The sedimentary record of drifting ice (early Wisconsin Sunnybrook deposit) in an ancestral ice-dammed Lake Ontario, Canada

Abstract

Outcrops of pebbly mud (diamict) at Scarborough in Southern Ontario, Canada (the so-called Sunnybrook ‘Till’) are associated with the earliest incursion of the Laurentide Ice Sheet (LIS) into mid-continent North America some 45,000 years ago. The Sunnybrook is a blanket-like deposit containing deepwater ostracodes and occurs conformably within a thick (100 m) succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake. Contextual evidence (associated facies, sedimentary structures, deposit geometry and landforms) indicates a low energy depositional setting in an ice-dammed ancestral Lake Ontario in which scouring by floating ice masses was an important process. U-shaped, iceberg-cut scours (with lateral berms) up to 7 m deep, occur on the upper surface of the Sunnybrook and are underlain by ‘sub-scour’ structures that extend several meters below the scour base. Ice-rafted concentrations of clasts (‘clast layers’), grooved surfaces formed by floating ice glissading over a muddy lake floor (‘soft sediment striations’) and melanges of sand and mud mixed by grounding ice keels (‘ice keel turbates’) are present and are all well known from modern cold environments. The wider significance of this depositional model is that the LIS margin lay east of Scarborough and did not overrun Southern Ontario. This finding is in agreement with recent data from the Erie Basin of Canada, Ohio, and Indiana where deposits formerly correlated with the Sunnybrook (and thus implying an extensive early Wisconsin ice sheet) are now regarded as Illinoian. A speculative hypothesis is proposed that relates deposition of the Sunnybrook and two younger deposits of similar sedimentology, to surge-like instabilities of the southern LIS margin.

Micromorphology of diamicton affected by iceberg-keel scouring, Scoresby Sund, East Greenland

“…Eyles and Clark, 1988;Woodworth-Lynas and Landva, 1988;Longva and Bakkejord, 1990;Woodworth-Lynas and Guigné, 1990;van der Meer et al, 1992;Rocha-Campos et al, 1994;Eyles et al, 1997;van der Meer and Warren, 1997;Eyles et al, 2005;Linch et al, 2012;Linch and van der Meer, 2014). Here, folds and sheath folds are of almost identical style and geometry to those identified in ice keel scoured sediments described in previous investigations (Linch et al, 2012;Linch and van der Meer, 2014).…”

“…Since planar shear deformation occurs commonly in ice keel scoured sediment (e.g. Eyles and Clark, 1988;Woodworth-Lynas and Landva, 1988;Longva and Bakkejord, 1990;Woodworth-Lynas and Guigné, 1990;Eyles et al, 2005;Linch et al, 2012;Linch and van der Meer, 2014), and because it is unlikely to be developed by other deformation processes (e.g. subglacial, mass-wasting) in Scoresby Sund (see above), it can also be attributed to iceberg scour in this investigation.…”

“…WoodworthLynas and Landva, 1988;Longva and Bakkejord, 1990;Woodworth-Lynas and Guigné, 1990;Woodworth-Lynas, 1992;Rocha-Campos et al, 1994;Eyles et al, 1997Eyles et al, , 2005Eden and Eyles, 2001;Eyles and Meulendyk, 2008;Linch et al, 2012;Linch and van der Meer, 2014) and offshore (Kilfeather et al, 2010). This previous work has shown that a distinctive suite of structures (dominated by planar shear, sediment mixing and porewater structures) characterises i) iceberg scoured clays and ii) ice keel scoured pebbly sandy mud and finegrained sands, which is unlike those structures associated with subglacial tills and masswasting deposits (Linch et al, 2012;Linch and van der Meer, 2014).…”

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

“…2a). Iceberg scours into sands (Eyles et al 2005) and intervening Seminary and Meadowcliffe diamicts (tills?) (see Karrow 1967; record persistent ice in the Lake Ontario basin until the region was eventually covered by Late Wisconsin (Michigan Subepisode) ice depositing the Catfish Creek and Newmarket-Northern tills sometime after 22.8 14 C ka BP (Hobson and Terasmae 1969;Fig.…”

A review on late Paleozoic ice-related erosional landforms in the Paraná Basin: origin and paleogeographical implications

“…Woodworth-Lynas & Dowdeswell 1994). Vesely & Assine (2014) argued that the features observed in the striated surfaces of southeastern Paraná are comparable to IKSM reported by Eyles et al (2005) in the Pleistocene of North America and by Dionne (1969) from modern tidal flats in Canada. Also, they speculated that similar late Paleozoic soft-sediment striated surfaces found in other localities of Gondwana and originally treated as subglacial landforms should have the same origin.…”