THE STRATIGRAPHY AND POLLEN ANALYSIS OF LAKE DEPOSITS NEAR TADGASTER, YORKSHIRE BY DAVID D. BARTLEY

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1 THE STRATIGRAPHY AND POLLEN ANALYSIS OF LAKE DEPOSITS NEAR TADGASTER, YORKSHIRE BY DAVID D. BARTLEY Department of Botany, University of Leeds {Received 2 March 1962) (With 4 figures in the text) SUMMARY The stratigraphy and pollen analysis of the deposits show that this is a lake basin which during the Late-glacial period was partially filled by lake clays and muds. One of the main interests of the pollen diagrams lies in the division of zone i into three suh-zones showing a minor climatic oscillation which seems to be comparable with the Boiling oscillation of northern Europe. During Post-glacial time the greater part of the deposits has been muds but on one side a fen developed which in early zone VI was sufficiently dry to support birch and pine wood. Later in zone VI the water table must have risen slightly because the fen peats were gradually covered by a rather oxidized mud suggesting that the fen became replaced by a shallow swamp with a widely fluctuating water table. In the Atlantic period the basin was reflooded and the more central deposits were covered by a layer of mud. Later in the central region, swamp and eventually Sphagnum bog communities developed. The whole area is now covered by a sihy soil and forms a flat meadowland. INTRODUCTION The lake deposits he in a hollow on the top of the Escrick Moraine. This is the southerly part of the York-Escrick Moraine belt, said to represent the end-moraine of the Vale of York glacier (Last Glaciation). According to the Sheet Memoir of the Geological Survey (Edwards, Mitchell and Whitehead, 1950) the deposit 'probably occupies an old lake basin and is now drained by a tunnel through the drift to an outfall in the Wharfe'. It is situated just west of Oxton near the village of Tadcaster. STRATIGRAPHY The stratigraphy shows that the deposits do indeed occupy a lake basin which in the region of the section is some 6.5 m (about 21 ft) deep. The basal material is variable hut consists in the main of a blue, sandy clay with pebbles. Near the edge of the deposit, particularly under the gley on the southern side, sand may form the basal material. On the extreme edges of the section the basal material is overlain by clay with gley characteristics but over the greater part of the section it is covered to a considerable depth by blue lake clay which in its upper layers contains much organic matter. The following example of a profile through the deposits will serve to show the sequence of layers: 0-25 cm black, silty soil, rather calcareous cm dark brown, peaty material with wood and bark, occasional pieces of Sphagnum palustre and cuticles of Eriophorum vaginatum cm brown, detritus mud with oospores of Chara; fruits and catkin scales of Betula pubescens and B. cf. verrucosa, seeds of Nymphaea alba, pyrenes of Potamogeton obtusifolius, nuts and fruits of Carex pseudocyperus. 277

2 278 D. D. BARTLEY cm - darker mud with Chara oospores, bits of wood, bark and twigs, pyrenes of Potamogeton obtusifolius, fruits of Carex pseudocyperus cm detritus type of mud with remains of Potamogeton obtusifolius, Alnus glutinosa, Betula pubescens and occasional bits of cuticle of Phragmites cm peat with bark, twigs and wood to 210 cm, pine wood at 190 cm, cuticles of Phragmites throughout, nuts of Cladium niariscus from 190 cm down, fruit of Cicuta virosa at 170 cm. From 230 cm the peat gradually hecomes muddy eventually forming a detritus at 260 cm, cm muddy peat with remains of Carex rostrata, C. pseudocyperus, Cladium, Phragmites, Betula pubescens and Nymphaea alba; seeds of Scirpus lacustris abundant at 240 cm and occasional at 260 cm, Carex paniculata at 240 cm and catkin scales of Populus tremula at 260 cm and 270 cm cm detritus mud, as ahove, hut lighter in colour, cm marl-like mud, very calcareous and with remains of Cladium, Phragviites, Chara, Nymphaea and Hypmim sp, ^^ cm dark brown mud, calcareous and with remains of Cladium, Scirpus lacustris and Betula pubescens cm blue lake clay, rather coarse and very slightly calcareous, with remains of Phragmites, Potamogeton praelongus, Betula pubescens and Chara cm light brown mud, calcareous and with Chara and Betula pubescens cm blue, lake clay, rather calcareous, 461 cm grits, no penetration after 470 cm. This example shows that above the blue lake clay there are various layers of muds and clay. The first is a calcareous mud with but little mineral content followed by a thin band of blue clay. Above this are two layers of mud (shown as one in Fig. 2) the uppermost of which is highly calcareous. This sequence of mud-clay-mud is very well developed on the northern side of the section but becomes confused on the south side where it is impossible to trace the various layers. MORAINIC DRIFT BOULDER CLAV UML UPPER MAGNE51AN LIMESTONE 1 KILOMETRE Fig, I, Map to show the location of the deposit, the geology of the area and the position of the section Fig, 2 (based upon Crown Copyright Geological survey map hy permission of H,M, Stationery Office), This asymmetry appears again in the upper layers since on the north side the basal muds are succeeded by a layer of peat, which is quite absent on the southern side. This suggests that the northern side was more sheltered so that deposition was able to proceed undisturbed. The peat has a basis of Phragmites with remains of sedges and aquatics and in parts, for example below 190 cm at T,i2, remains of Cladium. In the lowermost layers catkin scales of Populus tremula were found and in the upper layers wood and twigs, especially of pine, make up a large part of the material. The centre of the basin is filled by lake muds which can be separated into two distinct layers. Much the greater part consists of a dark brom^n, amorphous mud with very few recognizable remains. These include fruits and seeds oi Betula pubescens and B. verrucosa Alnus glutinosa (in the upper layers), Nymphaea alba, Carex rostrata, C. paniculata, C.

