Stratigraphy of the North Cliff section, Wellsch Valley site, Saskatchewan

Abstract

Eight separate till sheets are displayed at the North Cliff, which is part of the Wellsch Valley site in Saskatchewan. Those tills are differentiated by using physical characteristics, particle size, clay and primary mineralogy, and sediment chemistry. Grain size tends to fine downward in the section, and a significant increase in the mean [Formula: see text] centre of gravity indicates that some weathering occurred after deposition of the tills. Within the clay mineral suites, smectite tends to dominate in all eight tills, indicating that the paleoclimate was generally as dry as the present-day climate. Only till number 4 (counting from the bottom) contains halloysite; this halloysite may have been entrained from a preweathered surface by the glacier, or it may have formed in situ following deposition. Among the primary minerals, quartz dominates throughout the section, whereas plagioclases are least abundant in tills 4 and 5, possibly as a result of postdepositional weathering. Element composition shows only minor changes for Cu, Pb, Zn, Co, and Ni, whereas Mo increases upward in the section, Cr remains uniform in tills 1, 2, 3, 7, and 8 but increases slightly in tills 4–6, and Mn increases downward, possibly as a response to fluctuating amounts of groundwater. Till 4 forms the best stratigraphic marker in the sequence because of its high Mn content and the presence of halloysite, but till 5 also contains distinctive features in its element composition.The clay composition of the surface soil, which has formed in the top till since the departure of the last glacier, resembles that found in the underlying tills, whereas quartz and plagioclase are present in lesser amounts. These properties reflect both weathering in a semiarid climate and the presence of preweathered material from earlier paleosols.