Geomorphology and Quaternary geology of Codroy Lowland and adjacent plateaus, southwest Newfoundland

Abstract

The paper presents an interpretation of preglacial and glacial landforms and Quaternary sediments of approximately 2000 km2 of southwest Newfoundland. The area comprises lithologically controlled Codroy Lowland, floored by Late Wisconsinan glacial deposits, flanked by Long Range and Anguille Mountains plateaus, which bear pre-Quaternary fluvial denudation surfaces and evidence in weathering zones of multiple Quaternary glaciation. Part of Long Range Mountains bears no evidence of glaciation, and extensive areas there, including all of the Anguille Mountains, were ice-free at the Late Wisconsinan glacial maximum. The maximum glacial condition for which evidence is preserved prevailed some time before the Late Wisconsinan and surfaces exposed since then have not passed through an interglacial weathering regime, so that this condition probably can be assigned to an Early Wisconsinan glacial stade.Coastal cliffs on Cabot Strait expose a Late Wisconsinan drift sequence which indicates: (1) advancing ice moved perpendicular to the coast, striating rock and depositing till; (2) subsequently the coast was deglaciated and marine overlap ensued, approximately 14 000 years ago; (3) ice readvanced, probably down Codroy Lowland with a halt near the present coast, and deposited moraines at about 12 600 years ago.Total postglacial isostatic rebound has raised marine features only 5–10 m above rising sea level. The shoreline has likely been submerging since about 11 000 years BP under the combined influences of eustatic sea level rise, dominant over rebound, and possible subsidence beneath the load of more than 500 m of water in Laurentian Channel, only 30 km offshore.