Climatic interpretation of terrestrial malacofaunas of the

ELSEVIER Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321–336

Climatic interpretation of terrestrial malacofaunas of the lastinterglacial in southeastern France

Denis-Didier Rousseau a,b,Ł, Jean-Jacques Puissegur 1

a Paleoenvironnements et Palynologie, UMR CNRS 5554, Institut des Sciences de l’Evolution, Universite Montpellier II,place E. Bataillon, case 61, 34095 Montpellier cedex 5, France

b Lamont-Doherty Earth Observatory of Columbia University, Palisades NY 10964, USA

Received 25 September 1997; accepted 24 November 1998

Abstract

The sequence of the Ruisseau de l’Amourette, in the French Alps, covering the isotope stages 5e, 5d, 5c, and part of5a and 6, was studied for terrestrial mollusks. Correspondence analysis of the mollusk assemblages permits reconstructionof temperature and moisture trends using knowledge of the modern ecology of the recognized species. The classicenvironmental succession of the last Interglacial–Early Glacial (Wurmian) is recognized. The Eemian (Sub-stage 5e)suggests warm and moist conditions. It is followed by the cold Melisey I (Sub-stage 5d) showing moisture variation, fromdry in the lower part to moist in the upper part. The mollusk equivalent of St. Germain I and II also indicates warmand moist conditions. The Melisey II stadial (Sub-stage 5b) is missing but may be reflected by the deposition of barrengravel layers. All these environmental oscillations agree with the fluctuations described in the literature. However, Stage5e indicates a particular trend as the mollusks recorded two well individual cool events which seem to correspond tovariations identified in various west-European continental records. However, as no particular cold indicator species wereidentified, these events cannot be related to strong climatic fluctuations as emphasized in the early studies of the GreenlandGRIP ice-core or in North Atlantic and western European records. 1999 Elsevier Science B.V. All rights reserved.

Keywords: Eemian; terrestrial mollusks; paleoclimates; Alps; France

1. Introduction

Previous analyses of mollusks in Holocene sec-tions (Lozek, 1972, 1985; Piechocki, 1977; Keen,

Ł Corresponding author. Fax: C33 67 042032; E-mail:[email protected] Before the completion of this paper, Dr. Jean-Jacques Puis-segur died. All the material described in this paper is depositedat Montpellier, but is accessible upon request to DDR ([email protected]). The coded data are archived in Boul-der on line at ftp:==.ngdc.gov=paleo=contributions_by_author=rousseau1998=

1981; Alexandrowicz et al., 1984; Meijer, 1984;Alexandrowicz, 1985; Neck, 1985, 1989; Good-friend, 1988, 1991; Nyilas and Sumegi, 1989;Limondin and Rousseau, 1991; Rousseau et al.,1993, 1994, 1998; Somme et al., 1994; Limondin,1995) yielded paleoclimatic information that couldbe related to other paleoclimatic records. Older inter-glacial materials are difficult to find mainly becausesoil pedogenesis generally dissolves the shells. How-ever, in some particular cases, individuals can be pre-served, and provide enough material for paleocolog-ical interpretations. This is the case in slope deposits

0031-0182/99/$ – see front matter 1999 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 1 - 0 1 8 2 ( 9 9 ) 0 0 0 2 1 - 8

322 D.-D. Rousseau, J.-J. Puissegur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321–336

D.-D. Rousseau, J.-J. Puissegur / Palaeogeography, Palaeoclimatology, Palaeoecology 151 (1999) 321–336 323

as described by Lozek (1964) and Puissegur (1976),or in carbonate deposits such as tufa (Kerney etal., 1980; Alexandrowicz, 1985; Preece et al., 1986;Rousseau et al., 1992). Records that can be studiedfor the last interglacial are rare as the time resolutionis not generally as good as for the Holocene.

The aim of this paper is to present results ofthe statistical analysis of terrestrial malacofaunas,yielded by a well developed Quaternary sequence inthe French Alps. This record was not affected byerosion due to the glacier advance. The results willbe interpreted in relation to the recent published datafrom both continental and marine records.

2. Material and methods

The ‘Ruisseau de l’Amourette’ section is locatedin the Trieves basin (Fig. 1), a large depressionbordered by the Vercors Mountain to the west, theOisans Mountain to the east, the Devoluy Mountainto the south and opens north to the Drac valley.This area was not affected by Wurmian glaciers(Montjuvent, 1978, 1980). However, an ice damblocked the valley behind which a lake formed andlaminated clays were deposited.

131 samples from a 46 m deep section composedof clays and silts were analyzed for pollen and mol-lusks (Gremmen et al., 1984). All mollusk specieswere counted, and broken shells were included fol-lowing the method developed by Lozek (1964). Foreach mollusk assemblage, from one stratigraphicallayer, the number of species was counted and theShannon index H 0 computed. The Shannon indexdescribes the diversity of a biological communityusing the formula:

H 0 D �nX1

pk log2 pk

where pk is the frequency of one species in one

Fig. 1. Ruisseau de l’Amourette sequence. (a) Map showing the location of the Ruisseau de l’Amourette sequence. (b) Detail of thegeological area of the Ruisseau de l’Amourette sequence: 1 D substratum; 2 D Les Serres gravels; 3 D L’Amourette formation; 4 Dglacio-lacustrine clays (Wurmian); 5 D lower terraces gravels (Wurmian); 6 D valley bottom infilling (Holocene); 7 D Wurmian frontmoraines; 8 D area of ice-dammed lakes; Dev D Devoluy Mountain (modified from de Beaulieu et al., 1992). (c) The Ruisseau del’Amourette sequence. Numbering of the samples, and of the corresponding sections studied. Description of the lithology: 1 D calcareousgravels and pebbles; 2 D clay with macro-remains of plants and mollusks; 3 D sandy loam; 4 D shaly lignites with occurrence oflacustrine chalk and wood; 5 D dark shale (after Gremmen et al., 1984 modified).

determined assemblage. Such an index allows char-acterization of the structure of a given assemblageand permits us to detect any changes affecting the as-semblages. Additionally, the analysis of the speciesdiversity allows us to define assemblages relevant forenvironmental interpretations.

