EARLY TO MID HOLOCENE CLIMATE RECORD FROM SEVERN SOUND, SOUTHERN GEORGIAN BAY, LAKE HURON, LAURENTIDE GREAT LAKES

A regional grid of high-resolution shallow seismic reflection profiles was collected and analyzed to provide a Holocene seismostratigraphic framework for Severn Sound, Southern Georgian Bay, Lake Huron. Sediment cores were then recovered at selected sites for biostratigraphic, sedimentological and chronological analyses to reconstruct the Holocene geological and climate history of the Sound. The seismostratigraphy and sedimentology indicate the Sound contains a spatially and temporally discontinuous sediment sequence with associated disrupted geologic and climatic history particularly for the early to mid Holocene time period. In response to isostatic rebound of drainage outlets, arid climate regime in Georgian Bay and the waning of glacial meltwater input to the Great Lakes, water levels fluctuated significantly exposing Severn Sound to cyclic non-deposition and subaerial erosion between 9600 and 7500 BP. Rising water levels were associated with shoreline and lakebed erosion and the deposition of spatially discontinuous sediments across the Sound. Sediments deposited on the early Holocene regional seismic unconformity resulting from the low lake levels provide the basis for reconstructing the geological and climatic history of the Sound with the final rise in lake levels about 7200BP. Palynological analyses of these sediment samples were correlated with the chronologically controlled pollen stratigraphy of proximal small lakes to allow for the paleoclimate interpretation of the post 7200 BP time period. Early to mid Holocene lake level fluctuations in Severn Sound have controlled sediment deposition rates resulting in a non-uniform sediment depositional history. The spatial and temporal discontinuity and the thinness of the units subject to bioturbation have impeded our ability to provide a high-resolution continuous paleoclimatic reconstruction for the early to mid Holocene.