved nature of the malacofauna studied in core L 9906 has furthered our understanding of the evolution of the La Perroche marsh. Three periods of palaeo-environmental change can be distinguished (Dupont, 2000). Firstly,there is a period when marine influences ocurred. Then, after a sedimentary hiatus or a period of shell dissolution, both marine and continental influences are recognised in the sediments with a predominance of freshwater species. After the disapperarnce of shelly material between 377.5 to 150cm, we observe a tidal-dominated environment, enclosed from 127.5 to 62.5cm in the

9 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France proximity of a rocky coast. Estuarine conditions could be present in this area at this time. At 3170+/-40 years B.P.(14C dated) it was an enclosed environment subject to tidal influence. Then, after a reduction in shelly deposits, we observe both brackish and freshwater influences and progressively the marine influences disappear. A natural or anthropogenic infilling of the marsh occurred. Comtemporaneous coastline formation involved the infilling of the bays, becoming marshes.

This core does not provide definitive relative variation of sea-level. The altitude of the marine deposits observed in this core are in agreement with the present-day sea-level. On the other hand, even if we suppose a cramming of the peat layer, the level of the freshwater fauna is located in the intertidal zone. So, we have to suppose that the bay is closed by a sandy ridge to which could be added a hydraulic system controlling the penetration of the ocean into the marsh and the evacuation of fresh water.

The results given by geophysical analysis in the La Perroche marsh permitted the definition of four different layers corresponding respectively to (Figure P14.19):

· The calcareous substratum at the base: layers with high resistivity, appearing near the surface in transect 2 and separated in the middle by a layer with a lower resistivity. In the transects 1 and 3, these formations are present in most parts of the profiles. · A complex layer with a middle resistivity, probably corresponding to sand, which from the east go deeply to the west (transects 1 and 3). · Layers with very low resistivities which disappear to the N-E. They are well represented in transects 1 and 3. In this last transect, they form a channel which can reach a depth of 8m and can be interpreted as clay or peat. · Surface layer with high resistivity corresponding to hard surface structures (roads, car parks etc)

Information gained from the sedimentary archives and the geophysical analysis show an east- west asymmetry in the infilling of the marsh. Its evolution, subject to local influences, is driven by global parameters.

During the last glacial period and at the end of deglaciation, 10 000 years ago, Oléron Island looked like a vast calcareous platform due to “tectonic activity and important eolian erosion during the plio-quaternary regressive periods”. This platform was then connected with the continent (André 1986).

The ice melting led to the sea-level rising and reaching its current level around 6000 years B.P.. The flandrian transgression permitted the invasion of remote coastal depressions. Oléron became an island around 5500 years B.P..

The infilling of the La Perroche marsh began with a sea-level rise. The sandy-gravely units correspond to ancient alluvial terraces formed by an important fluviatile dynamic during the glacial break due to cooling (André, 1986). This infilling is demonstrated by the presence, at the base of the cores, of coarse sand with pebbles, coming from the erosion of the substrate. A more important fluviatile input may occur at the east leading to a more rapid and complete sandy-gravely infilling in this part of the marsh (L 9909 and L 9905) inducing an east-west asymmetry in the deposits.

In the western part, the infilling continues by the formation of silty-sandy levels often shelly containing characteristic fauna of brackish water conditions and showing some coastal to marine water species (cores H 9602, H 9603 and L 9906). This episode indicates a progressive closing of the La Perroche depression due to the formation of a high sandy foredune. The marsh then appeared like a brackish lagoon communicating with the ocean by a channel which allowed the penetration of marine water up to the sites of cores H 9602, H 9603 and L 9906.

10 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

The observations of ostracod fauna showed that coastal and marine species found in core L 9906 correspond to displaced individuals. It seemed that the marine water did not penetrate into the marsh until the L 9906 site but that the tidal currents permitted the displacement of part of the marine fauna up until the northern part of the marsh.

