A chronogram for postglacial soil-landscape change from the Palliser Triangle,Canada

Abstract

The soil-landscape chronogram summarizes the ways in which five slope-wash erosion cycles followed by two aeolian cycles interrupted postglacial soil formation in an enclosed hillslope system from hummocky moraine terrain. The four slope-wash cycles that followed the early-postglacial cycle occurred between 7.7 and 3 ka BP and caused about half of the total postglacial relief reduction. At the onset of the latter cycles, the locus of erosion switched from its prevalent position on the lower slope to the upper backslope, indicating recurrent fundamental changes in slope hydrology. The ensuing stratigraphic framework has a downslope thickening and fining clastic wedge, grading into the bottomland sequence and subdivided by soil catenas that merge upslope into a single compound mantle on the upland. The aeolian cycles entailed localized loess-dispersal systems, producing minor mantles of sandy-loam loess with saltation-load deposits on the leeward slope and suspension-load deposits elsewhere. Accumulation of long-range calcareous dust during the loess cycles supplied most of the secondary carbonates found in the buried soils. Three radiocarbon dates, together with Mazama tephra, enable partial correlation of these events to the regional Holocene-climate record.