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1. Introduction        The site of Nantois is located in northern Brittany        (48°35'50.57" N and 2°31'51.46"W). It is situated in the eastern part        of Saint Brieuc Bay, in the Pléneuf-Val-André area, almost at the        westernmost end of Europe. The Nantois cliff is the place where the        stratotype of the Nantois Formation was first defined (Loyer et al., 1995) (Figure 1). The Western part of this        cliff is characterized by the superimposition of two loess formations        of Saalian and Late Weichselian ages. This outcrop is important in the        regional geology because it is the only place where the Saalian loess        is not completely decalcified in Brittany. Out of this zone the loamy        pre-Eemian sediments are very patchy, affected by pedogenesis,        reworked and decalcified. They are always absent more to the West. The        sampled outcrop, which was first studied by Monnier (1973), consists        of loam, loess and soliflucted slope deposits which are actually        continuously eroded by the sea. Loess and loam accumulations are        better developed on the East-facing studied slope than on the northern        side of the Pléneuf-Val-André hill (Laforge, 2012).        The Nantois site corresponds also with a        Palaeolithic site (Monnier, 1986). It is considered to represent a        hunting rest area since it evidences well-preserved cut up remnants.        This place is one of the many Middle Palaeolithic sites discovered in        the area. Well-developed fauna assemblages characterize some of these        sites.        A rapid test with hydrochloric acid on various        layers of the cliff has shown that the levels containing rock        fragments and loam (soils) are completely decalcified. It is only in        the well preserved lower and upper parts of the outcrop that the        Nantois (Saalian) (section 1) and Sables-d’Or-Les-Pins (Late        Weichselian) (section 2) Formations contain some mollusc shells        (Figure 2). The main part of the palaeontological material was        collected during the Russian-French scientific research cooperation        developed between 2011 and 2015.        Figure 1: A. General situation of the Nantois        site in Westernmost Europe. B and C. Location of Nantois in the        framework of the Saint Brieuc Bay (A, B and C insets were copied from        https://maps.google.com/). 1 –        Section 1 (Saalian loess); 2 – Section 2 (Weichselian loess) / A. Situation générale du site de Nantois en Europe de        l’ouest. B et C. Localisation du site de Nantois dans le cadre de la        Baie de Saint-Brieuc (les vignettes A, B et C sont tirées du site        https://maps.google.com/). 1-        Section 1 : loess Saaliens; 2- Section 2 : loess Weichseliens.                We have been interested to compare these two        formations thanks to the incorporated fauna and with the contribution        of the physical characteristics of the sediment. The final purpose of        this study was to check if the environmental conditions prevailing        during the loess accumulations were identical or partly different        since both types of sediments deposited during two successive cold        periods.        Figure 2: A: Panoramic view of the Nantois site        showing the position of the two excavated sections. J.-L. Monnier and        J.-P. Lefort give the scale. B: General view of the studied section        (after Monnier, 1973) / A: Vue panoramique du site        de Nantois montrant la position des deux sections. J.-L. Monnier et        J.-P. Lefort donnent l’échelle. B: Vue générale de la falaise (d’après        Monnier, 1973).                      2. General background        The general characteristics of the studied zone are        briefly summarized below.                  General framework and regional setting          Studies developed at the regional scale (Lefort          et al., 2011; Danukalova et          al., 2013) show that the Upper Pleistocene loess of Northern          Brittany and Normandy result from the accumulation of a thin dust          originating mainly in the central part of the Western English          Channel and which were transported by strong winds blowing towards          the south or the southeast (Bigot, 1986). The onshore loess contains          heavy minerals and mainly garnets which can be used as markers          (Lefort et al., 2011). The enrichment of the          loess deposits in garnets can be compared with the concentration of          the garnets found in the submarine placers associated with the now          submerged Channel River (Lericollais, 2007), this comparison          demonstrates the close relationship existing between the offshore          and onshore mineralogical concentrations. Loess also contains          coccoliths and foraminiferous (Estéoule et          al., 1971) resulting from the frost chattering (Lautridou,          1971) of the offshore Cretaceous and Eocene outcrops. Loess deposits          are now preferentially coating the north or northwest facing          basement cliffs of the Northern shore of the Brittany Peninsula          (Lefort et al., 2013).                          General stratigraphy of the outcrop          The general stratigraphy of the Nantois cliff          will not be described again. We send back the reader to a former          paper where the main features of this cliff have been previously          described (Loyer et al., 1995). In this paper          we will only describe the stratigraphy of the two sections we          studied.                          Geochronological background                      Dating evidences            Clear stratigraphic similarities observed            between the Nantois cliff and the nearby sites of Piégu and Les            Vallées, where radiometric datings have been carried out (Bahain            et al., 2012), confirm the            chronostratigraphic scheme previously suggested on the basis of            field observations and major stratigraphic landmarks such as            paleosols, palaeo-beaches and dunes, loamy facies etc. The            regional Pleistocene stratigraphic scheme established during a            period of forty years is, thus, fully confirmed and can be now            incorporated with the geochronological data (Monnier, 2006;            Laforge, 2012). In summary, the “Old loess” of Nantois site which            is lying under a soliflucted layer represents the bedrock of a            paleosol which can be correlated with the Eemian and rest above a            sandy layer which is also present at Les Vallée site. At its top a            Palaeolithic layer can be recognized (Huet, 2011). Because the            archaeological layer is dated at about 165 Ka by ESR-U/Th (Bahain            et al., 2012), the age of the “old loess”            of Nantois can be estimated as ranging between 170 Ka and 130            Ka.            The “Younger loess” is clearly resting above            the Eemian paleosol and above the characteristic deposits of La            Haute-Ville and Port-Morvan formations. The direct radiometric            dating made by OSL technic (Loyer et al.,            1995) provided an age of 18 Ka ± 2.5. Other OSL datings have been            made on the same levels in the nearby site à Sables-d’Or-Les-Pins            (Folz, 2000). The ages obtained on these equivalent layers are            close to 20 Ka (21.9 ±1.9 and 21.4 ± 1.9). These results are not            very different from those obtained by Manfred Frechen (Van Vliet            et al., 1997) who evidenced a very rapid            loess deposition reaching 1,5 m for 1 000 years!                                MIS equivalences and correlations with the            Global Quaternary scales            The equivalences which will be used further in            this paper must be first defined for a better clarity. It is now            estimated that the Formation of Nantois ranges between MIS 6 and            MIS 9 (and probably also MIS 10) that is to say approximately            between 330 (or 350?) and 127 ka. The formation of La Haute Ville            can be correlated with MIS 5 which ranges between 127 and 75 ka.            The formation of Port-Morvan spreads between MIS 4 and the            beginning of MIS 3, between 75 and 40 ka. The formation of            Sable-d’Or-Les-Pins developed between the second half of MIS 3 and            MIS 2, between 40 and 15 ka (Monnier, 1973; Monnier and Bigot,            1987; Bigot, 1986; Loyer et al., 1995;            Monnier et al., 2011; Bahain et al., 2012). Taking account of all these data            correlations between the Middle and Upper Pleistocene subdivisions            of Northern Brittany with other units of Western Europe is            proposed in Table 1.            Table 1: Comparison between the Middle to            Upper Pleistocene stratigraphic units previously recognized in the            Northern part of Brittany with known successions of Western Europe            / Comparaison entre la stratigraphie des unités            reconnues au nord de la Bretagne avec des unités connues en Europe            de l’Ouest.                                          Global Quaternary scheme Gibbard &#38; Cohen                (2008)                West European stratigraphic                divisions* (The Netherlands) / Ma Turner (1998), Zagwijn                (1996), Busschers et al.                (2008)                Sibrava, Bowen &#38; Richmond                1986                Northern Brittany Monnier et al. (1997)                Marine Isotope Stages                                            System                Series                Subseries, stages                                             QUATERNARY                HOLOCENE                UPPER                Upper                Holocene                Holocene                                                            MIDDLE                Middle                1                                            LOWER                 Lower 0.01                                                            PLEISTOCENE                UPPER                Upper Weichselian                Weichselian                Sable-d’Or-les-Pins Formation                2                                            Middle Weichselian                Port Morvan Formation                3                                            Lower Weichselian                4                                            La Haute-Ville Formation                5a-d                                            Eemian 0.127                Eemian 0.132                5e                                            MIDDLE                Saalian                Drenthe glaciationCold Interval with                permafrost                Warthe 0.198                Nantois Formation                6                                            Bantega interstadial                Drenthe-Warthe 0.252                7                                            Cold Interval                Drenthe                8                                            Hoogeveen Interstadial                Domnitz 0.338                9                                            Cold interval with permafrost                Fuhne 0.352                10                                            Holsteinian Interglacial 0.427                Holsteinian 0.428                                11                                            Elsterian                Elsterian 0.480                                12                                      *West European stratigraphical divisions            for the upper Middle Pleistocene are given according to Busschers            et al. (2008) and Turner (1998), Late            Pleistocene divisions according to Zagwijn (1996)                                    Malacological background          Some mollusc shells have been previously          discovered in the Nantois site, but were never described completely          in any journal. The first informations regarding this site were          given by Mazeres (1938), Beigbeder (1964) and Monnier (1973).          Monnier took individual samples from Nantois which were studied by          Puisségur for the mollusc species. They are listed in his PhD thesis          (Monnier, 1973). Afterwards, this cliff only attracted the attention          of sedimentologists (Monnier et al., 2011;          Laforge, 2012). It was also one of the selected sites used to show          the Pleistocene stratigraphy to students. In 2008 the Nantois cliff          was shown to the participants of the INQUA SEQS field excursion in          relationship with the meeting held in Rennes (Excursion Guidebook,          2008). In 2011-2015 the authors described and studied again this          section.                      3. Materials and methods                  Description on the field          The colors of the Munsell Soil Color Chart have          been used to describe the natural sediment before drying.          For the Nantois loess, colors vary between          yellowish-brown and brownish-yellow (10 YR 5/4, 10 YR 5/5, 10 YR          6/6) but, at the base of the profile, the colors are darker (dark          yellowish-brown = 10 YR ¾, 10 YR 4/4, 10 YR 4.5/6).          The colors of the Sable-d’Or-Les-Pins loess are          not very different. The main colors also vary between          yellowish-brown and brownish-yellow but at the top of the profile          the colors are darker (dark yellowish-brown = 10 YR 4.5/6, 10 YR          4.5/4, 10 YR 4/6). It is a usual phenomenon in the post-glacial          soils because of the clay illuviation and the oxidation.                          Procedure used in the malacological          study          The work on the molluscs of the Nantois section          started in 2011 in the western part of the cliff where Late Middle          Pleistocene loess deposits were known (section 1). A new section          (section 2) was investigated in the eastern part of the same cliff          in 2012 and 2014. We mainly concentrated on the loess layers.          The sediments of sections 1 and 2 were sampled at          10 cm intervals; each sample represented a mass of approximately          2,5 kg or a volume of one cubic decimeter. In total 79 samples were          examined. The thickness of the sampled Nantois loess was of 490 cm          (49 samples); the thickness of the Sable-d’Or-Les-Pins loess was of          300 cm (30 samples) (Figures 3 and 4).          Figure 3: Photograph (B) and schematic          organization (A) of the Western part (late Middle Pleistocene) of          the Nantois site / Photographie (B) et          organisation schématique (A) de la partie orientale (Pléistocène          Moyen terminal) du site de Nantois                    Arabic numbers correspond with layers          recognized in section 1. The little squares indicate the location of          the samples (numbers are given in the text). The photographs shown          in a dashed rectangle indicate: a – the lower and b – the middle          parts of the Section 1Les chiffres arabes          correspondent aux niveaux reconnus dans la coupe 1. Les carrés          indiquent la localisation des échantillons (les numéros sont donnés          dans le texte). Les photographies présentées dans le rectangle          hachuré indiquent: a: la partie inférieure et b:la partie moyenne de          la section 1          Figure 4: Photograph (B) and schematic          organization (A) of the eastern part (late Late Pleistocene) of the          Nantois site / Photographie (B) et organisation          schématique (A) de la partie orientale (Pléistocène Supérieur          terminal) du site de Nantois                    Large Arabic numbers correspond with the          layers recognized in section 2. Small Arabic numbers located close          to the little squares correspond to the sampling references. J.-L.          Monnier and J.-P. Lefort give the scale / Les grands chiffres arabes correspondent aux niveaux          reconnus dans la coupe 2. Les petits chiffres arabes situés prés des          petits figurés carrés correspondent aux références          d’échantillonnage. J.-L. Monnier et J.-P. Lefort donnent          l’échelle          The methodology described by Sümegi and Krolopp          (2002) was followed, with the single difference of a closer spacing          for sampling.          After their collection on the field, the samples          were numbered and placed in plastic bags. In the laboratory, they          were placed on plates and covered by water. After soaking overnight,          they were washed through sieves of 0.5 mm and then air-dried. After          drying, they were stored in plastic containers and labeled. The          visual inspection of the samples revealed unbroken mollusc shells,          big fragments of shells and fine impossible to describe detritus.          Because the number of mollusc shells is important in the          interpretation of the Upper Pleistocene terrestrial deposits, the          shells were examined and extracted individually. The quantity of          extracted shells was very different depending on the investigated          level (See Tables 2 and 3). Their abundance is given according to          the method of Ložek (1964). The number of complete shells plus the          number of apices or apertures which were considered as equivalent to          one shell when taken together were counted. Then, the resulting          amount of species, matched on the fragments, was added to the          unbroken specimen. Additionally we counted undetermined shell          fragments in order to get quantitative information on the          environmental characteristics. The percentage of species in the          samples was not counted, because this method needs more than 200          specimens of shells in each sample (White et          al., 2008) to be valid.          Afterwards, each sample was calibrated according          to the species structure with the help of brushes and with a MBS 10          binocular microscope with different amplification (×4 – ×10).          The determination of the species was done          according to the detailed works of Likharev and Rammelmeier (1952),          Shileyko (1978, 1984), Shileyko and Likharev (1986), and Kerney and          Cameron (1999). The classification was given according to Falkner          et al. (2002).          The published data about the modern mollusc          species and their ecological preferences for air temperature,          humidity, and vegetation cover were considered (Germain, 1930;          Likharev and Rammelmeier, 1952; Adam, 1960; Zilch and Jaeckel, 1962;          Ložek, 1964; Puisségur, 1976; Kerney et al.,          1983; Shileyko, 1978, 1984; Kerney and Cameron, 1999; Willis et al., 2000; Sümegi and Krolopp, 2002; Sysoev          and Shileyko, 2009; Animal base, n.d.).          The palaeontological collections are kept at the          Institute of Geology (Ufa Scientific Centre RAS, Ufa).          Shells of the molluscs were photographed in the          laboratory of Archéosciences of the University Rennes 1 (Rennes,          France) on a stereomicroscope Leica M205С with a camera Leica          DFC295.                          Procedure used in the physical study of the          sediments          The granulometry has been made with the help of a          Laser particle size analyzer (Cilas 1180L) after elimination of the          calcium carbonate by hydrochloric acid. This first step is necessary          in order to homogenize the results of the different series of          samples. It is known that after deposition, the calcium carbonate          contained in the loess almost always moves under the effect of          different pedological processes and precipitated as “conglomerate”          and calcareous concretions (“loess doll”). This elimination of          CaCO3 is also necessary to avoid clay          flocculation. Calcium carbonate has been measured by X Fluorescence.          Granulometry and Carbonates analysis have been made on the loess          samples selected for malacology.                      4. Results of the recent investigations                  Stratigraphy          The description of the late Middle (section 1)          and Late Pleistocene (section 2) deposits investigated in this study          is given below. The two sections are separated by a horizontal          distance of 45 m (Figure 2).                      Section 1: Late Middle Pleistocene (Figure            3)            1. Brown and black angular fragments of            Palaeozoic rocks analog to slope deposits (soliflucted?) with sand            layer (0.35 m thick) and lens of gravel colored in black by Fe and            Mn oxides (total thickness: 6.0 m). 2. Alternation of poorly            rounded rock fragments and yellowish grey loess-like loam with            possible traces of pedogenesis (thickness: 0.3 m). 3. Dark            yellowish brown loam (soil?) (thickness: 0.2 m). 4. Dark yellowish            brown loess with rock fragments in the upper part of the layer            (thickness: 1.0 m). 5. Brownish yellow loess with very thin layers            showing a different color (thickness: 0.7 m). 6. Brownish yellow            loess with rock fragments (thickness: 0.2 m). 7. Yellowish brown            loess (thickness: 0.2 m). 8. Yellowish brown loam (soil)            (thickness: 0.3 m). 9. Yellowish brown loess (thickness is 0.9 m).            10. Yellowish brown loess with rock fragments (thickness: 1.1 m).            11. Reddish loam with fragments of rocks (thickness: 0.4 m). The            total thickness of the deposits including the loess is of 15.3            m.            Layers 1 to 10 correspond to the Nantois            Formation (Middle Pleistocene).                                Section 2: Upper Pleistocene and Holocene            (Figures 4 and 5)            1. Alternation of yellowish grey loess-like            loam and poorly rounded rock fragments (thickness: 1.0 m). 2.            Alternation of very thin layers of a yellowish grey loess-like            loam, sand and angular rock fragments. Cryoturbations were not            observed in our sections but are known in the same horizon a            little bit further West (Loyer et al.,            1995). The size of the rock fragments and their quantity decreases            towards the top of the layer (thickness: 0.5 m). 3. Light            yellowish grey porous calcareous loess with calcareous rhizomorph            concretions. The upper part (0.3 m) of the layer is decalcified            (thickness: 1.2 m). 4. Reddish brown clay-rich loam alternating            with loess-like loam influenced by soil processes; it corresponds            to what is called “striped illuviation” at the base of a brown            illuviated forested soil (thickness: 0.6 m). 5. Light grey            dust-like calcareous sandy loam (horizon A2).            Traces of weathering (thickness: 0.2 to 0.3 m). 6. Dark grey sandy            loam (horizons A1/A2 and Bt) (thickness: 0.3 m). 7. Light            yellowish grey aeolian sand (thickness: 0,2 m). 8. Dark grey sandy            loam (modern soil) (thickness: 0,2 m). The total thickness of the            deposits of Section 2 is 4.3 m.            Layers 1 to 5 correspond to Sable-d’Or-Les-Pins            Formation (upper part of the Upper Pleistocene). Layers 6 to 8 are            Holocene in age.            Figure 5: Nantois site / Site de Nantois                        Deposits of the Sable-d’Or-Les-Pins            Formation (late Late Pleistocene), Section 2: 1 – slope            (soliflucted?) and aeolian deposits observed in layer 1; 2 –            aeolian and slope (ravine) deposits observed in layer 2; 3 –            aeolian deposits typical of layer 3; 4 – aeolian deposits affected            by soil processes in layer 4. Scale: 10 cm / Dépôts de la formation de Sables-d’Or-les-Pins (fin            du Pléistocène terminal), Section 2 : 1-Dépôts de pente            (soliflués ?) et dépôts éoliens observés dans la couche 1 ;            2-Dépôts de pente (ravinement) et éoliens observés dans la couche            2 ; Dépôts éoliens typiques de la couche 3 ; Dépôts éoliens            affectés par la pédogenèse dans la couche 4. Échelle :            10 cm                                    Sedimentological study          The analysis of the granulometric curves of          Nantois and Sable-d’Or-Les-Pins loess (Figs 6 and 7) generated the          following results:                      The median Md is, by enlarge, a little            bit higher for the Sable-d’Or-Les-Pins loess but the standard            deviation is a little bit lower, which suggests that they are in            general a little bit coarser.            On the stratigraphic diagrams showing the            Nantois and Sable-d’Or-Les-Pins profiles, the Nantois profile            shows thinner sediments at the base and coarser deposits at the            level of samples 8 and 9. The rest of the profile is irregular            which may result from some trickling effects.            The index sorting Hq is slightly higher            for the Nantois loess but with a lower standard deviation, showing            that they are less well sorted.             The stratigraphic diagrams show an            irregular sorting for the Nantois loess (more irregular than in            the Sable-d’Or-Les-Pins loess), save at the level of two anomalies            (samples 8 and 28) where the sorting is better and even better            expressed towards the bottom of the profile.             The Asq index is slighly lower for the            Nantois loess. The curves are, by enlarge more symmetric but            always positive which show a better sorting of the coarser            particles.             On the stratigraphic diagram the symmetry            is good towards the bottom of the profile but decrease rapidly            between samples 2 and 10. Then it is variable towards the top. The            Sable-d’Or-Les-Pins loess displays a random asymmetry and in            general a very asymmetric trend.             0.2 micron clay diagrams:                 Nantois loess show a higher rate at                the bottom of the profile (samples 1 and 2) which could be                related with some trickling of the thin particles originating                in the underlying eroded soil.                Sable-d’Or-Les-Pins loess display                rapidly increasing values towards the top of the profile                (samples 25 to 30) which is probably related with the post                glacial pedogenesis                           2 microns clay diagram:                Nantois loess show a higher rate at                the bottom of the profile (samples 1 and 2) but an anomaly of                unknown origin towards the bottom (sample 26)                 Sable-d’Or-Les-Pins loess does not                display any particular trend.                           6 microns clay diagram:                Nantois loess show a high rate at the                bottom of the profile but then decreases, becomes irregular                and looks lower save for sample 26.                Sable-d’Or-Les-Pins loess display                variable rates between 7 and 14%, some horizons are richer                than others in particles thinner than 6 microns. There is no                enrichment at the top.                          Carbonates:                 Nantois loess is poorly carbonated in                the lower part. Then it increases with the concretions level                (migrated calcium level). On top it is decalcified under the                Eemian soil.                The Sable-d’Or-Les-Pins is moderately                carbonated in its lower part and then clearly enriched in                calcium and at last decalcified under the post-glacial                soil.                                  Figure 6. Frequency of terrestrial molluscs,          granulometry and calcimetry curves measured in the deposits of the          Nantois Formation (Middle Pleistocene) of the Nantois site and          possible attribution to the regional (A) and general (B)          stratigraphical schemes used in this paper / Fréquence des mollusques terrestres, granulométrie et          calcimétrie mesurées dans la Formation de Nantois (Pléistocène          moyen) du site de Nantois et correlation possible avec le schéma          stratigraphique régional (A) et général (B) utilisés dans cette          publication                    C Section: Nantois loess section: paleosol          sequence according to Monnier (1973) and Laforge (2012): small          Arabic numbers indicate the numbering of the lithological units. D          Section: investigated loess interval (Saalian), molluscs occurences,          granulometry and calcimetry data. The given values represent the          numbers of total land snails found in a sample. The symbol +          indicates the presence of shells detritus in a sample. Lithologic          symbols: 1: soil (A horizon); 2: soil (B horizon); 3: colluvium          (angular rock fragments) (=head); 4: loess or loess-like loam; 5:          loamy sand; 6: sand; 7: basement; 8: pebbles; 9: loam; 10: OSL ages.          Measured physical and chemical parameters: Hq: sorting; Asq:          asymmetry; 0.2 μ clay: rate of 0.2 μ clay; 2 μ clay: rate of 2 μ          clay; 6 μ clay: rate of 6 μ clay; CaCO3:          carbonate of calcium rate. Symbols given in column 1: Cross in a          circle – TL dates (Ka) after Loyer et al.,          1995, double circle – ESR / U-Th data after Bahain et al., 2012Coupe C:          Loess de la section de Nantois: séquence de paléosol d’aprés Monnier          (1973) et Laforge (2012) : les petits chiffres arabes indiquent la          numérotation des unités lithologiques. Coupe D: section de loess          étudiés (Saalien), présence de mollusques, données granulométriques          et calcimétrie. Les valeurs données représentent le nombre total de          gastéropodes continentaux trouvés par échantillon. Le symbole +          indique la présence de fragments coquilliers par échantillon.          Symboles lithologiques:1: sol (horizon A) ; 2 : sol (horizon B) ;          3 : colluvion (fragments anguleux de roche) (=head) ; 4 : loess ou          limon loessique; 5:sables limoneux; 6 : sable ; 7 : socle ;          8:galets ; 9 : limon ; 10 : age OSL ; Mesure des paramètres          physiques et chimiques: Hq : tri ; Asq:asymétrie; 0.2 μ : taux          d’argiles à 0,2 μ ; 2 μ : taux d’argiles à 2 μ ; 6 μ : taux          d’argiles à 6 μ ; CaCO3 : concentration en carbonate de calcium.          Symboles: croix dans un cercle: age TL (Ka) d’après Loyer et          al., 1995, double cercle : age ESR/U-Th d’aprés          Bahain et al., 2012          Figure 7: Frequency of terrestrial molluscs,          granulometry and calcimetry curves measured in the deposits of          Sable-d’Or-Les-Pins Formation (Upper Pleistocene) of the Nantois          site and possible attribution to the regional (A) and general (B)          stratigraphical schemes used in this paper / Fréquence des mollusques terrestres, granulométrie et          calcimétrie mesurées dans la Formation de Sables-d’Or-les-Pins          (Pléistocène Supérieur) du site de Nantois et correlation possible          avec le schéma stratigraphique régional (A) et général (B) utilisés          dans cette publication                    C Section: Nantois loess: paleosol sequence          according to Monnier (1973) and Laforge (2012): small Arabic numbers          indicate the numbering of the lithological units. D Section:          investigated loess interval (Weichselian), mollusc occurance,          granulometry and calcimetry data. See figure 6 for the other          symbolsSection C : Loess de la section de          Nantois : séquence de paléosols d’aprés Monnier (1973) et Laforge          (2012) : les petits chiffres arabes indiquent la numérotation des          unités lithologiques. Coupe D : section de loess étudiés          (Weichselien), présence de mollusques, données granulométriques et          calcimétrie. Voire la figure 6 pour les autres symboles                          Malacological study                      Molluscan distribution according to the            depth respect to the surface:            In sections one and two the analysis of the            distribution of the molluscs according to the depth respect with            the surface shows that the mollusc shells are irregularly located            in the loess (Tables 2 and 3).            