3 Lake deposits near Tadcaster 279 pseudocyperits and in the lower layers Ceratophyllum demersum and Najas marina. This mud gives the impression of having been formed under conditions which favoured a considerable amount of decomposition, as for example in a rather shallow swamp liable to occasional drying out. The dark layer is succeeded by a much thinner layer of light brown mud. In this there are many more remains including those of Alnus, various Carex species, Potamogeton obttisifolius, P. praelongiis, P. filiformis, Cicitta virosa and Nymphaea alba. The completely different nature of this mud suggests rather rapid deposition in deeper water where it was not liable to drying out. Enophorur c DcCritus -;, L^ght-colourzo Mud rijji Dark Mud Fig. 2. Section showing the stratigraphy of the deposit, with a key to the symbols used throughout. The surface of these muds is concave and the central depression is filled by peat. The lowermost layers of this peat are swamp peats, superseded by Sphagnum-Eriophoriini peat. The whole area is sealed in by a layer of worked soil, very peaty in nature but with a considerable amount of mineral matter. A typical central sequence is seen at T.io, Fig cm black, silty soil with few recognizable remains cm peat with cuticles of Eriophorum vaginatum abundant, also remains of Dicranum scoparium. Sphagnum plunndosum, Calliina vidgaris and Alnus glutinosa cm golden-brown peat with Sphagnum cuspidatum, fruits and seeds of Betula pubescens, B. verrticosa, Nvntphaea alba, Potamogeton spp. and bits of fern leaves cm brown mud, very light in colour. POLLEN ANALYSIS The pollen diagrams are constructed from a boring at T.14, Fig. 2. The first diagram (Fig. 3) includes the whole profile and is based on percentages of total tree pollen. The other diagram (Fig. 4) covers the Late-glacial period and is based on percentages of total pollen (excluding bryophyte and pteridophyte spores). Betula nana pollen was identified according to the method described by Terasmae (1951) using the size and proportions of the apertures. After a little experience B. nana pollen could be distinguished from that of tree Betulas without resort to actual measurements, but always

