Of Achenheim, Alsace, France

A 350,000-year climatic record from the loess sequence of Achenheim, Alsace, France

DENIS-DIDIER ROUSSEAU AND JEAN-JACQUES PUISSEGUR

Rousseau, D.-D. & Puissegur, J.-J. 1990 09 01: A 350,000-year climatic record from the loess sequence BOREAS of Achenheim, Alsace, France. Boreas, Vol. 19, pp. 20S216. Oslo. ISSN 0300-9483. Up to now the best Quaternary climatic sequences come from oceanic isotope studies, but terrestrial sequences are also well known, usually for pollen or ice core data. A new sequence providing climatic information for the last 500,000 years has been studied in the loess series of Achenheim (Alsace), using the mollusc record in relation to other stratigraphical data. Mollusc assemblages are analysed using a multivariate method. The correspondence analysis used here allows us to explain, in ecological terms, the general variability of the Achenheim set. Most Pleistocene mollusc species have the advantage that modem individuals live in the same assemhlages. So, the known ecology and distribution of the modern molluscs allow us to conclude that the first two factors explain variations in temperature and moisture. Each loading, on a factor, of each association in its stratigraphical level contributes to characterizing the evolution of each climatic parameter through time. For the last five climatic cycles, these evolutions are expressed as a function of the depth within the series. As they are well preserved, the last three glacial cycles are studied in detail. They correspond to the last 350,000 years, are compared with SPECMAP data and particularly show correlations between continental and marine climatic indicators. The mollusc assemblages of the loess sequence also provide information on temperature and moisture conditions. The evolutions of each parameter are not identical during the last three cycles, indicating that the climatic history of one cycle cannot be transferred to the others. The mollusc assemblages also record the occurrence of an oscillatory system, especially during the Weichselian Upper Pleniglacial (isotopic stage 2) when it announces the Late Glacial variations. Similar oscillating excursions seem to have occurred during the older glacial stages. Denis-Didier Rousseau and Jean-Jacques Puisskgur, LIRA CNRS 157, Centre des Sciences de la Terre, Universitk de Bourgogne, 6 Bd Gabriel, 21100 Dijon, France; 27th December, 1989 (revised 22nd March, 1990).

Continuous Pleistocene climatic records have related with interglacial-glacial cycles in marine been described from deep sea sediments (Emiliani l80 records, especially in Central Europe (Kukla 1966; Shackleton & Matthews 1977; Imbrie et 1977) and China (Kukla 1987; Liu et al. 1985). al. 1984; Martinson et al. 1987), but terrestrial Kukla defined two key sites in central Europe, sequences also provide good data which can easily Cerveny Kopec and Krems (Kukla 1977). be correlated with oceanic results. The significant However, recently, the loess site of Achenheim terrestrial records concern the last climatic cycle (France), famous for its fauna, was investigated and come from polar ice sheets (Lorius et al. 1985; by a multidisciplinary team, and has provided a Dansgaard et al. 1969; Dansgaard et al. 1982) or more or less continuous record of the climatic pollen sequences (Woillard 1978; de Beaulieu & changes during the last 500,000 years (Heim et al. Reille 1984). Other records comprise more than 1982; Lautridou et al. 1985, 1986; SommC et al. one cycle but few of these give really informative 1986). Five interglacial-glacial cycles have been data about the climatic oscillations of, for recognized, which are correlated to Kukla’s example, the last 500,000 years. Apart from the cycles with the help of pedostratigraphical and Macedonian sequence (van der Hammen et al. .palaeontological analyses. Following Kukla’s 1972), few long sequences recording several cycles approach, the purpose of this paper is to compare have been investigated in Europe. the climatic variations recorded in the Achenheim Loess sequences provide important palaeo- sequences by mollusc assemblages with the SPEC- climatic information even taking into account MAP isotopic stratigraphy, the oscillations of the occurrence of discontinuities. It was demon- which are taken as representative of the global strated that long loess cyclothems can be cor- volume of glacial ice (Imbrie et al. 1984). 204 Denis-Didier Rousseau and Jean-Jacques Puisskgur BOREAS 19 (1990)