The upper part of Section 1 (Nantois            Formation), layers 10 and partly 9 (1.2 m thick) does not contain            any shell. These deposits were affected by the formation of the            brown soil (Eemian) which deposited above the “old loess”. This            part of the section is slightly reddish because of the Fe and Al            oxides which were washed out from the overlying soil. The largest            amount of shells is concentrated at the lower part of the studied            section (layer 2), between 1.20 and 1.40 m depth (layer 4) and            between 2.80 and 3.00 m depth (layer 8). It is likely that these            sedimentary zones deposited in slightly better climatic            conditions. The other zones of the investigated section contain            fewer mollusc shells.            The upper part of the Section 2            (Sable-d’Or-Les-Pins Formation) (layer 4 of 1.0 m thick) does not            contain any shell. These deposits were affected by the formation            of the overlying soil (Holocene). The biggest amount of shells is            concentrated at the depth of 0.80-1.60 m (layer 2 and partly layer            3). The lower part (layer 1) of the investigated section contains            smaller amounts of mollusc shells.            Table 2: Composition of the mollusc species            found in the Nantois site, Nantois Formation (Saalian, Late Middle            Pleistocene) / Espèces de mollusques trouvées            dans le site de Nantois, Formation de Nantois (Saalien,            Pléistocène Moyen Terminal)                        Legend: + - shell fragments with size less            than 1 mm; juv. – juvenile mollusc shell.Légende : + - fragments de coquilles dont la taille            est inférieure à 1 mm; juv. – coquilles de mollusques            juvéniles.            Table 3: Composition of the mollusc species            found in the Nantois site, Sable-d’Or-Les-Pins Formation (Upper            Weichselian, Upper Pleistocene) / Espèces de            mollusques trouvées dans le site de Nantois, Formation de            Sables-d’Or-les-Pins (Pléistocène Supérieur).                        Legend: + – shell fragments with size less            than 1 mm; juv. – juvenile mollusc shell.Légende: + – fragments de coquilles dont la taille            est inférieure à 1 mm; juv. – coquilles de mollusques            juvéniles.                                Systematic composition analysis            The examined shells only belong to one class of            Gastropods. The samples include terrestrial mollusc shells (6            species, 5 genera) but also numerous fine shell detritus. The            mollusc species composition is shown in tables 2 and 3.            A total amount of 397 terrestrial mollusc            shells (and 2018 fragments) belonging to 7 species were identified            in the Late Middle Pleistocene deposits of Nantois (Succinella oblonga (Draparnaud, 1801), Pupilla muscorum (Linnaeus, 1758), Cochlicopa lubrica (Müller, 1774), Vertigo cf. alpestris            Alder, 1838, Vallonia pulchella            (Müller, 1774), Hydromiidae, Limax            sp.) and a total of 62 mollusc shells (and 2424 fragments)            belonging to 1 species were identified in the Upper Pleistocene            deposits (Pupilla muscorum and Pupilla sp.) (Tables 2 and 3; Figures 6 and            7).            The presence of small detritus of marine shells            was also observed in these deposits. Marine molluscs were living            in a sea which existed before the cold phases when loess            accumulated. During these cold phases the sea was located at a            lower level and part of the marine sediments were open to the air.            The marine winds, blowing towards the Nantois cliff, were strong            enough to carry at the same time, the loess particles and very            small fragments of shell and juveniles of marine bivalves or            gastropods (Bigot, 1986; Danukalova et al.,            2013). Fragments and juvenile shells of marine molluscs are            difficult to determine because of their bad preservation, only Acmaea sp., Peringia            sp., Muricidae (possibly Ocenebra sp.),            Trochidae, Ostrea sp. and Cardiidae were            present amongst the studied fragments            The dominant and single species found in            Sable-d’Or-Les-Pins loess is Pupilla            muscorum. The dominant species recognized in Nantois loess is            also Pupilla muscorum, the second            prevailing species are Hydromiidae and Vallonia            pulchella. Species of Succinella, Vertigo, Cochlicopa and            slug shells are rare.            Pupilla (Figures 8, 9, 11). This genus is            represented by numerous shells of P. muscorum species in the Sable-d’Or-Les-Pins            Formation (52 individuals) and Nantois Formation (360            individuals). In both Formations the morphology of the shells is            similar. The shape of the shells is spiral conical            (oval-cylindrical) with evenly convex weakly striated 5-6 whorls.            The shells of the Nantois Formation have more solid walls than the            shells of Sable-d’Or-Les-Pins Formation which are thinner and more            fragile. When we compare the thickness of the walls of the shells            with the results of the carbonates analysis we can notice that the            calcium carbonate content in the Nantois sediments (level 1.2-1.3            m) is of 6000-7000 ppm, and that of the Sable-d’Or-Les-Pins            Formation is less than 5000-5500 ppm (level 0.9-1 m). Whorls are            well separated by well-marked and not very deep suture. The mean            characteristics of the shells of the Nantois deposits are as            follow: shell length: 3.5 mm, width: 1. 8 mm, coefficient of            elongation (width / length): 0.46. The mean characteristics of the            shells from Sable-d’Or-Les-Pins deposits are: shell length: 3.5            mm, width: 1.7 mm, coefficient of elongation: 0.5. It must be            noted that the shells of the Nantois Formation are            oval-cylindrical, and differently elongated (the height ranging            from 2.8 to 4.2 mm). We assume that this discrepancy is due to the            differences in age (adult or juvenile) of the studied molluscs.            The aperture is irregularly semi-circular with well developed lips            turned towards the outside, with well developed cervical callus on            the palatal side (like the constriction and the dam above it) and            with a parietal tooth which is better developed in the apertures            of Pupilla shells collected in the Nantois            loess than in the Sable-d’Or-Les-Pins deposits (Likharev and            Rammelmeier, 1952, p. 146, fig. 59; Danilovskyi, 1955, p. 96,            tabl. 7, fig. 177-182; Ložek, 1964, p. 215, tabl. 9, fig. 1, 7;            Shileyko, 1984, p. 179, fig. 97; Kerney, Cameron, 1999, p.            120).            