Paléophytogéographie de la formation de Scarborough : nouvelles données et implications

Palynological study of the upper part of the Don Formation, in the Toronto area, confirms the progressive change from a mixed forest with numerous thermophilous trees (Quercus, Ulmus, Carya) to a cold balsam fir forest (Abies balsamea, Picea mariana, Pinus banksiana) towards the end of the Sangamonian climatic optimum. The Scarborough Formation pollen content indicates a forest-tundra or treed tundra environment similar to modern subarctic conditions. Macrofossil content also points to harsh climatic conditions. Mean annual temperature could then have been 10°C lower than the present in the Toronto area. Our data refute the reconstruction of a climatic cycle (cold-warmer-cold) within the Scarborough Formation. To explain the simultaneous presence of floristic elements typical of presently contrasted climatic regions (cold boreal, warm temperate), we propose that Lake Scarborough acted as a climatic buffer for riverine plants: thermophilous species survived in an englaciation context in remote regions. The...