The glacigenic deposits of Western Lleyn, North Wales: Terrestrial or marine?

Abstract

This paper describes a complex sequence of glacigenic sediments occupying a faultbounded depression at Aberdaron Bay, western Lleyn. The sequence offers an insight into sedimentary environments during deglaciation of the Irish Sea Basin. A lower stratified diamict association (LDA) containing contorted units of fine sandhilt and displaying strong, consistent clast fabrics, is overlain by an upper diamict association (UDA) with weaker fabrics and extensive sand and gravel layers and channel fills. Certain characteristics of the sequence can be explained by a glacimarine depositional model, but there are several problems. In particular, the geometry of the sediments is difficult to explain without recourse to the melting of buried ice. An alternative model that overcomes these problems involves the decay of a terrestrial glacier containing reworked marine sediments. Supraglacial sediment flows released during decay of thinner ice covering the surrounding hills (UDA) would have rapidly buried a thick stagnant ice mass in the Aberdaron depression, facilitating slow melting and release of basal meltout till (LDA). A model is presented that accounts for the stagnation and in situ decay of a debris-rich Irish Sea glacier, and which could explain many of the deposits and landforms surrounding the Irish Sea Basin without recourse to high relative sea-levels.journal of Quaternary Science

Timing and depositional environments of a Middle Pleistocene glaciation of northeast England: New evidence from Warren House Gill, County Durham

“…11) are 'clast and tail' features, with the narrow clay beds extending out to form the augens' 'tails'. The non-graded clay laminations, the rotated, augen-shaped clay clasts, and the lack of lateral continuity of the clay laminations are similar to structures observed in Norfolk and elsewhere (e.g., McCarroll and Harris, 1992;Roberts and Hart, 2005;Hart, 2007;Ó Cofaigh et al, 2008), where they are indicative of compression, longitudinal extension and rotational shear through subglacial deformation (Hart and Boulton, 1991;Piotrowski and Kraus, 1997;Hart, 2007). The augen structures are overlain by LF 2b, where evidence of loading, soft-sediment deformation, fluidisation and dewatering (as defined by 1983) are apparent.…”

Bedrock controls on subglacial landform distribution and geomorphological processes: Evidence from the Late Devensian Irish Sea Ice Stream

“…These authors believed that this resulted in a rise in relative sea-levels up to 100 m OD, interpreting most of the outcropping glacigenic sequences below this height as glaciomarine in origin. Subsequent work around the Irish Sea basin (Harris, 1991;McCarroll, 1991McCarroll, , 1995McCarroll, , 2001McCarroll, , 2005Scourse, 1991a, b;Austin and McCarroll, 1992;McCarroll and Harris, 1992;Harris et al, 1997;Thomas et al, 2004;Merritt and Auton, 2000;Hambrey et al, 2001;Ó Cofaigh and Evans, 2001;Scourse and Furze, 2001;Evans and Ó Cofaigh, 2003;Glasser et al, 2004;Etienne et al, 2006;Thomas and Chiverrell, 2007;Roberts et al, 2007) has rejected this model and the consensus view is that the deposits associated with the Irish Sea Ice Stream, including those on Anglesey, are principally terrestrial in origin.…”

Progressive soft sediment deformation within a subglacial shear zone—a hybrid mosaic–pervasive deformation model for Middle Pleistocene glaciotectonised sediments from eastern England

“…Their augen-like appearance has been often explained by the shearing of incorporated masses of sand by either gravitational flow (Eyles et al, 1985;McCarroll and Harris, 1992;Lunkka, 1994) or subglacial deformation (Hart and Boulton, 1991;McCarroll and Harris, 1992;Hart and Roberts, 1994).…”