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The flora and fauna of Late Pleistocene deposits in St. Aubin's Bay, Jersey, Channel Islands
The flora and fauna of Late Pleistocene deposits in St. Aubin's Bay, Jersey, Channel Islands G. R. Coope, R. L. Jones, D. H. Keen and P. V. Waton COOPE, G. R. , R . L. JONES, D. H . KEEN & P. V. WATON. 1985. The flora and fauna of Late Pleistocene depo sits in SI. Aubin 's Bay, Jersey, Channel Islands. Proc. Geol. A ss., 96(4), 315-321. Pockets of peat on top of the rock platform of SI. Aub in's Bay, southwest Jersey, have yielded pollen and plant macro-remains and an insect fauna indicative of tundra conditions. The stratigraphic and geomorphological setting of the deposits suggests formation either in a period of climatic deterioration following an interglacial , or in an interstad ial. An Early Devensian age is proposed for the depos it. G. R. Coope, Department of Geological Sciences, University of Birmingham, P. O. Box 363, Birmingham B15 2TT R. L. Jones, D. H. Keen and P. V. Waton, Department of Geography, Coventry (Lanchester) Polytechnic, Priory Street, Coventry CV1 5FB
3. FLORA
1. INTRODUCTION Severe gales during September 1981 cleared some of the sand seaward of the gravel storm beach at La Vau Varin (UTM ref. WV 60774830), St. Aubin 's Bay, on the southwest coast of Jersey (Fig. 1). Hitherto unreported Pleistocene organic and mineral deposits were exposed by this activity. Subsequent investigation revealed that the deposits could be traced for about 30 m north-south and 10 m west-east along the lower limit of the storm beach. The total thickness does not exceed 0.30 m, and is also very variable , in places ranging from total absence to the maximum in less than 0.50 m. The bulk of the deposits consist of a compacted mid-brown detrital peat with sand and angular clasts of shale of up to 0.03 m long axis. The basal 0.05 m is composed mainly of dark grey organic, silty gravel with both angular and sub-rounded shale fragments . The lowest 0.02-0.03 m has a reddishbrown colouration, which suggests that it has been oxidised.
2. STRATIGRAPHY The fossiliferous deposits rest on a wave-worn surface cut in shales and greywackes of the Late Proterozoic Jer sey Shale formation, and are intermittently overlain by up to 0.25 m of modern beach sediment, the latter preventing the mapping of their full extent. While it is possible that a former cover of beach deposits could have led to the compaction of the sediments, a more likely cause was their burial by, and subsequent exhumation from bene ath a cover of head which forms the backing cliff to a height of some 15 m. Nowhere is a contact between the two sediments visible, the base of the head at the cliff resting on Jersey Shale . However, the possibility that the sediments are not in situ , and could have been deposited via a mud-flow or similar mass-movement phenomenon cannot be discounted .
(a) Palynology
Pollen samples were taken at 0.02 m interval s from an open section at the maximum observed thickness of the deposit. The stratigraphy is given in Table 1. Samples were prepared and pollen identified using standard methods (Faegri & Iversen , 1975). The identification of Thelycrania pollen follows Moore and Webb (1978). A minimum count of 500 total land pollen and spore s (TPS) was made at each level. The curve for pollen abundance refers to the number of slides counted per level. Values range from 0 to 4, with the maximum value representing the minimum number of slides. The curve for pollen degradation also ranges over a scale 0 to 4, in this case representing an absence to maximum presence of degraded grains . The pollen diagram (Fig. 2) The pollen spectra are relatively homogeneous throughout, and as a result the diagram is considered to represent a single pollen assemblage biozone. The tree and shrub pollen total less than 15 per cent TPS, and are dominated by Pinus at up to 12 per cent. Betula and Salix are consistently recorded at 2 per cent or less, with the sporadic occurrence of Corylus, Alnus, Thelycrania and Fagus. The dwarf-shrubs, Calluna vulgaris and Ericaceae undiff. are recorded at TABLE 1. Stratigraphy of deposits
2.
0-0 .29 m
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Fig. 1. The western side of St. Aubi n's Bay. l aoLocation diagram . lb . Site of the deposits . Ic. Sketch section of the deposits .
