Internet science gadfly, Mr. Thomas Lee Elifritz, suggested a couple of years ago that the subtle elevation feature in Ontario described in his monograph below might be a candidate for what might remains after a large impact into the Pleistocene ice sheet. Like Mr. Elifritz or not, it is an interesting feature and I thought worth posting. If someone has access to Canadian LiDAR imaging I would love to see it more clearly.
Here is a Google Maps link, check out the dramatic and unmistakable outwash channel “spurting” from the southeast terminus of the feature.

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I really don’t like working you guys up into a frenzy again, but here goes :
http://www.lifeform.org/2012/02/02/extraterrestrial-material-found-in-younger-dryas-black-mat/
I knew it, TL, but you announced it! Thanks, GAH.
Although their reasoning is even more circuitous, THIS GROUP apparently agrees with the YD impact hypothesis as well.
I know.
I’m still skeptical. I need more. This kind of horizon should be able to yield something a little more definitive.