The complete Achenheim sequence red sands and grey loam (2m), at the top with large cryoturbations. Greyish or yellowish loam Achenheim is located in Alsace (France) in the (1-2m thick) with iron beds and Fe-Mn con- Rhine graben, at 48”35”-7”38’E and 170 m above cretions and with big flat calcareous concretions sea level (Fig. 1). The ancient Hurst and Sund- at the bottom. A yellow loam (1-2 m thick) with hauser quarries provide sections where a suc- big rounded calcareous concretions (‘limon jaune cession of different sedimentary environments has canari’). Finally, a 1-4 m thick sandy clayey loam, been recognized from the bottom to the top (Fig. reddish brown with polyhedral structure (‘Limon 2): Rhine alluvial sandy deposits, Vosges alluvial rouge de plateau’). sandy deposits with yellow ‘canary’ sandy loam, The grey sands (top only visible) and red sands old loess deposits - lower, middle and upper - constitute the upper part of the fluviatile and a younger loess. The loess deposits, following sediment. The material originates in both the the nomenclature of Schumacher (1914) and Wer- Vosges mountains and the river Rhine but nert (1957) start at the bottom with a pedo- becomes purely Vosgian at the top (the red complex, mostly with an interglacial soil (Bt sands). In the past, these fluviatile deposits were horizon), and continue upwards into typical car- related to a warm temperate phase, but the mal- bonate loess. acofauna indicates cold conditions (as described The stratigraphy of each cycle, previously later). Cryoturbated red sands, grey loam and described by Heim et al. (1984), can be summa- also the overlying red sands correspond to pleni- rized as follows (Fig. 2). glacial conditions (a malacofauna with Columella columella) which later became less severe as indi- Fluviatile terrace formation. - From bottom to cated by the loess-like upper loams, especially the top (Fig. 2). Grey sands (‘sables rhCnans’) with ‘canari’ loam (PuissCgur 1978). loamy-clayey layers, some metres thick. Cross- At the top, the reddish (‘limon rouge de bedded red sands (‘sables vosgiens’), 2-3 m thick; plateau’) mud was traditionally attributed to the in the lower part cross-bedded and cryoturbated Mindel-Riss interglacial. Remains of Citellus cf.

Fig. 1. Map of Western Europe. with the location of Achenheim, Cerveny Kopec and Krems in the loess belt. Achenheim had a privileged position near the ‘corridor’, surrounded by the Alpine and Scandinavian glaciers, and the more open plain of Western Europe. a, loess; b, last maximum glacial advance; c, overall maximum glacial advance. BOREAS 19 (1990) Climatic record. Achenheim loess 205

Achenheim I no molluscs 2o 1 1 UpEOlder

b Achenheim I1 30 E

Lower Older Loess

Fig. 2. Local pedosedimentary units with sedimentological 60 interpretation. 1, loess; 2, pellet sands (stratified deposits); 3, humic soils; 4, Bt (interglacial) m soil horizon; 5, colluvium; 6, fluviatile sands; 7, sandy layered loam. Arrows indicate discontinuities recognized in the field, the large ones being of notable stratigraphical value and taken into account in the time calibration of the sequence.

dietrichi with other micromammals (Aruicola cf. careous loam (1.5m thick) which is the first mosbachensis, Microtus arualis, M. ratticeps, M. appearance of typical loess at Achenheim. gregalis, Sorex cf. araneus), discovered in the lower part of the red sands were considered Min- Middle Older Loess. - From bottom to top (Fig. del in age (Chaline & ThCvenin 1972). 2). The pedocomplex 'Achenheim 111': a humic soil complex (very dark brown clayey loam with Lower Older Loess. - From bottom to top (Fig. charcoal and a non-calcareous mottled (iron) 2). The lower part of the sequence is not observ- horizon. Brownish pellet sands (1.4 m thick). A able but has been described by Schumacher (1914) brownish loam, less and less sandy in the upper and Wernert (1957). Noticeable first are slope part and slightly stratified (1.9 m thick). A brown- deposits with alternating loamy, sandy, clayey ish loess, with pseudornycelia and big calcareous and gravelly layers reworked from the terrace concretions, and then a yellowish loess (4m formations. Above follows a brownish clayey cal- thick). 206 Denis-Didier Rousseau and Jean-Jacques Puisskgur BOREAS 19 (1990)

