Subglacial landforms and deposits in central and northern Québec, Canada, with emphasis on Rogen moraines

Abstract

The development of the anatomy and the morphology of a relatively simple till sheet deposited over parts of the Canadian Shield is discussed. This is characterized by the common occurrence of well-developed streamlined landforms and Rogen moraines. The sedimentation of the till sheet was an alternating succession of depositional and erosional (or landforming) events, the former leading to the sedimentation of various till lithofacies, the latter leading to the development of various morainic terrains. This orderly sequence of subglacial events occurred during the deglaciation of central and northern Québec, with the controlling factors being bed rock topography and geology, ice thickness and basal ice temperatures. Till lithofacies include in ascending stratigraphic order, lodgement till, subglacial melt-out till, immature lodgement till, and varieties of supra-glacial ablation deposits. Morainic terrains include drumlinized and fluted ground moraine, Rogen moraines, as well as fluted and unfluted hummocky moraine. Rogen moraines are formed subglacially, a few kilometers behind the glacier margin, as a consequence of localized compressive stresses which result in shearing and stacking of slices of near-base englacial debris, later deposited as a basal melt-out till. The moraines are believed to be a characteristic landform associated with Shield-type rock surfaces, namely an irregular topography of asymmetric rock basins of all sizes resulting from the areal scouring of hard rocks. As well, the moraines are believed to be as well a characteristic landform resulting from the flattening profile of the margin of the waning ice sheet. The formation of the moraines led to enhanced flow in marginal areas, generating late events of streamlining and boulder plucking.