Then, an increase in the coastal dune system led to the closing of the depression in which, due to the accumulation of fresh water, aquatic plants developed. This episode, marked by the formation of a peat layer in the whole study area, is dated from 5290 to 3630 years B.P.(H 9606, L 9818 and L 9908). Dates given by Gabet in 1973 on the coastal peat layers of the La Perroche bay, confirmed the period of this peat layer formation and indicated that the marsh had had a more important extension seaward than was presently the case. The sea-level rise led to rocky coast erosion and to the migration of the sandy foredune north-eastward due to the action of dominant winds. It is probably around 2800 years B.P., that a positive tendency of sea- level occurred and stopped the coastal swamp developing and top erosion by the establisment of a tidal dynamic.

After the infilling of the tidal channels a new period of marsh development occurred. At the top of the cores, between 2830 and 2070 years B.P.(L 9906 and L 9817), we observe peat or silty formation containing essentially fresh and brackish water faunas. This situation corresponds to an alternating period of definite closure of the marsh with short and episodic periods of opening in the sandy dunes whilst the accumulation of fresh water due essentially to rain and hinterland drainagecontinues.

Conclusions

This study has shown an evolution of La Perroche marsh in five steps:

1. Erosion of the calcareous substrate and deposition of a sandy-gravely unit under fluvial dynamic. This essentially happens during deglaciation. The deposits invade the eastern part of the La Perroche depression, preventing later deposition. 2. A rise in sea-level and invasion of the depression after 6000 years B.P.; at the west, sand and clay formations containing brackish to coastal water species develop (H 9602, H 9603 and L 9906). 3. Formation of a coastal sandy dune system stopping communication with the ocean. The fauna become fresh to brackish water species. This fauna disappears with the establishment of a swamp in the whole study area (between 5000 and 3500 years B.P.). 4. Short and episodic re-opening of the coastal dune barrier responsible for transitions between brackish (L 9817), coastal (H 9602) and fresh water draining from the catchment area (H 9602). 5. Closure of the coastal sandy dune and return to swamp development from 2000 years B.P.(L 9818).

The story of the infilling of La Perroche marsh is then linked to both local (moving of the sandy dunes and location of the channel permitting the inputs of marine water) and the global (post- glacial erosion, the sea-level rise) events which have effected the area since 10 000 years B.P.

5.2 Archaeological potential of the Southwestern Coast (Plate P14b)

To study the coastal changes, four archaeological sites were chosen on the western and southern coasts of Oléron Island (Laporte et al, 1998; Laporte et al, 1995).

11 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

The La Perroche site

The La Perroche site is located on the edge of the marsh near the sandy dune system, on a small rocky promontory (Laporte et al 1996). This site was buried under marsh sediments after the Bronze Age period. It was discovered during a trench recalibration to improve drainage of the marsh. Calcareous blocks on the substrate seem to indicate the location of buildings. The archaeological layer outcrops for100m. It is progressively overlain by silty sediments as the substrate disappears under the marsh. Abundant archaeological remains were found: ceramic shards, lithic industry, bones and shells. One part belongs to the Artenacian period (cultural group from the Late Neolithic period, from 2000 to 1800 years B.C., in central western France). Most of the ceramic ornaments were gained using the technique of "poinçonné-tiré". Some elements lead us to believe that there has been continuous occupation until the beginning of the Bronze Age. Actually, an excavation (a ditch of 10m in length) allowed the discovery of abundant furniture, marine fauna and numerous scories of metallurgy.

The Ponthezière site

This site is located a few kilometers from the sea (Soler 2000), on the western coast of Oléron Island. The site is in the middle of a small depression, on the edge of a freshwater marsh which is separated from the ocean by a narrow sandy dune system. Four excavations, taking place between 1988 to 1991, allowed the removal of 500 m3 of soil (the total suface reached 2ha). Under 30 to 40cm of soil, lies a unique archaeological layer from the Artenacian period (Late Neolithic). A part of an uninterrupted ditch and the base of several buildings were discovered. This site seems to correspond to a particular skilled activity: the making of discoid pearls from shells.

L'Ecuissière site

In the Passe de l'Ecuissière, a peat layer outcrops on the beach and extends over 60m seawards (Bougeant, 2000). In this place, ceramics from the Peu-Richard period (Early Neolithic period, from 2200 to 2000 years B.C.) and abundant furniture of the same period were discovered. A few connected human bones were found in the axis of the channel, at the top of the peat layer.

