Les côtes de la Gaspésie, et plus globalement du Québec maritime, sont particulièrement exposées ... more Les côtes de la Gaspésie, et plus globalement du Québec maritime, sont particulièrement exposées à l’érosion et la submersion côtières. En raison de l’importance historique du Saint-Laurent comme voie de navigation et de l’établissement des populations le long de son littoral, les enjeux relatifs au patrimoine (ressources archéologiques, bâti, monuments et lieux de mémoire) y sont particulièrement sensibles. L’étude présentée a comporté trois volets. Le premier a permis de dresser l’état d’une douzaine de sites archéologiques côtiers connus situés dans les zones à risque, tandis que le deuxième évaluait le potentiel archéologique de secteurs exposés aux aléas côtiers, où cinq nouveaux sites d’intérêt ont été identifiés. Le troisième volet s’intéressait au patrimoine bâti menacé par ces aléas : 39 bâtiments ou sites patrimoniaux menacés ont ainsi été répertoriés. Une revue des modes de gestion des ressources patrimoniales exposées aux aléas côtiers est proposée en conclusion. The coasts of Gaspe Peninsula, and more generally of Maritime Quebec, are particularly exposed to coastal erosion and flooding. Because of the historical importance of the St. Lawrence as a shipping lane and the establishment of populations along its shoreline, heritage stakes (archaeological resources, buildings, monuments and places of memory) are particularly sensitive. The study presented was three-fold. The first stage identified the state of preservation of a dozen known coastal archaeological sites located in risk areas, while the second evaluated the archaeological potential of areas exposed to coastal hazards, where five new sites of interest were identified. The third stage focused on built heritage exposed to these hazards: 39 buildings or exposed heritage sites were identified. A review of management methods for heritage resources exposed to coastal hazards is proposed in conclusion.
ABSTRACT Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations wit... more ABSTRACT Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations with sub-arctic winter conditions. The present paper explores sedimentary processes in the Pointe-aux-Épinettes marsh during the ice-free period. Currents, waves, suspended sediment, and sedimentation rates have been measured in June, August and October 2009. Vegetation growth was monitored during one year on a monthly basis to understand the seasonal impact on the marsh. Vegetation attenuates currents and waves, but this attenuation changes over the year as vegetation disappears along winter. Results show that suspended sediment transport and deposition are controlled by vegetation, wave height, currents, distance from the marsh edge and distance from sediment sources. Suspended sediment concentrations and sedimentation rates were significantly correlated to wave height, highlighting the importance of waves for sediment resuspension transport. Transport was lowest in August when vegetation was high and wave occurrence low. However, vegetation growth didn't change fundamentally sediments dynamic of the marsh. Within one tide, an important part of sediment transport is only local within the marsh, as shown by the maximum sedimentation rates occurring near unvegetated areas of the marsh. Data provide a spatial understanding of summer sedimentology on cold climate marshes.
... 6). Preserving natural coastal zones in urban areas is therefore necessary to maintain health... more ... 6). Preserving natural coastal zones in urban areas is therefore necessary to maintain healthy coastal resilience ... 8 shows the limit reached by flooding during the event. ... 8). Analysis of the flood map, geomorphological indicators and anthropogenic factors allows us to identify five ...
