Holocene Development of Parabolic Dunes in the Central St. Lawrence Lowland, Québec

Abstract

Stabilized parabolic dunes in the central St. Lawrence Lowland are oriented NE-SW, in the postulated direction of dune-building winds coming from anticyclonic air circulation induced by the retreating Laurentide Ice Sheet about 10,000 yr ago. The eolian chronology reconstructed from several sections in mixed dune-peatland environments indicates that postglacial plant colonization, characterized by a fortuitous assemblage of arctic-subarctic and boreal elements, preceded dune formation during Champlain Sea regression around 10,000 yr B.P. Confined peatlands and small forests were buried by eolian sands between 10,000 and 7500 yr B.P. under dry and temperate conditions. This eolian episode lasted about 2500 14C yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the Laurentide Ice Sheet over Hudson Bay and peripheral areas. Dune stabilization, through paludification of well-drained eolian sands about 7500 yr B.P., suggests a major shift in climate toward wetter conditions that have been characteristic during most of the Holocene in eastern North America. Minor eolian erosion induced by wildfire was recorded during late Holocene time (about 1250 yr B.P.). Anthropogenic perturbation (logging and agriculture practice) was also responsible for recent very local eolian activity.

Paléophytogéographie et paléoclimats postglaciaires dans l’ouest du Bas-Saint-Laurent, Québec

“…Entre 10 000 et 8000 ans avant l'actuel, la relative proximité du front de l'inlandsis par rapport à la région du Bas-Saint-Laurent autorise à croire que cette région fut alors soumise à l'influence de vents catabatiques (donc secs) orientés du nord-est au sud-ouest, provenant de la masse de glace sise au nord. Cette dernière interprétation est renforcée par l'existence à la même époque de dunes mises en place par de tels vents, au sud-ouest de la ville de Québec (Filion, 1987), donc en aval de notre région. Par ailleurs, les contrastes saisonniers marqués de la radiation solaire incidente prévus par la théorie de Milankovitch, aux moyennes latitudes de l'hémisphère nord durant l'Holocène inférieur (Kutzbach et Guetter, 1986), bien qu'elles permettent d'envisager l'existence de conditions climatiques estivales pré-sentant une plus forte évapotranspiration, favorisant les incendies, sont peu compatibles avec l'existence de conditions froides pour la même période, dans la région à l'étude.…”

Decline of Two Open Champlain Sea Dune Systems in Eastern Ontario and Their Characteristic and Restricted Plants and Insects

“…Although dune activity (movement) apparently ceased several thousand years before present (David 1988), the higher parts of the sandy deposits were probably prone to fire and drought and may have remained as open sand, sandy grassland and scrub for thousands of years as islands in a largely forested landscape. Supporting this view, Filion (1987) reported minor eolian erosion of Champlain Sea dunes at Rivière-du-Chêne, Quebec, as a result of wildfire 1250 years before present.…”

“…It has been suggested that the dunes in eastern Ontario became active only during post-European set tlement times because of the absence of buried soil horizons (e.g., Johnson quoted in Porsild 1941) but this is contrary to Filion's (1987) observation and the subject has not been studied extensively. Regardless, open sandy areas can exist without dune activity.…”

“…The onshore winds from the east resulted in characteristic parabolic dunes growing from the shore westward into the conifer forest (Terasmae and Mott 1959;Filion 1987;David 1988). The highest crests of the dunes evidently return to forest very slow ly after forest removal by fire.…”

Perturbations des tourbières de la région de Bécancour, Centre-du-Québec, entre 1966 et 2010

“…Des dépôts éoliens forment un corridor nord-sud au centre de la zone. Ils sont bordés d'arêtes subparallèles et les zones inter-dunes sont souvent occupées par des tourbières (Filion, 1987). Une synthèse complète et récente de la géologie du Quaternaire est présentée dans Godbout et collab.…”