Abstract

Skeleton Lake, Ontario (lat. 45°15′N, long. 70°27′W), contains an approximately circular depression, 3.6 km in diameter and 65 m maximum depth, which appears to truncate the regional geological and physiographic trends of the local Precambrian gneisses and migmatites. Outcrops of breccia are present on the northern lake shore, and erratics of Ordovician limestone, evidently scoured from the lake bottom by glaciation, occur along the south shore. Aeromagnetic data indicate a field of low uniform magnetic intensity across the lake, in contrast to the variable regional magnetic pattern. A detailed gravity survey has revealed a circular gravity anomaly of −3.3 ± 0.7 mGal (−33 ± 7 μm∙s−2) over the depression. The anomaly has been modelled by bowl-shaped distributions of low density brecciated rocks. These observations suggest that the Skeleton Lake depression is the eroded remnant of an impact crater of Paleozoic age which has been preserved by a covering of Ordovician sediments until recently exhumed.

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