AN INTERGLACIAL DEPOSIT AT SCANDAL BECK, N.W. ENGLAND

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1 . (1978)81, AN INTERGLACIAL DEPSIT AT SCANDAL BECK, N.W. ENGLAND By P. A. CARTER, G. A. L. JHNSN and J. TURNER Departments of Botany and Geology, University of Durham {Received 1 May 1978) SUMMARY A lacustrine deposit with included peat was discovered beneath till at Scandal Beck, Cumbria. A pollen diagram from the organic layers has three pollen assemblage zones which cover the last part of an interglacial. It is argued that the deposit most probably dates from the Ipswichian. INTRDUCTIN Northern England was glaciated several times during the Pleistocene, but the bulk of the glacial deposits that cloak the present-day ground surface belong to the last or Devensian ice cover glaciation (Francis, 1970). Deposits of the previous glacial and interglacial episodes are relatively rare because the erosive power of the continental ice-sheets was sufficient to remove them. nly further south, towards the margin of the ice-sheets are full sections of Pleistocene deposits preserved (West, 1977). Thus, in Northern England, interglacial deposits are only known in places where they have been preserved from erosion in topographic hollows (Gaunt, et al., 1972; Gaunt, Bartley and Harland, 1974) or, in one place, as an allochthonous peat raft in the Devensian till (Beaumont, Turner and Ward, 1969). The discovery of a lacustrine succession with included peat preserved under till at Scandal Beck, Cumbria (Fig. 1) is therefore of great interest. Radiocarbon dating and a preliminary study of its stratigraphy and pollen content indicate that it was laid down during the closing stages of an interglacial. The deposits were found by one of the authors (GALJ) in 1966, at the base of a small cliff of drift on the west bank of Scandal Beck near Brunt Hill (Nat. Grid Ref. NY ). The locality is at 275 m.d. on undulating drift-covered ground at the foot of Wild Boar Fell at the head of the Vale of Eden. The bedrock is Lower Carboniferous-age limestones which outcrop both up and down stream of the deposits. They also form a ridge, cut by the beck, just to the north. The deposits appear to be lying in a hollow in this limestone surface. The ridge to the north may also have provided protection from the erosional scour of the Devensian ice-sheets which moved south and east from the Lake District and the Howgill Fells. Glacial drift is widespread and of variable thickness in the vicinity of the interglacial deposits, and a series of drumlins occur immediately to the north and west. Scandal Beck has laid down wide terraces of alluvium during Flandrian times. The possible extent of the interglacial lake deposits is shown by vertical shading on Fig. 1. STRATIGRAPHY AND PLLEN ANALYSIS The stratigraphy of the deposits as exposed in the bank of the stream was examined in X/78/ $ BlackweU Scientific Publications 785

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3 Interglacial at Scandal Beck 787 by PAC as part of an undergraduate project (Fig. 2a). Almost 4 m of till overlies 2 m of fluvial sands, silts and clays which contain small organic lenses and towards their base more substantial bands of peat and organic mud. Samples for pollen analysis were collected from the successive organic layers and the results are shown in Fig. 3(a). The site was revisited in 1972 by GALJ and an attempt made to examine the sediments below the present level of the stream with a hand auger. The stratigraphy of these is shown (a) SCANDAL BECK CUMBRIA A A A A A A A A A A A A A Till (b).. L.. L Grey clay, sand Peat o o 'o'o'o A A Sand iron at base clay: silt sand 7m Clay sand Peat: clay Yellow brown sand m Clay Peat: dark clay Dark grey silt sandy filaments Medium and coarse groined sands Clays sands silts organic lenses 8m L T Sondy cloy with peat fragments Peat sand clay Clay sand - i_.. I - Dark clay 5m Sand silts Peat flame Clay Rich organic layer Peat silt sand Grey sand: gravel Peat with wood and reed layers Brown silty organic band Cloy Grey sand o 0 r. o o o o o o o o o o o p wmm Grovel Sand Silt Boulder cloy Peat rganic mud Fig. 2. Stratigraphy of the interglacial deposit at Scandal Beck, (a) as exposed in the bank of the Beck and (b) as revealed by augering in the bed of the beck. Letters a-g in 2(a) refer to levels from which samples were taken for pollen analysis.

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In terglacial at Scandal Beck 789 in Fig. 2(b). Pollen analyses were also carried out on the organic bands and the results are given in Fig. 3(b). The results in Fig.

