ESKER MORPHO-SEDIMENTARY RELATIONSHIPS IN SOUTHERN ALBERTA, CANADA

Compared to numerous, large eskers on the Canadian Shield, the southern Alberta prairies have only a few, small examples. This limited esker development in Alberta has been attributed to: (1) active ice retreat, (2) high substrate permeability limiting R-channel formation, and/or (3) widespread fine-grained (deformable) till favoring the formation of canals not R-channels. Our previous work has shown that eskers are present on permeable as well as deformable substrates suggesting that glaciological and sediment supply may, locally, have been more important controls on esker formation. In this paper we use sedimentary, geophysical and mapping techniques to establish the morpho-sedimentary relationships of eskers in southern Alberta. The larger eskers are found within tunnel channels where they are continuous and sharp-crested, often possessing regular longitudinal undulations (macroforms). Ground penetrating radar (GPR) investigations confirm the presence of these bedforms. Large fans, at the termini of tunnel channels are dissected by eskers. In these settings, eskers are discontinuous, broad, may be flat-topped and are onlapped by glaciolacustrine sediment. Based on our investigations, we conclude: (1) tunnel channel formation was essential for concentrating coarse sediment necessary for the preservation of R-channels (eskers), (2) tunnel channel fan sediment was recycled into the discontinuous esker beads, and (3) the changes in sedimentary architecture between the tunnel channel and lake basin segments indicate a dramatic change in conduit conditions.