Transportation 2014: Past, Present, Future - 2014 Conference and Exhibition of the Transportation Association of Canada // Transport 2014 : Du passé vers l'avenir - 2014 Congrès et Exposition de 'Association des transports du Canada, 2014
EGU General Assembly Conference Abstracts, Apr 1, 2012
ABSTRACT Coastal erosion is an important issue within the St-Lawrence estuary and gulf, especiall... more ABSTRACT Coastal erosion is an important issue within the St-Lawrence estuary and gulf, especially in zones of unconsolidated material. Wide beaches are important coastal environments; they act as a buffer against breaking waves by absorbing and dissipating their energy, thus reducing the rate of coastal erosion. They also offer protection to humans and nearby ecosystems, providing habitat for plants, animals and lifeforms such as algae and microfauna. Conventional methods, such as aerial photograph analysis, fail to adequately quantify the morphosedimentary behavior of beaches at the scale of a hydrosedimentary cells. The lack of reliable and quantitative data leads to considerable errors of overestimation and underestimation of sediment budgets. To address these gaps and to minimize acquisition costs posed by airborne LiDAR survey, a mobile terrestrial LiDAR has been set up to acquire topographic data of the coastal zone. The acquisition system includes a LiDAR sensor, a high precision navigation system (GPS-INS) and a video camera. Comparison of LiDAR data with 1050 DGPS control points shows a vertical mean absolute error of 0.1 m in beach areas. The extracted data is used to calculate sediment volumes, widths, slopes, and a sediment budget index. A high accuracy coastal characterization is achieved through the integration of laser data and video. The main objective of this first project using this system is to quantify the impact of rigid coastal protective structures on sediment budget and beach morphology. Results show that the average sediment volume of beaches located before a rock armour barrier (12 m3/m) were three times narrower than for natural beaches (35,5 m3/m). Natural beaches were also found to have twice the width (25.4 m) of the beaches bordering inhabited areas (12.7 m). The development of sediment budget index for beach areas is an excellent proxy to quickly identify deficit areas and therefore the coastal segments most at risk of erosion. The obtained LiDAR coverage also revealed that beach profiles made at an interval of more than 200 m on diversified coasts lead to results significantly different from reality. However, profile intervals have little impact on long uniform beaches.
ABSTRACT Gibeault, C.; Neumeier, U., and Bernatchez, P., 2016. Spatial and temporal sediment dyna... more ABSTRACT Gibeault, C.; Neumeier, U., and Bernatchez, P., 2016. Spatial and temporal sediment dynamics in a subarctic salt marsh (Gulf of St. Lawrence, Canada). Sediment transport in the salt marsh and the lagoon of Penouille is driven by tidal currents, waves, wind, and ice rafting, which interact with topography and vegetation to control the spatial distribution of surface sediments. Multiple linear regressions of 203 samples of marsh surface sediments show that grain size gets finer and organic matter content increases with distance from the lagoon inlet, the sandy peninsula, the closest creek, and the lagoon. The vegetation parameters and surface microtopography have only a minor influence. Locally, grain size can get finer with elevation, while organic matter content increases. However, across the entire marsh, grain size exhibits the opposite trend with elevation, a consequence of aeolian transport and ice rafting. The 94 samples covering the lagoon show a trend of finer grain size with distance from the lagoon inlet and with sea grass cover. Penouille marsh has been relatively stable from 1975 to 2008: analysis of five georeferenced aerial photographs shows that only 3% of the marsh area was lost due to outer marsh edge retreat. Ten sediment cores collected in the marsh show a thickness of 0.14–0.72 m of marsh sediments overlying a sandy substrate. Radiocarbon dates suggest that marsh establishment occurred in the north side of the lagoon around 1000–1200 cal BP. Accretion rates based on radiocarbon dates are 0.4–1 mm/y for several centuries, whereas 137Cs dating indicates rates of 1–3 mm/y since 1963, and accretion plates indicate 2.9 ± 0.9 mm/y between 2010 and 2012. Accretion rates since 1963 are similar to the relative sea-level rise (RSLR) of 1.5 mm/y at Penouille for the 1969–2014 period. However, the accelerated RSLR of 3.7 mm/y observed over the last 20 years and additional RSLR due to climate change may progressively drown the marsh if accretion rate does not substantially increase.
Transportation 2014: Past, Present, Future - 2014 Conference and Exhibition of the Transportation Association of Canada // Transport 2014 : Du passé vers l'avenir - 2014 Congrès et Exposition de 'Association des transports du Canada, 2014
Deux projets ont ete menes par le Laboratoire de dynamique et de gestion integree des zones cotie... more Deux projets ont ete menes par le Laboratoire de dynamique et de gestion integree des zones cotieres (LDGIZC) et la Chaire de recherche en geoscience cotiere aux Iles-de-la-Madeleine soit “Caracterisation geomorphologique et sedimentologique des unites hydrosedimentaires de la baie de Plaisance et de Pointe-aux-Loups, route 199, Iles-de-la-Madeleine” pour le ministere des Transports du Quebec et “Marges de securite en erosion cotiere : evolution historique et future du littoral des iles de la Madeleine” remis au ministere de la Securite publique du Quebec. Les iles de la Madeleine ont ete choisi pour ces deux etudes etant donne sa sensibilite a l’erosion puisque 68% de ses cotes sont en erosion (LDGIZC, 2006). Situe dans le golfe du Saint-Laurent, l’archipel madelinien est fortement expose aux ondes de tempete. La vitesse de la hausse du niveau marin relatif est passe de 1,6 mm/an au cours des 600 dernieres annees a 3,5 mm/an depuis 1950 (Juneau, 2012). Ce contexte augmente la vulnerabilite des infrastructures cotieres, notamment la route principale, le seul lien entre les differents ilots rocheux qui est menacee a differents endroits. Cette problematique liee a l’erosion n’est pas prevue de diminuer en raison des changements climatiques apprehendes puisque les processus d’erosion devraient augmenter en raison d’une reduction de 60 a 70 % de la couverture de glace de mer (Senneville et Saucier, 2007), d’une hausse des tempetes effectives, d’une acceleration de la hausse du niveau marin (Vermeer et Rahmstorf, 2009; Koohzare et al., 2008) et d’une hausse des cycles gel-degel et des redoux hivernaux (Bernatchez et al., 2008).
The landscape and landforms of the Magdalen Islands are uniquely varied for such a small archipel... more The landscape and landforms of the Magdalen Islands are uniquely varied for such a small archipelago. Geomorphologically they are a part of the Maritime Plain which is located near the center of the Maritime Basin (375–325 Ma). The Magdalen Islands were pushed to the surface by salt-diapirs (~300 Ma). Formed by volcanic hills (basalt) surrounded by a low sandstone platform, the main islands are interconnected by late Holocene sand spits and tombolos. Located in the southern part of the Gulf of St. Lawrence, the Laurentide Ice Sheet (LIS) did not reach the Magdalen Islands during the last glaciation, but possibly much earlier (≥170 ka). Three different sets of geomorphological processes have impacted the landscape: structural, periglacial, and coastal. Sandstone platforms adjacent to volcanic hills are the structural controls. Superimposed on the sandstone platforms, cryopediments, ice-wedge pseudomorphs and dry valleys are the dominant periglacial landforms. Coastal landforms are dominated by cliffs, tombolos, and littoral spits. Perhaps the single most surprising fact is that eight islands with a cumulative area of 202 km2 can demonstrate such a remarkable variety of landscapes and landforms. The glacial record remains contentious.
The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southe... more The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southern Magdalen Islands (Québec, Canada), belong to two units of different origin, glacial and glaciomarine. At Anse à la Cabane, the glacial deposit comprises two subunits: a glacitectonite at the base and a subglacial traction till at the top. Numerous glaciotectonic deformation structures suggest ice flow towards the southeast. The till is above an organic horizon dated to ∼47–50 ka BP. New data presented here show that the southern part of the Magdalen archipelago was glaciated during the Late Wisconsinan. We relate this ice flow to the Escuminac ice cap, whose centre of dispersion was located in the Gulf of St. Lawrence, northwest of the islands. At Anse au Plâtre, the top of the Drift des Demoiselles is a glaciomarine deposit. At Anse à la Cabane, the till is covered by a stratified subtidal unit located at ∼20 m above sea level. Both were deposited during the marine transgression that followed deglaciation. At Anse à la Cabane, three ice-wedge casts truncate the till and the subtidal unit, providing evidence that periglacial conditions occurred on the archipelago after deglaciation.
Extensive shell beds were found in the valley of Rivière aux Anglais, near Baie-Comeau, along the... more Extensive shell beds were found in the valley of Rivière aux Anglais, near Baie-Comeau, along the North Shore of lower St. Lawrence River. Those particular accumulations, more or less well stratified and ranging from 2 to 15 m thick, represent the top parts of unconsolidated formations of the Goldthwait Sea between 10.4 and 9.6 ka BP. About 10 mounds have been discovered up to now. Their sizes vary, but reach 50 × 103 m2. Most overlie fine stratified sediments, such as fine sand, silt, and clay. They consist mainly of shell remains, which sometimes represent up to 90-95% of the volume. We can find various species of cirripeds (3), gastropods (7), brachiopods (1), echinoderms (1), and mostly pelecypods (11) including a large percentage of unbroken shells. Stratigraphic evidence suggests that these are natural formations (faluns) formed in a marine environment by sedimentation inside a seashore of ria type, where the sea currents and waves played a prominant role in the concentration of shell remains. The quantity of shells implies an environment of strong primary productivity, but also particular climatic conditions (frost) leading to a high number of deaths.
Les côtes de la Gaspésie, et plus globalement du Québec maritime, sont particulièrement exposées ... more Les côtes de la Gaspésie, et plus globalement du Québec maritime, sont particulièrement exposées à l’érosion et la submersion côtières. En raison de l’importance historique du Saint-Laurent comme voie de navigation et de l’établissement des populations le long de son littoral, les enjeux relatifs au patrimoine (ressources archéologiques, bâti, monuments et lieux de mémoire) y sont particulièrement sensibles. L’étude présentée a comporté trois volets. Le premier a permis de dresser l’état d’une douzaine de sites archéologiques côtiers connus situés dans les zones à risque, tandis que le deuxième évaluait le potentiel archéologique de secteurs exposés aux aléas côtiers, où cinq nouveaux sites d’intérêt ont été identifiés. Le troisième volet s’intéressait au patrimoine bâti menacé par ces aléas : 39 bâtiments ou sites patrimoniaux menacés ont ainsi été répertoriés. Une revue des modes de gestion des ressources patrimoniales exposées aux aléas côtiers est proposée en conclusion. The coasts of Gaspe Peninsula, and more generally of Maritime Quebec, are particularly exposed to coastal erosion and flooding. Because of the historical importance of the St. Lawrence as a shipping lane and the establishment of populations along its shoreline, heritage stakes (archaeological resources, buildings, monuments and places of memory) are particularly sensitive. The study presented was three-fold. The first stage identified the state of preservation of a dozen known coastal archaeological sites located in risk areas, while the second evaluated the archaeological potential of areas exposed to coastal hazards, where five new sites of interest were identified. The third stage focused on built heritage exposed to these hazards: 39 buildings or exposed heritage sites were identified. A review of management methods for heritage resources exposed to coastal hazards is proposed in conclusion.
ABSTRACT Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations wit... more ABSTRACT Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations with sub-arctic winter conditions. The present paper explores sedimentary processes in the Pointe-aux-Épinettes marsh during the ice-free period. Currents, waves, suspended sediment, and sedimentation rates have been measured in June, August and October 2009. Vegetation growth was monitored during one year on a monthly basis to understand the seasonal impact on the marsh. Vegetation attenuates currents and waves, but this attenuation changes over the year as vegetation disappears along winter. Results show that suspended sediment transport and deposition are controlled by vegetation, wave height, currents, distance from the marsh edge and distance from sediment sources. Suspended sediment concentrations and sedimentation rates were significantly correlated to wave height, highlighting the importance of waves for sediment resuspension transport. Transport was lowest in August when vegetation was high and wave occurrence low. However, vegetation growth didn't change fundamentally sediments dynamic of the marsh. Within one tide, an important part of sediment transport is only local within the marsh, as shown by the maximum sedimentation rates occurring near unvegetated areas of the marsh. Data provide a spatial understanding of summer sedimentology on cold climate marshes.
... 6). Preserving natural coastal zones in urban areas is therefore necessary to maintain health... more ... 6). Preserving natural coastal zones in urban areas is therefore necessary to maintain healthy coastal resilience ... 8 shows the limit reached by flooding during the event. ... 8). Analysis of the flood map, geomorphological indicators and anthropogenic factors allows us to identify five ...
Transportation 2014: Past, Present, Future - 2014 Conference and Exhibition of the Transportation Association of Canada // Transport 2014 : Du passé vers l'avenir - 2014 Congrès et Exposition de 'Association des transports du Canada, 2014
EGU General Assembly Conference Abstracts, Apr 1, 2012
ABSTRACT Coastal erosion is an important issue within the St-Lawrence estuary and gulf, especiall... more ABSTRACT Coastal erosion is an important issue within the St-Lawrence estuary and gulf, especially in zones of unconsolidated material. Wide beaches are important coastal environments; they act as a buffer against breaking waves by absorbing and dissipating their energy, thus reducing the rate of coastal erosion. They also offer protection to humans and nearby ecosystems, providing habitat for plants, animals and lifeforms such as algae and microfauna. Conventional methods, such as aerial photograph analysis, fail to adequately quantify the morphosedimentary behavior of beaches at the scale of a hydrosedimentary cells. The lack of reliable and quantitative data leads to considerable errors of overestimation and underestimation of sediment budgets. To address these gaps and to minimize acquisition costs posed by airborne LiDAR survey, a mobile terrestrial LiDAR has been set up to acquire topographic data of the coastal zone. The acquisition system includes a LiDAR sensor, a high precision navigation system (GPS-INS) and a video camera. Comparison of LiDAR data with 1050 DGPS control points shows a vertical mean absolute error of 0.1 m in beach areas. The extracted data is used to calculate sediment volumes, widths, slopes, and a sediment budget index. A high accuracy coastal characterization is achieved through the integration of laser data and video. The main objective of this first project using this system is to quantify the impact of rigid coastal protective structures on sediment budget and beach morphology. Results show that the average sediment volume of beaches located before a rock armour barrier (12 m3/m) were three times narrower than for natural beaches (35,5 m3/m). Natural beaches were also found to have twice the width (25.4 m) of the beaches bordering inhabited areas (12.7 m). The development of sediment budget index for beach areas is an excellent proxy to quickly identify deficit areas and therefore the coastal segments most at risk of erosion. The obtained LiDAR coverage also revealed that beach profiles made at an interval of more than 200 m on diversified coasts lead to results significantly different from reality. However, profile intervals have little impact on long uniform beaches.
ABSTRACT Gibeault, C.; Neumeier, U., and Bernatchez, P., 2016. Spatial and temporal sediment dyna... more ABSTRACT Gibeault, C.; Neumeier, U., and Bernatchez, P., 2016. Spatial and temporal sediment dynamics in a subarctic salt marsh (Gulf of St. Lawrence, Canada). Sediment transport in the salt marsh and the lagoon of Penouille is driven by tidal currents, waves, wind, and ice rafting, which interact with topography and vegetation to control the spatial distribution of surface sediments. Multiple linear regressions of 203 samples of marsh surface sediments show that grain size gets finer and organic matter content increases with distance from the lagoon inlet, the sandy peninsula, the closest creek, and the lagoon. The vegetation parameters and surface microtopography have only a minor influence. Locally, grain size can get finer with elevation, while organic matter content increases. However, across the entire marsh, grain size exhibits the opposite trend with elevation, a consequence of aeolian transport and ice rafting. The 94 samples covering the lagoon show a trend of finer grain size with distance from the lagoon inlet and with sea grass cover. Penouille marsh has been relatively stable from 1975 to 2008: analysis of five georeferenced aerial photographs shows that only 3% of the marsh area was lost due to outer marsh edge retreat. Ten sediment cores collected in the marsh show a thickness of 0.14–0.72 m of marsh sediments overlying a sandy substrate. Radiocarbon dates suggest that marsh establishment occurred in the north side of the lagoon around 1000–1200 cal BP. Accretion rates based on radiocarbon dates are 0.4–1 mm/y for several centuries, whereas 137Cs dating indicates rates of 1–3 mm/y since 1963, and accretion plates indicate 2.9 ± 0.9 mm/y between 2010 and 2012. Accretion rates since 1963 are similar to the relative sea-level rise (RSLR) of 1.5 mm/y at Penouille for the 1969–2014 period. However, the accelerated RSLR of 3.7 mm/y observed over the last 20 years and additional RSLR due to climate change may progressively drown the marsh if accretion rate does not substantially increase.
Transportation 2014: Past, Present, Future - 2014 Conference and Exhibition of the Transportation Association of Canada // Transport 2014 : Du passé vers l'avenir - 2014 Congrès et Exposition de 'Association des transports du Canada, 2014
Deux projets ont ete menes par le Laboratoire de dynamique et de gestion integree des zones cotie... more Deux projets ont ete menes par le Laboratoire de dynamique et de gestion integree des zones cotieres (LDGIZC) et la Chaire de recherche en geoscience cotiere aux Iles-de-la-Madeleine soit “Caracterisation geomorphologique et sedimentologique des unites hydrosedimentaires de la baie de Plaisance et de Pointe-aux-Loups, route 199, Iles-de-la-Madeleine” pour le ministere des Transports du Quebec et “Marges de securite en erosion cotiere : evolution historique et future du littoral des iles de la Madeleine” remis au ministere de la Securite publique du Quebec. Les iles de la Madeleine ont ete choisi pour ces deux etudes etant donne sa sensibilite a l’erosion puisque 68% de ses cotes sont en erosion (LDGIZC, 2006). Situe dans le golfe du Saint-Laurent, l’archipel madelinien est fortement expose aux ondes de tempete. La vitesse de la hausse du niveau marin relatif est passe de 1,6 mm/an au cours des 600 dernieres annees a 3,5 mm/an depuis 1950 (Juneau, 2012). Ce contexte augmente la vulnerabilite des infrastructures cotieres, notamment la route principale, le seul lien entre les differents ilots rocheux qui est menacee a differents endroits. Cette problematique liee a l’erosion n’est pas prevue de diminuer en raison des changements climatiques apprehendes puisque les processus d’erosion devraient augmenter en raison d’une reduction de 60 a 70 % de la couverture de glace de mer (Senneville et Saucier, 2007), d’une hausse des tempetes effectives, d’une acceleration de la hausse du niveau marin (Vermeer et Rahmstorf, 2009; Koohzare et al., 2008) et d’une hausse des cycles gel-degel et des redoux hivernaux (Bernatchez et al., 2008).
