Illinoian to Late Wisconsinan stratigraphy at Woodbridge, Ontario

Abstract

Near Woodbridge, northwest of Toronto, Ontario, a 15 metre-high railroad cut and associated borrow pit, first excavated in 1962, exposed a multiple till sequence and intervening fossiliferous sediments. Work over the next 35 years revealed that Illinoian York Till, early Wisconsinan Sunnybrook Till, and late Wisconsinan Humber till, Halton Till, and Wildfield Till are interbedded with fossiliferous sediments equivalent to the Sangamonian Don Formation, early Wisconsinan Scarborough Formation (>50 ka BP), and middle Wisconsinan Thorncliffe Formation (45 ka BP). A complex periglacial record displays multistage fossil frost wedges, indicating intervals of severe climate in late Illinoian and early Wisconsinan time. Cored boreholes indicate deep gravel below and a till on Ordovician shale bedrock (Georgian Bay Formation). Vertebrates, molluscs, ostracodes, insects, and plants (diatoms, wood, seeds, pollen) indicate mostly cool conditions (boreal to tundra) for interstadial sediments. Interglacial conditions are represented by vertebrates, molluscs, and plants above York Till. Many taxa are new to the Quaternary of the Toronto area.

The pre-Late Wisconsin stratigraphy of southern Simcoe County, Ontario: implications for ice sheet buildup, decay, and Great Lakes drainage evolution

“…Trough and hummocky cross-stratified sands along the Scarborough Bluffs (Eyles and Clark 1986) suggest a water plane of approximately 130 m asl (similar to postglacial Lake Iroquois water levels, which also drained through the Rome outlet). Karrow et al (2001) report dates of 45.0 ± 0.9 and 29.7 ± 0.9 14 C ka BP for wood and bone, respectively, recovered from peat beds within a gravel unit overlying the Sunnybrook drift at approximately 152 m asl at Woodbridge (Figs. 1a, 2).…”

“…1a; Dreimanis 1992), as well as weathering profiles that developed on colluvium overlying the York Till at Woodbridge ( Fig. 1a; Karrow et al 2001), suggesting Sangamon Interglacial conditions. Regional base levels were at least 35 m lower than at present in southern Simcoe County during this interval.…”

“…Thick, stacked sequences of diamicton and stratified sediment attributed to SU3 in the southern part of the county may record ice-marginal sedimentation as debris flows (flow tills) during the retreat phase of SU3 (Evenson et al 1977). Depletion of carbonate and colour staining in the upper part of SU3 indicate prolonged subaerial exposure and incipient soil development following glacier retreat (Karrow et al 2001). …”

“…Although tills of presumed Illinoian age have been recognized in southern Ontario for several decades, relatively little insight has been gained on the characteristics of the ice sheet(s) that deposited them. Classic exposures of York Till in Toronto (Terasmae 1960;Karrow 1967;Eyles 1987;Karrow et al 2001) are generally described as thin, weathered units that indicate conflicting paleoice flows from the northeast (Karrow 1967) and (or) from the south (Terasmae 1960). Watt (1954) and Lajtai (1969) reported York Till interbedded with and overlain by lacustrine sediments in subway tunnel exposures in downtown Toronto, but these are the only references to multiple till layers within the formation in southern Ontario.…”

“…Paleozoic bedrock is overlain by a number of Illinoian tills in southern Ontario, the York Till in Toronto (Terasmae 1960;Karrow 1967;Karrow et al 2001;Fig. 2a) and the Bradtville Till along the north shore of Lake Erie (Dreimanis 1992).…”