Hello,
I have undertaken a great deal of investigation in this area as well. Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay has stated that Hudson's Bay, and the Michigan Basin are not Astroblemes. Yet Richard Donofrio, consulting geologist from Oklahoma City says that they are. The underlying geology of Western Hudson's Bay appears to be signatory of a large astrobleme, while the eastern, more visible crater-like structure does not seem to have any striking underlying structure and yet a ridge of hills in Northern Ontario trace where the crater rim would extend. Donfrio's logic regarding these structures seems secure and he says that oil forms around these structures. The presence of oil in Southern Ontario just where it should be seems to support this supposition. I am inclined to agree. Another large Astrobleme seems to be what forms Lake Nipigon in Northern Ontario. This lake is very circular, but the structure is very eroded. The erosion is very similar to the erosion found associated with the Brent Crater in Algonquin Park. What is most interesting about the Lake Nipigon "crater" is that there has recently been found at the southern end where the material that would have been scraped out due to ersion, is a deposit of iridium and other Platinum group metals. The evidence presented by Donfrio regarding the Michigan basin is very good and I think that he is correct. The evidence for the eastern, visible structure of Hudson's Bay is less clear, while the underwater structure in the western half of Hudson's Bay seems very clear. A telltale sign of whether the Hudson's Bay structures are Astroblemes will be if oil is found in the correct proximities.

Brian Johnston