The stratigraphy and sedimentology of the Cinq Isles formation, Fortune Bay, Newfoundland

Calcutt, Michael (1974) The stratigraphy and sedimentology of the Cinq Isles formation, Fortune Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Cinq Isles Formation consists of up to 1500 feet of limestones, sandstones, shales and conglomerates, well exposed around the shores of Fortune Bay, southern Newfoundland. -- The succession unconformably overlies the Simmons Brook batholith towards the southeast and Cambrian shales toward the southwest. The Formation is overlain disconformably by thick red conglomerates, of the Pools Cove Formation in the northeast and it is overlain disconformably by lithologically similar thick red conglomerates that were mapped previously as the Great Bay de l'Eau Formation toward the southwest. West of Salmon River the Pools Cove Formation oversteps the Cinq Isles Formation to lie directly on the Simmons Brook granite. -- The Cinq Isles Formation consists of thinly bedded unfossiliferous limestone, red and grey shales, sandstones and pebble beds. There is every gradation from laminae to discrete blebs of limestone within shale. Pebble beds, many with a carbonate groundmass, become dominant in the upper part J of the sequence. Within the succession, lateral and vertical variations are common. Gneissic clasts from the metamorphic Bay d'Espoir belt and granite clasts are abundant in many of the pebble beds and in the coarse conglomerates overlying the Cinq Isles Formation. Current direction features in sandstone and pebble beds indicate incoming currents from the north and northeast. The coarseness' of the clasts suggests a nearby source area. The nature of the gneissic clasts and their provenance implies Precambrian crystalline basement within the Avalon Zone toward the northeast. -- The age of the Cinq Isles Formation is uncertain, however, it is regarded as being Upper Silurian or Devonian because of its close stratigraphic relationship to the possibly Devonian Pools Cove Formation and the fossiliferous Devonian Great Bay de I'Eau Formation. The Pools Cove Formation is assigned to the Devonian because it contains granite boulders lithologically similar to Devonian granites in central Newfoundland and it is cut by the -Devonian Ackley batholith. -- Terrestrial conditions were prevalent during Middle-Late Silurian and Devonian times throughout much of Newfoundland. The lithologies of the Cinq Isles Formation suggest a near shore carbonate environment bordering an alluvial fan chain. Periodic flooding and entrenchment of the fan surfaces brought coarse material into the carbonate basin from the north and northeast. Subsequent encroachment of the alluvial fan across the near shore carbonate environment gave rise to the coarse upper deposits of the Cinq Isles Formation and the overlying Pools Cove conglomerates.

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