Hillslope sediments and landscape evolution in Wanuskewin Heritage Park : a geoarchaeological interpretation

Wanuskewin Heritage Park is situated approximately three kilometres north of the City of Saskatoon, Saskatchewan and is the location of 19 precontact archaeological sites. This study examines hillslope sediments and processes at four of the archaeological sites: Cut Arm, Meewasin, Amisk, and Thundercloud. The Cut Arm and Meewasin sites are in the South Saskatchewan River valley and the Amisk and Thundercloud sites are in the Opimihaw Creek valley. The Opimihaw Creek is a tributary of the South Saskatchewan River. The record of postglacial hillslope development is complex and fragmentary because not all erosional and depositional events are preserved at each of the study sites. However, the physical characteristics of the soil and sediment coupled with radiocarbon dates and dates from diagnostic cultural material indicate general trends. Hillslope activity began before 5.42 ± 0.12 ka BP in the Opimihaw Valley and 3.864 ± 0.055 ka BP in the South Saskatchewan Valley. Opimihaw Valley hillslope activity began during the Altithermal period, a period of aridity and warm temperatures between approximately 9 ka BP and 4 ka BP. In both valleys, numerous but weakly developed buried soils separated by hillslope sediment record repeated episodes of slope erosion and deposition between approximately 4.5 ka BP and 3.5 ka BP. Comparison with prairie lake sediments indicates this phase of slope erosion corresponds to a climatic change from the dry conditions of the Altithermal to a period of maximum Holocene humidity (ca. 4.5 ka BP to 3 ka BP). In addition, thin intermittent weakly developed soils are generally overlain by thicker soil profiles. The thicker soils suggest longer periods of nondeposition, landscape stability and soil formation and thus, a reduction in the frequency of hillslope erosion and deposition. This reduction in slope activity occurred after approximately 2 ka BP. Prairie paleoenvironmental data suggest the longer periods of landscape stability are related to moister climatic conditions and increased vegetation cover. Lastly, poorly sorted debris flow sediments ranging in size from clay to boulders are generally overlain by fine-grained sediments deposited from overland flow. Therefore, in addition to a reduction in slope activity there is a decrease in the competence of the slope processes in these stratigraphic sequences