Each count was also coded for multivariate analy-sis by transforming the values into abundance classeson a logarithmic scale, following the method de-scribed by Rousseau (1987). Such a coding retainsinformation on representative variations, while sup-pressing the differences between the well representedand the poorly represented species. Correspondenceanalysis (Benzecri and Benzecri, 1980) applied to themollusk data (see Rousseau, 1991; Rousseau et al.,1993) allows simultaneous study of mollusk assem-blages (represented by rows) and mollusk species(represented by columns). This allows statistical in-terpretation of species behaviour in terms of eco-logical niches. Consequently, results from rows andcolumns can be plotted in a single diagram, fa-cilitating environmental interpretation. This methodhas already been successfully applied to Quaternarymollusk assemblages (Rousseau, 1986, 1987, 1991;Rousseau and Puissegur, 1989, 1990; Limondin andRousseau, 1991; Rousseau et al., 1993; Rousseauand Kukla, 1994). The environmental interpretationof the Ruisseau de l’Amourette mollusk assemblagesis based on information on the current ecologicaltolerance of individual living species (thermal andmoisture requirements, and vegetation association)(Kerney and Cameron, 1979; Kerney et al., 1983).Indeed, all the recognized fossil species have moderncounterparts exhibiting the same ecological charac-teristics (Rousseau, 1989).

Both mollusk and pollen studies show two warmintervals separated by a cold interval (Gremmen etal., 1984) (Fig. 2). This interpretation was acceptedlater by de Beaulieu et al. (1992) when taking intoaccount the succession of the reconstructed vegeta-



tion. Although they support the earlier chronology ofEemian to St. Germain I defined for the Ruisseau del’Amourette sequence, de Beaulieu et al. (1992) statethat the “pollen diagram is atypical leading to a veg-etation history peculiar to the southern Alps”. Thisassumption is based on the high percentages of Pinus(pine) during the early temperate phases of the Inter-glacial and by the significant role of Fagus (beech)associated with Carpinus (hornbeam) and Abies (fir)during the late temperate phase of the Interglacial (deBeaulieu et al., 1992). Preliminary results of oxygenisotope studies of mollusk shells from the Ruisseau del’Amourette support this interpretation (Ch. Hannss,oral commun.). Eight mollusk zones were recognized(Figs. 3 and 4) according to the species composition(Gremmen et al., 1984). The first three are interpretedas corresponding to the previous glacial period of aRiss age. The fourth is a warm interval correlated withthe Eemian interglacial. This agrees with the pollenrecord (Fig. 2). A relatively cold phase (zones E andF) overlies the Eemian, and in turn is followed byanother warm interval, zone G, assumed to be theequivalent of St Germain I. This also is in agreementwith pollen data (Fig. 2). Gravel layers interrupt thesequence. They are overlain by sediments indicatinganother warm interval, zone H, showing a truncatedupper part by early Wurm deposits.

3. Results

Mollusk assemblages from the Ruisseau del’Amourette sequence reveal relatively high valuesof the Shannon index that seem to be in agreementwith the earlier biostratigraphical interpretation forinterglacial assemblages (Rousseau et al., 1993). Thevalues vary between 0.5 and 4.5, indicating that sev-eral environmental variations occurred in the fossilsequence.

An earlier survey of modern mollusk assemblages(Rousseau et al., 1993) indicates that mollusk assem-blages from forest environments show the highest

Fig. 2. Simplified pollen diagram of the Ruisseau de l’Amourettesequence (modified from Gremmen et al., 1984). Plot of themain arboreal taxa against depth. The non-arboreal taxa are notrepresented here.

diversity values. The high diversity is related to nu-merous ecological opportunities present in a forestenvironment. On the contrary, open environments,and especially those in northern Europe, or at highelevations offer fewer niches, resulting in a lowerspecies diversity. In this case, the index values arelow, between 1.5 and 2.5. However, low values arealso characteristic of assemblages that are affectedby problems in sediment deposition (Rousseau et al.,1993). In fluvial deposits mollusk shells are gener-ally broken or dominated by aquatic taxa.

Several assemblages indicate a low diversity, aswell as a low number of individuals, suggesting thatdeposition conditions disturbed the distribution ofthe species among the assemblages (Fig. 4). This im-plies that such assemblages cannot be considered forfurther ecological interpretations. On the other hand,assemblages that show a low number of individualscoupled with diversity values related to assemblagesin natural conditions will be used for ecologicalanalyses.

Following this procedure, the majority of sam-ples show a diversity index varying between 2.8 and4.3. There are, however, three assemblages whichshow low values (0.63, 1.6 and 1.8) (Fig. 4). Sucha distribution is in agreement with the occurrenceof environments ranging from cool (values tendingto 2) to warm climate conditions (values tendingto 4.3). Assemblages allocated to warm periods inthe earlier biostratigraphic study present the highestdiversity values, although the lowest value of thewhole sequence is recorded in mollusk zone G. Onecan notice also that warm intervals show assem-blages with diversity values fluctuating between 1.8and 4. Cold assemblages also vary between 1.5 and4 (Fig. 4). The correspondence analysis of the set ofselected assemblages permits interpretation of thesevariations (Figs. 5 and 6).

The first two axes explain 21.4% of the total vari-ance, based on 98 samples containing 46 taxa recog-nized. If each taxon had a contribution equivalent tothe general variability, the theoretical value would be1=46 D 0.022. Each taxon indicating higher valuesthan this threshold is used for the interpretation ofthe results.

The first axis discriminates Abida secale, Clausiliaparvula, Pupilla muscorum, Vallonia costata, Punc-tum pygmaeum, Vertigo pygmaea, Vallonia pulchella,

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Fig. 3. Simplified mollusk diagram of the Ruisseau de l’Amourette against depth. The abundance scale used is a logarithmic one applied for the multivariate analysis. Themollusk zones are from Puissegur in Gremmen et al. (1984).