The landscape and landforms of the Magdalen Islands are uniquely varied for such a small archipel... more The landscape and landforms of the Magdalen Islands are uniquely varied for such a small archipelago. Geomorphologically they are a part of the Maritime Plain which is located near the center of the Maritime Basin (375–325 Ma). The Magdalen Islands were pushed to the surface by salt-diapirs (~300 Ma). Formed by volcanic hills (basalt) surrounded by a low sandstone platform, the main islands are interconnected by late Holocene sand spits and tombolos. Located in the southern part of the Gulf of St. Lawrence, the Laurentide Ice Sheet (LIS) did not reach the Magdalen Islands during the last glaciation, but possibly much earlier (≥170 ka). Three different sets of geomorphological processes have impacted the landscape: structural, periglacial, and coastal. Sandstone platforms adjacent to volcanic hills are the structural controls. Superimposed on the sandstone platforms, cryopediments, ice-wedge pseudomorphs and dry valleys are the dominant periglacial landforms. Coastal landforms are dominated by cliffs, tombolos, and littoral spits. Perhaps the single most surprising fact is that eight islands with a cumulative area of 202 km2 can demonstrate such a remarkable variety of landscapes and landforms. The glacial record remains contentious.
The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southe... more The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southern Magdalen Islands (Québec, Canada), belong to two units of different origin, glacial and glaciomarine. At Anse à la Cabane, the glacial deposit comprises two subunits: a glacitectonite at the base and a subglacial traction till at the top. Numerous glaciotectonic deformation structures suggest ice flow towards the southeast. The till is above an organic horizon dated to ∼47–50 ka BP. New data presented here show that the southern part of the Magdalen archipelago was glaciated during the Late Wisconsinan. We relate this ice flow to the Escuminac ice cap, whose centre of dispersion was located in the Gulf of St. Lawrence, northwest of the islands. At Anse au Plâtre, the top of the Drift des Demoiselles is a glaciomarine deposit. At Anse à la Cabane, the till is covered by a stratified subtidal unit located at ∼20 m above sea level. Both were deposited during the marine transgression that followed deglaciation. At Anse à la Cabane, three ice-wedge casts truncate the till and the subtidal unit, providing evidence that periglacial conditions occurred on the archipelago after deglaciation.
Extensive shell beds were found in the valley of Rivière aux Anglais, near Baie-Comeau, along the... more Extensive shell beds were found in the valley of Rivière aux Anglais, near Baie-Comeau, along the North Shore of lower St. Lawrence River. Those particular accumulations, more or less well stratified and ranging from 2 to 15 m thick, represent the top parts of unconsolidated formations of the Goldthwait Sea between 10.4 and 9.6 ka BP. About 10 mounds have been discovered up to now. Their sizes vary, but reach 50 × 103 m2. Most overlie fine stratified sediments, such as fine sand, silt, and clay. They consist mainly of shell remains, which sometimes represent up to 90-95% of the volume. We can find various species of cirripeds (3), gastropods (7), brachiopods (1), echinoderms (1), and mostly pelecypods (11) including a large percentage of unbroken shells. Stratigraphic evidence suggests that these are natural formations (faluns) formed in a marine environment by sedimentation inside a seashore of ria type, where the sea currents and waves played a prominant role in the concentration of shell remains. The quantity of shells implies an environment of strong primary productivity, but also particular climatic conditions (frost) leading to a high number of deaths.
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Papers by Pascal Bernatchez