CGRG Bibliography of Canadian Geomorphology
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Author : Catto, N. R.
Date : 1990
Title : Clast fabric of diamictons associated with some roches moutonnées
Publication : Boreas
Issue : 19(4):
Page(s) : 289-296.
Abstract
Clast fabric patterns in thin, dense, over-consolidated diamictons overlying and abutting the stoss sides of 23 Canadian and Swedish roches moutonnees were investigated. These diamictons display sedimentary characteristics that are commonly regarded as typical of basally-deposited tills formed under actively flowing ice. The macrofabrics are marked by strong unimodal orientations in the direction of ice flow, parallel to the long axes of the roches mountonnees. Many have low down-ice plunge angles, in contrast to the up-ice plunges normally associated with ortho-till deposited under actively flowing ice. The degree of divergence between the macrofabric mode and the long axis of the roche moutonnee is related to the distance between the macrofabric site and the axis, whereas the plunge angle is highest in the central part of the stoss slope. The down-ice plunge of the large clasts appears to be a consequence of deposition in areas where glacial flow and shear stress surfaces are oriented at a shallow angle towards an ice/rigid substrate interface. The angle of plunge depends upon the relative importance of the vertical and lateral stress components, pervasive deformation during deposition, and subsequent reworking. The presence of diamictons over rigid substrates on the stoss flanks of roches mountonnees is an uncommon situation, suggesting that this macrofabric pattern may be relatively rare in general for ortho-tills deposited under actively flowing ice.
Bibliography of Canadian Geomorphology