GLWG 4: Kells, Co. Meath, Ireland, 10th - 12th March, 2000
The fifth meeting of GLWG took on a (slightly) more international flavour, with a close examination of the evidence for and against the Drumlin Readvance in Ireland, recently invoked by McCabe and others as a response to the North Atlantic Heinrich events after the Last Glacial Maximum. The meeting was organised by Robbie Meehan (TEAGASC), and was enthusiastically attended by over thirty researchers from Britain and Ireland. The meeting was accompanied by an impressive field guide, which made good use of an excellent digital elevation model of the area which clearly identified many of the excursion sites.
Day 1The various hangovers from the Friday evening gossip in the pub were hastily blown away at the windy summit of Slieve na Calliagh, where the geology and Quaternary geomorphology of the area was introduced. In addition to the Quaternary history of the region, Robbie Meehan briefly described the rich archaeology of the region, clearly demonstrated by the nearby megalithic tombs of Loughcrew. Having seen an overview of the large drumlin fields to the north, and the more complex, hummocky terrain to the south of the Slieve na Calliagh, the group investigated the prominent ridge at Murrens, by looking at two gravel pits excavated into and through the ridge. This feature, traditionally interpreted as an esker, was suggested to have formed as a delta complex between two lobes of the Irish ice sheet during deglaciation, with an interlobate esker clearly feeding a large fan of gravels thought to have been deposited into a large proglacial lake (Glacial Lake Murrens). Dave Evans (Glasgow) supported this idea with contemporary examples of similar features at the margins of Breidamerkurjokull, Iceland, although questioning the need to have an extensive proglacial lake during formation, on the basis that the Icelandic fans were deposited subaerially. Subsequent discussion was curtailed by an impressive feat of fly-tipping and fork lift manoevring put on by the Co. Meath synchronised lorry display team, only to be resumed a second pit in the Murrens esker/delta complex, which supported the models put forward of a 'sub-aerial', rather than subglacial origin to the esker complex.
After a relaxing lunch stop at Lough Bane, where a potential palaeokarst landscape was preserved, the group moved on to McGraths pit, near Milltown, interpreted to compose of more distal delta deposition within the proglacial lake introduced earlier at Murrens. Having seen enough of sand and gravel for an hour or two, the group proceeded to a series of south-southwest aligned ridges at Diamor, south of the Slieve na Calliagh. These ridges, with heights of up to 30 metres were clearly picked out on a digital elevation model presented by Chris Clark (Sheffield), with the illumination perpendicular to that presented in the field guide. The origin of these landforms, apparently extending en echelon on to the Slieve na Calliagh was extensively debated, with suggested interpretations of push moraines, mega-flutes, crevasse squeeze ridges, rogen and de Geer moraines all being put forward, and questioned, mainly by Brice Rea (Cardiff), Dave Roberts (Durham), Dan Praeg (Trinity) and Richard Hindmarsh (BAS). Having agreed that the group could not adequately interpret these features without substantial sedimentary exposures, a final site was visited to the north of Kells, where once again the discussion returned to sand and gravel.
Hartons pit, in the Blackwater valley, preserved an interesting sequence of glacifluvial sands and gravels, which displayed considerable evidence of slumping. This site was suggested to have formed as a proglacial kettled sandur associated first with deposition into the standing water of a lake within the Blackwater valley, with subsequent drainage and rapid development of a sandur. The first day concluded with a brief lecture by Robbie Meehan to place the sites examined within the context of the deglacial history of the Irish ice sheet, and to introduce the mapping ambiguity and contrasting opinions over the status of the Drumlin Readvance. Jasper Knight (University of Ulster, Coleraine) furthered the discussion by mentioning the evidence supporting the readvance, with the albeit few dates constraining the deglacial history of Ireland. This was followed up with extensive sampling of the local black stuff in Kells, and a session in the local nightclub for the more energetic.
Day 2With some attendees slightly worse for wear (including the field leader), the group was eased into the day with a relaxing walk to the first site at the 'Kells moraine', just to the north of Kells at Cakestown. This feature is the type site for the Drumlin Readvance, and was originally interpreted as a series of ice contact gravel ridges formed during an ice sheet readvance. In fact, as demonstrated by Robbie Meehan, the ridges predominantly consist of a diamict interpreted as a subglacial till, with only a thin surface veneer of glacifluvial gravels. It was agreed by all capable of thought that there was no convincing evidence to support an ice marginal origin to any of the sediments or landforms at the site, thus bringing the entire principle of a single 'Drumlin Readvance' into question, although this was countered by Jasper Knight who suggested that there would have been a number of minor advances during this period. In a return to concepts discussed at a memorable meeting of the forerunner to GLWG, a brief stop at Castletown allowed brief discussion of the idea of buried drumlins. In the examples at Castletown, the drumlins deposited were partially buried by stratified gravels during continued, and relatively uninterrupted ice margin retreat. The consequent 'buried' features at Castletown are difficult to map in the field, and are only really clear on the DEM of the area, with small scale slope convexities identifying a consistent grain in the landscape. Both Richard Hindmarsh and Chris Clark noted that the DEM also highlighted strong transverse elements to those of the buried drumlins that may reflect the progressive drumlinisation of the pre-existing landscape, or the formation of retreat stage moraines.
The final site visited by GLWG was at Mullaghmore, just to show the British contingent how many impressive sections there are in Ireland that have not been investigated. Due to time constraints, the group only briefly discussed the impressive glaciotectonised sands and gravels at the site. Initially interpreted as a cross section through a drumlin, it was pointed out that the section was within an interdrumlin area, and probably reflected a localised small readvance, resulting in proglacial thrusting of glacifluvial sediments during progressive regional ice retreat.
A group photo was taken at Mullaghmore, fitting because this site can be seen as a good summary of the whole meeting. Almost all of the sites visited displayed superb sedimentological and geomorphological evidence that can be interpreted using a landsystems approach, yet very few of these sites has been reported or discussed under such a framework. An established hypothesis of considerable regional stratigraphic importance (the Drumlin Readvance) does not stand up convincingly to re-evaluation of the processes that result in the sediment-landform associations investigated on this trip, and highlights the need for such an approach when examining Quaternary glacial stratigraphy.
The GLWG would like to express its wholehearted thanks to Robbie Meehan for providing such a comprehensive meeting, which examined significant and relevant issues at a range of superb sites. The substantial and extremely glossy field guide sets a challenge for subsequent meetings, and I believe everyone concerned will agree that this meeting will be a hard act to follow.