4 28o D. D. BARTLEY c a <u <1> Ul as 60 CO

5 Lake deposits near Tadcaster 281 a few defied certain identification. For this reason, in Fig. 3, Betula nana pollen is included in the total of tree pollen, though it is given a separate curve. This also means that the rest of the diagram remains comparable with other British diagrams. The diagrams have been zoned according to the general sequence for this country. The Late-glacial period (see Fig. 4) Zone I ( cm) - corresponds to the blue lake clay and is clearly divisible into three sub-zones, though the changes involved are for the most part small. The most obvious change is the rise in Betitla pollen and the decrease in gramineous pollen in sub-zone ib. Sub-zone la ( cm)~ Betula pollen very low; Gramineae and Cyperaceae constitute more than 50% of the pollen. The presence of Corylus (up to 16%) and Finus pollen below 300 cm suggests the presence of derived pollen so that this region (i.e. below 300 cm) must be viewed with suspicion. Even so the disappearance of tree birches at the base of the diagram must surely be regarded as significant. Sub-zone Ib ( cm) Betula pollen rises to about 25% and there is a corresponding decrease in gramineous pollen. Of the non-tree pollen types Jmiiperus and Thalictrum make a definite appearance. Sub-zone Ic ( cm) a return of the conditions of sub-zone la, with a minimum of only 6 'o tree Betula. Grass pollen values do not rise to their former level possibly because of the increase in other herbs, e.g. Helianthemum, and in juniper values. Juniper, which was present in sub-zone Ib, rises to a maximum of 44% of total pollen near the top of this zone. Zone II ( cm) is represented by a calcareous mud and in it there is a rise in Betula values up to 50 of the total pollen. B. nana which decreased slowly through sub-zone Ic becomes intermittent in zone II and Juniper pollen disappears almost completely. All non-tree pollen is at a minimum except for that of Filipendula. Zone III { cm) shows a return to cold conditions refiected in the reappearance of blue clay, a decline in Betula values and an increase in pollen of B. nana. Gramineous pollen continues to decrease but there is a sharp increase in pollen of Cyperaceae, Artemisia and Thalictrum. Lycopodium selago which was present in sub-zone la reappears in zone III. The Fost-glacialperiod (see Fig. 3) The very sharp rise in Betula pollen and the sudden disappearance of pollen of B. nana and most of the herbaceous types marks the beginning of the Post-glacial period, i.e. zone IV. The zoning of this period is not easy since there appears to have been contamination of certain layers by downwash, possibly during a period of low water level. Above 105 cm (Fig. 3) the changes are reasonably clear and show a rapid rise in Corylus and Finus pollen. Ulmus is present in small amounts and at 85 cm it shows the beginnings of a rise to dominance over other trees cm is therefore placed in zone V and cm is placed in sub-zone Via. Above 60 cm Quercus pollen values increase; Finus, Ulmus and Quercus come to have approximately equal values, though the two former, together with Corylus, decrease steadily. This section, from 60 to 45 cm is regarded as a combination of sub-zones VIb and Vic. Above 45 cm Finus pollen declines to very low values and Alnus rises suddenly; features characteristic of the beginning of sub-zone Vila. D N.P.

6 282 D. D. BARTLEY 1m 1 = Ii 1, gghljul 1 1 sridhs vinisa a c: 3 " 13 C f 2 > r 11

7 Lake deposits near Tadcaster 283 Zone IV can be extended from 160 cm to 140 cm and between 140 cm and 105 cm there is a zone which appears to have been contaminated by an accumulation of pollen from the upper layers. DISCUSSION The main interest of these diagrams lies in the Late-glacial period and especially in the threefold division of zone I. There have already been examples of such a subdivision in this country, at Seamer (Walker and Godwin, 1954) and at Hawes Water (Oldfield, i960). Both these diagrams show similar features to the present diagram, e.g. an expansion of Betula in sub-zone Ib and an increase in Helianthemmn in sub-zone Ic. The existence of such an oscillation at widely spaced sites in the north of England suggests that this is part of a widespread chmatic oscillation, even though a minor one, and not a purely local phenomenon. This type of oscillation has been recorded from many sites in Europe under different names (Faegri, 1939; Iversen, 1942; Van der Hammen, 1952; MuUenders and Gullentops, 1950; Mullenders, Gullentops and Crevecoeur, 1957). Although the oscillation at Tadcaster differs from these floristically, yet the broad outlines are similar and it is difficult to avoid the conclusion that they are all the result of the same climatic change. The lowest levels of zone I contain rather large amounts of Corylus pollen and must therefore be viewed with caution. With this in mind it is nevertheless possible to gain some insight into the early development of vegetation in the area. At the lowest levels pollen of tree birches is absent and the sparse vegetation must have had a preponderance of grasses with some sedges and such plants as Betula nana, Artemisia and Lycopodium selago. Then through sub-zone la the pollen diagram shows an increase in Betula nana and a gradual spread of tree birches culminating in a maximum of the latter in sub-zone Ib. Throughout the early period (la) the grasses predominate but other herbaceous types become more abundant, e.g. Empetrum, Rumex acetosa type, Plantago?najor and Rubiaceae, together with single grains of such types as fmpatiens, Epilobium, Papaver {?), Campanula, Lycopodium inundatum, Selaginella and Botrychium (see Table i). In sub-zone Ib, following the spread of tree birches there is a marked decrease in the amount of grass pollen but an increase in Thalictrum, the latter perhaps being a swamp species. Single grains of interest are Lycopodium annotinum and Gentianella campestris (?). Then in sub-zone Ic the return to cold conditions reduced the tree birches to very low amounts (from a maximum of 33% in Ib to a minimum of 6% in Ic). An increase in Helianthemum suggests a not very extreme climate at this time. Sub-zone Ib saw the introduction of juniper and this increased considerably in sub-zone Ic rising to a maximum of 44% towards the end of the period. Such a juniper maximum is now generally accepted as marking the passing of the tree line (in Lapland juniper and willow have their greatest expansion just about and somewhat above the tree hne, juniper being most abundant in drier situations; Van der Hammen, 1952). There must therefore have been towards the end of sub-zone Ic a spread of birch trees which led to the establishment of birch woods in zone II. This resulted in a marked decline in Betula nana pollen and all herbaceous types except Filipendula uhnaria which may have grown round the edges of the lake. In zone III there is a sharp fall in tree birches and an increase in Betula nana and certain herbaceous types, especially sedges, Artemesia, Thalictrum and Lycopodiitm selago. The fact that there is no return of Juniper and no increase in gramineous pollen