Fig. 4. Variation of the diversity index H 0 for the terrestrial assemblages plotted against depth. Mollusk zones and pollen biostratigraphyare from Gremmen et al. (1984). In temperate forest conditions, the values are generally varying above 3 (Rousseau et al., 1993).

Trichia hispida, and Cochlicopa lubrica on the pos-itive side (Table 1). These species mainly indicateopen environment conditions. Species with high con-tributions on the negative side of the first axis corre-spond to Helicodonta obvoluta, Cochlostoma septem-spirale, Discus rotundatus, Azeca goodalli, Cepaeasp., Aegopinella nitidula, Acicula polita, Aegopinellapura, Ena montana, and Acanthinula aculeata (Ta-ble 1). This second set groups together species thatrequire a forest cover, or at least shading from treesor bushes. Such discrimination is characteristic in themultivariate analysis of assemblages of land snails.However, in the particular case of the Ruisseau del’Amourette sequence, the open environment speciesdo not include numerous so-called cold species, thosethat now live in the Arctic tundra, or at high elevationsabove the tree-line.

The second axis discriminates on the positive sideVertigo angustior, Vallonia enniensis, Succinea pu-tris, Vallonia pulchella, Clausilia pumila, Vertigo an-tivertigo, Carychium minimum, Cochlicopa lubrica,Euconulus fulvus, Zonitoides nitidus, Acicula polita,Vertigo genesii, Vitrina sp. (Table 1). These differ-ent species indicate moist conditions. Vertigo genesiithat represents moist environments, also indicatescold conditions when associated with Columella col-umella or Pupilla alpicola. The negative side of thesecond axis groups Abida secale, Discus rotunda-tus, Cochlostoma septemspirale, Helicodonta obvo-luta, Cepaea sp., Ena montana, Aegopinella nitidula,Aegopinella pura, Azeca goodalli, Achantinula ac-uleata. (Table 1). The highest contribution is due toAbida secale. All these taxa characterize dry environ-ments. In the study of Quaternary snail assemblages


Fig. 5. Correspondence analysis of the Ruisseau de l’Amourette malacofaunas. Plot of the species on the first factor plane (axes 1–2).The arrows indicate how the species explain the variability of the general data set. Black arrows indicate the highest contributions whilewhite arrows show high values. Determination of temperature and moisture gradients by 40º rotation of the factors. The codes of thespecies correspond to those indicated in Table 1.

from northern France, Puissegur (1976) indicatedthat particular mollusk assemblages occurred duringtransitional times, i.e. Late Glacial, that were mainlycharacterized by substantial numbers of individualsof Abida secale.

The distribution of the different species on thefirst factor plane (Fig. 5) shows that the forest oropen-forest species are plotted together in the thirdquadrant (1� 2�). The other taxa indicating openenvironmental conditions are plotted following a fanshape with moist species on one hand opposed to dryones on the other hand.

The distribution of the mollusk assemblages in thecorrespondence analysis (Table 2) resembles that ofthe species (Fig. 6). However, it presents an L-shape,characteristic of the Guttman effect indicating a re-lationship between the two axes. Such a distribu-tion has already been described for other mollusksequences in which either extreme temperature ormoisture conditions were lacking. Indeed, when all

the boundary conditions are represented among themollusk assemblages of a given fossil sequence, thefirst axis opposes cold (i.e. arctic or steppe environ-ments) and temperate (i.e. forests) conditions, whilethe second axis opposes xeric (i.e. dry grasslands)and damp (i.e. swamp) conditions (Rousseau, 1987).Thus, the lack of one boundary condition leads to theinterpretation of the multivariate analysis in terms ofclimatic gradients, both ‘temperature’ and moistureafter a rotation of the first two axes.

We took the forest pole as a reference point forthe rotation by 40º because it is best expressed inthe analysis (Fig. 6). Species characteristic of for-est environment are also well grouped on the thirdquadrant (1� 2�). Subsequently, we calculated thecoordinates of the assemblages (Table 2) and bytaking into account both their stratigraphic positionand diversity index value, we extracted two relation-ships, one representing ‘temperature’ changes andthe other the moisture trend. The temperature label


Fig. 6. Correspondence analysis of the Ruisseau de l’Amourette malacofaunas. Plot of the mollusk assemblages on the first factor plane(axes 1–2). Determination of temperature and moisture gradients by 40º rotation of the factors.

is used better as an indication of climatic changesas the mollusk trend in this case has been shown tocompare well to the marine δ18O record (Rousseauand Puissegur, 1990).

The interpreted temperature values show markedvariations from temperate to cold conditions (Fig. 7).The lower part of the sequence (between 46 and 38m; mollusk zones A, B and C) represents cold condi-tions, which would agree with the assumption of itslate Riss age. The Eemian interval (between 38 and28 m; mollusk zone D) shows overall temperate con-ditions which are interrupted by two cool episodesnamed C1 and C2 (Fig. 7). These cool intervals aresufficiently marked to be considered in the discus-sion. They were named C for cool and numbered 1and 2 according to their occurrence in the chronol-ogy of the sequence. They apparently are not relatedto any other record because of the lack of reliableabsolute dates. The following interval (between 28and 14 m; mollusk zones E and F) indicates coldconditions with minor fluctuations. Towards the top

a warming trend appears. This is in agreement withthe interpretation of the pollen samples of this inter-val as an equivalent of Melisey I according to thepollen stratigraphy, and corresponds to isotope Sub-stage 5d. The interval from 14 to 5 m depth, molluskzone G, shows marked variations, ranging from coldto temperate, similar to the ‘Eemian’ mollusk zoneD. The temperate conditions are preceded and fol-lowed by cold and cool peaks. This mollusk zonewas interpreted as corresponding to the equivalent ofSt Germain I in the pollen Grande Pile stratigraphyor marine isotope Sub-stage 5c. The uppermost mol-lusk zone H, between 4 and the top of the sequence,once again shows particularly temperate conditionssimilar in magnitude to those indicated during themollusk zones D (Eemian) and G (St Germain I). Inthe earlier biostratigraphical study, Puissegur (Grem-men et al., 1984) interpreted this zone as being themollusk equivalent of the Grande Pile St GermainII. The gravels separating zones G and H would cor-respond in this case to marine Sub-stage 5b (or to


