Quaternary Science Reviews 24 (2005) 2449–2465 Lateglacial palaeoenvironments and palaeoclimates from Conty and Houdancourt, northern France, reconstructed from Beetle remains Philippe Ponel a, , Russell Coope b , Pierre Antoine c , Nicole Limondin-Lozouet c , Chantal Leroyer d , Andre´-Valentin Munaut e,{ , Jean-Franc - ois Pastre c , Fre´de´ric Guiter a a IMEP-CNRS, Europoˆle Me´diterrane´en de l’Arbois, Pavillon Villemin, BP 80, F-13545 Aix-en-Provence cedex 04, France b Centre for Quaternary Research, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK c Laboratoire de Ge´ographie Physique, CNRS UMR 8591, 1 Place Aristide Briand, F-92195 Meudon cedex, France d Centre National de Pre´histoire, CNRS UMR 5808, 38 rue du 26e R.I., F-24000 Pe´rigueux, France e Laboratoire de Palynologie et Dendrochronologie, 5 Place Croix-du-Sud, Universite´de Louvain-la-Neuve, B-3411 Louvain-la-Neuve, Belgique Received 2 April 2004; accepted 8 December 2004 Abstract Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley, both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology, geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it. Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe. r 2005 Elsevier Ltd. All rights reserved. 1. Introduction In the course of various archaeological excavations, several Weichselian Lateglacial deposits have been dis- covered in northern France. These have been the subject of a multidisciplinary investigation involving their stratigra- phy (Antoine, 1990; Antoine et al., 2000; Pastre et al., 2000), palynology (Munaut and Defgne´ e, 1997), and molluscan analysis (Limondin, 1995, Limondin-Lozouet, 1998; Limondin-Lozouet and Antoine, 2001). A palaeocli- matic synthesis focused on northern France including the Paris Basin has recently been carried out by Guiter et al. (2003). However, little palaeoentomological evidence was utilised in this synthesis, or in other recent works dealing with the same area (Limondin-Lozouet et al., 2002; Antoine et al., 2000, 2003; Pastre et al., 2003). Elsewhere in France, insect assemblages obtained from peat bogs in mountainous areas have provided valuable palaeoecological and palaeoclimatological in- formation on the last climatic cycle in the Vosges (Ponel, 1995) and on the Lateglacial-Holocene transition in the Massif Central (Ponel and Coope, 1990). This is the first investigation of the palaeoenvironment and palaeocli- mate for the Lateglacial period in the Paris Basin based on fossil insect assemblages. ARTICLE IN PRESS 0277-3791/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2004.12.010 Corresponding author. Tel.: +33 4 42 90 84 41; fax. +33 4 42 90 84 48. E-mail addresses: [email protected] (P. Ponel), [email protected] (R. Coope), [email protected] (P. Antoine), [email protected] (N. Limondin-Lozouet), [email protected] (C. Leroyer), [email protected](J.-F. Pastre), [email protected] (F. Guiter). { Deceased.
Lateglacial palaeoenvironments and palaeoclimates from Conty andHoudancourt, northern France, reconstructed from Beetle remains
Philippe Ponela,�, Russell Coopeb, Pierre Antoinec, Nicole Limondin-Lozouetc,Chantal Leroyerd, Andre-Valentin Munaute,{, Jean-Franc-ois Pastrec, Frederic Guitera
aIMEP-CNRS, Europole Mediterraneen de l’Arbois, Pavillon Villemin, BP 80, F-13545 Aix-en-Provence cedex 04, FrancebCentre for Quaternary Research, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
cLaboratoire de Geographie Physique, CNRS UMR 8591, 1 Place Aristide Briand, F-92195 Meudon cedex, FrancedCentre National de Prehistoire, CNRS UMR 5808, 38 rue du 26e R.I., F-24000 Perigueux, France
eLaboratoire de Palynologie et Dendrochronologie, 5 Place Croix-du-Sud, Universite de Louvain-la-Neuve, B-3411 Louvain-la-Neuve, Belgique
Received 2 April 2004; accepted 8 December 2004
Abstract
Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley,
both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology,
geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The
sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of
these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy
vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the
thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as
warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though
other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it.
Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe.
r 2005 Elsevier Ltd. All rights reserved.
1. Introduction
In the course of various archaeological excavations,several Weichselian Lateglacial deposits have been dis-covered in northern France. These have been the subject ofa multidisciplinary investigation involving their stratigra-phy (Antoine, 1990; Antoine et al., 2000; Pastre et al.,2000), palynology (Munaut and Defgnee, 1997), and
e front matter r 2005 Elsevier Ltd. All rights reserved.
molluscan analysis (Limondin, 1995, Limondin-Lozouet,1998; Limondin-Lozouet and Antoine, 2001). A palaeocli-matic synthesis focused on northern France including theParis Basin has recently been carried out by Guiter et al.(2003). However, little palaeoentomological evidence wasutilised in this synthesis, or in other recent works dealingwith the same area (Limondin-Lozouet et al., 2002;Antoine et al., 2000, 2003; Pastre et al., 2003).
Elsewhere in France, insect assemblages obtainedfrom peat bogs in mountainous areas have providedvaluable palaeoecological and palaeoclimatological in-formation on the last climatic cycle in the Vosges (Ponel,1995) and on the Lateglacial-Holocene transition in theMassif Central (Ponel and Coope, 1990). This is the firstinvestigation of the palaeoenvironment and palaeocli-mate for the Lateglacial period in the Paris Basin basedon fossil insect assemblages.
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2. Palaeoentomological methodology
2.1. Field methods
Bulk samples, each of several kilograms, are usuallyneeded for Coleoptera analysis. Such samples are bestcollected from freshly exposed open sections wherestratigraphical control is more easily maintained andcontamination from other levels in the section is moreeasily avoided. Borehole samples are often too small andthere is always a risk that sediment may be introducedfrom other horizons during the coring process. At bothConty and Houdancourt, large samples (1.2–6.6 and3.3–5.9 kg, respectively, see Tables 1 and 2 in theelectronic supplement to this article) were collectedfrom newly exposed sections and stored in air tightpolythene bags in field damp condition and in coolstorage prior to treatment in the laboratory.
2.2. Laboratory methods
Each sample was disaggregated in water, and theresultant slurry washed over a 300 mm sieve. Insectremains were separated using the standard paraffin(kerosene) flotation method (Coope, 1986). The insectfossils are preserved in 30% alcohol in glass tubes.Identification is by comparison with specimens frommodern reference collections.
The stratigraphical occurrences of the differentspecies are allocated to the traditional climatostratigra-phical nomenclature of the subdivisions of the Lategla-cial period (Mangerud et al., 1974) because, in spite ofits inadequacies, this terminology enables easy correla-tion with previously published studies. The moremodern usage of event stratigraphy based on theclimatic sequence in the Greenland ice-cores (Bjorck etal., 1998; Walker et al., 1999) will be inserted wherenecessary in parenthesis after the traditional stratigra-phical name.
