LATE-GLACIAL DEPOSITS AT LUNDS, YORKSHIRE

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1 [ 343 ] LATE-GLACIAL DEPOSITS AT LUNDS, YORKSHIRE BY D. WALKER University Sub-department of Quaternary Research, Botany School, University of Cambridge {Received 3 October 954) (With 3 figures in the text) Rowell and Turner (952), have described the Glacial deposits of the Mallerstang Fells around the head streams of the Rivers Eden and Ure. In general terms the river valleys are filled with drift, notably drumlins in the upper Ure, and the hillsides are more or less bare except for fresh, well-marked, corrie moraines beneath cliffs at about 800 ft. O.D. on Mallerstang Edge. The head streams of the River Ure, rising on Abbotside Common and Baugh Fell, join and flow south-eastwards for about i mile (i-6 km.) through a wide valley in the hmestone and shales. The growing river then turns sharply eastwards to fiow down Wensleydale. The upper valley, the bottom of which lies between 000 ft. (305 m.) and 00 ft. (335 m.) O.D., is about 4; mile (0-4 km.) wide and the floor is studded with drumlins, between which the Ure meanders. The hollows between these drift features are largely filled with sandy alluvium, forming a plain aggraded to a local base level of 000 ft. (305 m.) o.d. at Ure Foss, where the river is cutting down through the underlying limestone. STRATIGRAPHY At a point about mile (o-8 km.) upstream from Lunds Church (Fig. i) the river is cutting back into a drumlin exposing a deep section along its western bank. The river level is about 090 ft. (332 m.) o.d. at this point. The drumlin crest slopes downwards in each direction from a point 3'5 m. above the river level. Where the northern slope meets the alluvial spread of the valley bottom a small tributary stream enters from the northwest. The whole section is exposed along the convex edge of the river meander, and the diagram (Fig. 2) can only be taken as a close approximation to the truth. Although horizontal distances may not be accurate, vertical measurements are correct at the points indicated, at each of which detailed examination was made. Just above river level a lens of brown laminated detritus mud occupies the middle of the section and peters out both upstream and downstream. Below it the auger proved a considerable thickness of black micaceous silty mud, which in turn overlaid a thin layer of blue clay. Beneath the latter the auger struck a stiff grey-brown rocky clay which is assumed to be the basal boulder clay. Above the mud there is a great thickness of ' stony head', a stiff blue-grey sandy clay containing rocks of all sizes from small gravel to blocks almost a metre across. There is no indication of bedding in the deposit, and it can only be interpreted as glacial deposit or a solifiuction earth. The surface of the 'head' falls both upstream and downstream. The section is badly obscured by fallen rocks, but there

2 344 D. WALKER is no doubt that, even at the edges, the detritus mud is separated from overlying organic deposits by the stony head. A thin skin of peat covers the crest of the hill and thickens N MALLERSTANG I MILE. BAUGH FELL Fig. I. Sketch map showing location of the Late-glacial deposits of the Ure Valley. northwards as it falls into the tributary valley, where it reaches a thickness of 2 m. On the lower slopes a band of birch branches can be seen within the peat. Upstream from the tributary, the main stream has cut a shallow section in the main alluvial spread of the

3 Late-glacial deposits at Liinds, Yorkshire 345 z UJ a. UJ > TRIBUl VALL WATER L(iVEL O -00 A f o.5 Is > V^ / # - a! 3 o tlj I Vv u o UJ ' o: o: 3 \ -O CM CO Q Z D o o UJ a - UJ < / % < ^ m a ^ o, y y y \ <3 " -"' \ ^ ; 0.J o UJ z> _l -o O u i