Table 1Correspondence analysis of the malacological samples from theRuisseau de l’Amourette

Species Code Factor 1 Factor 2species

Acicula polita s002 �0.142 0.152Carychium minimum s004 0.251Carychium tridentatum s005Succinea oblonga s009 �0.025Succinea putris s010 0.468Azeca goodalli s015 �0.302 �0.141Cochlicopa lubrica s016 0.113 0.225Vertigo antivertigo s022 0.383Vertigo substriata s023 �0.095Vertigo pygmaea s024 0.213 0.048Vertigo moulinsiana s025Vertigo genesii s026 0.118Vertigo angustior s028 �0.024 0.701Orcula doliolum s030Abida secale s032 3.387 �1.075Pupilla muscorum s033 0.341Vallonia costata s038 0.328Vallonia pulchella s039 0.171 0.442Vallonia enniensis s040 0.033 0.524Acanthinula aculeata s043 �0.108 �0.101Ena montana s045 �0.121 �0.288Ena obscura s046Punctum pygmaeum s047 0.329Discus rotundatus s049 �0.435 �0.813Vitrina sp. s051 �0.042 0.121Vitrea subrimata s054 �0.035 �0.083Vitrea contracta s056 0.027Nesovitrea hammonis s058Aegopinella pura s059 �0.138 �0.180Aegopinella nitidula s060 �0.230 �0.274Oxychilus sp. s067Zonitoides nitidus s068 0.180Euconulus fulvus s069 0.036 0.207Clausilia parvula s079 1.456 0.815Clausilia bidentata s080Clausilia pimila s082 �0.036 0.388Perforatella bidentata s094 �0.030 �0.025Trichia hispida s097 0.150 �0.093Euomphalia strigella s099 0.049 �0.073Helicodonta obvoluta s100 �0.653 �0.450Arianta arbustorum s101Helicigona lapicida s102 �0.090 �0.058Capaea sp. s104 �0.302 �0.341Cochlostoma septemspirale s121 �0.526 �0.681Limax sp. s136Monacha sp. s173 0.034 �0.022Percentage of variance 12.15 9.24

Significant contributions (higher than the theoretical threshold D1=46) of species to the explanation of the variability of the dataset according to the first two factors. Positive and negative signsindicate the location on the axes. Codes of the species used inthe factor plane diagram.

the Melisey II interval in the Grande Pile chronol-ogy).

The moisture variations in biozones A, B andC relate to dry conditions with minor fluctuations(Fig. 7). On the contrary, mollusk zone D, of Eemianage, shows a moister environment. However, one cannote that the two cool episodes recognized in the‘temperature’ curve are different. The first one, C1,is drier than the second one, C2, which presents themoistest values of the sequence (Fig. 7). The follow-ing cold interval, mollusk zones E and F, suggeststhe driest conditions of the sequence with the occur-rence of mollusks characteristic of steppe conditions.This is in agreement with the general interpretationof marine Sub-stage 5d. The second part of this in-terval sees a return to intermediate (from a statisticalpoint of view, i.e., centre of the axis) conditions.The ‘temperate’ intervals corresponding to molluskzones G and H are mainly corresponding to moistconditions presenting some minor fluctuations.

4. Discussion

The results of the multivariate analysis supportthe biostratigraphic interpretation of the mollusk as-semblages. Biozones A, B, and C correspond to theupper part of the penultimate glaciation. Molluskzone D is the mollusk equivalent of the Eemian ac-cording to pollen data, or marine isotope Sub-stage5e. Mollusk zones E and F are indicative of cold con-ditions and are interpreted as the mollusk equivalentof pollen zone Melisey I, or marine isotope Sub-stage 5d. Mollusk zone G is the mollusk equivalentof the St Germain I or Sub-stage 5c.

Finding a mollusk sequence which relates to thepollen stratigraphy during marine isotope Stage 5 isof great importance as no similar record has beenfound in western Europe. However, mollusk datarender additional information of interest.

First, the Eemian interval, which was recognizedalso by the pollen content (Gremmen et al., 1984),shows a particular and complex trend with the occur-rence of two cool episodes with a different climaticsignature. This is also expressed in the pollen dia-gram through the percentages of arboreal taxa. C1 isexpressed by a decrease in Alnus and Quercus andthe appearance of Abies whereas C2 shows a strong


Fig. 7. Time series of mollusk assemblages from the Ruisseau de l’Amourette sequence on the temperature and moisture gradientsagainst depth. The values correspond to the variability of the general data set along the gradients. C1 and C2 indicate the occurrence ofthe two recognized cool Eemian events.

decrease in Alnus, Quercus, Corylus, Carpinus byhigh values of Abies (Fig. 2). The first one, C1, at thebase of the interval is cool and dry. The second peak,C2, is cool and moist. The recognition of these twocold episodes is of particular importance as similarevents were described from the GRIP Greenland ice-core as cold events, and named 5e4 and 5e2 (GRIPmembers, 1993). New analyses of the CH4 recordof the GRIP ice-core indicate that these events arerelated to older ice inserted into the Eemian interval,implying that these cold spells are invalid (Chappel-laz et al., 1997). The discussion nevertheless remainsopen as North Atlantic DSDP 609 (Broecker et al.,1990), NA87-25 (Cortijo et al., 1994), NorwegianSea V27-60 (Cortijo et al., 1994) also indicate one ortwo cooling events during Sub-stage 5e in the NorthAtlantic. Lauritzen (1995) also described an unsta-ble isotope record from Stage 5e from Norwegianspeleothems. He recognized two sharp variationsin the isotopic signal that he interpreted as relatedto the GRIP Eemian events. In northern Denmark,Seidenkrantz and Knudsen (1997) indicate the evi-dence of two major environmental and hydrologicalchanges during the Eemian from both benthic fora-minifera and stable isotopes. Southwards, Thouveny