To the south on top of the peat, furnitures from the Campaniforme period (Late Neolithic period, from 1800 to 1700 years B.C.) were found. In some places, several settlement structures appeared but they were rapidly destroyed by the sea.

New studies showed that the site extended under the sand of the beach. Excavations, from the surface to a depth of 8m, allowed the discovery of settlement structures, abundant organic material and a copper nodule linked to primitive metallurgy.

The Ors site (Terre Doux)

The Ors site corresponds to the south-eastern extremity of the island (Rubion 2000). The archaeological layer outcrops in the intertidal zone and at the promontory of Ors. The surface of the site is probably over 5ha. Excavations on this site delivered abundant furniture from the Peu-Richard period (Early Neolithic period) and stony srtuctures thought to be walls. Above these levels, a layer containing Artenacian artefacts was discovered. Some remains of a Bronze Age settlement were found (and possible middle neolithic furnitures).

12 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

A 20m wide megalith, found in 1884, is present in the middle of this settlement. Human bones were found close to the megalith associated with furnitures (ceramics from the Peu-Richard period, Early Neolithic period). The monument may contained a few megalithic chambers.

New studies focused on a ditch showing a settlement level from the Middle Neolithic overlain by 50cm of clay. Abundant furnitures were discovered.

Discussion

These archaeological remains help us to reconstruct the coastal changes and the location of the shoreline along the coast of Oléron Island. This information linked to the palaeo- environmental remains and a knowledge of coastal processes allows a good understanding of the coastal evolution of the island.

The presence of important littoral peatbogs with archaeological remains (La Perroche and L'Ecuissière sites) observed on the beaches on the south-western coast are evidence of sea level changes and show the active erosion of this part of the island. On the south-eastern coast, mudflat accretion led to a progressive infilling of depressions, thus preserving numerous archaeological sites.

6. CURRENT APPROACH TO THE PALAEO-ENVIRONMENTAL RESULTS

New cores were collected in the marsh and on La Perroche beach to complete the results obtained from previous surveys. Sedimentological and micropalaeontological analysis could improve our understanding of past sea-level variations and help in predicting its future evolution.

7. SUCCESSES AND PROBLEMS IDENTIFIED BY THE LIFE PROGRAM

These studies supported by the LIFE program have permitted an understanding of the Holocene evolution of Oleron Island. Understanding of the palaeo-environmental evolution which has taken place over the last 10 000 years allows provision for future coastal changes to be made.

In the La Perroche marsh study area there is evidence of global fluctuations in sea-levels. The palaeo-environmental analysis gives us evidence of two positive tendencies of the sea-level, around 6000 (ostracods analysis) and 3000 years B.P.(sedimentological data). Moreover, two negative tendencies of the sea-level appear around 5000 and 3000 years B.P.(sedimentological data).

8. COMMUNITY INVOLVEMENT ISSUES AND SOCIAL INCLUSION

8.1 Funding agency

Regional and local Councils : the Conseil Régional Poitou-Charentes and the Conseil Général de Charente-Maritime can, with or without the State, subsidize research or managment studies on the coastal zone, upon the request of a city council or of a group of cities. The Service Régional de l'Archéologie Poitou-Charentes, which depends on the Ministry of Culture, is the authority which grants authorization for an excavation and supports, at least partially, archaeological research.

13 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

8.2 Investigation and monitoring

A "Plan de Prévention des Risques de Submersion" (PPR: Prevention Plan of flooding Risks) is being made by the DDE (Direction Départementale de l'Equipement) and funded by the State. The DDE and the "Service Maritime" are levelling the coastline with a GPS. A private company funded by the State is evaluating the sedimentary processes along the coast.

8.3 Current status and action

Some action is in progress funded by the State, the Conseil Général and the cities,: the parts of the frontal dyke, damaged by the 27th December 1999 storm, are under repair and are being extended by wood or rock defences; some beaches have been supplied with sand. In addition, the Dune des Seulières in the city of Saint-Denis-d'Oléron is protected from aeolian erosion by fences ("barrières de Gironde") reinforced once a year; this operation is funded by the Conseil Général.