The soil complex seems apparently simple and assimilated to the Kesselt horizon, brownish cryo- different in facies from the Achenheim I and turbated soil (diagnostic horizon of western Euro- I1 pedocomplexes. Pollen and mollusc contents pean stratigraphy) (Gullentops 1954). indicate a climatic interglacial-early glacial evol- The Younger Loess shows the typical stra- ution and determine breaks in the stratigraphy. tigraphy of the Upper Pleistocene (Eemian- The stratified sandy loam were deposited in an Weichselian). The pedocomplex ‘Achenheim I’ open pine forest environment with alternating can easily be correlated with the same pedo- humidity and dryness. Cryoturbations have not stratigraphic unit of the other loess areas (War- been observed, but an unconformity below the neton Soil complex - Rocourt Soil in Belgium and sands is recognized. Northern France; Humic soils - Elbeuf I soil in Normandy; Stillfried A in Austria). The molluscs Upper Older Loess. - From bottom to top (Fig. and the pollen content of the dark brown complex 2). Pedocomplex ‘Achenheim 11’ 4 m thick: col- suggest an early Weichselian age of the deposit, luvium with black forest soil, a reddish brown with oscillating climatic conditions. loamy-clayey horizon (Bt horizon) and a humic The overlying loess represents the whole brownish loam with crotovines. Little greenish Weichselian Pleniglacial, clearly divided into two loess (1 m thick). Stratified brownish loamy sands main units by the cryoturbated horizon (Kesselt (3m thick) with sporadic lenses of gravel and horizon), which follows after a short warm inter- pebbles having eroded into the lower layers val (according to soil and mollusc fauna) and (pellet sands). A 1 m thick loess. Loamy stratified precedes the regular deposition of the Upper sediments (2 m thick) with syngenetic frost Pleniglacial Cover Loess deposited during the wedges. Above this is a 5 m thick yellowish and last glacial maximum. By its morphostratigraphic yellow-brown loess, very calcareous (pseudomy- characteristics and its facies, this cryoturbated celia), with cryoturbated horizons, a pseudo-gley horizon corresponds to the same type of level at the top and large loess dolls. defined at Kesselt (Belgium) (Gullentops 1954) The Upper Older Loess corresponds to an and observed in the same stratigraphic conditions interglacial-glacial cycle, with a thickness com- over great distances in Belgium and northern parable to that of the last cycle (max. 12 m) and France (SommC 1977; Lautridou 1985). Its occur- similar facies of the soil complex and loess, the rence in the loess of Alsace confirms the strati- latter also being divided into two units. The stratigraphic importance of this level in the Weichselian graphic system nevertheless seems related more Pleniglacial. Once more, the unconformity at the closely to that of loess of Central Europe. No base of the loess deposits corresponds to a great major unconformity has been recognized in this erosional hiatus which is common in all the Lower sequence. Pleniglacial of the northwest European stratigraphy (Paepe & SommC 1970; Paepe & Zag- The Younger Loess. - From bottom to top (Fig. wijn 1972; SommC 1977; Lautridou 1985). 2). Pedocomplex ‘Achenheim 1’: colluvium, a Each loess cyclothem has been interpreted as reddish brown clayey loamy horizon, non-cal- an interglacial-glacial cycle and correlated with careous, with prismatic structure and coatings, the isotopic stratigraphy (Heim et al. 1982; Lau- irregularly preserved, corresponding to a Bt hori- tridou et al. 1985, 1986; Somme et al. 1986). zon (brown podzolic soil). Above a thick dark Thus the 60m of the Achenheim sections re- brown clayey loam complex (‘grand lehm’) up to cord at least five glacial cycles. From the whole 5 m thick and including a black forest soil (0.4 m data, these cycles show a climatic evolution which, thick) overlain by several humic horizons. Pellet especially for the three last cycles, is nearly con- sands, having been eroded into the underlying tinuous in spite of discontinuities recognized in ‘Grand lehm’. Several yellowish or brownish grey the stratigraphy. Some of these discontinuities are loess horizons (8 m thick) with a frost-crack level important and represent major erosional events and a stratified loam at the top (0.20111 thick). (Fig. 2) which have stratigraphic value and which The last loess, ‘the cover loess’ (Hm thick), will be taken into account in the time calibration consists of typical yellowish loess with more of the sequence by reference to the stratigraphic brownish layers separated by small frost wedges; framework of the region which includes Achen- its bottom is