et al. (1994) also indicate the occurrence of twoenvironmental variations during the Eemian in theFrench Massif Central. They are both recorded inthe magnetic susceptibility and in the pollen signalsand are interpreted as related to the GRIP record.Finally, when calibrating the pollen record of LaGrande Pile sequence with both the beetles and theorganic matter studied in parallel, Guiot et al. (1993)indicated the occurrence of a cold spell in the earlyEemian temperature estimates by including Taxus inthe considered taxa for transfer function. Moreover,the deciduous percentages during the Eemian at LaGrande Pile indicate a first cold spell in the lowerpart due to the development of the Taxus forest. Thisis in agreement with the last temperature reconstruc-tion by Guiot et al. (1993). On top of the Grande PileEemian, the deciduous trees drastically and quicklyrecede (Woillard, 1979) during a second cold andrapid event described by Woillard and known in theliterature as the ‘Woillard event’ (Kukla et al., 1997).It is not the purpose of this paper to discuss thereliability of the Greenland ice-core and the othermarine and western European continental recordswhich indicate cold events during the Eemian. How-ever, if these events did in fact occur, it is truly


Table 2Correspondence analysis of the malacological samples from the Ruisseau de l’Amourette

Sample Depth (m) CTR1 CTR2 F1 F2 rF1 rF2

M058 0.69 �0.023 �0.041 �0.754 �0.878 �1.157 0.013M059 1.11 �0.079 �0.108 �1.214 �1.240 �1.730 0.133M060 1.29 �0.201 �0.356 �0.867 �1.008 �1.329 0.016M061 2.44 0.068 0.353 0.314 0.175M062 2.69 �0.168 �0.151 �0.773 �0.640 �0.987 0.181M065 4.02 �0.030 �0.064 �0.472 �0.603 �0.765 �0.026M066 4.30 �0.039 �0.046 �0.476 �0.449 �0.650 0.076M067 4.47 �0.028 �0.066 �0.288 �0.388 �0.482 �0.029M068 5.21 0.018 �0.161 0.579 0.340 0.495M069 5.45 0.053 0.008 0.314 0.246 0.196M070 5.70 0.112 �0.015 0.528 0.395 0.351M071 5.98 �0.034 �0.011 �0.440 �0.218 �0.450 0.197M072 6.50 0.094 �0.089 0.562 0.373 0.429M073 6.75 �0.023 �0.024 �0.153 �0.133 �0.080M074 7.03 �0.188 0.040 �0.090 0.170M075 7.27 �0.011 �0.028 �0.133 �0.182 �0.225 �0.015M076 7.58 0.023 �0.129 0.196 0.067 0.225M077 7.87 0.300 0.012 0.680 0.529 0.428M078 8.11 0.013 �0.059 0.157 0.082 0.146M079 8.43 0.068 0.188 0.656 0.623 0.278M080 8.67 �0.050 �0.017 �0.469 �0.236 �0.482 0.208M081 8.98 �0.260 �0.123 �0.673 �0.404 �0.742 0.256M082 9.27 �0.307 �0.162 �0.615 �0.389 �0.693 0.221M083 9.55 �0.225 �0.701 �0.684 �1.054 �1.247 �0.154M084 9.86 �0.102 �0.033 �0.554 �0.273 �0.565 0.249M087 10.70 �0.187 �0.734 0.036 �0.444 0.585M088 10.98 �0.011 0.204 �0.154 0.584 0.348 0.493M089 11.19 0.091 �0.119 0.374 0.210 0.332M091 11.64 �0.028 0.029 �0.418 0.372 0.016 0.559M092 11.75 �0.195 �0.027 �0.877 �0.285 �0.782 0.489M093 11.99 0.164 0.094 0.568 0.496 0.293M094 12.27 0.457 0.117 0.817 0.701 0.436M095 12.59 0.226 �0.019 0.732 0.549 0.485M096 12.94 0.283 �0.027 0.877 0.654 0.584M097 13.25 0.426 �0.158 0.885 0.576 0.690M098 13.53 �0.019 0.156 �0.263 0.651 0.330 0.620M099 13.88 0.038 �0.056 0.466 0.321 0.342M100 14.23 0.029 �0.301 0.645 0.301 0.645M101 14.62 0.013 0.029 �0.112 0.145 0.039 0.179M102 14.86 �0.018 �0.177 �0.042 �0.146 0.109M103 15.18 0.014 0.117 0.519 0.473 0.244M106 15.77 0.065 0.677 0.290 0.816 0.812 0.302M107 16.09 0.071 0.138 0.515 0.626 0.811 0.008M108 16.40 0.110 0.085 0.516 0.396 0.635 �0.141R648 19.20 0.039 0.047 0.610 0.498 0.356R650 19.69 0.056 0.241 0.594 0.610 0.197R651 20.01 0.037 0.043 0.433 0.404 0.588 �0.072R652 20.29 0.050 0.253 0.535 0.572 0.150R653 20.60 0.039 0.015 0.406 0.218 0.428 �0.171R654 20.81 0.319 �0.019 1.153 �0.245 0.553 �1.041R655 21.09 1.083 �0.452 2.717 �1.531 0.574 �3.065


Table 2 (continued)

