Isolation au postglaciaire d'un bassin côtier près de Kuujjuaraapik-Whapmagoostui, en Hudsonie (Québec) : une analyse biostratigraphique diatomifère

• Published in: Géographie physique et Quaternaire
• Main Authors: Saulnier-Talbot, Émilie, Pienitz, Reinard
• Format: Text
• Language: French
• Published: Les Presses de l'Université de Montréal 2001
• Subjects: Hudson Bay; Hudson; Baie d'Hudson; Baie-d'Hudson; Tyrrell; Whapmagoostui
• Online Access: http://id.erudit.org/iderudit/005662ar; https://doi.org/10.7202/005662ar

In order to retrace the successive postglacial isolation phases of a coastal lake located near Kuujjuaraapik-Whapmagoostui (eastern Hudson Bay), the diatom assemblages of a sediment core were analysed. The sedimentary sequence collected from Kachishayoot Lake shows three zones corresponding to paleoenvironmental changes brought about by isostatic rebound. Each zone is characterized by a contrasting sedimentology and fossil diatom assemblages. The transition from marine clays to gyttja and the evolution of the diatom assemblages, successively dominated by poly-mesohalobian, oligohalobian and finally halophobous species, documents the overall trend of decreasing salinity in the lake. Diatominferred alkalinity also decreased, most likely reflecting the change from a nutrient-rich to a nutrient-poor environment as the basin was isolated from the waters of the postglacial Tyrrell Sea and gradually purged of nutrients and major ions (dissolved inorganic carbon, Ca, Mg) from the carbonate weathering of glacial tills and marine clays. Chronological references obtained through AMS dating made it possible to evaluate sedimentation rates and the duration of the three different stages (marine conditions from 5400-4500 cal yr BP, isolation phase between 4500-1600 cal yr BP and modern lake phase since 1600 cal yr BP) of lake succession in the Kachishayoot Lake basin. This biostratigraphic study yields information about the evolution of the landscape in the southeastern Hudson Bay area following the retreat of the postglacial Tyrrell Sea about 5000 years ago. En vue de retracer les phases d'isolation postglaciaire d'un lac côtier situé près de Kuujjuaraapik-Whapmagoostui (baie d'Hudson), le contenu diatomifère d'une carotte de sédiments a été analysé. La séquence sédimentaire recueillie dans le lac Kachishayoot démontre trois unités de changements paléoenvironnementaux provoqués par le relèvement isostatique postglaciaire. Ces unités se distinguent entre elles par une sédimentologie et des assemblages fossiles de diatomées ...