51. AUBIN PERCENTAGE POLLEN DIAGRAM ANALYSIS, PV WATON 1982
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under 2 per cent, and it is possible that some of the Betula pollen is that of Betula nana. Gramineae are prevalent at between 39 and 56 per cent, and are generally lower by 10 to 15 per cent towards the centre of the sequence. Cyperaceae pollen is present throughout, with a maximum of about 24 per cent where Gramineae values are lowest. Other herbaceous taxa are diverse, and are particularly abundant (32-45 per cent). These include continuous records for Saxifragaceae, Umbelliferae, Polygonum bistorta type, Rumex, Plantago lanceolata, P. coronopus, P. maritima, Rubiaceae, and Compositae subfamily Liguliflorae. Pollen of aquatics is relatively sparse, whilst spores, particularly those of Botrychium lunaria, Polypodium vulgare and Filicales are more frequent. Sphagnum spores are also recorded at some levels, (b) Macroscopic plant remains
The sieved fragments from the pollen samples, and a 0.15 m block of peat from the top of the section were examined for plant macrofossils. These were, in general, poorly-preserved and thus probably unrepresentative. The sieved fragment samples from the top 0.10 m of the peat and the underlying silty gravel were devoid of identifiable material. The other sieved fragment samples and the peat block yielded Juncus, Viola and Ranunculus (subgenus Batrachium) seeds, together with Sphagnum leaves, unidentifiable moss stems, and Cenococcum geophilum sclerotia. (c) Interpretation
The pollen sequence indicates the existence of an open environment dominated by a herb-rich ground flora. The low values of tree and tall-shrub pollen are probably due to long-distance transport of their grains. It is also feasible that Betula, Pinus and Corylus occurred either as isolated trees and shrubs or in scrub woodland. The latter may have had a dwarf-shrub component including Calluna, although it is also probable that the Ericaceae were members of a heath community which included Betula nana, together with Gramineae and a range of other herbs. Salix, Alnus and perhaps some Betula may have been present in damper areas, such as the site of organic matter accumulation. The herb flora indicates a considerable variety of habitats within the pollen catchment. The original extent of the deposit is unknown, although the undulating and extensive shale platform below the cliffs in St. Aubin's Bay would have provided favourable situations for either continuous or scattered areas of wetland for several kilometres eastward of the deposit. It is probable that much of the extraneous pollen in a location of this type would be of relatively local origin, either from areas at the edge, or only a
few tens of metres from the edge of the marsh (Jacobson & Bradshaw, 1981). The pollen of Prunella type, Teucrium type, Bidens type, Epilobium and Thalictrum may be consonant with damp substrates and open habitats, as representatives of these taxa will tolerate abundant soil moisture. Open water occurred together with reedswamp, as the pollen of Nymphaea, Potamogeton and Typha indicate. Drier soils are, however, suggested by microfossil records for Pteridium, Poterium sanguisorba and Artemisia. The base-status of the soils also varied; P. sanguisorba, Linum catharticum, and perhaps Teucrium type, imply base-rich conditions, while the Ericaceae indicate acidity. Salt-marsh and/or short-turf maritime communities are suggested by the pollen of Chenopodiaceae, Cruciferae and Plantago maritima. Saxifragaceae, Artemisia and Thalictrum are bareground taxa. While the pollen of cold climate species were not identified amongst them, they may reflect periglacial soil disturbance. The presence of spores of the pteridophytes Botrychium lunaria and Lycopodium clavatum (common in, although not exclusive to cold conditions) in conjunction with the above taxa, lends support to this hypothesis. The evidence from plant macrofossils supports the notion of local freshwater marsh-indicated by the seeds of Juncus and probably Viola, and the remains of Sphagnum, and Ranunculus subgenus Batrachium. The occurrence of the fungus Cenococcum geophilum indicates the growth of woody plants, perhaps Betula, Salix or Alnus, nearby (van Geel, 1976). The pollen flora and inferred vegetation is comparable with palynological and ecological studies of present-day arctic environments (Fredskild, 1961, 1967; Lichti-Federovich & Ritchie, 1968). Where trees are absent in such localities, AP values, mainly of Pinus, are the result of long-distance pollen transport. Grasses and sedges are of major importance in the vegetation and pollen record, while dwarf birch, Salix, Artemisia, Rumex and Ericaceae are also of significance (Birks, 1973). 4. FAUNA Two bulk samples for insect analysis were taken from the maximum thickness of the deposit at the same location as the palaeobotanical sampling site. The upper sample corresponded to the top 0.10 m of the peat, and the lower to the bottom 0.20 m of peat plus the grey silty gravel at the base. All the insect fossils from these samples were of Coleoptera. (a) The Coleoptera diagram
The occurrence of Coleoptera in the samples is shown in Fig. 3. The species noted in the diagram are arranged in traditional taxonomic order and the numbers at each level represent the minimum number
319
PLEISTOCENE DEPOSITS IN JERSEY
5T AUBI N ABSOLUTE COLEOPTERA DIAGRAM ANALYSIS (Ul.COQPE 1983 QYTISCIQAE (ARAB IDAE