2.3. Choice of study sites
Sites selection was determined largely by the possibi-lity of collecting the relatively large samples required forinsect analysis, from good stratigraphical contexts. Bulksamples were available from exposures of two well-datedand studied sedimentary sequences: (a) Conty (in theSomme river catchment) and (b) Houdancourt (in theOise valley) (Fig. 1).
The Conty site is located near to Conty village, in agravel pit (02109009’’/49144029’’), 20 km S-SW ofAmiens, at the junction between the Selle and Evoissonsvalleys. The deposit yielded an exceptional Lateglacialrecord (Antoine, 1997a, b; Antoine et al., 2003; Limon-din-Lozouet and Antoine, 2001). The stratigraphy of thevalley fill has been based on a detailed 600m transect
with 35 borings and 8 core samples (for a description ofthe units: see caption, Fig. 2). The sedimentary sequenceshows the transition from a periglacial system (withbraided channels) to a transitional system characterisedby several well individualised low sinuosity and narrowchannels. This transition is marked by a major phase ofincision into the Pleniglacial deposits (gravels and loess)that appears to have taken place at the beginning of theBølling (GI-1e) event sometime shortly before 12,40014C-yrs BP (average cal. BP age: 14,500). This episode ofincision is followed by rapid sedimentation in theabandoned channels, of laminated silty peat followedby a typical woody peat that provided the following 14Cdates: 12,370770 BP at the bottom of the laminatedpeat, and 12,3007120 BP at the bottom of the woodypeat (Fig. 2, units 4a and 4b).
The end of the Bølling is marked by a suddencessation of peat accumulation in the channels, followedby deposition of calcareous fluvial silts showing a‘‘chalk-mud’’ facies closely similar to that of theYounger Dryas (GI-1d) (see Fig. 2, unit 5). The 14Cdates from above and below this layer, the occurrence ofthe arctic-alpine molluscan species Columella columella,and the lowering of the AP/NAP ratio, suggest that thisdeposit should be attributed to the Older Dryas coolingevent (Dryas II) (GI-1d).
The Allerød (GI-1c) event is represented by a periodof infilling of the valley by overbank deposits, withmoderate elevation of the alluvial plain. At this site theAllerød deposits can be subdivided into two organichorizons (Fig. 2, 6b1 and 6b3) separated by a layer oflighter-coloured calcareous silt (unit 6b2). The lowerhorizon was mainly formed during the Betula phase ofthe Allerød, i.e. between 11,800 and 11,500 BP, andincludes an Upper Palaeolithic level with large mammalremains (see caption of Fig. 2). The upper horizongrades laterally into a silty-peaty facies with plantremains (Fig. 2, unit 6c), which has been dated to11,130780 BP and 11,080765 BP, i.e. towards the endof the Allerød phase, and is characterised by a pollenspectrum that is dominated by Pinus. This markedincrease in Pinus at the base of unit 6b2, is associatedwith a decrease in total number of shells and changes inmalacofaunas composition, with a shift from Punctum
During the Younger Dryas (GS-1) (unit 7 in Fig. 2),the Allerød deposits were partially eroded and thencovered by a thick veneer of calcareous silts over theentire valley bottom. This ‘‘chalky mud’’ (detritalCaCO3: 55–70%, TOCo 1%), apparently formed bythe action of freeze-thaw processes on local chalk slopeswhich was then transported downslope during thespring melting of the snow cover, and laid down overthe entire valley as overbank deposits. The geometry
Fig. 1. Geographic location of the study sites, Conty and Houdancourt.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–2465 2451
and the facies of these deposits indicate a regime ofperiodic flooding over an alluvial plain with a singlechannel, leading to aggradation and progressive flatten-ing of the valley bottom. These sediments have beencorrelated with the Younger Dryas because of theirradiocarbon dates, the abundance of detrital carbonateand their malacological and palynological content,which indicate a well-marked climatic deterioration.This important phase of sedimentation with highcarbonate content characterises the Younger Dryasthroughout the whole Paris basin (Pastre et al., 1997,2000) as well as in the chalk areas of South-easternEngland (Preece and Bridgland, 1999) and over much ofNW Europe.
Finally, in the upper part of the Conty sequences thetransition to the Preboreal is characterised by a secondmajor phase of downcutting in a large single-channelsystem with meanders related to the rapid onset ofclimatic improvement, a response seen elsewhere in rivervalleys of NW Europe (Vandenberghe et al., 1994;Huisink, 1998; Tebbens et al., 1999; Van Huissteden andKasse, 2001). This is followed by the development of theearliest Holocene peat (Fig. 2: unit 9).
Altogether 10 samples were taken from two profiles atConty (CPM 4-C2 and CPM 2), spanning much of theLateglacial interstadial (Bølling, Older Dryas andAllerød). The stratigraphical position of these samplesis shown in Fig. 2. It should be observed that samples P4and P5, from profile CPM 4-C2, are subsamples of thesame stratigraphic horizon, as are samples P1, P2 andP3 which are stratigraphically equivalent to sample T1(profile CPM 2). Samples P6 and P7 were taken fromolder Dryas layers but yielded no insect remains. SampleP8 is stratigraphically equivalent to sample T2. Most ofthese samples yielded rich insect assemblages, with theexception of samples P6 and P7 which were relativelysmall samples of fine calcareous fluvial silts attributed tothe Older Dryas and, since any insect fossils wereprobably sparse for environmental and climatic reasons,much larger samples would be needed of this sediment inany future investigation if insect fossils of this age are tobe obtained.
The Houdancourt palaeochannel is located in the Oisevalley 15 km SW of Compiegne at ‘‘les Epinieres’’, 300mN of the modern river (213905000/4911903400). This is abroad and shallow channel (average width, 150m,
Fig. 2. CONTY, cores CPM2 and CPM4 (diameter: 16 cm): stratigraphy, location of the samples for palaeoentomological study and of radiocarbon
dates. 1—Valley-floor periglacial fluvial gravel (Units 2 & 3 represented by loess and a thin bed of grey silt are described in lateral cores, see: Antoine
et al., 2003). 4a—‘‘Laminated yellow silty peat’’ (Total organic carbon, TOC: 2–3%), with numerous plant remains (wood, bark, seeds), molluscs and
beetle remains. 4b—’’Reddish peat ‘‘(TOC: 15%), with numerous plant remains (wood, bark, seeds), some mollusc and beetle remains. 5—Thin
horizon of white calcareous silt (detrital CaCO3: 57%, COT o3%). 6b3—Grey calcareous organic silts (detrital CaCO3: 50%, TOC: 7.5%, with
Final Palaeolithic artefacts and large mammals remains (Equus caballus, Bos primigenius and Cervus elaphus) (Lower Federmesser level), charcoals,
with numerous molluscs and calcite biospheroids (earthworms). 6b2—Light grey calcareous silt (lightly organic) (detritalCaCO3 55%, TOC: 2.5%).
