ABSTRACT

The Attawapiskat Formation outcrops along a 50 km stretch of the Attawapiskat River in northern Ontario. The rocks consist of a series of patch reefs and their associated sediments. The age of the reefs is late Llandoverian to Wenlockian and possibly early Ludlovian, as determined by the Attawapiskat fauna. This fauna is similar to that found in the Guelph Formation of southern Ontario. The distribution and size of the patch reefs are similar to those in the modern Capricorn Reef complex, Australia. The Attawapiskat Formation in the study area is completely limestone. Five mappable facies are identified. The Framestone facies constitutes the main framework of the reefs, consisting of tabular stromatoporoids and corals bound together by algae and bryozoa. The centre of the larger patch reefs may be occupied by a sparsely fossiliferous zone that represents a Lagoonal facies. The reefs are capped by a fossiliferous Crinoidal facies, which grades laterally to the Off-Reef facies. In some patch reefs, bedded units of the Off-Reef facies drape over or are truncated against the reefs. The Attawapiskat Formation is the most important reservoir rock in the Hudson Bay Platform, but the distribution of the Attawapiskat is poorly understood. Geochemical evaluation indicates a low maturity level throughout the Hudson Bay Platform.

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