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of individuals present, based on the maximum number of identifiable skeletal elements. Twenty-eight taxa of Coleoptera were identified in the two samples, there being no significant difference in the fauna throughout the section. Seventeen species or species groups were identified, the other individuals grouped as genera only. Staphylinidae dominate (eight species, five genera), followed by the Carabidae (five species, one genus), with members of the Dytiscidae, Hydrophildae, Scarabaeidae, Byrrhidae, Chyrsomelidae and Curculionidae comprising the remainder. (b) Interpretation (i) Local environment. The limited coleopteran assemblage provides information on the habitats available when the sediment was deposited. Aquatic environments are indicated by Agabus bipustulatus and Hydroporus, though little can be said about the nature of the water. Species of Helophorus have predatory larvae but the adult animals feed on algal filaments or the superficial cells of plant tissues. The water may have been in the form of very small ponds to accommodate these species. Marshy ground adjacent to the pools would have provided the habitat for Agonum exaratum (Lindroth, 1966), and amongst the leaf-litter and moss remains would have been found the small, predatory Staphylinids. The four carabids, Loricera pilicornis, Patrobus assimilis, Patrobus septentrionis and Pterostichus diligens are rather eurytopic, but are often found in moist, meadow-like vegetation, the latter species being especially fond of acid situations. The local vegetation is hinted at by the food preferences of the phytophagous beetles. Simplocaria metallica feeds on wet moss. Notaris aethiops, though frequently said to feed on Sparganium ramosum, probably finds various Cyperaceae acceptable. The weevil Otiorhynchus rugifrons is rather polyphagous
but will feed on species of Saxifragaceae. Finally, Aphodius sp is normally a dung-beetle but several species can make do with rotting vegetation that has the physical properties of dung. (ii) Climate. This assemblage is very different from the modern insect fauna of Jersey. Four species (Agonum exaratum, Pycnoglypta lurida, Boreaphilus henningianus, and Simplocaria metallica) do not occur at all within the British Isles but have boreal or boreo-montane geographical ranges at the present time. A further four species (Patrobus septentrionis, Arpedium brachypterum, Olophrum fuscum and Notaris aethiops) also have boreo-montane distributions, but including the northern parts of the British Isles. There can thus be no doubt that the St. Aubin deposit was laid down under a cold climatic regime. One species, Agonum exaratum, is of great climatic significance. It is a circumpolar species ranging from arctic Russia to Alaska and northern Canada. It is the most pronouncedly arctic species of Agonum (Lindroth, 1966) and does not live below the tree-line. The presence of this species in Jersey strongly suggests that the climate at the time must have been very severe with average July temperatures at, or below, lOoC, the figure usually given as the limiting value for tree growth. The rest of this fauna, though not exclusive to such conditions, is fully tolerant of them. 5. DISCUSSION (a) Comparable sites Three sites in the western Channel area have comparable stratigraphic, palaeobotanical and coleopteran records to that of St. Aubin's Bay. These are Fliquet, Jersey, some 12 km to the northeast (Coope, Jones & Keen, 1980), and Petit-Beaumont and Herquemoulin on the west coast of the Cotentin
320
G . R . COO P E , R . L. JONES , D . H . KE EN A ND P . V . WATON
Peninsula, Normandy, about 60 km north northeast (Fig. 1). Fliquet and Petit-Beaumont are also foreshore exposures of organic materi al lying on a rock platform , backed by head cliffs. Th e Herquemoulin depo sits consist of clay-muds interc alated with, and overlain by, head . The upper part of the Fliquet sequ ence (Pollen Assemblage Zone F-2 and Coleopt era Assemblage Zone f-2), and the whole of those at Pet it-Beaumont and Herquemoulin (site D) are comparable with the St. Aubin site. Non-arboreal pollen dominates, with Gramineae and Cyperaceae most frequent , although Compositae , Rosaceae, Caryophyllaceae, Saxifragaceae and Cruciferae are also present in substantial amounts. Arboreal pollen is represented mainly by small amounts of Pinus. The only significant differences are the absence of the small quantities of Picea and Juniperus pollen found at Fliquet, and the Normandy sites, from the St. Aubin record, and the varying percentages of grass and sedge pollens. The lack of Picea at St. Aubin is unlikel y to be the result of a distance-decay effect of long-range arboreal pollen dispersal, which tend s to be less abrupt. It may mean that the Fliquet and Cotentin sites are of a different age to St. Aubin . However , the bulk of the fossil evidence is suggestive of temporal correl ation . Perhaps the most likely explanation is chance non-deposition , or non-encounter of the taxon at St. Aubin. Juniperus was a likely component of shrub heath around Petit-Beaumont, Herquemoulin and pre sumably Fliquet, but was absent near St. Aubin , where Ericales, and possibly Betula nana , may have belonged to such an association . The variations in percentages of Gramineae and Cyperaceae (the former at 15 per cent or less of total pollen and spores at Petit-Beaumont, Herquemoulin and Fliquet, and over 30 per cent at St. Aubin ; the latt er reaching over 70 per cent TPS at Petit-Beaumont, Herquemoulin and Fliquet, and achieving no more than 24 per cent at St. Aubin) may be explained by a rich herb flora at St. Aubin , such as typifies current local short-turf grassland on coastal headlands and dunes. The assembl age of Coleoptera from St. Aubin's Bay resembles that from Fliquet and the two Normandy sites in its boreal and arctic/alpine nature. In particul ar , A gonum exaratum occurs at St. Aubin, Petit-Beaumont and Herquemoulin, so far the only localities where this species has been found as a fossil. (b) The age of the St. Aubin deposits The flora and fauna from St. Aub in do not provide conclusive evidence for the date of these deposits. Indeed , the y do not resemble closely those of any establi shed Pleistocene event. The occurrence of these terrestri al and aquatic depo sits on a wave-washed platform and the incorporation into them of rolled pebbles of beach type , shows that the sediments