characterized by a cryoturbated hori- heim (SommC et al. 1980). The evidence of three zon, with small frost wedges (0.24.3111 deep), true interglacial soils, of interglacial and pleni- BOREAS 19 (1990) Climatic record, Achenheim loess 207 glacial malacofaunas and of interglacial pollen, Euconulusfuluus, Helicigona lapicida, Nesovitrea indicates that the cycles are possible to correlate hammonis, Oxychilus sp., Punctum pygmaeum, with Kukla’s glacial stages B, C, D, E and F Trichia hispida, Vertigo alpestris. (Lautridou et al. 1986; Chaline & Thevenin 1972). G7’ (Limacidae s.1.). Lima sp. G8 (hygrophilous species). Carychium triden- tatum, Succinea oblonga, Vertigo angustior, V. substriata. The mollusc profile G9 (palustral species). Carychium minimum, Oxyloma sarsi, Pupilia alpicola, Succinea putris, Sampling of sediments was done in the field for Vallonia enniensis, V. antivertigo, V. genesii. malacological and pollen investigations. While The richness and abundance of the mala- pollens are restricted to the pedocomplex soils, cological material makes possible a synthetic the terrestrial molluscs are present almost analysis based on multivariate analysis. Classical throughout the sequence and 197 of the 215 methods, like principal components, make it nec- samples were fossiliferous. Today, molluscs pro- essary to use the correlation matrix and analysed vide good environmental information because columns or rows. The method used here, cor- they are closely connected to their biotope. respondence analysis (Benzecri et al. 1973), pro- Consequently variations in the fossil faunal ceeds differently. Each element (point) I is assemblages can be correlated with Quaternary represented in a J dimension space by its coor- climatic oscillations. During interglacials, mollusc dinates on each J variable (kij; and Zkij = ki), faunas contain a large percentage of forest and but is also allocated a weight (= ki/k, k = Zki, semi-forest species, whereas during pleniglacial Zk = 1). For example, three assemblages yield stages assemblages comprise alpine-arctic and the following counts for three species a, b, c: sometimes North Asiatic species. The mollusc species used in the multivariate assemblage 1: a = 2, b = 4, c = 8, ki = 14, analyses are ecologically grouped in accordance assemblage 2: a = 4, b = 8, c = 16, ki = 28, with Lozek (1964) and Puissegur (1976). assemblage 3: a = 3, b = 10, c = 0, ki = 13; G1 (forest species). Acanthinula aculeata, k = 55. Aegopinella sp.,Aegopinella nitidula, Aegopinella pura, Aegopis verticillus, forest Clausilia, Coch- The coordinates (kij) of each assemblage will be: lodina laminata, Ena montana, Helicodonta obvo- 2/14, 4/14 and 8/14 for the first two and 3/13, luta, Monachoides sp., Orcula doliolum, 10/13andOfor the third. The weightswill be 14/55, Pagodulina pagodula, Trichia villosa, Vertigo 28/55 and 13/55. Since this procedure is avail- pusilla. able for both rows and columns, they yield G2 (semiforest species). Aegopinella minor, superimposable factors (reference axes of the Discus rotundatus, Eucobresia diaphana, Great hyperspace) that allow the simultaneous plotting species (Arianta arbustorum, Bradybaena fru- of both variables and individuals (rows). For the ticum or Cepaea sp.), Helix pomatia, Vitrea crys- Achenheim data, the mollusc species are columns tallina. and mollusc associations belonging to one strati- G3 (marshy forest species). Clausilia pumila, graphical level are rows. To avoid too much devi- Perforatella bidentata. ation in the variability, the data are coded G4 (steppe species). Cecilioides acicula, Can- following an abundance class principle (Rousseau didula unifasciata, Chondrula tridens, Helicopsis 1987). Apart from Pupilla loessica, which is striata, Pupilla sterri. extinct, all the fossil species have modern equiv- G5 (open ground environment). Catinella alents living in identical assemblages to those arenaria, Columella columella, Pupilla loessica, during the Pleistocene. The advantage of P. muscorum, Vallonia costata, V. pulchella, correspondence analysis is thus that the modern Vallonia tenuilabris, Vertigoparcedentata, V.pyg- ecology and distribution of the mollusc species can maea. be used to interpret the general variability of the G6 (xerophilous species). Cochlicopa lubri- data set and characterize each reference axis. cella, Euomphalia strigella. The first axis discriminates, according to the G7 (mesophilous species). Abida secale, Clau- positive coordinates, species and associations silia dubia, Clausiliaparuula, Cochlicopa lubrica, characteristic of an open temperate woodland 208 Denh-Didier Rousseau and Jean-Jacques Pukskgur BOREAS 19 (1990)

