Sedimentology and evolution of subarctic tidal flats along a rapidly emerging coast, eastern Hudson Bay, Canada

Detailed investigations were carried out on the sedimentology and evolution of tidal flats located in Manitounuk Sound, along the eastern Hudson Bay coastline. This area is still emerging today at a rate of 1 cm a(-1) in response to postglacial isostatic uplift. Surface sediments on the Manitounuk tidal flats are distributed in contour parallel fashion, grain-size coarsening seaward from the highest tide level to the shallow subtidal zone. Monitoring of the seasonal evolution shelved that sea ice processes are limited in this sheltered micro-tidal environment, contrary to most tidal flats located in high latitude regions. On a short-term scale, Manitounuk tidal flats are non-depositional. Most sediments derived from eroding bluffs cut into recently emerged fine-grained deposits are exported seaward. Short cores collected across the tidal flats revealed that recent sediments are structureless and are characterized by a compact silty-clay unit overlaid by few centimetres of reworked sediments. This unit is interpreted as fine-grained material originally deposited in deep water and exposed in the intertidal zone due to isostatic uplift. From this study it appears that Manitounuk tidal flats are actually erosion platforms cut into the postglacial Tyrrel sea deep water sediments.