post-date a phase of high sea-level that coincided approximately with that of the present day. Raised beaches of similar height and geomorphic position to that of St. Aubin 's Bay have been recogn ized elsewhere in Jer sey and have been attributed to the Ipswichian (Eemian) Interglacial (Kee n , 1978) . At that time , the sea reached a level of c. 8 m above pre sent mean sea-level. An age for this event of 1 21 , OOo~1~~BP is indicated by V-series dates obtained from the Belle Hougue Cave in the north of the island (Kee n, Ha rmon & Andrews, 1981). In Norm andy , the recognition of at least two phases of high sea-level near to that of the present day (Lautridou , 1982; Keen , 1982; Clet , 1983) , makes comparative dating of the St. Aubin depo sit on the basis of geomorphic position and height above sea-level difficult. The survival of such frail deposits as isolated and eroded remnants on the present-day wave-washed platform suggests, however , that these sediments are of Late Pleistocene age, and were laid down after the most recent intergl acial high sea-level. An altern ative correlation (Clet, 1983) would place organic deposits on the Normandy coast , in similar stratigraph ic positions to those of S1. Aubin and Fliquet , in an 'intra-Saalian' interglacial, and in the Eemian Intergl acial. This correl ation uses the stratigraphy of the overlying head which is interpret ed by Clet as a multi-ph ase deposit . We believe that this correlation is, on the basis of currently available inform ation , the least plausible alternative . At the two Jers ey and the two Normandy sites discussed above, there can be no que stion on floral or faunal grounds, that the deposits were laid down under per iglacial (or possibly inter stadial) rather than inter glacial conditions. (c) Synthesis The combined stratigraphical and palaeontological evidence from both the sites in Jersey (St. Aubin and Fliquet) and from the two localities on the coast of Normandy (Petit-Beaumont and Herquemoulin) indicates that these deposits were laid down on what must have been an extensive coastal plain, at a time when sea-level was well below that of the present-day. The flora provides little unequivocal evidence of any marine influence, and there are no species of Coleoptera present that prefer saline habit ats . Furthermore, the occurrence at the Jersey sites of similar flightless species of Coleoptera suggests that , at this time , sea-level was so low that Jersey was connected by con tinuous terrestrial habitat s to northern France. The close similarit y of both floras and fauna s indicates that the environment of this coastal plain was of very limited diver sity, with extens ive peaty swamps covered with Cyper aceae , and with isolated pond s scattered across a monotonous landscape probably devoid of trees . There can be little
PLEIST O CENE DEPOSITS IN J ERS EY
doubt that this environment was a true analogue of present-day tundra. Although it is difficult to date this episode , we suggest that the mo st likely period was sometime during the early phases of th e Devensian (Wurm , Weichsel) Glaciation. This is a period from which , up to now , very few flor as or faunas have been described . Our fossil assemblages show clearly that there was a marked climatic deterioration to condition s of ar ctic severity, aft er the lowering of sea -level but before the emplacement of the major head deposits. Radi ocarbon dates from site s on the Cotentin and from Fliquet (Delibrias & Lar sonneur , 1966; Shotton & Williams, 1971; Coope , Jones & Keen, 1980) have yielded ages from 12,600 ± 400 to in excess of 44,500 year s BP for organic material either below or in the lowest levels of head. In view of the uncertainties accompanying many of these assays (Coope , Jones & Keen, 1980), it is probable that the
321
age of the o rga nic deposits is older th an the limit of radiocarbon dating . While there is no evidence that the sub-head org an ic deposits ar e all of the same age , it is possible th at the y relate to cold periods not greatly separated in time. These periods were prior to an extremely cold ep isode that gave rise to a major phase of head developm ent. The latter probably equates with the Main Devensian Glaciation , post-30,OOO BP. Thus E arl y Devensian time see ms most likely for th e formation of th e St. Aubin and related organic deposits .
ACKNOWLEDGEMENTS We are grateful to Dr. J. H. Dickson (U nive rsity of Glasgow) for the report on the plant macr ofossils. The fieldwork at St. Aubin was supported by grants from the Jersey Heritage Trust and Coventry (Lanchester) Polytechnic, to whom thanks are due .
References BIRKS, H. J. B., 1973. Modern pollen rain in arctic and KEEN, D. B., 1978. The Pleistocene deposits of the Channel Islands. Rep. lnst. Geo l. Sci. , 78/26, 14pp. alpine areas. In Quaternary Plant Ecology (H. J. B. Birks & R. G. West, eds.) . Blackwell Scientific Publications, - -, 1982. Depositional sequence, age and palaeoenvironment of raised beaches and head in the Channel Islands Oxford, 143-68. CLET-PELLERIN, M., 1983. L e Plio-Pleistocene en and Central Channel. Bull . A .F.E.Q. , 2 (NS), 3-11. Norm andie. Apports de la Palyn ologie. Unpub 3rd cycle , R. S. HARMON, & J. T. ANDR EWS, 1981. U-series and amino-acid dates from Jersey. Nature, Lond., 289, thesis, Universite de Caen. 162-4. COOPE , G. R., R. L. JONES, & D. H. KEEN, 1980. The palaeoecology and age of peat at Fliquet Bay, Jersey, LAUTRIDOU , J. P. (ed), 1982. The Quaternary of No rman dy. Q.R.A . field guide, C.R.D.P., Caen. Channel Islands. J. Bioge ogr. , 7, 187- 95. DELIBRIAS , G. & C. LARSONNEUR , 1966. Datation LICHTI-FEDEROVICH, S. & J. C. RITCHIE, 1968. absolue de depots organiques wiirmiens en Normandie. Recent pollen assemblages from the western interior of C. R . Acad. Sci. Paris, 263, 1022-4. Canada. Rev. Palaeobotan. Palyn ol. , 7, 297-344. FAEGRI , K. & J. IVERSEN, 1975. Tex tboo k of Pollen LINDROTH , C., 1966. The ground-beetles of Canada and Analysis (3rd. Edition). Munksgaard, Copenhagen. Alaska. Part 4. Entomologiska Siillekap et, Lund, pp 409648. FREDSKILD, B., 1961. Floristic and ecological studies near Jakobshavn, West Greenland. Meddr . Grenland, 163, 4, MOORE , P. D. & J. A. WEBB, 1978. A n Illustrated Guide to Pollen Analysis. Hodder and Stoughton, London. 82 pp. - -, 1967. Palaeobotanical investigations at Semmermuit, SHOrrON , F. W. & R. E. G. WILLIAMS, 1971. Birmingham University Radiocarbon dates IV. RadiocarJakobshavn, West Greenland Meddr. Grenland, 178, 4, bon , 13 (2), 141-56. 54pp . JACOBSON, G. L. & R. H. W. BRADSHAW, 1981. The VAN GEEL , B., 1976. A Paleoecological Study of Holocene Peat Bog Sections. Hugo de Vries Laboratorium, selection of sites for palaeovegetational studies. Quat. Res. , 16, 80--96. Universitet van Amsterdam.
