Tephrochronology, magnetostratigraphy and mammalian faunas of Middle and Early Pleistocene sediments at two sites on the Old Crow River, northern Yukon Territory, Canada John A. Westgate a, ⁎, G. William Pearce b , Shari J. Preece a , Charles E. Schweger c , Richard E. Morlan d, 1 , Nicholas J.G. Pearce e , T. William Perkins e a Department of Geology, University of Toronto, Toronto, ON, Canada M5S 3B1 b 152 Indian Road, Kingston, ON, Canada K7M 1T4 c Department of Anthropology, University of Alberta, Edmonton, AB, Canada T6G 2H4 d Archaeological Survey of Canada, Canadian Museum of Civilization, Hull, Quebec, Canada J8X 4H2 e Institute of Geography and Earth Science, Aberystwyth University, Wales, SY23 3DB, UK abstract article info Article history: Received 28 March 2012 Available online 6 October 2012 Keywords: Pleistocene Tephrochronology Magnetostratigraphy Mammalian fossils Old Crow Basin Yukon Alaska Alluvial and lacustrine sediments exposed beneath late Pleistocene glaciolacustrine silt and clay at two sites along the Old Crow River, northern Yukon Territory, are rich in fossils and contain tephra beds. Surprise Creek tephra (SZt) occurs in the lower part of the alluvial sequence at CRH47 and Little Timber tephra (LTt) is present near the base of the exposure at CRH94. Surprise Creek tephra has a glass fission-track age of 0.17±0.07 Ma and Little Timber tephra is 1.37±0.12 Ma. All sediments at CRH47 have a normal remanent magnetic polarity and those near LTt at CRH94 have a reversed polarity — in agreement with the geomagnetic time scale. Small mam- mal remains from sediments near LTt support an Early Pleistocene age but the chronology is not so clear at CRH47 because of the large error associated with the SZt age determination. Tephrochronological and paleomag- netic considerations point to an MIS 7 age for the interglacial beds just below SZt at CRH47 and at Chester Bluffs in east-central Alaska, but mammalian fossils recovered from sediments close to SZt suggest a late Irvingtonian age, therefore older than MIS 7. Further studies are needed to resolve this problem. © 2012 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction Old Crow Basin in northern Yukon Territory (Fig. 1) escaped glacierization during the late Cenozoic; its thick sedimentary fill, composed mostly of fluviatile and lacustrine sediments, did not suffer the severe erosive effects of glaciers. However, the character of these sediments was controlled at times by the nearby presence of the Laurentide ice sheet to the east and this was certainly true during the late Pleistocene (Hughes, 1972, 1989; Vincent, 1989). A rich ar- chive of environmental change during the Pliocene and Pleistocene is preserved in these sediments (Schweger, 1989) as indicated by their highly fossiliferous nature and chiefly demonstrated by the many bone-covered sand bars along the Old Crow River (Harington, 1989, 2011). Importantly, distal tephra beds, derived from volcanoes of the eastern Aleutian arc and Wrangell volcanic field in Alaska (Westgate et al., 1983; Westgate et al., 1995) offer the prospect of good chronological control and reliable correlations. During the early 1980s, J.V. Matthews, Jr. (Geological Survey of Canada), Charles Schweger, and Richard Morlan conducted recon- naissance studies on Quaternary deposits exposed in the bluffs of Old Crow River. Among the numerous sites they examined, two were of special note because of their highly fossiliferous nature and presence of tephra beds: localities CRH47 and CRH94 (Fig. 1), hereaf- ter for brevity referenced as sites 47 and 94. These site designations were made by C.R. Harington (Canadian Museum of Nature, Ottawa) more than 40 years ago and continue to be used by scientists working in the Old Crow Basin. In 1985, Westgate was invited to participate in stratigraphic studies of these two sites with the aim of throwing light on the age of these sediments by means of tephrochronological and paleomagnetic investigations. This report contains the results of that study. Following a description of the lithostratigraphy, we give the sa- lient characteristics of the tephra beds, noting their glass fission-track ages, and provide information supporting recognition of correlative beds in Yukon and Alaska. The detailed magnetostratigraphic study provides corroborative chronological controls and enables local cor- relation of the defined lithostratigraphic units. Finally, we present Quaternary Research 79 (2013) 75–85 ⁎ Corresponding author. E-mail address: westgate@geology.utoronto.ca (J.A. Westgate). 1 Deceased. 0033-5894/$ – see front matter © 2012 University of Washington. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yqres.2012.09.003 Contents lists available at SciVerse ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres