Anticosti Island: Geomorphological Context of a Unique Karst Area

Abstract

The Gulf of St. Lawrence Lowlands geomorphological landscape region includes Anticosti Island, the Mingan Islands and several small areas bordering the Gulf of St. Lawrence, the Strait of Belle Isle and the Newfoundland Coastal Lowland. The region is underlain by the St. Lawrence Platform geological province whose formations are made up of different types and proportions of Paleozoic limestones and detrital rocks. Anticosti Island itself covers an area of 7,943 km² and is located between the Jacques-Cartier and Honguedo straits. The island is a monoclinal SSW dipping cuesta structure of carbonate strata with wave-cut terraces up to c.120 m asl. Two cuesta fronts and canyons are distinctive features of the island. The island was glaciated during MIS 2 and MIS 4. The central plateau and interfluves above 76 m are covered with thin discontinuous till (ground moraine) or thin (≤1 m) organic deposits. Outcrops of preglacial weathered bedrock remain. Karst features are found everywhere on the island. In most areas, karst is of recent Holocene age with shallow underground flows. The Upper Salmon River karst is the most developed and seems somewhat older and is partly inherited from an earlier period of karst development. Newly discovered springs and their associated dry valleys appear definitively older. The holokarst covers an area of ±23.7 km² and is fringed to the west and south by fluvikarst areas with surface and underground flows.