(i.e. comparable to those presently occurring in observed in the quality of the shell preservation Burgundy) and, on the negative side, species and (Rousseau 1987). associations characteristic of cold open ground Following this interpretation of the variability environments such as tundra. In fact a thermal of the Achenheim set, palaeoclimatic curves can gradient, temperate to pleniglacial, parallel to be drawn by plotting the loadings of each associ- this axis, is determined (Fig. 3). On the second ation, belonging to one stratigraphic level, onto axis, distribution of the species and the associ- the first two factors, interpreted as representatives ations depends on a moisture gradient: damper, of climatic parameters, following the principle marshy (negative coordinates) to dry grassland indicated in Fig. 4. The evolution of temperature (positive coordinates) (Fig. 3). Species and mala- as ithnction ofdepth in the sequence obtained cological associations are consequently dis- byhmethod (Fig. 5) is in general agreement tributed between four major poles according to with results from for example palynological or their ecological requirements and to the eco- pedological studies (Lautridou et al. 1986; Aitken logical properties of their habitats (Rousseau et al. 1986). As the three last interglacial-glacial 1987). The multivariate analysis allows us in this cycles are well preserved, these results allow a way to determine, with great precision and comparison between the continental and oceanic according to modern molluscan assemblages, the records. Of course some hiatuses occurring in the climatic oscillations. Once more, cluster analysis sequence are characterized by erosion levels and of molluscan faunas, which allows the testing of discontinuities which have morphoclimatic sig- reworked material, confirmed that there were no nificance and these will be taken into account in cases of redeposition of the molluscs, as already the following interpretation.