6b1—Grey organic silts (detrital CaCO3: 50%, TOC: 7.5%), with molluscs and some Final Palaeolithic artefacts at the top (Upper Federmesser
level). 6c—Lateral peaty facies of 6b1 (Channel IV). 7—Homogeneous light-grey silt (detrital CaCO3: 55–70%, TOCo 1%), with abundant
terrestrial molluscs, root tracks and organic horizons at the base (CPM2). 8—Loamy brownish peat with numerous molluscs and root tracks
(transition between 7 and 8). 9—Typical black peat.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–24652452
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maximal depth, 1.2m) that is part of a channel networkincised at the beginning of the Bølling (GI-1e) (Pastreet al., 2000, 2003). The studied profile was in a speciallyexcavated trench, where the channel deposits were attheir thickest.
The stratigraphical sequence at Houdancourt can besummarised as follows (Fig. 3). The basal exposedsediments are of sand and gravels resulting fromreworking of the surrounding Pleniglacial deposits (2b)during earliest Bølling channel formation. This basaldeposit is overlaid by two units of silty clay loam (beigeloam 3 and grey loam 4). These units are dated from thelatter half of the Bølling (cf. Fig. 3) and are from the firstphase of organic (fossiliferous) sedimentation (totalorganic carbon ‘‘TOC’’ layer 2 ¼ 4%, layer 3 ¼ 2.3%),and indicate a slowing down of the water velocity in thechannel. These organic deposits are overlain in turn by a30 cm thick peat layer that marks the growth of a smallpeat bog during the Allerød (GI-1c). This finelylaminated peat unit includes a loam-rich layer, locallyoverlain by a thin detrital layer that could be attributedto the Older Dryas (GI-1d). Above, a 20 cm thick peatylayer with Salix and Betula wood fragments(TOC ¼ 23%) is overlaid by a 10 cm peaty layer withoutwood fragments. The upper part of the peaty unit isstrongly affected by cryoturbation (involutions andsmall local cracks) attributed to the Younger Dryas(GS-1). The latter period is well indicated by an 80 cmthick white marly loam corresponding to the return ofseasonal fluvial sedimentation, and to a substantialcontribution of redeposited chalk (CaCO3 ¼ 60%)derived from upstream. No insect remains were recov-ered from this deposit. The profile is topped byHolocene deposits (fibrous peat 7a and organic clay7b, lower half of Postglacial; silty clay loam 8 and greysilty clay loam 9, post-Subboreal). No samples weretaken for insect analysis from the Holocene layers.
Lateglacial fossiliferous deposits are quite uncommonin the large valleys of the Paris Basin where the Bøllingis usually poorly represented and the Allerød charac-terised by a thin palaeosol which is devoid of insectremains.
Eight samples were collected for insect analysis fromthe Lateglacial organic sediments at Houdancourt, all ofwhich yielded insect fossils except for the uppermostsample, which may have lost its insect fossils throughoxidation. Together these samples span much of thelatter part of the Bølling and extend up to the lateAllerød climatic events.
Fig. 3. Stratigraphy of the Houdancourt sequence.
3. Results
Most of the identified fossils were of Coleoptera(beetles) which are listed in Tables 1 and 2 according tothe nomenclature and in the taxonomic order of Lucht
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(1987). These may not be the most up-to-date names,but they have been used extensively in many previousstudies of Quaternary Coleoptera and their use heremakes it easier for non-experts to make comparisons ofthese faunas with previously published fossil lists.Specialists can easily make the necessary nomenclaturaladjustments. In the tables the numbers opposite eachtaxon indicate the minimum numbers of individuals inthe sample.
Unless otherwise stated, biological, ecological andbiogeographical data were derived from the standardentomological literature: Angus (1992), Dauguet (1949),Doguet (1994), Guignot (1947), Hansen (1987), Hoff-mann (1950–1954), Holmen (1987), Horion (1963),Jeannel (1941–1942), Klausnitzer (1996), Koch(1989–1992), Leseigneur (1972), Lindroth (1985–1986,1992), Majerus (1994), Nilsson and Holmen (1995),Olmi (1976), Pirisinu (1981), Sainte-Claire Deville(1935–1938), Vienna (1980), Zanetti (1987). Much localinformation was also obtained from the excellent series‘‘Catalogue des Coleopteres de l’Ile de France’’, especiallyfrom Balazuc and Fongond (1989), Bergeal and Doguet(1992) and Voisin (1994). Climatic reconstructions weremade investigating the geographical overlap of theranges of the species in each assemblage and also byuse of the MCR programme devised by Atkinson et al.(1986).
4. Palaeoenvironmental interpretation
4.1. Conty
Most of the insect fossils were of Coleoptera becausetheir robust exoskeletons survive well. Altogether, 186taxa were recorded of which 110 (59%) could bedetermined to species or species group. The specificcomposition of the beetle assemblages appears to bevery similar throughout the Lateglacial sequence, andthe insect fauna will therefore be considered as a whole.Other insect Orders such as Heteroptera, Hymenoptera(Formicidae) and Megaloptera, were also present but inrelatively low numbers and have not been analysed indetail here.
4.2. Aquatic environments
Sedimentary analysis indicates that there is a differ-ence between the Bølling riverine system and that duringthe Allerød period. During the Bølling the riveroccupied narrow, stable and deeply incised channels,whereas during the Allerød it became confined to asingle large meandering channel with over bank calcar-eous and organic silt deposition linked to periodicflooding over the whole alluvial plain.
These riverine habitats are reflected in the aquaticfauna which includes a mixture of strictly running-watertaxa and predominantly standing-water taxa. TheDytiscid Platambus maculatus is mainly confined torunning water, and is associated with streams of allsizes, however this widespread species can be foundoccasionally at lake margins; it is also able to standbrackish water (Nilsson and Holmen, 1995). This is alsothe case of two Dryopidae taxa (Elmis, Limnius
volckmari), which are restricted to well-oxygenated partsof rivers. It is significant that these species are absentfrom the uppermost Bølling and from the Allerød levels.
