SEA-LEVEL CHANGE AND NEARSHORE STRATIGRAPHY: A COMPARISON OF NORTHERN IRELAND, UK AND THE WESTERN GULF OF MAINE, USA

Northern Ireland, UK and Maine, USA possess broadly similar, rock-framed coastal zones that have experienced similar late Quaternary histories. Recent seismic reflection observations and underwater vibracores allow us to evaluate their Quaternary evolution. Following glaciation, each was transgressed owing to isostatic depression of the land. Each emerged to a lowstand position, - 60 m at 10.5 ka in Maine, - 30 m at an unknown time in NI. Sea level has risen at varying rates in coastal Maine. During a mid-late Holocene slowdown in the rate of sea-level rise, extensive estuarine deposits apparently collected in many areas. Sea level has risen at decreasing rates since then, and much of the inner shelf has lost any regressive sediment. Two exceptions to this include lowstand deltas that continued to form up to recent times off large rivers. These sandy deposits have produced many of the best sea-level data we have gathered. Another possible terrestrial deposit preserved during transgression includes freshwater wetland deposits contained in bedrock depressions. These deposits have not been directly observed, but are inferred to underlie and source natural gas fields in muddy embayments. Off Northern Ireland, sea level rose several meters above present in the middle Holocene. It fell to the present location and is more or less stable today. Out to – 30 m depth, fine sand dominates vast areas off large beaches and rivers, though no lowstand deltas are yet recognized. In Belfast Lough, a muddy embayment, a sand deposit was cored over glacial-marine mud in several places. This appears to be a beach or shoreface deposit that is overlain by a sequence of intertidal to subtidal materials. Radiocarbon dates are awaited from Northern Ireland.