+-. +-. temperature gradient -+

Fig. 3. Correspondence analysis of the Achenheim malacofaunas. Plot of the species (columns) and c:A A of the malacological associations (rows), each one associated with rl one stratigraphic level, on the first A factor plane (axes 1-2). From the ecological characteristics of the species and the composition of the associations, four poles are determined: temperate to cold (temperature gradient parallel to the first axis); dry to damp and marshy (moisture gradient parallel to the second axis). The temperate pole is characterized by forest species living in middle latitudes in western Europe, all the other taxa correspond to an open ground environment. Species are shown by triangles, associations by stars. BOREAS 19 (1590) Climatic record, Achenheim loess 209

uL2

Fig. 4. Principle of drawing the climatic curves. (a) Eight associations in the hyperspace cloud with Occurrence of the first two reference axes. Loadings plotting of each association on each axis (or factor) is shown by the dotted lines with an arrow. (b) Time series of the associations with regard to their loadings on the first two axes (or factors) after having placed each association in its stratigraphic position.

Calibration of the last interglacial- cycles. The adopted equation is the following: glacial cycles and the climatic records Assuming a constant deposition rate for the last three interglacial-glacial cycles, in which all the where ai is the thickness of level i, n the total most important climatic events determined in the number of levels comprised between two ref- marine chronology have been recognized, each erence time points Tl and 12, Tm being the stratigraphic unit has its thickness weighted by calibration of the level m. The last cycle could be interpolation with the SPECMAP oxygen isotope considered a test for our procedure, because 14C average record (Imbrie et al. 1984). We calibrate and TL dates are available (Evin et al. 1980; our curve by taking into account the major dis- Aitken et al. 1986; Buraczinski & Butrym 1987). continuities and the general significance of pedo- The plots of rnalacofaunas on the first factor complexes in the bipartite subdivision of the analysis (the temperature factor) are scaled for 210 Denis-Didier Rousseau and Jean-Jacques Puisskgur BOREAS 19 (1990)

Mollusc faunas Datings Years B.P. 2 0 -2 0 15.400 f 2.200 17,000 k 3.200 ,21.100k 3.600

2 33.uw) +3.m-2.300 Younger :35,200 +2.200 - 1.800 10 Loess

a 51.ooO f10.600 Achenheim I

L 176.000 Upper Older 23.000 Loess

30 L 222.000 f 29.000 P.chcnheim I1

L 278000 f36000 Middle Older Loess 40 Achenheim 111

Lower Older Loess 50

? Achenheim 1V 7 +$=-++ Terrace 60 + m

Fig. 5. Plot of the malacological association loadings on the first factor, interpreted as indicating climate (mainly temperature), against depth in the complete Achenheim sequence. Location of datings in the sequence.

the sake of comparison to have similar amplitudes the Bt horizon without malacofauna is attributed as the 6l80variations. The major trends observed to the Eemian (event 5.5) and the overlying black in the biological variations correspond strikingly forest soil, also without malacofauna but with with those determined in the isotopic record. But pollens, to the 5.3 event. The validity of this the lack of malacological data made the test of chronological allocation is attested by the Bt soil some calibrations difficult, notably for the last truncation due to a main erosional phase attri- cycle. Nevertheless, the examination of other data buted to a cold event not recorded by any mal- (pollen, micromorphology, geomorphology, TL awfauna. So the conventional 99,000 BP age is and 14C datings) allows us to get around this thus attributed by micromorphology to the black problem. soil in order to allow the good calibration of the uppermost levels. The upper boundary of stage The last cycle (Fig. 6). - The limits of stage 5 are 5 is fixed at 71,000 BP in agreement with the defined in agreement with pedostratigraphy and SPECMAP data. The temperature variations are the palynological data of the pedocomplex Ach- in agreement with the palynological data, which enheim I (Lautridou et al. 1986; Somm& et af. indicate a more steppe-like environment. 1986). In the interglacial palaeosoil at the base, Stage 4 is not well preserved in the Achenheim BOREAS 19 (1990) Climatic record, Achenheim loess 211

