Braided River Deposits and their Relationship to the Pleistocene History of the Credit Valley, Ontario

Abstract

<p> The stratigraphy of the Pleistocene sediments of the Credit Valley of Ontario embraces two large fining-upwards sequences which correspond to the deposition of glacial debris during the retreat of the last two glacial periods in south central Ontario. The fining-upwards sequences have a basal gravel unit, a middle cross-stratified sand unit, and an upper unit containing small coarsening-upward sequences. All three of these sedimentary units are the result of deposition of sediment in a braided fluvial system. The basal gravel unit displays mid-channel gravel bars and side channel deposits. The cross-bedded sand unit exhibits incised bed-form deposits such as linguoid bars, dunes and ripples. The upper unit of coarsening-upwards sequences (which in places are interbedded with the cross-stratified sand facies) represents the deposits of bank overflow and consequent reactivation of unused channels on the braided river floodplain.</p> <p> During the Halton and Wentworth ice advances, till was deposited on the surrounding plain. With retreat of the ice masses, meltwater and outwash debris built up an alluvial plain in the lower and wider reaches of the Credit Valley near Glen Williams. These alluvial plains or sandurs were built up by deposition from braided streams. Outwash from the Halton Ice built a sandur plain on top of one constructed in Wentworth time. Post glacial drainage has incised these glaciofluvial deposits and leaves them exposed along the banks of the present Credit River. </p>