In these assemblages, species characteristic of stand-ing or slowly moving water were much more abundantand more diverse than those indicative of running water.Thus Haliplus confinis is a pond species which feedsupon characeans during its larval stages. Most of theother Dytiscidae (predatory diving beetles), in thisassemblage (Agabus spp., Ilybius fuliginosus, Rhantus
sp., Colymbetes fuscus) are species of standing-water, asare all the Hydrophilids and most of the Hydraenids.This is especially the case of Hydrobius fuscipes,Laccobius, Enochrus, Berosus signaticollis and B. luridus
which are restricted to shallow water at the margins oflakes and pools. Both Berosus species live in shallow,often temporary pools, but B. signaticollis seems toprefer clear oligotrophic and acid water, whereas B.
luridus is found in rather eutrophic and grassy ponds,sometimes in brackish water. Ochthebius minimus, oneof the commonest water beetles, is able to survive in alltypes of aquatic environments including brackish water.A very distinctive species, Helophorus nanus, inhabitsstagnant water, especially eutrophic temporary pools(Hansen, 1987). Only one species, the Gyrinid Gyrinus
minutus, seems to prefer larger stagnant bodies of water(Holmen, 1987). The well-adapted aquatic weevilEubrychius velutus feeds principally on the pond weedMyriophyllum. These beetle species either indicate a poolof standing water on the floodplain (possibly anabandoned channel) or else slackwater reaches of theriver which could mimic stationary or almost stationarywater.
4.3. Transitional environments (fresh water marshes)
Some species can be considered as a transitionalgroup between truly aquatic insects and predominantlyterrestrial Coleoptera, since they live in the fringe ofhabitats between the truly open water and the terrestrialground. This is the case for many Hydrophilids such asCoelostoma orbiculare, Cercyon tristis, Cercyon convex-
iusculus, and Chaetarthria seminulum, which can befound amongst partly submerged rotten vegetabledebris, or Dryops sp., which lives buried in the mud atthe water margin. Many species in this assemblage liveon the wet mud surface or in the fen vegetation along
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the margins of rivers and lake banks. Carabidae andStaphylinidae are chiefly predators and are abundantboth in species and individuals in such environments.The Carabidae Elaphrus cupreus lives at the margin ofstagnant or slowly running water, on muddy soilscovered with a dense vegetation. Trechus rivularis is aspecies of peaty woodland with birches, alders andwillows, and an herbaceous layer dominated by Carex
and ferns. It also occurs in open Sphagnum bogs. It isfrequently found today associated with Patrobus assim-
ilis as it is in three of the Conty samples. Bembidion
semipunctatum, B. schuppeli, B. doris and B. biguttatum,are all hygrophilous species living along rivers and bystill waters, on silty and shaded ground with abundantvegetation including grasses, Carex, Juncus, Equisetum.
Bembidion clarki and Pterostichus strenuus are found inswamps and bogs covered with alders and willows.Bembidion doris, Pterostichus diligens and Agonum
gracile are frequently found together in Sphagnum
marshes, on lake and pool margins, amongst Carex,Menyanthes, etc. Bembidion gilvipes inhabits moistshaded soils. B. obtusum shows a rather similar ecology.Surprisingly it is today frequently associated withcultivated, open soil in dry situations (Luff, 1998). It isnoteworthy that many of the Conty species clearlyprefer shaded areas such as riverine forests or marshywoodlands with Alnus or Salix and avoid places exposedto sun.
As regards Staphylinids, a majority of speciesrecorded here are highly hygrophilous insects, usuallyfound in marshes, around lakes and ponds and inpeatbogs. This is the case for Pycnoglypta lurida,Olophrum fuscum, Eucnecosum brachypterum, Acidota
crenata, A. cruentata, Lesteva sp., Boreaphilus hennin-
gianus, Cryptobium fracticorne and Gymnusa brevicollis;which live amongst rotten plant detritus accumulatednear water bodies or in very wet places, in mosses(especially Sphagnum), or in peat bogs (Horion, 1963).The larvae of Acidota crenata have been found in birchleaf litter, along with its possible prey, the larvae ofLycoria gregaria (Campbell, 1982). Many of these taxa,such as Platysthetus cornutus and P. nodifrons, andTrogophloeus spp., are found burrowing in silty andclayey soils, on muddy places. Species of Bledius alsoburrow in silty and sandy banks of rivers and lakeschurning the uppermost few centimetres of the sediment.Trogophloeus and Stenus live in marshy habitats.
Phytophagous Coleoptera (mainly Chrysomelidaeand Curculionidae) reflect the composition of the localflora. The vast majority of phytophagous beetles in thisassemblage feed upon hygrophilous plants. Most ofthem are monophagous or oligophagous, that is theyexploit a limited food source such as a single plantspecies, one genus or a restricted group of species. TheseColeoptera provide a useful a cross-check with plantrecords such as pollen or macrofossil data and some-
times indicate the presence of a plant that is nototherwise recognisable on palaeobotanical evidence.The local presence of Carex is suggested by Phalacrus
caricis, the larvae of which feed on the smut spores(Ustilaginales) infecting the spikelets of various sedgesand grasses (Cooter, 1991). The adult beetles are alsofound on the same plants, in flowers (Thomson, 1958).Telmatophilus feeds upon Typha pollen grains. Donacia
marginata feeds largely on the leaves of Sparganium
and Limnobaris pilistriata prefer Carex species. Notaris
scirpi lives on Scirpus, Carex and Typha, whereasN. aethiops appears to be more polyphagous and isfound also on Poacaeae, Sparganium ramosum, or evenIris pseudacorus. Prasocuris phellandrii develops onseveral tall aquatic Umbelliferae. Other hygrophilousplants indicated by oligophagous beetles are for exampleRumex and Polygonum amphibium, respectively sug-gested by the weevils Hypera rumicis and Rhinoncus
gramineus. Fabaceae were also probably present nearby,as indicated by the small weevil Apion elegantulum
(dependent on Onobrychis) and Sitona (dependent onvarious Fabaceae). Helophorus nubilus is a phytopha-gous species found chiefly in grassland or amongstruderal vegetation.
The presence of Bembidion minimum, Bembidion
aeneum and Bembidion fumigatum in the Conty assem-blage is ecologically enigmatic. These species are usuallycoastal in Europe or, if found inland, they generallyoccur in saline habitats. However Lindroth (1992)points out that they have also been recorded, rarelyand sporadically, in freshwater marshes where theamount of salt must be extraordinarily small. Thesespecies should thus be described as ‘‘salt-prefering’’ andnot necessarily ‘‘salt-demanding’’. The frequency oftheir occurrence as a Lateglacial fossil here, suggeststhat moderately saline habitats may have been availableat this time.
4.4. Dry and open environments
As might be expected from the discussion above, onlyvery few species from this assemblage indicate open ordry habitats. The leaf-beetle Chilotoma musciformisfeeds upon Rumex, Anthyllis vulneraria and Dorycnium.The weevil Fourcartia cf. squamulata is more polypha-gous feeding on a wide variety of low herbs in sunny anddry grasslands. H. nubilus is not at all an aquatic speciesliving ‘‘on sandy or clayey, sunny grounds, also oncultivated soil, usually rather dry places but also onmore humid habitats, at the roots of various plants, andin decaying debris such as compost heaps etc’’ (Hansen,1987). It is very occasionally found in ant nests, which isof interest because another myrmecophilous beetleAtemeles was also recovered from the Conty depositstogether with numerous Formica fragments.