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10 286 D. D. BARTLEY in zone III suggests that the tree line did not retreat as far south as this point, though there must have been a thinning out of the birch woods. The end of the Late-glacial period is marked as usual by the rapid increase of birch trees and the disappearance of Betula nana and most herbaceous types as the closed birch woods of zone IV developed. The other point of interest in the pollen diagrams lies in the tree pollen diagram (Fig. 3) and its relation to stratigraphy. The presence on the north side of a layer of Fhragmites peat of which the upper layers evidently carried pine trees early in zone VI suggests that the water table must have been fairly low at that time. The dark, oxidized nature of the central mud also supports this. Then a pollen diagram at T.ii shows that the peat was gradually covered by the dark mud later in zone VI. The plant remains Alnus glutinosa Betula pubescens B. verrucosa Pinus sylvestris Populus tremula Table 2. List of macroscopic remains found in the various zones Calluna vulgaris Carex paniculata C. pseudocyperus C. rostrata Ceratophyllum demersum Cicuta virosa Najas marina Nymphaea alba Potamogeton filiformis P. lucens P. obtusifolius P. perfoliatus P. praelongus P. pusillus PotentiUa palustris Rumex hydrolapathum Scirpus cf. lacustris Viola sp. CSC, CSC ov.sc, wood CSC. s. s. p. P- P- P- p. P- s. I-III IV V-VI Vila Icsc catakin scale; fruit; ov.sc. ovuliferous scale; p. pyrene; s. seed. found in this mud, e.g. Chara oospores, Fotamogeton pyrenes and fruits of Carex pseudocyperus, suggest formation in a shallow swamp. Furthermore the contamination of earlier zone \1 peat suggests for this time a fiuctuating water table which would dry out the upper layers temporarily and at the same time carry down pollen from the upper layers into the lower and earlier layers. This is partly supported by the fact that the lowest level of contamination follows the lower clay layers in much the same way that a water table might be expected to do. The presence of Alnus fruits in this zone VI mud indicates the presence of Alnus in the area in zone VI. At the Boreal-Atlantic transition the whole of the central basin was fiooded and a deep-water mud was deposited. Up to the end of zone VI the succession had been typical of a calcareous region with Fhragmites-Cladium fen giving way to birch and pine woods. The succession which followed was more typical of acid regions in that the mud deposited in the Atlantic period was followed by a swamp peat with Sphagnum followed by Sphagnum and Eriophorum vaginatmn peat. This change in the succession is a very common phenomenon

11 Lake deposits near Tadcaster 287 also found in other parts of the country. The whole of the deposit is covered by a layer of silty soil, the silt presumably being an erosion product following the clearance of the forest. REFERENCES EDWARDS, W,, MITCHELL, G, H, & WHITEHF.AD, T, H, (1950). Geology of the district north and east of Leeds, Mem. geol. Surv. U.K., N,S, 70. FAEGRI, K, (1940), Quatargeologische Untersuchungcn nn Westlichen Norwegen, IL Zur spatquataren geschichte Jaerens, Bergens Mus. Aorb., Naturvidenskapelig rekke, 7. IvERSEN, J, (1942), En Pollenanalytik Tidsfaestelsc af Fersksvandslagene ved Norre Lyngby, Medd. dansk. geol. Foren., 10, 130, MuLLENDERS, W, & GuLLENTOPS, F, (1956), Evolution de la vegetation et de la plaine alluviale de la Dyle, a Louvain, depuis Ie Pleni-Wurm, Bull. Acad. Belg., C'l. Sci., Ser, 5, 42, 1123, MuLLENDERS, W., GuLLENTOPS, F. & CREVECOHUR, E. (1958). L'Oscillation de Boiling a Lommel (Campine, Belgique), Bid!. Acad. Belg., 90, 315, OLDFIELD, F, (i960). Studies in the Post-glacial history of British vegetation: Lowland Lonsdale, Nezu PhytoL, 59, 192, TERASMAE, J, (1951). On the Pollen morphology of Betula nana. Svensk bot. Tidskr., 45(2), 358, VAN DER HAMMEN, TH, (1952), Late-glacial flora and periglacial phenomena in the Netherlands. Letd. geol. Meded., XVII, 71. WALKER, D, & GOD\MN, H, In: CLARK, J. G. D, (1954). Excavations at Star Carr. Cambridge,

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