4 346 D. WALKER valley which consists of pebbles (up to 5 cm. across) in a sandy matrix and is only vaguely bedded. In the region of the tributary mouth it interdigitates with the tapering edge of the stony head. POLLEN ANALYTICAL RESULTS A series of pollen anlysis samples was taken near the deepest point of the section. No samples were taken from the solifluction earth, and samples from below ground level were obtained with the Hiller borer. The rest of the samples were taken from a pit cut back into the face of the section for about half a metre. From the results of the analyses QUERCUS ALNUS ao o lo 20 CORYLUS POLLEN FnEOUENClES AS PERCENTACCS OP TOTJO. POLLEN OF ANeMOPHlLO<JS LAND PLANTS O BETULA PINUS LUNDS SAUX GRAMINE/iE CYPERACEAE OTHER LAND HERBS Fig. 3. Pollen diagram through the peat overlying the solifluction head, and the organic muds beneath the solifluction layer. All results are expressed in percentages of total pollen of land plants. a pollen diagram was compiled (Fig. 3), using as a basis for the calculation of the percentage figures the total pollen of anemophilous land herbs and trees, plus Ericales (Faegri & Iversen, 95). The sum of these standard pollen types counted varied between 600 and 000 grains from sample to sample. Cyperaceae pollen was included in this sum, although sedge remains (stems and fruits) were frequently encountered in the mud. It is notable, however, that the Cyperaceae pollen frequencies do not diminish significantly in the micaceous mud, which has practically no included macroscopic sedge remains, suggesting that sedges were in fact abundant in the dry land communities. The pollen diagram is clearly divisible into two major zones, separated by the solifluction earth. In the upper thin peat, tree pollen is abundant; in the lower zone, which embraces the lower mud, it is very sparse. In the latter, Betula, Pinus and Salix together make up the total tree pollen and, of these, Pinus occurs only as isolated grains, often badly eroded, which might have been carried a very considerable distance. The dominant pollen type of the lower zone belongs to the Cyperaceae, although Gramineae also play an important part. In addition, Compositae pollen and fern spores are consistently present and there are occasional occurrences of Artemisia, Helianthemum, Plantago media, Rumex, Thalictrum, Caryophyllaceae, Chenopodiaceae and Umbelliferae. This lower zone clearly belongs to the Late-glacial Period, (Godwin, 949).

5 Late-glacial deposits at Lunds., Yorkshire 347 Within this lower zone there is some evidence of a vegetational change. The samples at 275 and 270 cm. have considerably higher Betula and Salix frequencies than are found above or below them. Both Betula and Salix curves rise gently from the bottom of the zone to culminate in these maxima, and thereafter fall to lower levels. On the basis of this rise and fall in tree-pollen frequency the lower zone has been tentatively divided into three subzones, viz: cm.. Sub-zone a. Tree-pollen frequency very low (< 8 %). Pinus pollen present, Cyperaceae and Gramineae dominant '^'" > Sub-zone b. Tree-pollen frequency low, but higher than in sub-zones a and c. Pinus virtually absent. Cyperaceae dominance diminished as a result of expansion of trees and Gramineae cm.. Sub-zone c. Tree-pollen frequency low ( < 5 %). Pinus pollen appears towards the top. Cyperaceae dominant but the Gramineae curve rises steeply to the top sample. Selaginella spores are restricted to the top of this sub-zone. Table i Sample level (cm.) Betuta Pinus Quercus Percentages of total anemophilous pollen types Salix Corylus Gramineae Cyperaceae Fitipendula ulmaria Filicates Varia Zone 75 i8s I-I 2- I-o I-I 33'S 6-9 o-s 3-9 II-O IV- -V III The peat above the solifiuction earth contains abundant tree pollen, Quercus, Alnus and Corylus figuring largely and indicating that this peat formed at, or after, the Postglacial Warmth Maximum. The direct superposition of such material on top of solifiuction earth suggests that a discontinuity is present at the top of the latter deposit. A second, shorter, series of pollen-analysis samples was taken from a cleaned face at the mouth of the tributary stream (Fig. 2) where the section was as follows: o- 90 cm. Disturbed upper Sphagnum-Calluna peat cm. Dark brown Sphagnum-Molinia peat, with fragments of Betula and Salix wood cm. Dark brown muddy peat with Equisetum stems and red wood fragments at 80 cm cm. Medium-brown laminated detritus mud cm. Grey-brown laminated micaceous mud. 200 cm. Vaguely bedded gravels interdigitating with sohfiuction earth i m. downstream. No pollen was obtainable from the samples taken below 90 cm., but three samples above this level gave the results shown in Table i. These results refiect the increasing dominance of forest trees, particularly Betula, from conditions similar to those prevailing at the time of deposition of the mud beneath the stony head. The great increase in treepollen frequency between 90 and 85 cm. serves to divide the series into two zones. The upper of these zones has all the characteristics of Post-glacial Zone IV-V of the north of