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4.5. Tree-dependent environments
Relatively few tree-dependent species were recordedfrom Conty. Thus Plagiodera versicolora feeds on Salix
and Populus, Melasoma populi on Populus, Phyllodecta
tibialis, Chalcoides sp., and Rhynchaenus cf. stigma onSalix, indicating that the only tree species locally presentat this time was willow (and/or possibly poplar).
4.6. Summary of the local environment at conty
interpreted from the fossil Coleoptera
Most of the fossil beetle species in this assemblagecould live in a valley in the Paris Basin at the presentday. The coexistence in this assemblage of indicatorsof both shallow running water, as well as of slowlymoving or stationary water suggests that the riverflowed in a meandering channel between rifflesand pools, perhaps leading to cut-off channels inwhich sediment could accumulate. Bare muddy banksoccurred beside the river. The beetles indicate that theriver was fringed by marshy woodland made up chieflyof willows (and/or poplars). Patchy dry grasslands musthave been present from time to time in the immediatevicinity.
4.7. Palaeoclimatic implications of the Conty beetle
assemblage
Since almost all the species in the Conty assemblageslive today in the Paris Basin, it is likely that thepalaeoclimate did not differ much from that of thepresent. The few species that today have geographicalranges outside this area are of particular importancesince they have special climatic significance. Thesespecies are indicated by (*) and (**) in faunal lists.They include Patrobus assimilis, Pycnoglypta lurida,
Trechus rivularis, Otiorhynchus nodosus and Notaris
aethiops. All have relatively northern distributions(Hansen et al., 1960) or survive only in isolated pocketsfurther south, and are considered to be adapted toslightly colder climates than northern France at thepresent day (however Holocene records of Notaris
aethiops in Southern England (David Smith, pers.comm.) could suggest that the present northern dis-tribution of this species may relate to habitat loss ratherthan to climate only). Acidota cruentata and A. crenata
are very scarce or even extinct in the same area today. Itshould be emphasised that these somewhat cold-adaptedspecies are by no means arctic and they suggest that thethermal climate during the latter half of the Bølling andmuch of the Allerød period was only slightly cooler thanit is in the Conty area today.
In contrast to the cool indicators mentioned above,there are a small number of species in this fossil
assemblage, which, though living now in northernFrance, have ranges that do not extend much furthernorth than this, i.e. they reach only as far as southernFennoscandia (Hansen et al., 1960). Such species includeBembidion fumigatum, B. minimum, B. octomaculatum
and Berosus signaticollis. These relatively southernspecies are clearly not adapted to very cold conditions.
The area of overlap of both relatively northern andrelatively southern species is in southern England andsouthernmost Fennoscandia suggesting that in theseregions the thermal climate was acceptable to bothgroups. This area of overlap has today mean Julytemperatures close to 16 1C and mean January/Februarytemperatures between 0 and �5 1C.
A more detailed analysis of the stratigraphicaloccurrences of individual species in the Conty insectassemblages shows that such relatively southern speciesas Bembidion fumigatum, Bembidion octomaculatum, andBerosus signaticollis are only present in the lowest twosamples, namely P4 and P5. In contrast, severalrelatively northern species such as Trechus rivularis,
henningianus and Otiorhynchus nodosus occur only inthe higher samples P3, P2, P1, T1, T2 and P8, andanother relatively cold adapted species Notaris aethiops
is much more abundant in the upper samples. Thesespecies suggest the climate of the earlier part of theBølling was warmer than that during the latter part ofthe Bølling and Allerød periods.
In order to quantify any climatic changes that mayhave taken place during the time represented by thesamples, mutual climatic range (MCR) (Atkinson et al.,1987) analyses were carried out on the carnivorous orgeneral scavenging beetle species from each of the foursamples. Thus beetle species have been used that are notdependent on any particular plant for their food source,enabling palaeoclimatic estimates to be made that areindependent of those based on botanical data. In theseanalyses, Tmax is the mean temperature of the warmestmonth (July) and Tmin is the mean temperature of thecoldest months (January and February). As is to beexpected from the general uniformity of the fauna, theMCR figures show very little difference (Fig. 4).
There is a climatically important gap in the faunalsequence from Conty. No insect fossils were recoveredfrom the two samples (P6 and P7) attributed to theOlder Dryas period (GI-1d). It is highly unlikely that theabsence of fossils from this horizon was due to extremecold since fossil evidence from Britain and elsewhereshows that there were many cold adapted coleopteranspecies available to colonise northern France at this time(Coope, 1998). It is more likely that the Older Dryasdeposits, in this area at least, correspond to floodepisodes with rapid silt accumulation. This sort ofdrastic impoverishment of fossil insect fauna in thesedimentary record during flood episodes was described
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Fig. 4. Climatic reconstruction for Conty and Houdancourt, using the
Mutual Climatic Reconstruction Range Method.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–2465 2457
in a Lower Rhone Valley Holocene site (Andrieu-Ponelet al., 2000). If this problem is to be resolved and moresubtle climatic changes recorded higher resolutionsampling intervals must be employed, preferably in amore extended stratigraphical sequence than at Conty.It seemed possible that the fossiliferous sequence atHoudancourt might be more complete and thus yield aninsect fauna representative of the Older Dryas.
4.8. Houdancourt
The insect assemblage from Houdancourt spansapproximately the same period as that from Conty,namely from the second half of the Bølling to the latterpart of the Allerød period. The positions of the samplesanalysed are shown in Fig. 3. All these samples, with theexception of sample 1, yielded abundant insect fossils.Here again the fossil insect fauna was dominated byColeoptera with 149 taxa, of which 71 (47%) could beidentified to the level of species or species-group. Fossilsof other groups include Trichoptera, Megaloptera andHeteroptera.
The Lateglacial environments interpreted from theinsect assemblages from Houdancourt are very similarwith that from Conty and many species were in commonto both sites. To avoid duplication, the interpretation ofthe Houdancourt local environment will largely con-
centrate on those species which did not occur in theConty assemblages.
4.9. Aquatic environments
The water-beetle group includes insects of bothstanding or slowly running water, as well as speciesindicative of running-water. Here the relative propor-tions of these two ecological categories does notfluctuate in a significant way. In contrast to Conty,Esolus, Oulimnius, Limnius and Normandia occur in verylow numbers throughout the sequence and are notconfined to the Bølling period. Beetle species indicativeof standing water are much more abundant. Thus,Hygrotus decoratus ‘‘occurs in smaller water-bodies,such as ditches and detritus ponds, and on lakemargins’’ (Nilsson and Holmen, 1995). Noterus isexclusively found in stagnant waters with decaying plantdebris.