3. FLORA
1. INTRODUCTION Severe gales during September 1981 cleared some of the sand seaward of the gravel storm beach at La Vau Varin (UTM ref. WV 60774830), St. Aubin 's Bay, on the southwest coast of Jersey (Fig. 1). Hitherto unreported Pleistocene organic and mineral deposits were exposed by this activity. Subsequent investigation revealed that the deposits could be traced for about 30 m north-south and 10 m west-east along the lower limit of the storm beach. The total thickness does not exceed 0.30 m, and is also very variable , in places ranging from total absence to the maximum in less than 0.50 m. The bulk of the deposits consist of a compacted mid-brown detrital peat with sand and angular clasts of shale of up to 0.03 m long axis. The basal 0.05 m is composed mainly of dark grey organic, silty gravel with both angular and sub-rounded shale fragments . The lowest 0.02-0.03 m has a reddishbrown colouration, which suggests that it has been oxidised.
2. STRATIGRAPHY The fossiliferous deposits rest on a wave-worn surface cut in shales and greywackes of the Late Proterozoic Jer sey Shale formation, and are intermittently overlain by up to 0.25 m of modern beach sediment, the latter preventing the mapping of their full extent. While it is possible that a former cover of beach deposits could have led to the compaction of the sediments, a more likely cause was their burial by, and subsequent exhumation from bene ath a cover of head which forms the backing cliff to a height of some 15 m. Nowhere is a contact between the two sediments visible, the base of the head at the cliff resting on Jersey Shale . However, the possibility that the sediments are not in situ , and could have been deposited via a mud-flow or similar mass-movement phenomenon cannot be discounted .
(a) Palynology
Pollen samples were taken at 0.02 m interval s from an open section at the maximum observed thickness of the deposit. The stratigraphy is given in Table 1. Samples were prepared and pollen identified using standard methods (Faegri & Iversen , 1975). The identification of Thelycrania pollen follows Moore and Webb (1978). A minimum count of 500 total land pollen and spore s (TPS) was made at each level. The curve for pollen abundance refers to the number of slides counted per level. Values range from 0 to 4, with the maximum value representing the minimum number of slides. The curve for pollen degradation also ranges over a scale 0 to 4, in this case representing an absence to maximum presence of degraded grains . The pollen diagram (Fig. 2) The pollen spectra are relatively homogeneous throughout, and as a result the diagram is considered to represent a single pollen assemblage biozone. The tree and shrub pollen total less than 15 per cent TPS, and are dominated by Pinus at up to 12 per cent. Betula and Salix are consistently recorded at 2 per cent or less, with the sporadic occurrence of Corylus, Alnus, Thelycrania and Fagus. The dwarf-shrubs, Calluna vulgaris and Ericaceae undiff. are recorded at TABLE 1. Stratigraphy of deposits
2.
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Mid-brown sandy detritus peat with Carex tissue and angular shale clasts of up to 0.03 m long axis. Highly compacted. 1. 0.29-0 .30 m Grey silty gravel. Shale clasts of up to 0.03 m long axis. At base, wave-worn surface cut in Jersey Shale.
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318
G. R. COOPE, R. L. JONES, D. H. KEEN AND P. V. WATON
under 2 per cent, and it is possible that some of the Betula pollen is that of Betula nana. Gramineae are prevalent at between 39 and 56 per cent, and are generally lower by 10 to 15 per cent towards the centre of the sequence. Cyperaceae pollen is present throughout, with a maximum of about 24 per cent where Gramineae values are lowest. Other herbaceous taxa are diverse, and are particularly abundant (32-45 per cent). These include continuous records for Saxifragaceae, Umbelliferae, Polygonum bistorta type, Rumex, Plantago lanceolata, P. coronopus, P. maritima, Rubiaceae, and Compositae subfamily Liguliflorae. Pollen of aquatics is relatively sparse, whilst spores, particularly those of Botrychium lunaria, Polypodium vulgare and Filicales are more frequent. Sphagnum spores are also recorded at some levels, (b) Macroscopic plant remains
The sieved fragments from the pollen samples, and a 0.15 m block of peat from the top of the section were examined for plant macrofossils. These were, in general, poorly-preserved and thus probably unrepresentative. The sieved fragment samples from the top 0.10 m of the peat and the underlying silty gravel were devoid of identifiable material. The other sieved fragment samples and the peat block yielded Juncus, Viola and Ranunculus (subgenus Batrachium) seeds, together with Sphagnum leaves, unidentifiable moss stems, and Cenococcum geophilum sclerotia. (c) Interpretation
The pollen sequence indicates the existence of an open environment dominated by a herb-rich ground flora. The low values of tree and tall-shrub pollen are probably due to long-distance transport of their grains. It is also feasible that Betula, Pinus and Corylus occurred either as isolated trees and shrubs or in scrub woodland. The latter may have had a dwarf-shrub component including Calluna, although it is also probable that the Ericaceae were members of a heath community which included Betula nana, together with Gramineae and a range of other herbs. Salix, Alnus and perhaps some Betula may have been present in damper areas, such as the site of organic matter accumulation. The herb flora indicates a considerable variety of habitats within the pollen catchment. The original extent of the deposit is unknown, although the undulating and extensive shale platform below the cliffs in St. Aubin's Bay would have provided favourable situations for either continuous or scattered areas of wetland for several kilometres eastward of the deposit. It is probable that much of the extraneous pollen in a location of this type would be of relatively local origin, either from areas at the edge, or only a