Succinella (Figure 9). Only one juvenile shell            badly preserved represents this genus (Nantois Formation). This            shell is spiral conical and weakly striated with convex and            rapidly increasing whorls (3) well separated by a well-marked deep            suture. The last whorl is two times larger than the former one and            is almost destroyed on the studied specimen as well as its            aperture. The characteristics of the shell are: shell length: 3.5            mm, width: 1.9 mm. This shell probably belongs to S. oblonga (Likharev and            Rammelmeier, 1952, p. 122-123, fig. 32; Danilovskyi, 1955, p. 87,            tabl. 5, fig. 93, 101, 103-107, 108, 109; Ložek, 1964, p. 230,            table 12, fig. 7-9; Shileyko and Likharev, 1986, p. 200, fig. 1;            Sysoev and Shileyko, 2009, fig. 5, F; Kerney and Cameron, 1999, p.            98, pl. 2, fig. 2).            Vallonia (Figure 10). Seven shells from this            genus were recognized in the Nantois Formation. The shells are            circular, spiral low conical with slow increased 31/4 – 33/4 convex whorls separated by            a well-marked deep suture. The last whorl is wider than the            previous one and does not fall to the mouth. The mean            characteristics of the shells are: shell length: 1.3 mm, width:            2.5 mm. The aperture is circular; its attachment places are close            to each other. The outer side is retracted outward and is            thickening with a white lip; the inner edge is thin and adjacent            to the shell surface. The umbilicus is wide. The specimens belong            to V. pulchella            (Likharev and Rammelmeier, 1952, p. 164, fig. 77; Danilovskyi,            1955, p. 88, tabl. 6, fig. 117-118; Ložek, 1964, p. 221, tabl. 10,            fig. 5 a-c; Shileyko, 1984, p. 166, fig. 92, III; Sysoev and            Shileyko, 2009, fig. 16, C; Kerney and Cameron, 1999, p. 127).            Vertigo (Figure 9). Only one adult shell            represents this genus (Nantois Formation). The shape of the shell            is spiral conical (oval-cylindrical) with evenly convex weakly            striated progressively increased 4 ¾ whorls. The characteristics            of the shell are: shell length: 2.1 mm, width: 1.2 mm. The            aperture is irregularly semi-circular with well-developed lips            turned out, with developed cervical callus at the palatal side (it            can be absent) and with four teeth: one parietal, one columellar            and two palatal. This shell probably belongs to Vertigo cf. alpestris            (Shileyko 1984, p. 211, fig. 133, I; Sysoev and Shileyko, 2009,            fig. 20, G, H).            Cochlicopa (Figure 9). Only one shell of Cochlicopa lubrica was            found in the Nantois Formation. The shell has a spiral conical            shape with rounded apex, with 41/2 convex whorls subdivided by a deep suture. The            shell has a shinning surface. The characteristics of the shell            are: shell height: 4.1 mm, width: 2 mm. The aperture is oval, the            parietal side is cut, and the other sides are slightly thickened.            The aperture has no teeth. This shell probably belongs to a            juvenile mollusc (Likharev and Rammelmeier, 1952, p. 125, fig. 35;            Danilovskyi, 1955, p. 97, tabl. 8, fig. 193-197, 205; Ložek, 1964,            p. 193, tabl. 5, fig. 7, 8; Shileyko, 1984, p. 211, fig. 44, III;            Sysoev and Shileyko, 2009, fig. 8, E; Kerney and Cameron, 1999, p.            97, pl. 1, fig. 11).            Limacidae (Figure 10). Four reduced shells of            Limacidae have been found in the Nantois Formation (Section 1).            The shape of the shell is oblong-oval and thin slightly convex            with an inflated apex at the posterior margin but inclined towards            the left side. The medium length of the shell is 3.1 mm, width –            1.8 mm. All shells probably belong to the genus Limax (Steklov, 1966, p. 219, tabl. 9, fig.            175-177).            Hydromiidae (Figure 10). Twenty three juvenile            fragile shells of a bad and poor preservation coming from the            Nantois loess were studied. The general morphologies of these            shells are similar but show some slight differences, it is why            they have been subdivided in two groups. The photos illustrating            these groups are shown on Fig. 13, 1 and 2. The shells have a            spiral low conical depressed shape (the height of the spire is            less that the height of the aperture according to Shileyko, 1978,            fig. 2) with weakly striated 3 ¾ – 4 ¾ convex whorls, separated by            a deep suture. The spire is rounded; its height is 0.6 mm (group            1) or 0.4 mm (group 2). The last (= body) whorl is rounded (group            1) or is slightly angular at the beginning (group 2). All the            samples display a destroyed aperture. The characteristics of the            shells are: shell height: 4.1 mm, width: 2.6 mm; the coefficient            of elongation is of 0.63 (group 1) or the height is of 8 mm, the            width of 4.3 mm and the coefficient of elongation is 0.54 (group            2). The umbilicus is wide and open. The molluscs of group 2 have a            wider umbilicus than the molluscs of group 1. In general the            mollusc shells of these two groups differ in elongation, height of            spire and shape of the whorls and their relationship with the            suture. The shells belong to the family of the Hydromiidae and            probably belong to the Trichia genus            (Likharev and Rammelmeier, 1952, p. 450, fig. 377; Danilovskyi,            1955, p. 80, tabl. 3, fig. 57-58; Ložek, 1964, p. 300, tabl. 25,            fig. 1 a-c; Kerney and Cameron, 1999, p. 241, pl. 19).            Figure 8: Photos of Pupilla muscorum (L.) found in the Nantois            site, Brittany, France (Nantois Formation, late Middle            Pleistocene) / Photographies de Pupilla            muscorum (L.) observées dans le site de Nantois,            Bretagne, France (Formation de Nantois, Pléistocène moyen            terminal)                        1: IG no 183/3728/1,            section 1, depth 0-0.1 m; 2: IG no 183/3733/1,            section 1, depth 0.5-0.6 m; 3: IG no 183/3734/1, section 1, depth 0.6-0.7 m; 4: IG            no 183/3737/1, section 1, depth 0.9-1.0 m; 5:            IG no 183/3739/1, section 1, depth 1.1-1.2 m;            6: IG no 183/3741/1, section 1, depth 1.3-1.4            m; 7: IG no 183/3745/1, section 1, depth            1.7-1.8 m; 8: IG no 183/3753/1, section 1,            depth 2.5-2.6 m; 9: IG no 183/3754/1, section            1, depth 2.6-2.7 m; 10: IG no 183/3755/1,            section 1, depth 2.7-2.8 m; 11: IG no 183/3756/1, section 1, depth 2.8-2.9 m; 12: IG            no 183/3757/1, section 1, depth 2.9-3.0 m; a –            apertural view; b – abapertural view (view from the opposite side            of the aperture); c – lateral view (top right); IG no 183/3858/1: specimen number recorded in the            Institute of Geology USC RAS (Ufa) mollusc baseSe referer au texte anglais pour les            références            Figure 9: Photos of mollusc shells found in            the Nantois site, Brittany, France (Nantois Formation, late Middle            Pleistocene) / Photographies de coquilles de            mollusques trouvées dans le site de Nantois, Bretagne, France            (Formation de Nantois, Pléistocène moyen terminal)                        Pupilla muscorum            (L.) 1: IG no 183/3740/1, section 1, depth            1.2-1.3 m; 2: IG no 183/3740/2, section 1,            depth 1.2-1.3 m; 3: IG no 183/3740/3, section            1, depth 1.2-1.3 m; 4: IG no 183/3740/4,            section 1, depth 1.2-1.3 m; Cochlicopa            lubrica (Müll.): 5: IG no 183/3739/1,            section 1, depth 1.1-1.2 