4.10. Transitional environments (fresh water marshes)
Most of the Carabidae and Staphylinidae in thisassemblage are wetland species. In addition to thespecies already recorded from Conty this group alsoincludes Bembidion assimile which lives at the margin ofeutrophic standing waters or along slowly runningrivers, ‘‘on moist clayey or silty soil with luxuriantvegetation of Carex, Phragmites, etc, often near the sea’’(Lindroth, 1985–1986). Odacantha melanura has anextremely elongated body which allows it to penetrateinside hollow stems of tall marsh plants such asPhragmites, Typha and Glyceria where it preys uponsmall arthropods, probably Collembola (Lindroth,1985–1986). It is associated with clayey or muddymargins of eutrophic lakes and ponds. Pterostichus
gracilis and P. minor are both very hygrophilous species,the former preferring open environment with densegrassy vegetation, whereas the latter is rather ubiqui-tous. Bembidion obliquum is a rather eurytopic species,but seems to prefer bare, sunny ground surfaces(Lindroth, 1985–1986; pers. obs. in Russia by P.P.). B.
properans is usually found in sun exposed places onclayey or clay-mixed ground with sparse vegetation butusually in the vicinity of water where it is associated withMicrolestes minutulus (Lindroth, 1985–1986). Syntomus
obscuroguttatus is also hygrophilous, found in moss andleaf litter in damp situations (Luff, 1998). The presenceof Bembidion minimum may indicate moderate environ-mental salinity but, in contrast to Conty, any salinitywould seem to be confined to the upper part of theAllerød.
Many of the Staphylinidae are also riparian species.Hygronoma dimidiata has similar habitat requirementsto Odacantha melanura and lives in marshes withPhragmites and Typha; Euasthetus ruficapillus prefers
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marshy areas with a cover of Carex or Phragmites.
Hygrophilous beetles of other families are less numer-ous. Anisosticta 19-punctata is a ladybird which feeds onaphids, almost exclusively in wetlands with Typha
latifolia and Phragmites australis. Another ladybird,Coccidula rufa also feeds on aphids in wet grasslandsalong rivers (Majerus, 1994; Majerus and Kearns, 1998).Airaphilus elongatus is also a wetland species found inpeat bogs, in Sphagnum and in plant debris such asheaps of Carex, Juncus and dry grasses. Sphaerius
acaroides is frequently found on wet mud or sand withovergrowth of algae not far from water margins and sois regularly found in flood refuse (Klausnitzer, 1996).
As with the Conty assemblage, phytophagous speciesindicate that the local flora was dominated by reedyvegetation. Donacia clavipes is monophagous feedingchiefly on Phragmites stems. Donacia cinerea is chieflyassociated with Typha but also Phragmites, Sparganium
and Carex. Donacia tomentosa feeds exclusively uponthe rare Flowering Rush Butomus umbellatus.The weevil Limnobaris develops on Juncaceae andCyperaceae, mainly in bogs and wetlands. Thryogenes
festucae and Notaris scirpi develop almost exclusivelyinside the stems of Scirpus and Carex. Galerucella tenella
lives in marshy meadow-like places where it feeds on avariety of plants including Filipendula, Geum, Potentilla,
Fragaria and Alchemilla (Koch, 1989–1992).
4.11. Dry and open environments
Xerophilous species occur sporadically throughoutthe Houdancourt sequence probably accidentally in-corporated in the sediment from more distant habitats.Thus the ground-beetles Syntomus truncatellus is aspecies of rather dry and sunny, sparsely vegetatedground. Trachyphloeus is a weevil genus that is typicallyfound in open, dry and sunny places. The small chaferSerica brunnea is usually found on light, sandy and drysoils where there is abundant herbaceous vegetation,often where there are scattered trees. Species of Long-
itarsus are relatively abundant in this assemblage, livingin open grassland where they feed upon a large varietyof herbaceous plants. Though individual species of thislarge genus are often monophagous it has not beenpossible to identify the species and thus it has not beenpossible to identify any of these herbaceous plantspecies.
4.12. Tree-dependent environments
Tree-dependent beetles indicate that only Salix (and/or possibly Populus) grew in the immediate vicinity.Thus Plagiodera versicolor and Phyllodecta sp. both feedon species of willow tree with non pubescent leaves.Sometimes they also feed on the leaves of poplars. Thesaproxylophagous weevil Cossonus linearis develops
inside rotten wood of hollow trunks of old Salix andPopulus suggesting that some of the trees were in theform of old and decaying trunks probably along thewater course.
Summary of the local environment at Houdancourtinterpreted from the fossil Coleoptera
The beetle assemblage is indicative of a river mean-dering across a floodplain in a broad valley on whichgrew an extensive marsh of reeds and sedges withscattered willow (and/or poplar) trees. In places the soilwas bare and made up of organic silt. Exposedsandbanks were also available nearby. It is possiblethat there were saline influences in the environmentduring the Allerød period. Throughout the whole of thesection that yielded the coleopteran assemblages, thebeetles provide no evidence for any significant environ-mental change.
4.13. Palaeoclimatic inferences from the Houdancourt
coleopteran assemblage
As with the Conty fauna, the Houdancourt Lateglacialbeetle assemblages are made up almost entirely of speciesthat are still living in northern France and it seems likelytherefore that the thermal climate at the time was notmuch different from that of the present day.
However, three species, Patrobus assimilis, Gyrinus
opacus and Eucnecosum brachypterum are now extinct inFrance. They have predominantly northern ranges thatextend as far south as southern Fennoscandia. Threemore species Trechus rivularis, Acidota crenata andNotaris aethiops are also northern species that areextinct in the Paris Basin but occur as remnantselsewhere in France.
In contrast, three relatively southern species of Coleop-tera are also recorded in the Houdancourt assemblages.The northernmost limit of Bembidion octomaculatum
reaches only as far north as the extreme south of Englandand southern Fennoscandia (Hansen et al., 1960).Similarly, Badister dilatatus reaches only as far north assouthern England and Ireland and the south of Scandi-navia, and Syntomus obscuroguttatus reaches southernEngland (Luff, 1998), but does not occur in Fennoscandia.
The present day ranges of almost all the species in thisassemblage (both the relatively ‘‘northern’’ and ‘‘south-ern’’ species) overlap in southern Fennoscandia (parti-cularly in southern Finland), the present day regionwhere almost all of them find the climate acceptable. Inthis area the mean July temperature is about 16 1C andthe mean January/February temperatures about 0 1C.
It is climatically significant that Patrobus assimilis,Trechus rivularis, Gyrinus opacus and Notaris aethiops
were all absent from the lowest sample (number 8) i.e.from the earlier part of the Bølling period, suggestingthat, at this time, the climate was probably too warm forthem, a similar situation to that at Conty.
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MCR estimates for Houdancourt are shown in Fig. 4alongside those from Conty with which they can bedirectly compared. Here again the means of these figuresare effectively the same for all samples and are in broadagreement with those arrived at by comparing the limitsof the geographical distributions discussed above.
