Sedimentology and development of parabolic dunes, Grande Prairie dune field, Alberta

The Grande Prairie dune field in northwest central Alberta is composed of parabolic and dome dunes, presently inactive but which had developed under westerly winds. Two parabolic dune types are recognized on the basis of arm length, nose width, and dune height. Variations in parabolic dune morphology are attributed to spatial and (or) temporal differences in sediment budget as elucidated from sedimentary sequences preserved in the dunes. Seven facies and four subfacies are distinguished from sedimentary sequences examined in nine dune sections. Lee-side deposits of parabolic dunes are typically composed of concave-downward cross-strata that develop from grainfall on a cohesive slipface and are interbedded with avalanche cross-strata. Lee-side deposits interfinger downwind with low-angle to horizontal ripple and grainfall laminations of bottomset deposits and are overlain by shallow-dipping topset deposits. Topset deposits of type 2 parabolic dunes contain sedimentary structures that are indicative of moisture (e.g., adhesion laminae and wet grainfall deposits) and vegetation (e.g., scour surfaces associated with calcareous root tubules) during deposition. These indicators suggest that type 2 parabolic dunes retained sediment effectively, whereas their absence in type 1 parabolic dunes suggests that these dunes did not retain sediment effectively. Type 2 parabolic dunes contain abundant grainfall deposits in topset beds, indicating a high sediment supply, whereas type 1 parabolic do not, suggesting they had a lower sediment supply.