SEDIMENTOLOGY AND EVOLUTION OF SUB-ARCTIC TIDAL FLATS ALONG A RAPIDLYEMERGING COAST, EASTERN HUDSON-BAY, CANADA

Detailed investigations were carried out on the sedimentology and evol ution of tidal flats located in Manitounuk Sound, along the eastern Hu dson Bay coastline. This area is still emerging today at a rate of 1 c m a(-1) in response to postglacial isostatic uplift. Surface sediments on the Manitounuk tidal flats are distributed in contour parallel fas hion, grain-size coarsening seaward from the highest tide level to the shallow subtidal zone. Monitoring of the seasonal evolution shelved t hat sea ice processes are limited in this sheltered micro-tidal enviro nment, contrary to most tidal flats located in high latitude regions. On a short-term scale, Manitounuk tidal flats are non-depositional. Mo st sediments derived from eroding bluffs cut into recently emerged fin e-grained deposits are exported seaward. Short cores collected across the tidal flats revealed that recent sediments are structureless and a re characterized by a compact silty-clay unit overlaid by few centimet res of reworked sediments. This unit is interpreted as fine-grained ma terial originally deposited in deep water and exposed in the intertida l zone due to isostatic uplift. From this study it appears that Manito unuk tidal flats are actually erosion platforms cut into the postglaci al Tyrrel sea deep water sediments.