8.4 Public awareness

There is no accurate public awareness of coastal problems, apart from information given by the media or by elected members in periodic city reviews.

8.5 Experiences, sucesses and problems with current approach

The methods of hard defences used in the past against coastal erosion produced significant problems, in terms of sediment dynamics, and have been more or less abandoned in favour of soft intervention. The "fence method" used to protect the dune allows seaward accretion at a rate of 30 to 50cm/yr.

9. CONCLUSIONS

9.1 Threats

The beach and dune erosion and the danger of submersion of the saltmarshes are the main threats on the Oleron coastline.

The coastal cliffs of the northern part of the island are subject to a maximum erosion of 20 to 30cm/yr and, at the west, the dune coast isolating littoral swamps has a rate of erosion of 60 to 70cm/yr. The south-western and north-eastern coasts (Massif des Saumonards and Pointe de Gasteau) are accreting. The soft muddy coasts in the south-eastern part of the island show a low accretion rate (few centimeters per year).

9.2 Management needs

The different authorities are waiting for the results of the studies presently in progress before developing new managment plans. Only soft methods are currently being used.

10. KEY ISSUES

The variety of coastlines around Oléron Island makes this island an excellent example for the study of coastal changes. The sediment archives of La Perroche bay are representative of a marine marsh and completes the results obtained in the Gironde estuary marshes.

14 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Finally, Oléron Island is particularly rich in archaeological remains, and numerous sites situated in the intertidal zone are especially helpful in the reconstruction of coastal changes. The fact that the authorities are waiting for the results of the investigation in progress to develop new managment plans, demonstrates a new awareness amongst official staff. This was not always the case in the past.

11. BIBLIOGRAPHY

André A., (1986), Elaboration et analyse de cartes bathymétriques détaillées du proche plateau vendéo-charentais (Golfe de Gascogne), Reconstitution des paléorivages de la transgression holocène, Th 3 ème cycle, Univ.Bx I,1-274. Bougeant P. (2000). Demande de sauvetage sur l'habitat campaniforme de l'Ecuissière, Rapport, 3 p. Carbonel P., (1980), Les Ostracodes et leur intérêt dans la définition des écosystèmes estuariens et de la plateforme continentale. Essais d'application à des domaines anciens, Réf, Mémoires IGBA, 11, 1-350. Dupont C.,(2000), Rapport sur la carotte L9906 du marais de "La Perroche", rapport d'activité sur les analyses malacologiques, 13 p. Laporte L, (1994), Parures et centres de production dans le Centre-Ouest de la France au Néolithique Final, Th 3 ème cycle, Univ. I,1-231. Laporte L., de Regibus J.P., de Regibus G., Ricoux C. and Rodien-Laire C.(1995). Inventaire archéologique de l'Ile d'Oléron: premiers résultats. Bull. Amarai, 8 p. Laporte L, Bourhid J-R., Camarlynck D., Florsch N., Guerin R. and Le Mignot Y. (1996), La Perroche, Dolus/Saint Pierre d'Oléron, Charente-Maritime: Sondages. Rapport d'activité, 19 p. Laporte L., Cros J-P., Fontugne M., Geghardt A., Gruet Y., Marguerie D. and Oberlin C. (1998). Les ocupations néolithiques de la côte occidentale de l'Ile d'Oléron. L'Homme préhistorique et la mer, 120 éme Congrés CTHS, Aix en Provence, 21 p. Gabet C., (1973), Le banc de tourbe sur l’estran de la baie de Perroche (Ile d’Oléron), Bull. de la Société Archéologique et Historique de la Charente Maritime, 25, 297-307. Gruet Y., Dupont C., (2000), La Pêche des coquillages: reflets de l'environnement marin au Néolithique dans le Centre-Ouest de la France, 124e Congrès des sociètés historiques et scientifiques, in prep. Massé L.,Wang J., Tastet J.P. Vertical accretion of the Holocene infill of the Monards marsh (Barzan, Gironde Estuary, France) Quaternary International, in press. Pineau E., (1891), Nouvelle contribution à la géographie préhistorique des côtes occidentales de France, Assoc. Française pour l'avancement des Sciences, Congrés de Marseille, 206. Puissegur J.J, (1976), Mollusques continentaux quaternaires de Bourgognes, Thèse Univ.Quater.de Dijon, 3ème mémoires géologiques de l'Université de Dijon, Doin: Ed, Paris, 242 p. Pontee N, Tastet J.P., Massé L, (1998), Morphosedimentary evidence of Holocene coastal changes near the mouth of the Gironde and on the Médoc peninsula, SW Oceanologica Acta, 21 (2), 243-261. Rubion F.(2000). Demande de sondage sur l'enceinte supposée néolithique de Terdoux au Château d'Oléron, Rapport, 3 p. Shennan I., (1986), Flandrian sea-level changes in the Fenland II: tendencies of sea-level movement, altitudinal changes and local and regional factors, Journal of Quaternary Science, 1, 155-179. Soler L.(2000). Demande de fouille programmée sur les structures allongées de l'Ileau à Saint Georges d'Oléron (Marais de Ponthezière), Rapport, 3 p. Yassini, (1969), Ecologie des associations d'Ostracodes du Bassin d'Arcachon et du littoral atlantique : application à l'interprétation de quelques populaions du Tertiaire aquitain, Bull.Inst.Géol.Bassin Aquitain, n°7, 288. Welsch J., (1969), Les Lignites du littoral et les forêts submargées de l'Ouest de la France, Anthropologie, 23, 210-223.