6 348 D. WALKER England (Walker, 955). The lowermost sample, rich in herbaceous pollen and preceding Zone IV, must be referred to Zone III. This mud overlies the gravelly alluvium which is continuous with the stony head. DISCUSSION There can be little doubt that the ' stony head' is a solifluction deposit derived from the boulder clay of the drumlin and that the detritus mud beneath it accumulated at the margin of a lake of unknown size which lapped around the edges of the drumlin before the period of solifluction. The organic detritus mud itself is a temperate deposit compared with the underlying boulder clay and superposed solifluction earth. The stratigraphy, therefore, shows evidence of some climatic fluctuation. At the mouth of the tributary, the 'head' is overlaid by a muddy peat with a brown amorphous peat above that. The accumulation of these organic deposits indicates amelioration of the climate after the solifluction and it is probable that accumulation began in this tributary valley soon after the deposition of the stony head. The skin of peat over the better-drained crest of the hill might be expected to be younger, however. The lowermost layers of mud in the tributary section belong to Zone III and overlie the gravelly alluvium considered to be a contemporary deposit of the solifluction earth. The latter must therefore belong to Zone III. The pollen diagram from the mud below the solifluction earth has been divided into three sub-zones, but it cannot be decided whether the third of these (Sub-zone c) should be considered as the early part of Zone III (in which case Sub-zones a and b might be equated with Zones I and II respectively) or whether the whole of the lower mud is a Zone II deposit. If the second explanation is adopted it is necessary to suppose that herbaceous vegetation dominated this highland region throughout most of Zone II, woodland only encroaching from the lowlands at the middle of the period. The lower pebbly micaceous clay and the underlying blue clay must also be the only deposits of Zone I. No matter which interpretation is adopted, however, it is certain that Zones I, II and III (i.e. the Allerod oscillation) are all represented at this site. Zone II did not witness the complete afforestation of the region. Perhaps throughout the zone, perhaps only for a short period near the middle, birch trees did grow within the area, but herbaceous communities with abundant sedges and grasses maintained their dominance. During Zone III solifluction was very severe in the Lunds neighbourhood and seems not only to have brought great thicknesses of boulder clay down the drumlin sides, but to have spread the finer material over the bed of the shallow lake ponded up in the valley. It may be that the corrie moraines on Mallerstang Fdge (Rowell & Turner, 952) were formed at the same time. A number of borings made in the peaty infilling of an old tarn between the rock face and one such moraine at Coalwell Scar penetrated 2 m. of organic material, the base of which contained abundant pollen of Betula, Quercus and Corylus; a Post-glacial spectrum in the strict sense. There is therefore no evidence that these moraines pre-date the Lunds solifluction episode.

7 Late-glacial deposits at Lunds, Yorkshire 349 SUMMARY. Organic deposits underlying and overlying solifluction earth at iioo ft. O.D. in the upper Ure valley are described. 2. The solifluction earth is correlated with Zone III of the pollen-analytical chronology. 3. The possibility of corrie moraines on Mallerstang Edge proving contemporaneous with the solifluction is discussed. I wish to thank Dr H. Godwin, F.R.S., and Mr J. Selwyn Turner, F.G.S., for their encouragement and advice, the latter first bringing the site to my attention. I am also indebted to Miss Margaret E. Beatson as well as to Dr Eilif Dahl, Miss S. L. Duigan and Mr A. G. Smith for their help in the fleld. REFERENCES FAEGRI, K. & IvERSEN, J. (95). A Textbook of Modern Pollen Analysis. Copenhagen. GODWIN, H. (949). The spreading of the British Flora considered in relation to the Late-glacial period. y. Ecol. 37, 40. RowELL, A. J. & TURNER, J. S. (952). Corrie-glaciation in the Upper Eden Valley, Westmorland. Lpool. Manch. Geol.J. i. WALKER, D. (955). Studies in the Post-glacial History of British Vegetation. Skelsmergh Tarn and Kentmere Lake, Westmorland. New Phytol. 54, 2, 222.

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