5. Discussion
5.1. Comparison with pollen data
Pollen analyses are still in progress at Conty (Antoineet al., 2003), but Houdancourt has provided a detailedpicture of the vegetational changes during the Bøllingand Allerød periods (Leroyer, unpublished data). Theserecent high-resolution pollen records have allowed therecognition of six zones which are related to regionalpollen succession despite five gaps. These may besummarised as follows (Fig. 5).
At the beginning of the Bølling (Hou 1), the landscapewas entirely open with a very sparse vegetal cover,providing relatively high values of far-travelled Pinus
pollen as it is often the case in similar conditions (see forexample Andrieu et al., 1995; Ponel et al., 2001, p. 810).The banks of the river Oise were locally occupied by amarsh and a riparian forest of willow. After a gap(Juniper PAZ), there was a rise in the proportion ofArtemisia pollen at the end of the Bølling (Hou 2) with aconsequent diminution in the Pinus signal. At this timethere is an increase in the pollen of heliophilous treessuch as Betula and Juniperus. Stands of Salix were stillpresent on the river banks. After another gap (the OlderDryas) the landscape remained relatively open andsparsely vegetated but with a thicker cover of Betula
(Hou 3). It is likely that pine trees became progressivelyestablished at this time though not necessarily in theimmediate vicinity, since pine pollen is easily trans-ported on the wind. Alongside the river, marshy areaswere still widespread but the Salix forest declined. Thesecond half of the Allerød (Hou 4 and 5) is marked by afurther increase in Pinus pollen suggesting that pineswere becoming established on the drier ground. Thisphase was followed by an increased sedimentary fillingof the river channel associated with a decline in aquaticplants and the rise of marshland taxa. During theYounger Dryas (Hou 6), pollen assemblages demon-strates the opening of landscapes with the decrease ofPinus but with a slight development of Juniperus and anexpansion of herbaceous plants (Poaceae and thenArtemisia).
There is an excellent agreement with data obtainedfrom insect assemblages concerning vegetation andlandscape around the site, and both sources suggestthat local herbaceous vegetation was dominated bymarshy and helophytic plants, whereas the river was
certainly fringed by a thin gallery forest dominated bySalix. In the early stages of the Lateglacial Interstadialthe whole area away from the river was probablytreeless. The increase in pine pollen during the Allerødsuggests that pine trees became established in the areabut the fact that no insects were present at this time thatdepend on pine trees, suggests that pines were notpresent in the immediate neighbourhood of Houdan-court at any time during the Bølling-Allerød period(Ponel et al., 2001). However both analyses vary in therecognition of the Older Dryas. Despite the presence ofthe cold-adapted Gyrinus opacus at the top of theBølling levels, the gap in pollen assemblages betweenzones 2 and 3 shows that this short event is marked by asedimentological hiatus.
5.2. Comparison with molluscs
Molluscan successions from Conty have been de-scribed in detail (Limondin-Lozouet and Antoine, 2001)and are summarised in Fig. 6. During the Bølling periodmollusc assemblages indicate that the area was largely amarsh, whereas during the Allerød period there are hintsof a progressive drying of the environment (Limondin-Lozouet and Antoine, 2001). In contrast, the coleopter-an record continues to include hygrophilous speciesthroughout the whole of this period. Both the molluscsand the insects indicate that there was no closed canopywoodland at this time. Although no beetle fossils werefound in the calcareous silts attributed to the OlderDryas, the presence of the arctic-alpine snail Columella
columella (and the lowering at the same time of theArboreal:Non-arboreal pollen ratio) suggests a signifi-cant cooling in the temperature. Since fossil evidencefrom many sites in Europe shows that the Older Dryasclimate was certainly not cold enough to totallyeliminate insect faunas (Ponel and Coope, 1990), theabsence of insect fossils from the Older Dryas layers atConty would seem to be a result of some sedimentolo-gical or taphonomic processes rather than the inhos-pitality of the contemporary climate.
Malacofaunas from Houdancourt have been recordedby Pastre et al. (2003) and are detailed here (Fig. 7).Zones H1 and H2 are characterised by terrestrial faunasindicating an open ground environment developing intoa marsh. These faunas are allocated to the Bøllingbecause of their comparison with the Conty succession.This interpretation is supported by the palynologicalrecord and the radiocarbon dates. Zone H3 consists ofassemblages dominated by aquatic taxa. Faunal divi-sions within this zone point to differences in the flowconditions in the water body. In the Allerød peat (H3a)still water conditions occurred. The flow strengthened inH3b as Bithynia tentaculata is mainly represented byopercula at the base of the Younger Dryas calcareoussilts, but the assemblages of H3c reflect a stagnant
ARTICLE IN PRESS
Poaceae
Artemisi
a
Cyperace
ae
steppic
herbs
aquatic herbs
132
142
152
162
172
177
179
181
184
186
188
190
192
194
196198200
203205207
209211213
215217
219221
223225228231
234236238240242
1
2
3
4
5
6
Juniperus
BetulaPinus
Salix
a
b
c
=calcareous silt
1
2
3
4
5
6
7
a
b
a
b
c
a
b
a
b
c
a
b
c
d
ef
a
b
c
cold
even
ts rec
ords
= clayey silts
12 540 + 110
12 060 + 110
11 260 + 90
amphibious herbs
= silty peat = peat
Youn
ger
Dry
as
Old
er
Dry
asB
ollin
gA
llero
dHiatus
Regio
nal PA
Z
Chronost
ratig
raphy
Pollen zo
nes
Stratig
raphy
= organo-mineral silts
11 620 + 110
Hou
Ages BP
Fig. 5. Summarised pollen diagram from Houdancourt.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–24652460
environment. At the top of the Bølling a markeddecrease in mollusc richness suggests an environmentalcooling (see above for molluscan and sedimentologicalevidence for this episode at Conty). In this respect theoccurrence at Houdancourt of a single specimen of therelatively northern water beetle Gyrinus opacus at thislevel may be climatically significant, since though it isfound today in southernmost Finland, it is moreabundant further north (Holmen, 1987) and in Britainit is confined to the Highlands of Scotland (Foster,2001). This species may be the sole coleopteran indicatorof the short, cold Older Dryas period (GI-1d).
5.3. Comparisons with insect assemblages from other
North European sites
Because many local environmental conditions aredetermined by local factors, this broad comparison willconcentrate here on palaeoclimates which have moreregional significance. The nearest Lateglacial coleopter-an assemblages to Conty-Houdancourt were obtainedfrom Holywell Coombe, Kent (Coope, 1998). This sitewas especially valuable in this context since it yieldedmolluscs, pollen and macroscopic plant remains, en-abling a comparison to be made of the molluscan fauna
ARTICLE IN PRESS
Fig. 6. Summarised malacological zonation from Conty plotted
against generalised lithological sequence (see Fig. 2 for lithology).