few tens of metres from the edge of the marsh (Jacobson & Bradshaw, 1981). The pollen of Prunella type, Teucrium type, Bidens type, Epilobium and Thalictrum may be consonant with damp substrates and open habitats, as representatives of these taxa will tolerate abundant soil moisture. Open water occurred together with reedswamp, as the pollen of Nymphaea, Potamogeton and Typha indicate. Drier soils are, however, suggested by microfossil records for Pteridium, Poterium sanguisorba and Artemisia. The base-status of the soils also varied; P. sanguisorba, Linum catharticum, and perhaps Teucrium type, imply base-rich conditions, while the Ericaceae indicate acidity. Salt-marsh and/or short-turf maritime communities are suggested by the pollen of Chenopodiaceae, Cruciferae and Plantago maritima. Saxifragaceae, Artemisia and Thalictrum are bareground taxa. While the pollen of cold climate species were not identified amongst them, they may reflect periglacial soil disturbance. The presence of spores of the pteridophytes Botrychium lunaria and Lycopodium clavatum (common in, although not exclusive to cold conditions) in conjunction with the above taxa, lends support to this hypothesis. The evidence from plant macrofossils supports the notion of local freshwater marsh-indicated by the seeds of Juncus and probably Viola, and the remains of Sphagnum, and Ranunculus subgenus Batrachium. The occurrence of the fungus Cenococcum geophilum indicates the growth of woody plants, perhaps Betula, Salix or Alnus, nearby (van Geel, 1976). The pollen flora and inferred vegetation is comparable with palynological and ecological studies of present-day arctic environments (Fredskild, 1961, 1967; Lichti-Federovich & Ritchie, 1968). Where trees are absent in such localities, AP values, mainly of Pinus, are the result of long-distance pollen transport. Grasses and sedges are of major importance in the vegetation and pollen record, while dwarf birch, Salix, Artemisia, Rumex and Ericaceae are also of significance (Birks, 1973). 4. FAUNA Two bulk samples for insect analysis were taken from the maximum thickness of the deposit at the same location as the palaeobotanical sampling site. The upper sample corresponded to the top 0.10 m of the peat, and the lower to the bottom 0.20 m of peat plus the grey silty gravel at the base. All the insect fossils from these samples were of Coleoptera. (a) The Coleoptera diagram
The occurrence of Coleoptera in the samples is shown in Fig. 3. The species noted in the diagram are arranged in traditional taxonomic order and the numbers at each level represent the minimum number
319
PLEISTOCENE DEPOSITS IN JERSEY
5T AUBI N ABSOLUTE COLEOPTERA DIAGRAM ANALYSIS (Ul.COQPE 1983 QYTISCIQAE (ARAB IDAE
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Fig. 3. St. Aubin-absolute Coleoptera diagram.
of individuals present, based on the maximum number of identifiable skeletal elements. Twenty-eight taxa of Coleoptera were identified in the two samples, there being no significant difference in the fauna throughout the section. Seventeen species or species groups were identified, the other individuals grouped as genera only. Staphylinidae dominate (eight species, five genera), followed by the Carabidae (five species, one genus), with members of the Dytiscidae, Hydrophildae, Scarabaeidae, Byrrhidae, Chyrsomelidae and Curculionidae comprising the remainder. (b) Interpretation (i) Local environment. The limited coleopteran assemblage provides information on the habitats available when the sediment was deposited. Aquatic environments are indicated by Agabus bipustulatus and Hydroporus, though little can be said about the nature of the water. Species of Helophorus have predatory larvae but the adult animals feed on algal filaments or the superficial cells of plant tissues. The water may have been in the form of very small ponds to accommodate these species. Marshy ground adjacent to the pools would have provided the habitat for Agonum exaratum (Lindroth, 1966), and amongst the leaf-litter and moss remains would have been found the small, predatory Staphylinids. The four carabids, Loricera pilicornis, Patrobus assimilis, Patrobus septentrionis and Pterostichus diligens are rather eurytopic, but are often found in moist, meadow-like vegetation, the latter species being especially fond of acid situations. The local vegetation is hinted at by the food preferences of the phytophagous beetles. Simplocaria metallica feeds on wet moss. Notaris aethiops, though frequently said to feed on Sparganium ramosum, probably finds various Cyperaceae acceptable. The weevil Otiorhynchus rugifrons is rather polyphagous
