Evaluating the Interplay of Subglacial and Marine Processes at an Open Atlantic Tidewater Margin, SW Ireland

The relative importance of subglacial and marine processes, in a glacimarine (tidewater) setting, can be evaluated from sediments exposed on the Atlantic coast at Waterville, Co Kerry, SW Ireland. Here, three main sediment units (total 300 m long, 14 m high) are present. Rhythmically-laminated clay-silt is present across the base of the exposure. This unit comprises fluidally-deformed laminations that are truncated by undeformed planar-laminated rhythmites (1 cm thick). Overlying this unit is a massive sand unit forming tabular sheets that are interbedded with diamicton lenses. The uppermost part of the sand unit is penetrated by dish and lens- shaped density-driven structures that are infilled by diamictons. The sand unit is overlain by a gravely diamicton unit that varies from openwork gravel to matrix-dominant diamicton. Individual diamicton beds are sometimes arranged in normally graded and shallowly-dipping planar beds. The lower boundary of the diamicton unit is sometimes marked by glacitectonic open folds developed in the underlying sands. The sediments exposed at Waterville are interpreted as an open marine to subglacial (coarsening-up) sequence formed during high relative sea-level conditions by a marginal advance of the late Pleistocene Cork/Kerry ice sheet. Quiet-water deposition (clay-silt unit) was succeeded by deposition of water-sorted subtidal sands punctuated by episodic high-energy mass flows (forming diamicton lenses). The upper diamicton unit records more continuous and ice-proximal subaqueous mass and debris flows under varying energy and hydraulic conditions. The Waterville sequence, facing the open Atlantic, uniquely reflects the relative interplay between subglacial and marine processes in a NW European Atlantic setting.