MID-HOLOCENE GEOMORPHIC AND HUMAN HISTORY AT THE ATKINSON SITE, GLACIAL LAKE HIND BASIN, SOUTHWESTERN MANITOBA

A sedimentary sequence spanning much of the Holocene is exposed in cut-banks of the Souris River in glacial Lake Hind Basin, southwestern Manitoba. Unit A, at the base of the sequence is a glaciolacustrine silty-clay with peat and logs (A1) grading upward to alluvium (A2), is overlain by Unit B, a fine- to medium-grained sand unit with steep foresets dipping east to southeast (mid-Holocene dune deposits). Unit B is overlain in turn by Unit C, a thin eolian sand sheet capped by a well-expressed buried soil profile(s), and Unit D, an upper fine- to medium-grained sand unit containing buried soil horizons (late Holocene dunes). At the Atkinson cut-bank, however, mid-Holocene dunes interfinger laterally with fluvial sediments that host rare mid-Holocene Gowen archeological material (radiocarbon age from charcoal: 5280±50 BP). The purpose of this study is to determine the nature of the relationship between mid-Holocene dunes (Unit B) and the adjacent alluvium (Unit A2) and to clarify the paleoenvironmental context of the archeological site. Cut-bank and core data combined with a topographic survey were used to develop a three-dimensional reconstruction of the stratigraphy of the study site. At the eastern end of the cut-bank, Unit B thins and terminates as it interfingers with a silty clay texture facies of Unit A, which is interpreted as overbank fluvial. Within Unit B, poorly expressed A-C buried soil profiles are developed on a few dune foresets where the lower 1 to 1.5 m of the foreset is draped with a millimeter-scale layer of silty sediment. Foresets displaying these characteristics are more closely spaced at the east end of the cut-bank, where the silty drapes extend laterally and merge into adjacent stream floodplain sediments. These observations indicate that during the mid-Holocene, the dune encroached onto the floodplain, but periodically stabilized, permitting soil formation on the dune surface and overbank stream flooding of the dune toe. The proximity of dune and stream environments provided a resource-rich habitat for mid-Holocene people. Except for more active dune migration, the landscape was similar to the modern setting. The apparent lack of Gowen archaeological sites in Manitoba may result from burial by late Holocene sediments rather than abandonment of the area in response to mid-Holocene aridity.