Stages Age 6'80 Mollusc Datings Pedo- Kj. 2 0 -2 faunas Years B.P. complexes

1 0 2 3 4

5 100 ACH I

200 7 ACH II

8 300 k 9 LACH 111

Fig. 6. Time series of molluscs from the Achenheim sequence. Variations in smoothed and stacked 6'"O (crosses) during the last three climatic cycles (Cb339,OOO BP) are from Imbrie er uZ. (1984). Plot of the variationsin malacological associations (dark squares) on the temperature factor (first factor of the multivariate analysis) against the proposed calibration of the levels (sedimentation rate/age) and the isotopic stratigraphy. The factor vaiues are scaled for the sake of comparison to have similar amplitudes as the 6IROvariations. Ach I, 11, 111 are pedocomplexes.

sequence. Six related stratigraphical levels are at the base level yielded an age of 51,000 & 10,600 surrounded by two discontinuities, where the BP by TL (Aitken et al. 1986), which corresponds upper one has a main stratigraphical value. This to the calibrated age. The evolution of tem- important erosional level, corresponding to the perature at this time was relatively monotonous Lower Pleniglacial as defined in Northwest and in agreement with variations determined for Europe (SommC et al. 1986; Zagwijn & Paepe the oceanic isotopic curve. But a more pro- 1968), is correlated to the 4.2 event at 65,000 BP. nounced cooling than indicated by the isotopic This date fixes the upper limit of our calibration. data is observed at the base of the Achenheim Two levels yielded malacofauna. Nevertheless, record. taking geomorphological and pedosedimentary The chronostratigraphic limits of stage 2 are information into account, they are interpreted as defined following conventional values: 12,000 BP preceding the 4.2 event. at the bottom of the top sequence soil and 24,000 Stage 3 is well preserved and also surrounded BP for the level with great wedges which identifies by the major discontinuity previously mentioned this unit in the local stratigraphy. Dates provided at the base, and a level with large ice-wedges on by calibration are in agreement with those the top. The conventional limits 24,000 BP and obtained by the 14C and TL methods at the site. 59,000 BP are used. Stratified sediment observed The position of the Kesselt level in our calibration 212 Denis-Didier Rousseau and Jean-Jacques Puisskgur BOREAS 19 (1990) is in agreement with the TL, datings obtained in of the sequence. The overlying stratified sediment Achenheim (Aitken et al. 1986) and is close to indicates a warming trend which is inscribed in the new estimates proposed by Juvigne & Wintle the logic of the curve, but the magnitude of this (1988). The cold maximum falls near 15,000 BP, event is probably overestimated, as seen by com- followed by a significant warming interrupted by parison with the isotopic curve. However, that a new cooling. These dates agree with those the malacological association indicates a clear obtained from the Atlantic Ocean for the same warming is attested by the occurrence of taxa like period (Duplessy et al. 1981; Ruddiman & McIn- Discus rotundatus, Helicodonta obuoluta, Arianta tyre 1981a; Bard et al. 1987). The recorded tem- arbustorurn. The location of this mollusc assem- perature variations in the Achenheim sequence blage on the first factor which is interpreted as a indicate the occurrence of an oscillatory system temperature factor indicates a similarity of this throughout stage 2, which has had a mor- component with typical temperate associations. phosedimentary effect in other loess sites too, in Stage 6 begins with the typical loess deposits, Belgium and Northwestern France (Somme et al. which correspond to a great cooling period during 1986; Somm6 et al. 1980; Lautridou 1985). Such which we observe again, more softened, the oscil- variations are also observed in for example Vos- latory system determined in stage 2. The small tok and Camp Century ice-cores (Lorius et al. event observed in the oxygen curve, corre- 1985; Dansgaard et al. 1969) and in the Xifeng sponding to a cool period, is also recognized in loess section (Kukla 1987). This record implies the mollusc curve. A TL dating is in agreement that the climatic oscillatory system of the Late with the proposed calibration (Buraczinski & Glacial was not initiated at the end of the Pleni- Butrym 1987). glacial, but corresponds to the end of a general system characterizing stage 2 itself. The detailed The antepenultimate cycle (Fig. 6). - Stage 9 is record of the Upper Recent Loess appears as recorded in the pedocomplex Achenheim I11 and a particularly interesting model for the climatic 339,000 BP is fixed for the lower limit. According evolution of this period. to the pedostratigraphy, the upper limit (303,000) In brief, the last cycle, as recorded in the cali- is located at the basis of a brown loam overlying a brated Achenheim sequence, is in agreement with main stratigraphical discontinuity. Two different conventional SPECMAP and general palaeo- warmings are separated by a slight cooling. The climatic data. Although erosional hiatuses of first interval between the two records is explained, as stratigraphical order occur, the calibration of the previously, by the occurrence of a discontinuity, ages as a function of their thickness is satisfactory represented by the truncation of a soil which was and allows the application of this method also on not taken into account in the calibration. the two underlying cycles, which probably yield The loam at the beginning of stage 8 represents a complete record of sedimentation. the first significant cooling of the sequence. It is overlain by a stratified sediment which records a The penultimate cycle (Fig. 6). - Stage 7 is rec- slight warming, significantly less marked than in orded in the pedocomplex Achenheim 11, with the isotopic curve. On top of this follows the 245,000 BP fixed as the lower limit. The upper cooling characterized by a loess with a typical limit (186,000 BP) is located at the top of pellet Pupilla fauna (Evin et al. 1980; Rousseau 1986). sands (stratified sediment) overlying a loess. The The large interval between the samples here does variations in temperature as determined by the not allow as precise a comparison of the different molluscs are similar to those recorded by 6l80, events with the isotopic curve as previously. in spite of a small interval due to the occurrence of two soils. The first warming corresponds to a soil, cut at its top by a small erosional level, which is not taken into account in the calibration. In the Discussion same way the second warming is represented by Globally seen, the variations recorded by the a truncated Bt horizon (incomplete interglacial terrestrial molluscs and the age interpolations are soil). The loess in the pedocomplex Achenheim in agreement with TL and I4C datings and with I1 is interpreted as a marker (diagnostic horizon the astronomical calibrations of the 6I8O record. of the central European loess stratigraphy) and The three sequences indicate a clear cyclic evol- indicates the first significant cooling in this part ution in the mollusc record as well as in the BOREAS 19 (1990) Climatic record, Achenheim loess 213 morphosedimentary context. Each cycle can be each phase within the cycle. Their duration is split as follows: at the base a pedocomplex yield- proportionally constant through the different ing a varying number of temperate maxima, a cycles. The position of the stratified sediments thin loess corresponding to the first significant (pellet sands) in each cycle history is constant and cooling of the cycle, which generates strong ero- attests the validity of our calibration. sion indicated by the deposition during a short But the malacofauna can also give other cli- period of stratified sediments (‘interglacial matic information. Using the plotted values on stage’). On top the beginning of the generalized the second factor of the multivariate analysis we cooling is indicated by the deposition of the ter- can propose variations in moisture during these minal (‘glacial stage’) loess. This succession is three last cycles, as recorded in the Achenheim cyclic, as shown by the relative importance of sequence (Fig. 7).