but will feed on species of Saxifragaceae. Finally, Aphodius sp is normally a dung-beetle but several species can make do with rotting vegetation that has the physical properties of dung. (ii) Climate. This assemblage is very different from the modern insect fauna of Jersey. Four species (Agonum exaratum, Pycnoglypta lurida, Boreaphilus henningianus, and Simplocaria metallica) do not occur at all within the British Isles but have boreal or boreo-montane geographical ranges at the present time. A further four species (Patrobus septentrionis, Arpedium brachypterum, Olophrum fuscum and Notaris aethiops) also have boreo-montane distributions, but including the northern parts of the British Isles. There can thus be no doubt that the St. Aubin deposit was laid down under a cold climatic regime. One species, Agonum exaratum, is of great climatic significance. It is a circumpolar species ranging from arctic Russia to Alaska and northern Canada. It is the most pronouncedly arctic species of Agonum (Lindroth, 1966) and does not live below the tree-line. The presence of this species in Jersey strongly suggests that the climate at the time must have been very severe with average July temperatures at, or below, lOoC, the figure usually given as the limiting value for tree growth. The rest of this fauna, though not exclusive to such conditions, is fully tolerant of them. 5. DISCUSSION (a) Comparable sites Three sites in the western Channel area have comparable stratigraphic, palaeobotanical and coleopteran records to that of St. Aubin's Bay. These are Fliquet, Jersey, some 12 km to the northeast (Coope, Jones & Keen, 1980), and Petit-Beaumont and Herquemoulin on the west coast of the Cotentin
320
G . R . COO P E , R . L. JONES , D . H . KE EN A ND P . V . WATON
Peninsula, Normandy, about 60 km north northeast (Fig. 1). Fliquet and Petit-Beaumont are also foreshore exposures of organic materi al lying on a rock platform , backed by head cliffs. Th e Herquemoulin depo sits consist of clay-muds interc alated with, and overlain by, head . The upper part of the Fliquet sequ ence (Pollen Assemblage Zone F-2 and Coleopt era Assemblage Zone f-2), and the whole of those at Pet it-Beaumont and Herquemoulin (site D) are comparable with the St. Aubin site. Non-arboreal pollen dominates, with Gramineae and Cyperaceae most frequent , although Compositae , Rosaceae, Caryophyllaceae, Saxifragaceae and Cruciferae are also present in substantial amounts. Arboreal pollen is represented mainly by small amounts of Pinus. The only significant differences are the absence of the small quantities of Picea and Juniperus pollen found at Fliquet, and the Normandy sites, from the St. Aubin record, and the varying percentages of grass and sedge pollens. The lack of Picea at St. Aubin is unlikel y to be the result of a distance-decay effect of long-range arboreal pollen dispersal, which tend s to be less abrupt. It may mean that the Fliquet and Cotentin sites are of a different age to St. Aubin . However , the bulk of the fossil evidence is suggestive of temporal correl ation . Perhaps the most likely explanation is chance non-deposition , or non-encounter of the taxon at St. Aubin. Juniperus was a likely component of shrub heath around Petit-Beaumont, Herquemoulin and pre sumably Fliquet, but was absent near St. Aubin , where Ericales, and possibly Betula nana , may have belonged to such an association . The variations in percentages of Gramineae and Cyperaceae (the former at 15 per cent or less of total pollen and spores at Petit-Beaumont, Herquemoulin and Fliquet, and over 30 per cent at St. Aubin ; the latt er reaching over 70 per cent TPS at Petit-Beaumont, Herquemoulin and Fliquet, and achieving no more than 24 per cent at St. Aubin) may be explained by a rich herb flora at St. Aubin , such as typifies current local short-turf grassland on coastal headlands and dunes. The assembl age of Coleoptera from St. Aubin's Bay resembles that from Fliquet and the two Normandy sites in its boreal and arctic/alpine nature. In particul ar , A gonum exaratum occurs at St. Aubin, Petit-Beaumont and Herquemoulin, so far the only localities where this species has been found as a fossil. (b) The age of the St. Aubin deposits The flora and fauna from St. Aub in do not provide conclusive evidence for the date of these deposits. Indeed , the y do not resemble closely those of any establi shed Pleistocene event. The occurrence of these terrestri al and aquatic depo sits on a wave-washed platform and the incorporation into them of rolled pebbles of beach type , shows that the sediments
post-date a phase of high sea-level that coincided approximately with that of the present day. Raised beaches of similar height and geomorphic position to that of St. Aubin 's Bay have been recogn ized elsewhere in Jer sey and have been attributed to the Ipswichian (Eemian) Interglacial (Kee n , 1978) . At that time , the sea reached a level of c. 8 m above pre sent mean sea-level. An age for this event of 1 21 , OOo~1~~BP is indicated by V-series dates obtained from the Belle Hougue Cave in the north of the island (Kee n, Ha rmon & Andrews, 1981). In Norm andy , the recognition of at least two phases of high sea-level near to that of the present day (Lautridou , 1982; Keen , 1982; Clet , 1983) , makes comparative dating of the St. Aubin depo sit on the basis of geomorphic position and height above sea-level difficult. The survival of such frail deposits as isolated and eroded remnants on the present-day wave-washed platform suggests, however , that these sediments are of Late Pleistocene age, and were laid down after the most recent intergl acial high sea-level. An altern ative correlation (Clet, 1983) would place organic deposits on the Normandy coast , in similar stratigraph ic positions to those of S1. Aubin and Fliquet , in an 'intra-Saalian' interglacial, and