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A series of northwest-southeast aligned, large-scale (up to 30 m high) eolian dunes, occurring in a confined (600 km2) desert area in northern Saskatchewan, Canada, was examined in the field. Observations were made of dune morphology and internal structure, and patterns of sand movement on the dunes were analyzed in relation to wind events during the summer of 1981.
Present cross-sectional profiles exhibit steeper northeast slopes, the lower segment of which are intermittently covered by psammophilous grasses. Dune structure is dominated by northeast-dipping accretion laminae. Three 14C dates from organic material cropping out on the lower southwest slopes reveal that the dunes have migrated as transverse bed forms at rates of roughly 0.5 m/yr during the last few hundred years. However, a progressive increase in height, bulk, and symmetry along the dune axis from northwest to southeast, suggests an along-dune component of sand transport. This view is supported by (1) field measurements of airflow and along-dune sand transport patterns on 2 dunes, and (2) the present-day wind regime (1963-78). Dominated by north-northeast to northeast w nds from January to June and by west-southwest winds from July to December, the resultant potential sand transport vector is toward the southeast, virtually identical to the dune axis.
The dunes are viewed as a hybrid type, forming in response to a combination of transverse and longitudinal processes and are probably not uncommon in many deserts. The discordance between the dune structure
(and migration direction) and the resultant effective wind vector may have significant implications for paleowind analysis in the geologic record. In this instance, the structure reflects only west-southwest (July-December) winds, owing to a southwest-northeast imbalance in sand movement. This imbalance is due mainly to the effect of sand-trapping by vegetation on northeast slopes, as well as to seasonal differences in sand mobility, the latter correlating partly with the semi-annual shift in the wind regime.
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