Age Moisture Temperature Datings Isotopic KY Years B.P. stages 0 2 4 1.1.1.1.1.1. 0 J ......

[r“;c L4C 33.200 +3.200 -2,300 I4C 35.200 +2.200 -1,800 ...... L...... -n si.000 *10.600 ...... 100 =t J 3......

...... -n 176.000 f23.000 200 -n 222,000i!29,000

~~~~ ......

-n 278,000~36.000

300

-1-b temperate

Fig. 7. Variations in estimated moisture, as expressed by the second factor, against variations in estimated temperature, as expressed by the first factor, during the last 339,000 yrs BP. The values have the same scale as in Figs. 3 and 6, although the value 2 was added to the temperature values to facilitate comparison with the moisture curve. 214 Denis-Didier Rousseau and Jean-Jacques Puissgur BOREAS 19 (IYYO)

Parallel projections of the temperature and tation regime, as observed by Woillard in La moisture curves allow us to conclude that during Grande Pile (Woillard 1978), B. Van Vliet Lanoe the last three cycles, their evolutions were not by micromorphology in Weichselian sections (van homologous. Estimation of the moisture indicates Vliet-LanoC 1988), and Guiot with transfer func- that the Achenheim sequence was generally tion applied to the La Grande Pile and Les Echets deposited under dry soil surface conditions. sections (Guiot et al. 1989). Nevertheless, the In stage 9 a warm peak corresponds to an increasing moisture determined during the last increase in moisture, but as temperature glacial maximum, isotopic stage 2, is in agreement decreases conditions became dry. Strikingly, the with the simulation results of Joussaume (1989) cold maximum of stage 8 coincided with moister using the LMD 3 D model. For this period she conditions, with a maximum during the tran- observed that in Europe her moisture estimates sitional phase between the cold peak and the indicated increased values which do not agree warmest part of stage 7. Thereafter the evolutions with the palaeo-data. She recognized increasing of temperature and moisture are parallel. The moisture in winter and in summer for western cold maximum of stage 6 coincided with dry con- Europe while palaeo-data (especially results from ditions (Fig. 7). Unfortunately interglacial event transfer functions applied to pollen assemblages) 5.5 is not preserved in the Achenheim mollusc and other simulation models indicate a drying record. But up to the maximum cold stage 2 trend. The precise interpretation of the mollusc the environmental conditions were dry, stage 2 assemblages, indicating important variations by revealing alternating dry and moister environ- the loss of indicator species, suggest major cli- ments in close connection with the fluctuations in matic changes which up to now have not been temperature (Fig. 7). These results imply two recognized (Rousseau 1986). The fact that the main fundamental developments. First, con- Achenheim record shows the same trends while tinental conditions during the last cycle, mainly having been obtained in a way other than via during the pleniglacial stages, cannot be gen- circulation models implies that this locality is eralized to all the previous climatic cycles and really a first-rate site for palaeoclimatic and bio- need to be further tested by GCM. Second, the stratigraphic studies in Europe. generally assumed cold and dry continent during From the evidence of the temperature and the pleniglacial stages, as recently suggested by moisture curves, the Achenheim record shows an Ruddiman & Mclntyre (1981h), has to be mod- oscillating system during stage 2 similar to the erated with regard to the location of the studied record found during the Late Glacial and which sites and with respect to the maximum ice sheet can also be observed in the previous cycles (Fig. advances which generated changes in the 7). This is of fundamental interest because it was atmospheric circulation. also found in the ice cores, with more details 'The important point to determine is the mag- (e.g. Camp Century; Dansgaard el al. 1969). This nitude and general climatic significance of the means, first, that cold maxima are never simple mollusc fauna variations. First, references are phenomena, as described in smooth curves; provided by present climatic data. For example, second, that the oscillatory variations during the the malacofauna significant of the cold maxima in Late Glacial are not typical of this period alone, stage 2 is a Colurnella colurnella fauna and C. but belong to the general 'system' which begins columella is considered as a moisture loving with the cold maxima. Such variations can also species. At the present time such an association contribute to explaining the disagreements which can be observed in the Scandinavian mountain are often observed in the literature concerning tundras, e.g. at Abisko (68"21'N, 18"40'E) close the recognition and dating of short-lived but to lake Tornetrlsk in Sweden. Here the average important events like Younger Dryas, which are annual temperature at low altitudes is -1°C and inscribed in a general oscillatory system, but not the annual precipitation 300 mm, with a maximum necessarily globally well preserved, and conse- in summer (40mm in July). The reference to quently invite different interpretations. present conditions allows us to relativize the moisture variations observed in the Achenheim record. Apart from the interglacial periods, most of the hygrometric oscillations indicate dry con- Conclusions ditions with great deficits in the summer precipi- Information obtained from Achenheim gives us BOREAS 19 (1990) Climatic record, Achenheim loess 215 the first mollusc-based unambiguous description (eds): Chronostratigraphie et faciPs culturels du Paldolithique of climatic variations from a continental section infgrieur et moyen dans I'Europe du Nord-Ouest, Suppl. Bul- covering the last three climatic cycles. letin ak I'Association fraqaire dEtude du Quaternaire 26, 7- 14. Well preserved, they have been time-scaled by Bard, E., Arnold, M., Maurice, P., Duprat, J., Moyes, J. & interpolation with the SPECMAP isotopic stage Duplessy, J. CI. 1987: Retreat velocity of the North Atlantic limits. 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L. de & Reille, M. 1989: Although the primary interest is to reconstruct A 140,OOO year climatic reconstruction from two European the local palaeoenvironments, these parameters pollen records. Nature 338, 309-313. also provide more general climate-history infor- Gullentops, F. 1954: Contributions a la chronologie du Pltis- mation. So it is hoped that, in a second step, tocene et des formes du relief en Belgique. Mdmoire de I'lnstitut gdologique de I'Unioersrtd de Louuain 18, 125-252. the transfer functions which are in progress will Hammen van der, T., Wimjstra, T. A. & Zagwijn, W.H. greatly extend climatic information on continental 1972: The floral record of the Late Cenozoic of Europe. In conditions. Turekian, K. K. (ed.): The Lace Cenozoic Glacial Ages, 391- 424. Yale Univ. Press, New Haven. Heim, J., Lautridou, J. P., Maucorps, J., PuissCgur, J. J., Acknowledgements. -We thank Drs J. C. Duplessy, J. Jouzel, Rousseau, D. D., Somrnk, J., Thkvenin, A. & Vliet-Lano6, G. Kukla, L. D. 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