PALEOMAGNETIC EVIDENCE FOR LATE CENOZOIC GLACIATIONS IN THE MACKENZIEMOUNTAINS OF THE NORTHWEST-TERRITORIES, CANADA

The Mackenzie Mountains were affected by montane valley glaciers durin g the Pleistocene and peripherally by the Laurentide Ice Sheet during the last glaciation. In this paper we report on magnetostratigraphic d ating and correlation of three sections recording Late Pliocena to Lat e Pleistocene glaciations: Katherine Creek, Little Bear River, and Inl in Brook (located around 65 degrees N, 127 degrees W). Each section co nsists of a colluvial unit overlying a Pliocene pediment surface cut i nto Proterozoic or Paleozoic bedrock. or Tertiary gravel, which is in turn overlain by a stack of five, and in places six, montane tills, us ually with soils developed al their surfaces, and capped by a Laurenti de till. Normal and reversed magnetizations were recognized with singl e-domain magnetite as a dominant remanence carrier, The Katherine Cree k section has a normally magnetized colluvium at its base, which is ov erlain by two reversed tills, succeeded by three normal tills. We inte rpret the top two tills to be of Brunhes age (<780 ka) but argue that tile lowermost normal till is of probable Olduvai age (ca. 1.8 Ma). Th e two underlying tills are of Matuyama age (2.6 Ma to 780 ka), and the colluvial base is assigned to the Gauss (3.5-2.6 Ma). The Little Bear River section exposes a stratigraphic record similar to that found at Katherine Creek. Only four units could be assigned a paleomagnetic po larity, the others yielding incoherent results. Paleosols on the first and second till units were reversed and normal, respectively, and the top till was normal. Thus there is clear evidence of an older (revers ed) Pleistocene glaciation and a magnetostratigraphic record compatibl e with that found at Katherine Creek. Magnetic measurements from Inlin Brook gave largely incoherent results. with the exception of the surf ace (Laurentide) till, which is normal. The glacial history recorded i n the Mackenzie Mountains correlates well with other studies carried o ur in the Cordillera. The large-scale changes in climate revealed in t hese terrestrial records provide baseline data Tor paleoenvironmental reconstruction.