15 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

12. ACKNOWLEDGEMENTS

We thank the Municipalities of Oleron Island, the D.D.E (Direction Départemental de l'Equipement), M.Gruet and Melle Dupont (malacofauna analysis) and all our partners for their active paticipation in the production of this document.

16 CORE LAMBERT II EXTENDED GRID ALTITUDE

NUMBER REFERENCE m (*N.G.F)

X Y

H 9602 318.280 2106.860 +0.52

H 9603 318.205 2106.810 +1

L 9817 318.260 2106.680 +2.086

L 9818 318.408 2107.240 +0.8

L 9906 318.720 2107.710 +0.85

L 9908 318.210 2107.110 +1.17

L 9909 318.550 2106.760 +1.02

L 9910 318.310 2106.450 +0.13

*Nivellement général de la France

Table 1 Core Locations, Oleron Island.

CORE Depth (cm) Age Calibrated Sample Ref. Meas.

NUMBER (years B.P.) Age type labo type

H 9602 55 3740+/-50 2335-1935 BC Plant debris Beta 102691 Trad

160 4870+/-50 3795-3395 BC Plant debris Beta 102692 Trad

L 9818 20 3630+/-50 2135-1885 BC Plant debris Beta 130951 Trad

145 5290+/-50 3945-3665 BC Plant debris Beta 130950 Trad

185 5850+/-40 4790-4605 BC Ostracods Beta 139287 AMS

L 9908 92-95 4140+/-70 2895-2485 BC Plant debris Beta 135316 Trad

157-162 4880+/-70 3790-3615 BC or 3595-3525 Plant debris Beta 135315 Trad

197-200 5270+/-70 BC Plant debris Beta 135314 Trad

4305-4305 BC or 4255-3960

BC

L 9817 110 2070+/-70 350-300 BC or 220BC-75 AD Plant debris Beta 130953 Trad

160 2710+/-40 920-805 BC Ostracods Beta 139285 AMS

290 3080+/-40 1425-1260 BC Shells Beta 139286 AMS

L 9906 97 3170+/-40 1515-1390 BC Ostracods Beta 139288 AMS

Table 2 14C dates obtained on samples from the La Perroche marsh, Oleron Island.

