Deglaciation of the Dungiven Basin, north-west Ireland

Abstract:This paper describes glacigenic landforms and sediments occurring within the Dungiven Basin, north-west Ireland. It relates them to the pattern and timing of deglacial events within several sectors of the late Midlandian British–Irish Ice Sheet. The distribution, association and sedimentology of relatively well-preserved relict deglacial landforms are used in combination to reconstruct the nature and pattern of deglaciation in the region. An intricate pattern of ice-marginal and topographic control on the formation of glacially fed water bodies within the basin occurred during glacial down- and back-wastage toward ice-source areas. The dominant ice masses in the basin retreated west and south-west toward the south Donegal Highlands and Omagh Basin regions (Derrynaflaw Morphostratigraphic Unit). During evacuation of the Dungiven Basin by these ice fronts, the easternmost valleys of the northern Sperrin Mountains were deglaciating south-eastward, in the direction of the Lough Neagh Basin (Banagher Morphostratigraphic Unit). A proglacial lake in the mid- to lower Roe Valley during initial stages of the Derrynaflaw Unit was caused by the impoundment of proglacial drainage by a lobe of Donegal ice occupying the Foyle Basin. Subsequent glaciolacustrine environments in the valleys of the northern Sperrin Mountains were created by the interaction of retreating ice margins with local topography. Local watersheds provided control of water-body elevations as ice margins retreated south and west toward ice-dispersal centres.