5 In terglacial at Scandal Beck 789 in Fig. 2(b). Pollen analyses were also carried out on the organic bands and the results are given in Fig. 3(b). The results in Fig. 3(a) indicate an orderly sequence of vegetational succession typical of the closing stages of an interglacial period. Three pollen assemblage zones were recognized. ScB 3 Pinus pollen assemblage zone ScB 2 Alnus pollen assemblage zone ScB 1 Quercus pollen assemblage zone The first or earliest (ScB 1) contains appreciable quantities of Quercus pollen, together with pollen of Alnus, Pinus, Betula, Corylus and Ilex all native trees of the region today. Single grains of Ulmus and Taxus were also recorded. This indicates the presence of thermophilous woodland, presumably growing both in the valley and on the surrounding hills. The presence of Ilex means that the mean temperature for the coldest month cannot have been below -WiC (Iversen, 1944). The second zone (ScB 2) contains very little Quercus, but large quantities of Alnus. There are also substantially higher values for the pollen of the water plants, A^wp/iar and Nymphaea, and for the spores of Filicales, the latter possibly from the ground layer of the woodland. Wetter conditions in the valley are thus indicated for the period. There are also small amounts of Carpinus pollen in this zone, a tree which occurs in substantial quantities, sometimes, but not always, together with Alnus, in zone III of the Ipswichian (last) interglacial. The values, however, are far too low to allow a confident dating of the deposit to the Ipswichian purely on palynological grounds. The third (ScB 3) contains mainly Pinus pollen and indicates that a boreal, rather than a temperate climate was prevailing, with Pinus woods having replaced those of Alnus. The pollen diagram in Fig. 3(b) appears to cover the period between the end of ScB 2 and the beginning of ScB 3 with the Alnus frequency decreasing and that of Pinus increasing. If this is so, it means that the original deposit has over-thrust at least a couple of metres vertically since it was laid down separating contemporaneous levels over distances of a few metres. The only other possibility is that the sediments are in situ and have not moved since deposition and that the pollen diagram in Fig. 3(b) pre-dates that shown in Fig. 3(a). This would imply a complex vegetational and climatic sequence from temperate mixed oak wood, through alder woods to boreal pine woods, and then an amelioration of climate which allowed the return of mixed oak woods before another deterioration caused their replacement by alder and then pine woods again. The former explanation would seem the most likely. This particular sequence of pollen assemblage zones is not directly comparable with those from the few other interglacial sites so far described from northern England, but it does resemble one described by Edwards, Caseldine and Chester (1976) from Teindland in the Grampian region of Scotland and attributed by them to the Ipswichian. ScB 2 may correspond to their T-1, an Alnus-GirniinesLe-Plantago lanceolata zone, and ScB 3 to their T-2, a Pinus-Calluna-Gidimmedie zone. RADICARBN DATING The peat from the lower of the two organic layers in Fig. 2(a) was kindly radiocarbondated for us by Professor Shotton (Shotton, Blundell and Williams, 1970). Two dates were obtained, one after alkali pre-treatment (a), the other from the humate extract (b).

6 790 P. A. Birm-161 (a) 36,300 ± (b)> 25,000 These dates fall within the Upton Warren interstadial of the last glaciation and were thus considered inconsistent with the pollen evidence. Because of this a further sample was dated, a piece of wood from the upper of the two organic layers. This wood appeared to be inactive (Shotton and Williams, 1971). Birm-234 >32,500 It seems most likely then, that the deposit pre-dates the Upton Warren Interstadial and that the finite date obtained was due to contamination of the sample. CNCLUSIN There can be little doubt that the Scandal Beck deposits were laid down during the latter stages of an interglacial. As the glacial drift has been attributed on morphological grounds to the last glaciation (Edwards and Trotter, 1954) and these deposits lie beneath it, they may well date from the Ipswichian. Certainly the palynological evidence is not inconsistent with this view. ACKNWLEDGMENTS We are most grateful to Professor Shotton for his interest in the project and for providing the radiocarbon dates, and to Mrs L. Larkin and Mr H. Whittle for drawing Fig. 1 and 2 respectively. REFERENCES BEAUMNT, P., TURNER, J. & WARD, P. F. (1969). An Ipswichian peat raft in glacial till at Hutton Henry, Co. Durham. New Phytol, 68, 979. EDWARDS, K. J., CASELDINE, C. J. & CHESTER, D. K. (1976). Possible interstadial and interglacial pollen floras from Teindland, Scotland. Nature, 264, 742. EDWARDS, W. & TRTTER, F. M. (1954). British Regional Geology-The Pennines. H.M.S.., London. FRANCIS, E. A. (1970). Quaternary. Trans, nat. Hist. Soc. Northumb., 41, 134. GAUNT, G. D., BARTLEY, D. D. & HARLAND, R. (1974). Two interglacial deposits proved in boreholes in the southern part of the Vale of York and their bearing on contemporaneous sea levels. Bull geol. Surv. Gt. Br., 48,1. GAUNT, G. D., CPE, G. R., SBRNE, P. J. & FRANKS, J. W. (1972). An interglacial deposit near Austerfield, southern Yorkshire. Rep. No. 72/74, Inst. geol. Set IVERSEN, J. (1944). 'Viscum, Hedera and Ilex as climatic indicators. Geol For. Stockh. Forh., 66, 463. SHTTN, F. W., BLUNDELL, D. J. & WILLIAMS, R. E. G. (1970). Birmingham University radiocarbon dates YW Radiocarbon, 12, 385. SHTTN, F. W. & WILLIAMS, R. E. G. (1971). Birmingham University radiocarbon dates V. Radiocarbon, 13, 141. WEST, R. G. (1977). Pleistocene Geology and Biology. Longmans, Green & Co. Ltd., London.

POST-GLACIAL DEPOSITS AT TARN WADLING, CUMBERLAND

POST-GLACIAL DEPOSITS AT TARN WADLING, CUMBERLAND BY D. WALKER University Sub-department of Quaternary Research, Cambridge, and Research School of Pacific Studies, The Australian National University, Canberra