Figure P14.1 Location of Oléron Island. Figure P14.2 Geological map of Oléron Island. Figure P14.3 Location of the archaeological sites along the coasts of the island. Figure P14.4 The “La Perroche” marsh: location of the cores and Transects A and B (sedimentological analysis). Figure P14.5 Associations of Ostracods: Plate 1: Ostracods of the fresh water Association. Plate 2: Ostracods of the brackish water Association. Figure P14.6 Associations of Ostracods: Plate 3: Ostracods of the phytal-coastal Association. Plate 4: Ostracods of the marine Association. Figure P14.7 Location of the geophysical analysis in “La Perroche” marsh (“Sondages TDEM” and “Pseudo-sections de résistité” methods). Figure P14.8 Lithology of cores H 9602 and H 9603. Figure P14.9 Lithology of cores L 9818 and L 9908. Figure P14.10 Lithology of cores L 9909 and L 9817. Figure P14.11 Lithology of cores L 9906 and L 9910. Figure P14.12 Diagram of the malcofauna in core L 9906: palaeoenvironmental evolution. The shells were gathered in 5 groups characteristic of different environments: No1: an intertidal zone. No2: an estuarine zone. No3: a lagunar zone. No4: a marshly zone. No5: a continental zone. Figure P14.13 Geophysical results (the “Pseodo-résistivité” method): transect 1 through the marsh. Figure P14.14 Geophysical results (the “Pseodo-résistivité” method): transect 2 through the marsh. Figure P14.15 Geophysical results (the “Pseodo-résistivité” method): transect 3 through the marsh. The TDEM method

Figure P14.16 Geophysical results (the “TDEM” method). Figure P14.17 Sedimentological analysis: Transect A through the marsh (see Figure P14.4 for location). Figure P14.18 Sedimentological analysis: Transect B through the marsh (see Figure P14.4 for location). Figure P14.19 Interpretation of the geophysical profiles of resistivity: 1-Calcareous substrate, 2-Sandy gravely formation at the base of the depression infilling, 3-Clay and peat from the upper Holocene, 4-«Hard» surface structures (roads, parking,...) Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Plate P14aa The ‘La Perroche’ marsh with the archaeological site on the right

Plate P14ab Coring the ‘La Perroche’ marsh

17 Archaeological Inventory: Oleron Island

Cultural Visible Classificatio Coastal Sea-level Environment Climatic Running Unvalidated Coastal Unit Coastal Coastline Altitude Name Classification1 Source 1 Source 2 Description X Lamb2ext Y Lamb2ext Amenity Amenity Fragility n 2 Managment Change al Change Change Chronology Code Risk Context Type Value Bonus Early La Pointe des Surface site containing marine sheels and 5 to 10 m Surface site Neolithic OL1 578 315.6 2119.225 3 1 1 1 1 2 0 3 and 4 D E 1 and 2 hard coast Boulassiers several artefacts as flints and ceramics artefatcs

Les Prés artefatcs 5 to 10 m Moines (Les Surface site (tegula, OL2 13979 Discovery of these artefacts in a field 314.95 2118.75 4 1 0 0 1 0 3 I F 6 soft coast Bois Lattes) ceramics)

Le Pont de Burial fence, surface 5 to 10 m l'Angle artefacts OL3 13977 Surface site composed of burial fence 315.5 2118.4 4 1 0 0 1 0 0 3 I F 6 soft coast site (Pattenoutes)

building, Gallo-Roman settlement, four anthic basin La Croix 5 to 7.5 m Villa ceramics OL4 3430 probably for brine making or dedicate to the 317.1 2115.05 4 1 1 0 1 2 0 3 I F 6 soft coast Matelôt sherds conserving of fishing products

Layer of 5 cm containing traces of Late flints, pottery 2.5 m Ponthezière Settlement OL5 582 Neolithic settlement and remains of artisanal 313.13 2112.75 4 2 3 1 1 3 0 3 I F 6 soft coast sherds activity for shells ornament production

La Conche campaniform Neolithic artefacts in peat layers outcroping 0 to 2.5 m Surface site OL6 8122 312 2112.25 3 3 2 1 1 2 0 4 D E 4 soft coast Madame artefatcs on the beach

