Figure 8.26 Track of Mariana reference point from 0 to 100 Ma.
other half is buried beneath the St Lawrence River. The Siljan structure in Sweden is currently exposed at a height of about 500 feet. It is possible that one or both of these localities were covered by sea-water at the time of impact. In any event, it is interesting to note that the Siljan event, dated at 368 Ma, occurs within 1 Ma of the assigned Famennian/Frasnian stratigraphic boundary at 367 Ma. The Charlevoir event is dated at 357 Ma, which is within 1 Ma of the Ivorian/ Hastarian stratigraphic boundary at 356 Ma, or possibly the Devonian/Carboniferous subera boundary at 360 Ma.
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