CGRG Bibliography of Canadian Geomorphology
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Author : Allard, S.; Pronk, A.G. ; Boldon, G.R.; and Broster, B.E.
Date : 2003.
Title : Wisconsinan ice flow trajectories and till geochemistry: Southwestern, New Brunswick.
Publication : Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group. Halifax, Nova Scotia, June 8-12, 2003.
Issue :
Page(s) :
Abstract
In recent years, exploration activity has increased substantially in southwestern New Brunswick due in large part to the delineation of gold skarn deposits at Freewest Resources Canada Inc.'s Clarence Stream property. In response to this increased interest, till sampling has been conducted in the McDougall Lake (21 G/07), Rollingdam (21 G/06), St. Stephen (21 G/03) and the southern third of Fredericton Junction (21 G/10) map areas at a sample density of 1 sample/4km2. In total, 732 samples were collected, and subjected to geochemical (ICP-MS and INAA), lithological and granulometric analyses. Although the primary focus of this study was to identify potential exploration targets, attention was also given to the delineation of glacial transport trajectories in this area of complex ice-flow history. A single basal till unit of local derivation with texture and colour reflecting local bedrock units occurs in the study area. Till deposition was accomplished by an Early or Mid-Wisconsinan south-eastward flowing ice sheet. This till unit was later reworked (imprinted) by a series of relatively weak Late Wisconsinan ice-flow events. The younger events did not produce a recognizable deposit but, instead, altered the pre-existing till through a moderate redistribution of the matrix components, slight redistribution of the clast medium and realignment of clast fabric. The result was the formation of a hybrid till demonstrating characteristics of multiple ice flow events. The observations discussed here, and the lack of complex glacial/de-glacial stratigraphy, indicate that the various flow trajectories represent a shift in outflow orientation within a common ice sheet, rather than multiple glacial advances and retreats by individual ice masses. Geochemical dispersal patterns form short high-contrast 'bulls-eye'- or 'amoeboid'-shaped anomalies that are lost within approximately 12 km of the presumed source. Clast lithology trains are elongated up to 40 km, parallel landform fluting and demonstrate clearly the dominant southeasterly transport path. Although some matrix geochemistry dispersal trains form palimpsest dispersal patterns, reflecting the hybrid nature of the till and the multidirectional transport history, many elements show dispersal patterns complicated by epigenetic redistribution. These results imply that for simple drift prospecting exercises in areas of complex glacial history, dominant transport path and source unit are more clearly delineated by shape and size of till clast dispersal patterns than by analysis of matrix geochemistry. However, to fully understand the depositional history of a till sheet and fully assess the mineral potential of an area, a comprehensive but cautious examination of the till geochemistry is required.
Bibliography of Canadian Geomorphology