m; Succinella oblonga            (Drap.): 6: IG no 183/3757/2, section 1,            depth 2.9-3.0 m; Vertigo cf. alpestris Alder, 1838: 7: IG no 183/3740/1, section 1, depth 1.2-1.3 m; a –            apertural view; b – abapertural view (view from the opposite side            of the aperture); c: lateral view (top right)Se referer au texte anglais pour les            références            Figure 10: Photos of mollusc shells found            in the Nantois site, Brittany, France (Nantois Formation, late            Middle Pleistocene) / Photographies de coquilles            de mollusques trouvées dans le site de Nantois, Bretagne, France            (Formation de Nantois, Pléistocène moyen terminal)                        Hidromiidae (L.): 1: IG no 183/3741/1, section 1, depth 1.3-1.4 m; 2: IG            no 183/3756/1, section 1, depth 2.8-2.9 m; Vallonia pulchella (Müll.): 3: IG no 183/3754/1, section 1, depth 2.6-2.7 m;            Limacidae: 4: IG no 183/3728/1, section 1,            depth 0-0.1 m; 5: IG no 183/3728/2, section 1,            depth 0-0.1 m; 6: IG no 183/3740/5, section 1,            depth 1.2-1.3 m; a: apertural view; c: lateral view (top right);            d: umbilical view; e: apical view            Figure 11: Photos of Pupilla muscorum (L.) found in the Nantois            site, Brittany, France (Sable-d’Or-Les-Pins Formation, Upper            Pleistocene) / Photographies des Pupilla            muscorum (L.) observées dans le site de Nantois,            Bretagne, France (Formation de Sables-d’or-les-pins, Pléistocène            Supérieur)                        1: IG no 183/3858/1,            section 2, depth 0.8-0.9 m; 2: IG no 183/3859/1, section 2, depth 0.9-1.0 m; 3: IG            no 183/3860/1, section 2, depth 1.0-1.1 m; 4:            IG no 183/3861/1, section 2, depth 1.1-1.2 m;            5: IG no 183/3863/1, section 2, depth 1.3-1.4            m; 6: IG no 183/3865/1, section 2, depth            1.5-1.6 m; a: apertural view; b: abapertural view (view from the            opposite side of the aperture); c: lateral view (top right); IG            no 182/3858/1: specimen number recorded in the            mollusc base of the Institute of Geology USC RAS (Ufa)                                5. Discussion                  Sedimentological interpretation          The granulometric curves are characteristic of          loess sediments (as shown by the Md, Hq and Asq parameters), the          asymmetric sigmoid curve being steeper towards the coarse grains. In          general the Sable-d’Or-Les-Pins loess is slightly coarser than the          Nantois loess (Figures 6 and 7).          Sorting is not as good in the Nantois loess since          the symmetry of the distribution is slightly less pronounced.          Nantois loess appears also to be more heterogeneous than          Sable-d’Or-Les-Pins loess with higher median variations but with          smaller variation of the sorting index. In total the difference          between the two loesses can be summarized as follow:                      Nantois loess is relatively thin (mean of            the medians: 27 microns; minimum: 14.4 microns; maximum: 37.1            microns; standard deviation: 5.9). They are well sorted (Hq: 2.8;            minimum: 2.1; maximum: 3.2; standard deviation: 2.4). They are            carbonated and rework foraminiferous, coccoliths and fragments of            shells. The sandy fraction is made of a blending of blunted quartz            grains (coming from the beaches), of angular quartz grains and of            micas flakes probably coming from the rocky slopes. All the grains            are clay-coated. Clay is likely inherited from littoral or            lacustrine mud-banks. Ca rate in ppm: 32484; minimum: 5052;            maximum: 70223; standard deviation: 240105            Sable-d’Or-Les-Pins loess is relatively            coarse (mean of the medians: 37.2 microns; maximum: 48.7 microns;            minimum: 26; standard deviation: 5.1). Ca rate in ppm: 30963;            maximum: 57276; minimum: 3970; standard deviation:            21184.                                    Environmental considerations based on mollusc          study          The groups of molluscs were classified according          to their modern ecological preferences in air temperature, humidity,          and vegetation cover following the criteria proposed by Ložek          (1964), Likharev and Rammelmeier (1952), Sümegi (in Willis et al., 2000) and Puisségur (1976). After          analyzing the data and according to the authors experience          (Danukalova et al., 2013; Osipova et al., 2013), it has been possible to determine          five mollusc zones in Section 1 and three mollusc zones in Section          2.                      Nantois Formation (Table 2, Figure            6)                          Malacozone 1              This zone corresponds with layers 2, 3 and              the lower part of the layer 4 (interval 0-1 m) and with the              samples numbered from 1 to 10. Pupilla              muscorum is the dominant species, and is represented almost              in all the studied samples; its amount varies between 1 and 5.              The sample 1 is the richest sample in shells since it contains              46 shells. Limacidae (Limax sp.) are rare              and are only present in the sample 1. All the samples contain              numerous fine shell detritus. The landscape which prevailed              during the accumulation of these deposits corresponded with open              grassy habitats (tundra, cold meadows or littoral dunes).                                      Malacozone 2              This zone corresponds with the upper part of              the layer 4 (interval 1-1.4 m) and with the samples numbers 11              to 14. Pupilla muscorum is the dominant              species. There is a large number of shells of this species in              the middle part of this interval where a single shell of Cochlicopa lubrica, Vertigo cf. alpestris,              Limacidae and Hydromiida were also found. According to the              modern presence of mollusc as a function of climates this              species was living in mesophilous conditions. The classification              of those molluscs according to the present-day humidity rate              indicates that all these species are mesophilous and can live in              a normal or moderately wet environment. These species preferred              an open habitat with well-developed              vegetation. During the accumulation of those deposits, the              landscape corresponded with wet grassy open habitats probably              associated with bushes and trees.              Vertigo alpestris – indicates the              existence of cold climate conditions. But the Limacidae shells              show that the climate around Nantois site was not extremely              cold. The mollusc community (Limacidae, Pupilla muscorum, and              Cochlicopa lubrica) do not reflect the              existence of an extremely cold climate during accumulation of              these deposits, and the cooler global environment was only              recognized thanks to the presence of Vertigo alpestris.                                      Malacozone 3              This zone corresponds with the uppermost part              of the layer 4, the layers 5 and 6 (interval 1.4-2.4 m) and with              the samples numbered between 15 and 24.              Pupilla muscorum is the only species present. Complete              shells were found mainly in the middle part of this zone. All              the samples contain many fine shell detritus. The landscape              which prevailed during the accumulation of these deposits may              have corresponded with open grassy habitats (tundra, cold              meadows or littoral dunes).                                      