Quaternary geology and environmental geochemistry of the Flin Flon region, Manitoba and Saskatchewan.

摘要

The Quaternary geology of the Flin Flon region reflects a complex glacial history at the confluence of two major Sectors of the Laurentide Ice Sheet during the Pleistocene. Surficial glacial deposits exhibit contrasting composition, distribution and morphology related to differences in provenance and glacial sedimentation processes associated with the two ice masses during the last glaciation, and the contrasting nature of the Paleozoic and Shield terrains which underlie the region. The rarity of older glacial sediments beneath surface till demonstrates almost complete glacial erosion during the latest glacial events. Following deglaciation, the area was inundated by Lake Agassiz. Post-glacial lake strandlines record a series of six regressive lake levels formed as the ice front retreated and lower outlets were opened. Glacial rebound has tilted the paleo-water planes to the northeast during the Holocene, with gradients decreasing from the highest to the lowest level, from about 0.34 in km−1 to 0.22 in km−1. This suggests significant differential uplift in the region following final drainage of Lake Agassiz.; The soils of the Flin Flon region are naturally elevated in metals, but concentrations are considerably augmented by atmospheric fallout of smelter-derived particulate emissions. In surface organic soils, the concentrations of smelter elements (As, Cd, Cu, Hg, Pb, Zn) decrease with increasing distance from the stack, and regional patterns reflect the historical record of smelter contamination. In the underlying C-horizon till, concentrations show the absence of significant contamination at depth, except at highly contaminated sites (4 km from the stack) where metals can be leached from humus into the underlying sediments. The contaminant pathways in the soils vary with the element and distance from the smelter, as indicated by the chemical speciation of the metals in labile and non-labile phases. The maximum radius of detectable contamination varies among the smelter elements, ranging from 70 km for Cd to 104 km for As. Beyond these ‘background’ distances, the relative proportion of anthropogenic contamination in the surface terrestrial environment is more difficult to estimate, as the geochemical response to bedrock composition becomes more obvious.