in the Eemian Intergl acial. This correl ation uses the stratigraphy of the overlying head which is interpret ed by Clet as a multi-ph ase deposit . We believe that this correlation is, on the basis of currently available inform ation , the least plausible alternative . At the two Jers ey and the two Normandy sites discussed above, there can be no que stion on floral or faunal grounds, that the deposits were laid down under per iglacial (or possibly inter stadial) rather than inter glacial conditions. (c) Synthesis The combined stratigraphical and palaeontological evidence from both the sites in Jersey (St. Aubin and Fliquet) and from the two localities on the coast of Normandy (Petit-Beaumont and Herquemoulin) indicates that these deposits were laid down on what must have been an extensive coastal plain, at a time when sea-level was well below that of the present-day. The flora provides little unequivocal evidence of any marine influence, and there are no species of Coleoptera present that prefer saline habit ats . Furthermore, the occurrence at the Jersey sites of similar flightless species of Coleoptera suggests that , at this time , sea-level was so low that Jersey was connected by con tinuous terrestrial habitat s to northern France. The close similarit y of both floras and fauna s indicates that the environment of this coastal plain was of very limited diver sity, with extens ive peaty swamps covered with Cyper aceae , and with isolated pond s scattered across a monotonous landscape probably devoid of trees . There can be little
PLEIST O CENE DEPOSITS IN J ERS EY
doubt that this environment was a true analogue of present-day tundra. Although it is difficult to date this episode , we suggest that the mo st likely period was sometime during the early phases of th e Devensian (Wurm , Weichsel) Glaciation. This is a period from which , up to now , very few flor as or faunas have been described . Our fossil assemblages show clearly that there was a marked climatic deterioration to condition s of ar ctic severity, aft er the lowering of sea -level but before the emplacement of the major head deposits. Radi ocarbon dates from site s on the Cotentin and from Fliquet (Delibrias & Lar sonneur , 1966; Shotton & Williams, 1971; Coope , Jones & Keen, 1980) have yielded ages from 12,600 ± 400 to in excess of 44,500 year s BP for organic material either below or in the lowest levels of head. In view of the uncertainties accompanying many of these assays (Coope , Jones & Keen, 1980), it is probable that the
321
age of the o rga nic deposits is older th an the limit of radiocarbon dating . While there is no evidence that the sub-head org an ic deposits ar e all of the same age , it is possible th at the y relate to cold periods not greatly separated in time. These periods were prior to an extremely cold ep isode that gave rise to a major phase of head developm ent. The latter probably equates with the Main Devensian Glaciation , post-30,OOO BP. Thus E arl y Devensian time see ms most likely for th e formation of th e St. Aubin and related organic deposits .
ACKNOWLEDGEMENTS We are grateful to Dr. J. H. Dickson (U nive rsity of Glasgow) for the report on the plant macr ofossils. The fieldwork at St. Aubin was supported by grants from the Jersey Heritage Trust and Coventry (Lanchester) Polytechnic, to whom thanks are due .
References BIRKS, H. J. B., 1973. Modern pollen rain in arctic and KEEN, D. B., 1978. The Pleistocene deposits of the Channel Islands. Rep. lnst. Geo l. Sci. , 78/26, 14pp. alpine areas. In Quaternary Plant Ecology (H. J. B. Birks & R. G. West, eds.) . Blackwell Scientific Publications, - -, 1982. Depositional sequence, age and palaeoenvironment of raised beaches and head in the Channel Islands Oxford, 143-68. CLET-PELLERIN, M., 1983. L e Plio-Pleistocene en and Central Channel. Bull . A .F.E.Q. , 2 (NS), 3-11. Norm andie. Apports de la Palyn ologie. Unpub 3rd cycle , R. S. HARMON, & J. T. ANDR EWS, 1981. U-series and amino-acid dates from Jersey. Nature, Lond., 289, thesis, Universite de Caen. 162-4. COOPE , G. R., R. L. JONES, & D. H. KEEN, 1980. The palaeoecology and age of peat at Fliquet Bay, Jersey, LAUTRIDOU , J. P. (ed), 1982. The Quaternary of No rman dy. Q.R.A . field guide, C.R.D.P., Caen. Channel Islands. J. Bioge ogr. , 7, 187- 95. DELIBRIAS , G. & C. LARSONNEUR , 1966. Datation LICHTI-FEDEROVICH, S. & J. C. RITCHIE, 1968. absolue de depots organiques wiirmiens en Normandie. Recent pollen assemblages from the western interior of C. R . Acad. Sci. Paris, 263, 1022-4. Canada. Rev. Palaeobotan. Palyn ol. , 7, 297-344. FAEGRI , K. & J. IVERSEN, 1975. Tex tboo k of Pollen LINDROTH , C., 1966. The ground-beetles of Canada and Analysis (3rd. Edition). Munksgaard, Copenhagen. Alaska. Part 4. Entomologiska Siillekap et, Lund, pp 409648. FREDSKILD, B., 1961. Floristic and ecological studies near Jakobshavn, West Greenland. Meddr . Grenland, 163, 4, MOORE , P. D. & J. A. WEBB, 1978. A n Illustrated Guide to Pollen Analysis. Hodder and Stoughton, London. 82 pp. - -, 1967. Palaeobotanical investigations at Semmermuit, SHOrrON , F. W. & R. E. G. WILLIAMS, 1971. Birmingham University Radiocarbon dates IV. RadiocarJakobshavn, West Greenland Meddr. Grenland, 178, 4, bon , 13 (2), 141-56. 54pp . JACOBSON, G. L. & R. H. W. BRADSHAW, 1981. The VAN GEEL , B., 1976. A Paleoecological Study of Holocene Peat Bog Sections. Hugo de Vries Laboratorium, selection of sites for palaeovegetational studies. Quat. Res. , 16, 80--96. Universitet van Amsterdam.