Sample Depth (m) CTR1 CTR2 F1 F2 rF1 rF2

R656 21.41 0.420 �0.038 1.557 �0.407 0.689 �1.454R657 21.58 0.607 �0.146 2.753 �1.180 0.866 �2.867R529 25.25 0.171 0.957 �0.001 0.614 �0.734R530 25.46 0.454 �0.114 1.844 �0.805 0.569 �1.930R531 26.97 1.221 �0.404 1.953 �0.980 0.505 �2.126R532 27.28 0.821 �0.261 1.570 �0.772 0.418 �1.699R533 27.56 0.146 �0.026 0.585 �0.215 0.211 �0.586R534 27.88 0.086 0.499 �0.020 0.305 �0.395R535 28.12 0.064 �0.021 1.268 �0.636 0.328 �1.380R536 28.40 0.031 0.686 �0.040 0.410 �0.551R537 28.72 �0.192 �0.184 �0.730 �0.624 �0.947 0.158R538 29.03 �0.200 �0.171 �0.559 �0.450 �0.704 0.139R539 29.28 �0.059 �0.109 �0.582 �0.693 �0.905 0.000R540 29.56 �0.059 �0.109 �0.582 �0.693 �0.905 0.000R541 29.80 �0.069 0.196 �0.700 �0.410 �0.600R547 31.41 �0.018 0.081 �0.335 0.620 0.260 0.655R410 31.52 0.053 �0.097 �0.426 0.500 0.109 0.648R415 32.74 0.186 �0.213 0.941 0.584 0.768R417 33.06 �0.036 0.033 �0.457 0.379 �0.003 0.594R419 33.47 �0.081 �0.070 �0.525 �0.426 �0.664 0.128R420 33.65 0.100 �0.269 �0.142 �0.250R421 34.00 �0.038 �0.021 �0.566 �0.367 �0.645 0.198R422 34.17 �0.090 �0.113 �0.748 �0.733 �1.042 0.102R424 34.59 �0.227 �0.251 �0.880 �0.806 �1.183 0.156R425 34.77 �0.062 �0.175 �0.481 �0.707 �0.851 �0.086R301 36.52 0.063 0.263 0.669 0.682 0.229R302 36.83 �0.039 �0.073 �0.384 �0.455 �0.595 0.002R303 37.11 0.017 0.310 �0.023 0.182 �0.252R305 37.46 0.098 �0.316 1.367 0.844 1.121R307 37.99 0.092 �0.181 0.540 0.297 0.486R308 38.16 0.046 0.076 0.448 0.392 0.230R208 38.34 �0.275 �0.119 �0.268 0.134R207 38.65 0.079 0.016 0.531 0.206 0.499 �0.274R206 38.93 0.036 0.014 0.816 0.449 0.868 �0.336R205 39.25 �0.048 �0.245 �0.738 �0.723 �0.287R204 39.56 �0.024 �0.123 �0.339 �0.339 �0.124R203 39.84 0.162 �0.166 0.932 �0.822 �0.031 �1.242R202 40.12 0.121 �0.054 0.674 �0.391 0.134 �0.768R201 40.44 0.107 0.556 �0.014 0.347 �0.435R101 42.05 0.020 �0.011 0.245 �0.157 0.037 �0.289R102 42.36 0.091 0.615 0.084 0.460 �0.417R103 42.68 0.068 �0.055 0.919 �0.723 0.037 �1.169R104 43.06 0.035 0.808 �0.236 0.339 �0.771R105 43.41 0.065 �0.013 0.904 �0.348 0.314 �0.916R107 44.57 0.014 0.042 0.322 0.491 0.583 0.069R108 44.81 0.070 0.105 0.448 0.480 0.656 �0.035R109 45.27 0.067 �0.023 1.001 �0.510 0.253 �1.095

Significant contributions (higher than the theoretical threshold D 1=98) of the terrestrial assemblages to the explanation of the variabilityof the data set according to the first two factors (CTR1, CTR2). Positive and negative signs indicate the location on the axes. Coordinatesof the assemblages on the first two factors (F1, F2), and on the two climatic gradients (rF1, rF2) after a rotation of 40º of the axes.


amazing that they would seem to have a reduced dis-tribution limited to the North Atlantic and westernEurope. Recent investigations from the Nordic Seas(Norwegian, Iceland and Greenland seas) by Fron-val and Jansen (1997) support such interpretationindicating that the sea-surface temperature of theNorwegian–Iceland Sea was less stable during theEemian interglacial indicating marked shifts. Con-cerning the Ruisseau de l’Amourette record, the lackof species indicating cold environments, i.e. Col-umella columella, Vertigo genesii, Pupilla alpicola,which occur presently at high elevations in the Alps(Kerney and Cameron, 1979), leads us to better in-terpret the cool events recognized in the Alps asregional variations. Such interpretation is reinforcedby the lack of any physical dates and would agreewith the Southern Alps significance of the pollendiagram as noticed by de Beaulieu et al. (1992).Recent reconstructions from mollusk assemblages ina British late glacial-Holocene sequence also indi-cated a significant cooling event although the typicalcold indicator species did not occur (Rousseau etal., 1998). In that case, as in the Amourette se-quence, the general composition of the assemblageand the ratios between the different species countscontribute to such reconstructions. Then the plac-ing of these particular events within the chronologyof the interglacial needs to be improved. The presentresults allow only hypothetical correlations with sim-ilar events reported elsewhere as it was proposed forthose characterized at the Lac du Bouchet (Thouvenyet al., 1994).

The bipartition of the Melisey I interval is inter-esting because it resembles the succession describedfrom the GRIP Greenland δ18O record (GRIP mem-bers, 1993). In that case, however, mollusk zone Ewould last three times longer than zone F. The factthat the lower part of mollusk zone E is colder than theupper part concurs with both marine and ice-core iso-tope studies. Not surprisingly, Vertigo genesii, an Arc-tic indicator species (Kerney et al., 1983), only occursduring that peculiar interval. Mollusk zone G showsa simpler pattern of a temperate episode bracketedby cold and cool intervals. This also agrees with theclassical interpretation of marine isotope Sub-stage5c. Finally the marked warming at the end of mol-lusk zone H is in agreement with the climatic trendexpressed at the base of marine isotope Stage 5a.

5. Conclusions

The multivariate analysis of the mollusk recordfrom the Ruisseau de l’Amourette sequence indi-cates several major oscillations, in agreement withthe pollen record, that do not correspond to localchanges. However, during isotope Sub-stage 5e, twocool events are characterized. The moisture analysisshows that these two cool Eemian events were dif-ferent, with the first one dry and the second moister.These events could be interpreted as the equivalentof cold events recognized in other continental se-quences corresponding to different locations: in theGRIP ice-core and in western European records.The lack of any cold indicator species during theseparticular events suggests that may reflect local envi-ronmental fluctuations. Despite the lack of any abso-lute time scale, the Ruisseau de l’Amourette sectionnevertheless shows a climatic sequence which is inagreement with the general interpretation of marineisotope Stage 5.

