Sedimentology and development of parabolic dunes in the Seward Sand Hills, Saskatchewan.

摘要

The Seward Sand Hills, southwestern Saskatchewan, is composed of parabolic dunes, most of which are presently inactive. Eight facies were determined through the examination of 5 parabolic dunes. One unique facies developed from sediment adhering to a damp surface, with a grey colouration resulting from acidic rainwater leaching away the oxidized coating from the quartz grains. Other facies found in the lee-side deposits of parabolic dunes were composed of high-angle cross-strata that develop from grainfall and avalanching. Lee-side deposits interfinger downwind with facies that have low-angle horizontal ripple and grainfall laminations.;The variation in sedimentary structures observed in the dune field can be attributed to differences in modes of deposition. The different modes of deposition are grainfall, grainflow, and tractional deposition. These different modes of deposition, as well as the different depositional conditions, resulted in the eight facies established for the Seward Sand Hills. The various depositional conditions which assisted in creating the eight facies include: geomorphology of the depositional surfaces; wind speed and direction; moisture conditions; sediment supply; and vegetation cover. The geomorphology of the depositional surface controls the distribution of facies. Wind speed and direction controls the sedimentation rates and migration rates of parabolic dunes. The different facies that comprise topset deposits are controlled by the moisture of the depositional surface, sediment supply, and vegetation cover.