Postglacial evolution of a fine-grained alluvial fan in the northern Great Plains, Canada

This paper reports on the first subsurface core taken from an alluvial fan in the interior plains of western Canada. Sedimentary structures, grain size, grain roundness, loss on ignition, charcoal abundance, bulk authigenic geochemistry, colour, mineralogy and microscopic charcoal identifications show that a fine-grained fan developed through a succession of depositional environments. Within each environment, sediment erosion, transportation and deposition processes were conditioned by changing dominant partial area contributions and complex geomorphic responses. Neither the rate nor the processes of aggradation have been constant through time. Succession from one depositional environment to another involved the crossing of geomorphic thresholds. While climate may have affected sediment yield and therefore the timing of threshold crossings, the basic sequence was controlled by aggradation alone. The sensitivity of this site to climate change is thus overwhelmed by internal processes.