Similar events have been recorded in both highand middle latitudes in Europe, from different envi-ronmental contexts and biological and non-biologi-cal proxy data. This suggests that these new resultsfrom mollusk assemblages are mainly responses tochanges in the macro-climate over Europe during thepast 130,000 years and subsequently further investi-gations are needed in this region.

Acknowledgements

We would like to thank V. Lozek, R. Preece andan anonymous reviewer for comments and criticismsabout this paper, and Sonia and Greg Hamilton forimproving the English. This work was supported bythe CEC-EPOCH programme and an NSF-CNRS fel-lowship (DDR). This is ISEM (Institut des Sciencesde l’Evolution de Montpellier) contribution 98-051.

Appendix A

Coded values used for the correspondence analysis. Code of theassemblages and depth (in metres)

m1: Acicula polita; m24: Discus rotundatus;m2: Carychium minimum; m25: Vitrina sp.;


m3: C. tridentatum; m26: Vitrea subrimata;m4: Succinea oblonga; m27: Vitrina contracta;m5: S. putris; m28: Nesovitrea hammonis;m6: Azeca goodalli; m29: Aegopinella pura;m7: Cochlicopa lubrica; m30: A. nitidula;m8: Vertigo antivertigo; m31: Oxychilus sp.;m9: V. substriata; m32: Zonitoides nitidus;

m10: V. pygmaea; m33: Euconulus fulvus;m11: V. moulinsiana; m34: Clausilia parvula;m12: V. genesii; m35: Cl. bidentata;m13: V. angustior; m36: Cl pumila;m14: Orcula doliolum; m37: Perforatella bidentata;m15: Abida secale; m38: Trichia hispida;m16: Pupilla muscorum; m39: Euomphalia strigella;m17: Vallonia costata; m40: Helicodonta obvoluta;m18: V. pulchella; m41: Arianta arbustorum;m19: V. enniensis; m42: Helicigona lapicida;m20: Acanthinula aculeata; m43: Cepaea sp.;m21: Ena montana; m44: Cochlostoma septemspirale;m22: E. obscura; m45: Limax sp.;m23: Punctum pygmaeum; m46: Monacha sp.

References

Alexandrowicz, S.W., 1985. Malacofauna of the Holocene cal-careous tufa from the Podhale and Pieniny Mts. XIIIth Congr.Carpatho–Balkan Geol. Assoc., Proc. Rep., pp. 7–10.

Alexandrowicz, S.W., Snieszko, Z., Zajaczkowska, E., 1984.Stratigraphy and malacofauna of Holocene deposits in theSancygniowka valley near Dzialoszyce. Quat. Stud. 5, 5–28.

Benzecri, J.P., Benzecri, F., 1980. Pratique de l’analyse desdonnees. Dunod, Paris, 424 pp.

Broecker, W., Bond, G., Klas, M., 1990. A salt oscillator in theglacial Atlantic? 1. The concept. Paleoceanography 5, 469–477.

Chappellaz, J., Brook, E., Blunier, T., Malaize, B., 1997. CH4and δ18O of O2 records from Antarctic and Greenland ice:a clue for stratigraphic disturbance in the bottom part ofthe Greenland Ice Core Project and the Greenland Ice SheetProject 2 ice cores. J. Geophys. Res., in press.

Cortijo, E., Duplessy, J.C., Labeyrie, L., Leclaire, H., Duprat, J.,van Weering, T.C.E., 1994. Eemian cooling in the NorwegianSea and North Atlantic Ocean preceding continental ice-sheetgrowth. Nature 372, 446–449.

de Beaulieu, J.L., Montjuvent, G., Nicoud, G., Richard, H., Seret,G., Campy, M., Clerc, J., Dricot, E., Eicher, U., Mandier, P.,Ponel, P., Reille, M., Rousseau, D.D., Ruffaldi, P., Wansard,G., 1992. Long pollen sequences and the last glaciations fromthe Southern Alps to the Vosges mountains. Cah. Micropale-ontol. 7, 215–257.

Fronval, T., Jansen, E., 1997. Eemian and Early Weichselian(140–60 ka) paleoceanography and paleoclimate in the Nordicseas with comparisons to Holocene conditions. Paleoceanog-raphy 12, 443–462.

Goodfriend, G.A., 1988. Mid-Holocene rainfall in the Negev

Desert from 13C of land snail shell organic matter. Nature 333,757–760.

Goodfriend, G.A., 1991. Holocene trends in δ18O land snailshells from the Negev Desert and their implications forchanges in rainfall source areas. Quat. Res. 35, 417–426.

Gremmen, W., Hannss, Ch., Puissegur, J.J., 1984. Die warmzeit-lichen Ablagerungen am Ruisseau de l’Amourette (Trieves,franzosiche Alpen). Eiszeitalter Gegw. 34, 87–103.

GRIP members, 1993. Climate instability during the last inter-glacial period recorded in the GRIP ice core. Nature 364,203–207.

Guiot, J., de Beaulieu, J.L., Cheddadi, R., David, F., Ponel, P.,Reille, M., 1993. The climate in Western Europe during thelast Glacial=Interglacial cycle derived from pollen and insectremains. Palaeogeogr., Palaeoclimatol., Palaeoecol. 103, 73–93.

Keen, D.H., 1981. The Holocene deposits of the Channel Islands.Rep. Inst. Geol. Sci. 81=10, 1–13.

Kerney, M.P., Cameron, R.A.D., 1979. A Field Guide to the LandSnails of Britain and north west Europe. Collins, London, 288pp.

Kerney, M.P., Preece, R.C., Turner, C., 1980. Molluscan andplant biostratigraphy of some Late Devensian and Flandriandeposits in Kent. Philos. Trans. R. Soc. London B 291, 1–43.

Kerney, M.P., Cameron, R.A.D., Jungbluth, J.H., 1983. DieLandschnecken Nord- und Mitteleuropas. Paul Parey, Ham-burg, 384 pp.

Kukla, G., McManus, J.F., Rousseau, D.D., Chuine, I., 1997.How long and how stable was the last interglacial? Quat. Sci.Rev. 16, 605–612.

