Late Glacial De Geer moraines with glaciofluvial sediment in the Chapais area, Québec (Canada)

Glaciofluvial De Geer moraines have rarely been described in detail in the literature. This study presents a model for the genesis of moraines of this type in the Chapais area, Quebec. The model is based mainly on facies and deformatin structures analysis, and geomorphological data. Well-stratified glaciofluvial material is commonly found in the core of the moraines, whereas till or glacial diamicton may be present as surficial cover on their proximal side or as injected lenses in the sorted sediments. The paleocurrents are systematically directd downglacier. The moraines were built up in subglacial crevasses in areas where meltwater was channelized. Water flowed under pressure from small upglacier cavities, carrying a load of coars-grained material When flowing water entered crevasses already occupied by water, flow sparation occurred, reducing the capacity of the flow to carry the particles, and avalanching glaciofluvial material on the leeside of the piled sediments. The occurrence, in these sediments, of glaciotectonic deformation structures such as overturned to recumbent folds and thrust faults is evidence that the glacier was still active to some degree during and after the sedimentation phase.

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