Gallo-Roman building, flints Surface site with Gallo-Roman ceramics and 4 to 5 m Méré settlement, medieval OL7 3334 323.25 2107.5 4 2 1 1 3 2 2 0 I F 6 soft coast pottery remains of artisanals basins fortified settlement

building, Stratified settlement (70 cm) from the Late pottery Neolithic showing artisanal activities linked to 2.5 m La Perroche Stratified settlement sherds, OL8 8101 318.2 2106.75 2 2 3 2 1 3 0 3 I F 6 soft coast the ornament production and to the primitive copper copper metallurgy metallurgy

La Perroche Neolithic artefacts in peat layers outcroping 0 to 2.5 m Surface site artefacts OL9 8102 318.55 2106.4 2 2 3 2 1 3 0 3 I E 4 soft coast Plage on the La Perroche beach

La Rémigeasse ceramic Gallo Roman settlement (villa) discovery of 2.5 to 5 m Settlement (villa) OL10 13953 319.025 2105.925 3 1 1 0 1 0 0 3 I E 3 dune coast (les building buldings and ceramics Renfermis)

Les Sables ceramic Gallo Roman villa with ceramics and 5 to 7.5 m Settlement (villa) OL11 12793 319.525 2105.475 3 1 1 0 1 0 0 3 I E 3 dune coast (Les Gatines) building buldings

L'Ecuissière bulding, Discovery of Gallo Roman villa with bulding 5 to 7.5m (Le Renclos Settlement, villa OL12 12795 319.875 2105.45 3 1 0 0 1 2 0 3 D-I E 3 soft coast ceramic and ceramics des Sables)

Campaniforme settlement with structures of woody La Passe de settlement, remains of primitive metallurgy. In 2.5 to 5 m Settlement, burial structures, OL13 2558 319.5 2105 3 3 3 1 1 2 0 3 D-I E 4 soft coast l'Ecuissière the proximity, traces of a burial and a stony pottery erected and eroded coffer were discovered

tegula, Discovery of a Gallo Roman artefacts, Gallo Roman 0 to 5 m Montravail ceramics, OL14 13951 probably a small bulding near a Gallo Roamn 325.875 2104.3 4 1 0 0 1 2 0 0 D F 6 soft coast artefacts coins villa (at 250m from the site) Archaeological Inventory: Oleron Island

pottery Site of few hectares showing settlement from Megalith, settlement, sherds, flint, 0 to 2.5 m La Pointe d'Ors OL15 584 the Middle Neolithic to the begin of the Bronze 325.7 2101 3 3 2 1 2 2 2 3 D-I E 3 and 4 soft coast burial woods,anim Age. Megalith with several burial chambers al bones

Ditch fence crossed by acropole lithic managment works, remains of a Middle and 0 to 2.5 m Terre Doux Ditch, fence OL16 8110 325.25 2101.75 4 2 2 1 1 2 0 0 I F 3 and 4 soft coast ceramics Late Neolitic settlement (and a soil showing a settlement contemporaneous of this period)

Church and cemetry mentionned in modern Le Bourg de St 0 to 5 m Church cemetery nothing OL17 3758 literature as progressively buried under the 324.8 2099.75 4 1 0 0 1 2 0 0 I E 1 dune coast Trojan dunes

Surface site on the intertidal area, discovered La Pointe Prehistoric 0 to 5 m Surface site OL18 8144 during managment of dikes marine sheels 325.35 2099 2 3 2 1 3 2 0 3 D E 3 and 4 soft coast Manson artefatcs and several artefacts as flints and ceramics Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Plate P14ac The peat layer on the beach at ‘La Perroche’

Plate P14ad Coring on the beach

18 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Plate P14ba The ‘La Perroche’ site: the layer of blocks indicate the position of a Neolithic human occupation

Plate P14bb The ‘Ors’ site: The intertidal archaeological site of Ors dated from the Middle Neolithic to the late Bronze Age. The block in the foreground shows polishing traces

19 Palaeo-environmental Study Area P14 Oleron Island, near La Rochelle, west coast, France

Plate P14bc The ‘Ors’ site: the megalith in the foreground

Plate P14bd The ‘Ponthezière’ site :traces of Neolithic settlement and remains of artisanal activities (shell ornament production)

20