New Canadian Cryptoexplosion Crater at Lake St Martin, Manitoba

Abstract

LAKE ST MARTIN (51° 43′ N, 98° 30′ W) forms a broad shallow depression on nearly flat lying Palaeozoic carbonate rocks between Lake Winnipeg and Lake Manitoba. The occurrence of crystalline Pre-Cambrian rocks, fresh looking vesicular volcanic rocks and extensive post-Palaeozoic gypsum deposits within an area of about 200 square miles on the north side of the lake suggests that unusual structural complexities are present. The relations between these rocks are obscured by poor outcrop and extensive swamp, but a series of shallow bore holes in the anomalous area, together with re-examination of the surface outcrop, have recently made it apparent that they are the surface expression of a resurgent cryptoexplosion crater of Permian or Triassic age.