Accelerator mass spectrometry and conventional radiocarbon age determinations of organic matter from paleosols indicate that the Brandon Sand Hills area of southern Manitoba has been subjected to recurrent intervals of eolian activity in the past 5000 years. Although precise regional correlations are precluded by dating uncertainties, periods of most notable paleosol development occurred around 2300 to 2000, 1400 to 1000, and 600 to 500 cal yr BP with eolian activity occurring before and after each of these periods. Episodes of eolian activity may correspond to periods of regional drought, whereas paleosols mark periods of increased moisture availability and stabilization by vegetation. The geochemistry of the eolian sands, paleosols and source sediments indicates that partial leaching of carbonates occurs from pedogenesis during humid climatic phases, and that this is probably the primary mechanism of carbonate depletion of eolian sands in this area. Recent trends in sand dune activity from historic aerial photography and early explorers' accounts indicate that the few active dunes that presently exist have stabilized at a rate of 10}20% per decade, despite several severe droughts in the 20th century. This may be attributed to pre-settlement droughts that were more severe than those in historic times although regional dune stabilization may also be related, in part, to the spread of forest cover in the past few hundred years. Crown copyright
Stabilized dune ridges occurring in northern Saskatchewan have previously been identified as variedly as "ice-crack moraines" and longitudinal dunes. Investigations of their morphological, structural, and sedimentary attributes reveal that they are, indeed, of eolian origin, but they form a particular group within the parabolic dune association, namely, the "Cree Lake type dune ridges." The ridges occur in association with other types of parabolic dunes and other eolian features, such as loess and wind-abraded glacial blocks and bedrock outcrops. The dunes and the associated eolian features were all formed by southeasterly paleowinds of uniform direction. The dune ridges developed from primary parabolic dunes of simple and composite types through the process of dune elongation. At the same time, exposed rock surfaces were abraded by the wind and loess was deposited downwind from the developing dune fields. The southeasterly direction of the paleowinds, which is almost directly opposite to the direction of the present-day winds affecting dunes in the Lake Athabasca area, was due to adiabatic air masses coming off the ice sheet from the east and affected eolian activity in quite a large region in northern Saskatchewan and Alberta. The somewhat cool and sufficiently dry adiabatic winds checked the vegetation on the dunes and in the areas around them. The development of the dune ridges came to an end when a sudden climatic change evoked the rapid stabilization of the dunes by vegetation but not before most of the ridges became partly deformed by southwesterly crosswinds resulting from the same climatic change. The period of eolian activity is estimated from the age of the local ice frontal positions to have been between 10 000 and 8800 years BP. Only one other region is known from North America, namely, the St. Lawrence Lowland in the east, where analogous eolian environment prevailed in the zone peripheral to the continental ice sheet and produced comparable eolian features.
Geomorphic evidence and optical ages from seven locations indicate that widespread dune activity occurred within the last 200 years in the Great Sand Hills region of southwestern Saskatchewan. Optical ages (n = 36) define an interval of dune activity bracketed by the earliest age of back ridges in the Seward sand hills (185 ± 8 years) and the average age of stabilized dune heads (about 105 years). During this interval, parabolic dunes were active in all areas studied. These ages indicate that the most recent interval of activity was initiated about AD 1800, and continued at a level higher than present for approximately 80 years. The most likely cause of dune activation was lower-than-average precipitation (relative to 19601991 values) through the 1700s, culminating in drought in the late 1700s, as evidenced in dendroclimatic records from the Cypress Hills and from the Rocky Mountain foothills. Dunes affected by such climatically induced regional activity require many decades to restabilize. Historical observations show that dunes in this area have been restabilizing throughout the 20th century. For the southern Canadian Prairies, a region with serious concerns about the implications of global warming, this study highlights the sensitivity of sand dunes to drought and cumulative moisture stress.
The lithological content of tills in central Gaspésie is evaluated by pebble counting of 231 samples collected in excavation pits and containing 200 pebbles each. The results are used here to establish the pattern of debris dispersal and to infer the glacial history of the area. The dispersal pattern is characterized by well-defined southeasterly (160–170°) and northeasterly (40–60°) trending trains. Half-distance values of glacial transport along the trains range from 5 to 9 km for both directions, suggesting ice flow events of considerable magnitude. The volume of material in the trains represents 1–6 m of glacial erosion of the bedrock. Glacial cirques and short U-shaped valleys, about 100–200 m deep, are incised into the McGerrigle Mountains granite pluton as well as the adjacent metabasalt. The corresponding trains are aligned with these erosional features, indicating that their clast content was derived from those features during an early Alpine Glacier Phase. The southeasterly trending dispersal trains are associated with an invasion of central Gaspésie by the Laurentide Ice Sheet during the Early Wisconsinan, whereas the northeasterly trending trains are associated with a local centre of outflow over Gaspésie during the Late Wisconsinan.
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