Lauritzen, S.E., 1995. High-resolution paleotemperature proxyrecord for the last interglaciation based on NorwegianSpeleothems. Quat. Res. 43, 133–146.

Limondin, N., 1995. Late-Glacial and Holocene malacofaunasfrom archaeological sites in the Somme Valley (North France).J. Archaeol. Sci. 22, 683–698.

Limondin, N., Rousseau, D.D., 1991. Holocene climates re-flected by malacological sequence at Verrieres, Seine valley,France. Boreas 20, 207–229.

Lozek, V., 1964. Quatarmollusken der Tschechoslowakei. Rozpr.Ustred. Ustavu. Geol. 31, 1–374.

Lozek, V., 1972. Holocene interglacial in Central Europe and itsland snails. Quat. Res. 2, 327–334.

Lozek, V., 1985. The site of Souteska and its significance forHolocene climatic development. Cs. Kras 36, 7–22.

Meijer, T., 1984. Holocene Molluskenfauna’s Uit de Stevenshof-jespolder in Leiden. Bodemond. Leiden 6, 134–151.

Montjuvent, G., 1978. Le Drac. Morphologie, stratigraphieet chronologie quaternaires d’un bassin. These, UniversiteGrenoble, 433 pp.

Montjuvent, G., 1980. Alpes du Nord. Bull. Assoc. Fr. Et. Quat.,Suppl. 1, 31–39.

Neck, R.W., 1985. Paleoecological implications of a Holocenefossil assemblage. Pearce–Sellards Ser. 41, 1–20.

Neck, R.W., 1989. Holocene nonmarine molluscs from the LeviRock shelter, Travis Co., Texas. Texas Conch. 25, 97–103.

Nyilas, I.F., Sumegi, P., 1989. The mollusc fauna of Hortobagy at


the end of the Pleistocene (Wurm 3) and in the Holocene. In:Meier-Brook, C. (Ed.), Proceedings of the Tenth InternationalMalacological Congress. Unitas Malacologica, Tubingen, pp.481–486.

Piechocki, A., 1977. The Late Pleistocene and Holocene mol-lusca of the Kunow region (N-E margin of the SwietokrzyskieMts.) Folia Quat. 39, 23–36.

Preece, R.C., Thorpe, P.M., Robinson, J.E., 1986. Confirmationof an interglacial age for the Condat tufa (Dordogne, France)from biostratigraphic and isotopic data. J. Quat. Sci. 1, 57–65.

Puissegur, J.J., 1976. Mollusques continentaux quaternairesde Bourgogne. Significations stratigraphiques et climatiques.Rapports avec d’autres faunes boreales de France. Mem. Geol.Univ. Dijon 3, 241 pp.

Rousseau, D.D., 1986. Application de la methode d’analysefactorielle des correspondances aux malacofaunes de Tourville(Saalien). Bull. Cent. Geomorphol. Caen 31, 5–20.

Rousseau, D.D., 1987. Paleoclimatology of the Achenheim series(middle and upper Pleistocene, Alsace, France). A malacolog-ical analysis. Palaeogeogr., Palaeoclimatol., Palaeoecol. 59,293–314.

Rousseau, D.D., 1989. Reponses des malacofaunes terrestresQuaternaires aux contraintes climatiques en Europe septen-trionale. Palaeogeogr., Palaeoclimatol., Palaeoecol. 69, 113–124.

Rousseau, D.D., 1991. Climatic transfer function from Quater-nary molluscs in European loess deposits. Quat. Res. 36, 195–209.

Rousseau, D.D., Kukla, G., 1994. Climatic records from the Eu-stis loess section (Nebraska, USA) during the Late Pleistocene.Quat. Res. 42, 176–187.

Rousseau, D.D., Puissegur, J.J., 1989. Analyse de la malacofaunecontinentale. In: Tuffreau, A., Somme, J. (Eds.), Le gisement

paleolithique de Biache–St-Vaast (Pas-de-Calais). Mem. Sp.Soc. Prehist. Fr. 21, 89–102.

Rousseau, D.D., Puissegur, J.J., 1990. A 350,000 years climaticrecord from the loess sequence of Achenheim, Alsace, France.Boreas 19, 203–216.

Rousseau, D.D., Puissegur, J.J., Lecolle, F., 1992. West-Euro-pean molluscs assemblages of Stage 11: climatic implications.Palaeogeogr., Palaeoclimatol., Palaeoecol. 92, 15–29.

Rousseau, D.D., Limondin, N., Puissegur, J.J., 1993. Holoceneenvironmental signals from mollusk assemblages in Burgundy(France). Quat. Res. 40, 237–253.

Rousseau, D.D., Limondin, N., Magnin, F., Puissegur, J.J., 1994.Temperature oscillations over the last 10,000 years in westernEurope estimated from terrestrial mollusc assemblages. Boreas23, 66–73.

Rousseau, D.D., Preece, R., Limondin-Lozouet, N., 1998. Britishlate glacial and Holocene climatic history reconstructed fromland snail assemblages. Geology 26, 651–654.

Seidenkrantz, M.S., Knudsen, K.L., 1997. Eemian climatic andhydrographical instability on a marine shelf in Northern Den-mark. Quat. Res. 47, 218–234.

Somme, J., Munaut, A.V., Emontspohl, A.F., Limondin, N.,LeFevre, D., Cunat-Boge, N., Mouthon, J., Gilot, E., 1994.The Watten boring. An Early Weichselian and Holocene cli-matic and palaeoecological record from the French North Seacoastal plain. Boreas 23, 231–243.

Thouveny, N., de Beaulieu, J.L., Bonifay, E., Creer, K.M., Guiot,J., Icole, M., Johnsen, S., Jouzel, J., Reille, M., Williams,T., Williamson, D., 1994. Climate variations in Europe overthe past 140 kyr deduced from rock magnetism. Nature 371,503–506.

Woillard, G.M., 1979. Abrupt end of the last interglacials innorth-east France. Nature 281, 558–562.

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