The dates (14C yr BP) correspond to extreme values obtained for
molluscan zones boundaries (modified after Limondin-Lozouet and
Antoine, 2001).
Fig. 7. Malacological diagram from Houdancourt. Sample 8, taken in
a thin local sandy layer, yielded few shells so percentages were not
calculated and numbers of specimen per species are mentioned.
Lithology see Fig. 3.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–2465 2461
and vegetation between the two sites. These showed verysimilar palaeoenvironments (Preece and Bridgland,1999; Limondin-Lozouet and Antoine, 2001). At Holy-
well Coombe this coleopteran sequence starts at about13,000 BP at a time when the climate had alreadybecome at least as warm as that of the present day(Preece and Bridgland, 1998, p. 230). However, thelatter parts of the Late-glacial Interstadial (i.e. theAllerød and the start of the Younger Dryas period) arenot represented in the Holywell Coombe record because
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a 1500 year phase of pedogenesis destroyed most of theinsect fossils. Immediately after this gap a suite ofexclusively northern Coleoptera, indicating severely coldclimatic conditions, are dated from the closing part ofthe Younger Dryas period.
Further north in the British Isles, a wealth of data areavailable from insect studies on Lateglacial palaeocli-mates (Coope, 1968; Coope, 1971; Coope and Brophy,1972; Ashworth, 1972, 1973; Osborne, 1972, 1973;Bishop and Coope, 1977; Coope and Joachim, 1980;Osborne, 1980; Walker et al., 1993; Coope, 1998; Coopeet al., 1998; Walker et al., 2003). In Ireland a YoungerDryas fauna of arctic affinities has been described(Coope et al., 1979). These insect faunas show aconsistent picture of climatic changes which may besummarised as follows. The intensely cold-adaptedinsect fauna that characterised the terminal phase ofthe Last Glaciation was replaced abruptly by a totallytemperate assemblage, which included many exclusivelysouthern species, indicating a sudden and intenseclimatic amelioration shortly after 13,000 yrs BP. Thistemperate episode was followed by a series of faunalchanges indicative of about three temperature oscilla-tions involving progressive cooling which culminated inthe severe cold period of the Younger Dryas. The end ofthis cold interlude was also sudden and intense and veryrapidly gave place to climates at least as warm as thoseof the present day during the Preboreal (Lowe andWalker, 1997).
This pattern of climatic change for the British Isleswas by no means the same as that in southernScandinavia where the early Bølling was not warm-temperate as it was in Britain at this time but muchcolder (Lemdahl, 1997). This local chilling would appearto be the result of the proximity of the FennoscandianIce sheet. In southern Sweden the subsequent decline intemperatures during the Allerød leading into a severelycold Younger Dryas, followed much the same pattern asit did in Britain and this was followed by the sudden andintense warming at the start of the Preboreal. In northJutland, Denmark, the Allerød period was similarly coldas it was in adjacent areas of Sweden (Coope andBøcher, 2000).
Lateglacial climate changes in Switzerland also haveinteresting differences and similarities from thosefurther north. Abundant insect assemblages have beendescribed from the Neuchatel area (Coope and Elias,2000) and these show a sudden and intense climaticwarming at the start of the Bølling which would seem todate from about 12,700 BP leading to a sudden rise inmean July temperatures of at least 7 1C. The Neuchatelinsect record is poor during the Allerød because oferosion on the site, but there is no evidence yet for thestepwise deterioration of the climate seen at this time inBritain. The Younger Dryas was also poorly registeredbut there is evidence that in Switzerland the climate
became cooler at this time though not cold enough toinhibit tree growth altogether (Lemdahl, 2000).
This brief review of the Lateglacial climatic changes inEurope shows that there was considerable regionalvariation at this time with steep temperature gradientsand climatic patterns that differ considerably from thoseof the present day (Coope and Lemdahl, 1995). Thus itcannot be assumed that Lateglacial climatic changes areeither synchronous or necessarily always in the samedirection, even within the relatively small area ofnorthwestern Europe.
Some indication of these regional climatic differences(Tmax) based on MCR analyses of coleopteran assem-blages from a number of locations from the British Isles,central Poland, southern Sweden and western Norwayhas been given in a graphic form in Coope and Lemdahl(1995) where the temperature curves from the four areaswere superimposed upon one another on the same basescale so the patterns in each region could be directlycompared. In Fig. 8, the MCR reconstructions for Tmax
from Conty-Houdancourt have been superimposed onthese regional graphs showing consistent differencesbetween them. Although the Conty-Houdancourt curvespans only part of the Lateglacial period it is clear thatthe temperatures during the latter part of the Bøllingand the Allerød periods differ considerably from theTmax curves for further north in Europe. Though notrecorded at these two sites, there must have been anearly and intense warming at the start of the Bølling asthere was in the British climatic record. The coleopteranassemblages from northern France provide little evi-dence for any climatic cooling during the Allerød periodsuch as was seen in the British Isles at that time and theymay thus resemble more closely the climatic record fromSwitzerland (Coope and Elias, 2000; Hadorn et al.,2000).
It is unfortunate that Tmax figures cannot yet begiven for the Older Dryas interval in northernFrance because insect fossils were totally absentfrom the critical horizons at Conty. However atHoudancourt the presence of Gyrinus opacus at thislevel, may hint at somewhat colder conditions during theOlder Dryas.
The Conty-Houdancourt climatic figures based oncoleopteran assemblages provide valuable new palaeo-climatic information from an area which was notavailable when the Lateglacial temperature gradientswere reconstructed for northern Europe (Coope et al.,1998). When compared with other sites in northernEurope, they show important similarities and differencesin Lateglacial palaeotemperature patterns and gradientseven within the space of a few hundred kilometres.Nevertheless, these new figures fit into a consistentpattern of regional climatic differences that can now beextended southwards for the first time into northernFrance.
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Fig. 8. Generalised climatic curves of estimated Tmax for the British
Isles (BI), central Poland (CP), southern Sweden (SS), western Norway
(WN) and northern France (NF). Redrawn and modified from Coope
and Lemdahl (1995). The horizontal axis indicates age in uncalibrated
radiocarbon years.
P. Ponel et al. / Quaternary Science Reviews 24 (2005) 2449–2465 2463
Acknowledgements
The research on the evolution of the river systems ofthe Somme Basin during the Lateglacial and Holocenehas been supported by the CNRS Palaeoenvironmentsand Hominids programme, 1997–2000, and since 1995by the General Council of the Somme Department(Valley Bottoms programme). The research onHoudancourt has been supported by the CNRSPalaeoenvironments and Hominids Programme,1997–2000, and the CNRS Environment and SocietyProgram (2000–2002).
Appendix A. Supplementary Materials
The online version of this article contains additionalsupplementary data. Please visit doi:10.1016/j.quascir-ev.2004.12.010.
References
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