Formational history of the Wicklow Trough: a marine‐transgressed tunnel valley revealing ice flow velocity and retreat rates for the largest ice stream draining the late‐Devensian British–Irish Ice Sheet

Mark Coughlan,Katrien J J Van Landeghem,Zsuzsanna Tóth,Stephen Mccarron,Andrew J Wheeler

doi:10.1002/jqs.3234

Abstract

ABSTRACTThe Wicklow Trough is one of several Irish Sea bathymetric deeps, yet unusually isolated from the main depression, the Western Trough. Its formation has been described as proglacial or subglacial, linked to the Irish Sea Ice Stream (ISIS) during the Last Glacial Maximum. The evolution of the Wicklow Trough and neighbouring deeps, therefore, help us to understand ISIS dynamics, when it was the main ice stream draining the former British–Irish Ice Sheet. The morphology and sub‐seabed stratigraphy of the 18 km long and 2 km wide Wicklow Trough is described here from new multibeam echosounder data, 60 km of sparker seismic profiles and five sediment cores. At a maximum water depth of 82 m, the deep consists of four overdeepened sections. The heterogeneous glacial sediments in the Trough overlay bedrock, with indications of flank mass‐wasting and subglacial bedforms on its floor. The evidence strongly suggests that the Wicklow Trough is a tunnel valley formed by time‐transgressive erosional processes, with pressurised meltwater as the dominant agent during gradual or slow ice sheet retreat. Its location may be fault‐controlled, and the northern end of the Wicklow Trough could mark a transition from rapid to slow grounded ice margin retreat, which could be tested with modelling.

Highlights

The seafloor of the western Irish Sea reveals a number of deeps which include the Lambay Deep, Codling Deep and Wicklow Trough (Jackson et al, 1995) (Fig. 1)These bathymetric deeps have steep sides, are linear, and have been described as tunnel valleys (Eyles and McCabe, 1989)
The Trough is approximately 18 km long and is generally 2 km wide throughout. It is 82 m below sea-level at its deepest point and incised roughly 60 m relative to the surrounding seabed. It has an abrupt initiation at its northern terminus with the seabed morphology consisting of sediment waves that form the northern tip of the adjacent India Bank (Fig. 1) which continues into the Trough here separating it from the Codling Deep (Fig. 1)
From the synthesis of this data and analysis, the following conclusions can be drawn: 1. The Wicklow Trough is a tunnel valley that is part of a series of tunnel valleys generated by the Irish Sea Ice Stream; 2

Summary

Introduction

The seafloor of the western Irish Sea reveals a number of deeps which include the Lambay Deep, Codling Deep and Wicklow Trough (Jackson et al, 1995) (Fig. 1) These bathymetric deeps have steep sides (with slopes up to 12°), are linear, and have been described as tunnel valleys (Eyles and McCabe, 1989). Sea (Ehlers and Linke, 1989; Piotrowski, 1994; Huuse and Lykke-Andersen, 2000) They are inferred as formed by glacial processes at the Last Glacial Maximum (LGM) (Eyles and McCabe, 1989; Wingfield, 1989), when the Irish Sea Ice Steam (ISIS) advanced through the basins of the Irish Sea and Celtic Sea and retreated rapidly, draining the British-Irish Ice Sheet (BIIS) (Lockhart et al, 2018; Small et al, 2018; Scourse et al, 2019). Following an initial rapid phase of retreat between Scilly and the Wexford

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