Speleogenetic evidence from Ogof Draenen for a pre‐Devensian glaciation in the Brecon Beacons, South Wales, UK

Abstract

The British Isles have been affected by as many as 30 glaciations during the Quaternary.However, the evidence for pre-Devensian glaciations in upland regions is scarce.Understanding the extent and timing of earlier upland glaciations is essential for modelling the long term evolution and sensitivity of the British Ice Sheet (BIS). Caves, being protected from surface erosion and weathering, can preserve evidence of earlier glaciations in the form of speleothem and sediment archives. The ~70 km long Ogof Draenen cave system in South Wales, UK, contains multiple cave levels related to changes in the surface topography and drainage during the past 0.5 Ma. The cave contains evidence of massive influxes of sediment that were sufficient to choke the cave and alter the underground drainage. Analysis of the cave sediments, passage morphology and geometry suggests the cave once acted as a subterranean glacial spill-way before being overridden by ice. Speleothem U-series data demonstrates that this sediment influx occurred before Marine Isotope State (MIS) 9, probably during the Anglian glaciation (MIS 12). Evidence from Ogof Draenen indicates the impact of subsequent glaciations on the landscape evolution of the region was minimal and that much of the surface topography dates from the Anglian.Keywords: speleothem, glaciation, Wales, U-series dating, U-Th, landscape evolution, Ogof 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 (Note: Welsh terms used in this paper: Ogof = Cave, Afon = River, Cwm = Valley, Mynydd = Mountain) IntroductionMost of the upland karst areas in the north and west of the UK have been glaciated multiple times during the past million years, with the greatest advances during Marine Isotope Stage (MIS) 12 (Anglian) and MIS 2 (Devensian) glaciations. Until recently there was evidence for only a small number of glaciations in the UK (Bowen, 1999; Bowen et al., 1986; Clark et al., 2004). Now perhaps as many as 30 glaciations are known (Böse et al., 2012; Lee et al., 2012; Lee et al., 2011; Thierens et al., 2012; Toucanne et al., 2009), dating back about 2.6Ma, although the timing of many remains equivocal. Equally, recent work has shown that the climatic thresholds required to build glaciers in Britain were much lower than previously considered with glaciers existing throughout the Little Ice Age (LIA), from the mid-16 th to mid-19 th centuries (Harrison et al., 2014; Kirkbride et al., 2014). Collectively, they indicate the British Ice Sheet (BIS) was as dynamic and responsive as other Northern Hemisphere ice sheets, and highly responsive to even subtle changes in climate.Frequently, the evidence for pre-Devensian glacial activity in many upland areas is often lacking, and is often inferred only from exotic clasts in river terrace deposits (Whiteman and Rose, 1992). Typically this absence is attributed to the e...

Late Wolstonian and Ipswichian (MIS 6/5e) sediment fill in a limestone sinkhole, Askham Fell, northern England

“…Indeed, pre‐existing subterranean cave networks have been proposed as significant controls on meltwater drainage routes (e.g. Ford, 1979, 1983, 1987; Lauritzen, 1984, 1986; Murphy et al, 2001; Farrant et al, 2013; Telbisz, 2019). In contrast, cold‐based ice at higher elevations probably was associated with little or no subglacial meltwater production, as is evident in the widespread development of diagnostic cold‐based ice indicators such as lateral meltwater channels on upper valley slopes (cf.…”

Isostatic compensation of Quaternary vertical crustal motions: coupling between uplift of Britain and subsidence beneath the North Sea

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