A shear-diffusion model of till genesis based on the dispersal pattern of indicator rocks in the Grand-Volume Till of central Gaspésie, Québec, Canada |
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| Authors: | RÉMI CHARBONNEAU PETER P DAVID |
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| Institution: | Rémi Charbonneau and Peter P. David, Départernent de géologie, Uniuersitéde Montréal, C.P. 6128, succursale centre-ville, Montréal, Québec, H3C 3J7, Canada |
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| Abstract: | Dispersal patterns of indicator rocks in central Gaspésie reveal that glacial debris is entrained in a basal debris-rich zone of shearing where clast diffusion takes place. The Grand-Volume Till forms a thin till sheet over the high plateaus of Gaspésie Peninsula and resulted from a succession of two Wisconsinan ice flows of distinct orientations (SSE and NE). The lithological composition of this till determined by pebble counts and the three-dimensional dispersal patterns of indicator rocks in it suggest that debris transport occurred principally by simple shear deformation of glacial debris. In addition, the intermixing of clasts at the intersection of two lithologically distinct dispersal trains of SSE and NE orientations, respectively, suggests that extensive mixing takes place during shearing. Physical interactions among the clasts lead to both upward and downward movements which cause the clasts to diffuse across the zone of shearing. This process of shear-diffusion results in continuous incorporation and mixing of the newly encountered rock types during glacial transport. |
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