Chronology and geochemistry of late Holocene eolian deposits in the Brandon Sand Hills, Manitoba, Canada

Abstract

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

Holocene Stratigraphy and Geomorphology of Flintstone Hill, Lauder Sandhills, Glacial Lake Hind Basin, Southwestern Manitoba

“…Therefore, we recognize that the sedimentary sequence at Flintstone Hill considered alone does not necessarily reflect regional-scale climatic variability. However, the similarity of the mid-and late Holocene eolian sequences at Flintstone Hill to those observed nearby in Manitoba (elsewhere in the GLHB, Wallace, 2001; the Brandon Sand Hills, David, 1971;Wolfe et al, 2000), and North Dakota (the Minot Dune Field, Muhs et al, 1997; the Sheyenne Delta, Running, 1997;Hopkins and Running, 2000) does suggest that regional-scale climate variability is the likely causal mechanism.…”

“…In the Brandon Sand Hills, about 100 km northeast of Flintstone Hill, a phase of dune activity occurred around 3500-3300 BP (Wolfe et al, 2000), suggesting that unit D may have formed during a regional period of dune activity.…”

“…Eolian units B through D may reflect regional-climatic variability because landscape response in eolian systems has been linked to climate (Clayton et al, 1976;Muhs et al, 1996Muhs et al, , 1997Running, 1997;David et al, 1999;Muhs and Wolfe, 1999;Wolfe et al, 2000;Hopkins and Running, 2000). In general, these climate-landscape response models indicate greatest landscape stability occurs during climatic episodes characterized by moist, cool, relatively drought-free conditions when water tables are high and vegetation cover is abundant.…”

“…Researchers working in parabolic dune-dominated landscapes identify several lines of evidence that strongly suggest parabolic dunes may have been present in their study areas during the mid-Holocene yet parabolic dune deposits from the mid-Holocene are rare (Muhs et al, 1996(Muhs et al, , 1997Running, 1997;David et al, 1999;Muhs and Wolfe, 1999;Wolfe et al, 2000). Complete reactivation of these deposits during intense mid-Holocene and later episode(s) of dune activity is considered the most likely reason that mid-Holocene parabolic dune deposits are not preserved.…”

Dedication

“…With a renewed interest in geomorphic processes and environmental change in the southern Canadian prairies, Peter's understanding of eolian systems in this region were invaluable. During the next decade, Peter published extensively with newly established colleagues (David, 1993a(David, , 1998David et al, 1999;Wolfe and David, 1997;Wolfe et al, 2000Wolfe et al, , 2001. From these contributions, it is recognized that eolian landscapes in prairie drylands are the most sensitive geomorphic systems to climate variability, and that much of the region lies near a threshold of extensive eolian activity.…”