Malacozone 4              This zone corresponds to the layers 7 and 8              and most of the lower part of layer 9 (interval 2.4-3 m) and              with the samples numbered between 25 and 30. Pupilla muscorum stays the dominant species,              its abundance increases in the middle part of this zone. Vallonia pulchella, Hydromiida, Limacidae and              Succinella oblonga are present. According              to the modern mollusc climatic distribution and to the              present-day humidity rate all these species preferred from              slightly cool to “warm” and wet environments. The landscape,              which prevailed during the accumulation of these deposits,              corresponded with open habitats rich in vegetation cover.                                      Malacozone 5              This zone corresponds with the layers 9 and              10 (interval 3-4.9 m) and with samples numbered between 31 and              49. This zone contains very rare shell detritus in its lower              part. The landscape, which probably prevailed during the              accumulation of these deposits, corresponded with open              habitats.              The presence of numerous fine shell detritus              may result from strong winds blowing towards the cliff. The              presence of some juvenile shells of marine gastropods observed              in those samples supports this idea.                                            Sable d’Or les Pins Formation (Table 3,            Figure 7)                          Malacozone 1              This zone corresponds with the layer 1              (interval 0-0.6 m) and with the samples numbered between 1 and              6. The only shell of Pupilla sp. and the              shells of marine gastropods were found in this zone. All the              samples contain numerous shell detritus. The size of the              detritus of all the deposits of Sable-d’Or-les-Pins Formation is              coarser than the size of the detritus found in the Nantois              Formation.                                      Malacozone 2              This zone corresponds with the uppermost part              of layer 1, with layer 2 and with the lower half of layer 3              (interval 0.6-1.9 m) and with samples numbered between 7 and 19.              Pupilla muscorum is the only abundant              species found in the middle part of this zone. All the samples              contain numerous shell detritus. According to the modern mollusc              climatic distribution and the present-day humidity rate all              these species preferred cold and dry or slightly wet open              habitat. The landscape which prevailed during the accumulation              of these deposits corresponded with open grassy habitats              (tundra, cold meadows or littoral dunes).                                      Malacozone 3              This zone corresponds with the upper half of              the layer 3 and with the layer 4 (interval 1.9-3 m) and with              samples numbered between 20 and 30. This zone has no complete              mollusc shells and contains only rare detritus at the base of              this interval.                                                Integration of the malacological, chemical          and physical data collected in the studied sites          The integration of the malacological observations          with the chemical and physical characteristics of the Nantois and          Sable-d’Or-Les-Pins loess of Nantois site provide interesting          information and correlations.                      Nantois (late Middle Pleistocene)            correlations (Figure 6)            Before to start any correlation between the            various analysis made on the loess we must underline that the            physical and chemical analysis we obtained are restricted to the            zones where loess and loam were not mixed with fragments of rocks            or boulders, the two types of sediments being deposited in            different conditions.            The correlations between different data suggest            the following comments:                          a/ The zone of decalcification almost              perfectly fits with the zone where the mollusc shells are absent              (or with very rare shell detritus) (f arrows, Figure 6). This              decalcification has been explained by the existence of an              overlying soil. The dramatic change of the values corresponds              with the lower front of alteration of the pedological              profile.              b/ The abrupt increase in clay              contribution is concentrated in five zones located in the upper              part of the sections (a, b, c, d, e alignment of arrows of              Figure 6). There is no such a rapid increase in the middle part              of the profile. Since we know that the very thin loess particles              only deposited when the strong North blowing wind was weakening              (Lefort et al., 2013b), we suggest that              this phenomenon may corresponds with a small warming episode.              This progressive warming can be better appreciated when we              notice that the contribution of clays is increasing towards the              top of the sections. Unfortunately, we cannot check this              interpretation with fauna since there is no more gastropods              shells at this level.              c/ The decreasing granulometry front of              these abrupt clay contributions is a logical              correlation.              d/ The progressive and larger clay              contribution in the lowermost part of the clay sections may              suggests the same interpretation.              e/ The very large and isolated              contribution in terrestrial molluscs in the middle of malacozone              2 perfectly fits with the abrupt increase in calcium (g arrows              of Figure 6). This observation may suggest that the high calcium              values observed in the lower part of the section is associated              with the accumulation of dead shells. However, when we compare              the amplitude of this maximum with the calcium values reported              in the middle part of the section where shells are very few, we              must conclude that the calcium contribution is mainly associated              with the calcareous dust contained in the loess and that only a              small part of it is associated with the dead shells. This very              high value is also clearly the result of the downward migration              of the calcium, which precipitated at this level as shown by the              many calcareous concretions observed at this depth.                                            Sable-d’Or-Les-Pins (late Late Pleistocene)            correlations (Figure 7)            Some of the correlations made for the Nantois            loess are also present on the Late Pleistocene data:                          a/ Here again, the zone of              decalcification almost perfectly fits with the zone where the              mollusc shells are absent (h arrows, Figure 7). This              decalcification has been explained by the presence of a younger              overlying soil. The abrupt change in the calcium values              corresponds with the lower front of alteration of the paleosoil              profile. This depth which is reaching 1.25 m is the same for the              Middle and Late Pleistocene loess.              b/ The contribution of the clay              particles is getting larger for all the sizes of particles              towards the top of the analyzed loess. But the larger              contribution of the smallest particles (0.2 microns) (i arrow,              Figure 7) is closer to the top of the sections which suggests a              weakening of the winds and thus the beginning of a warming              episode (see explanation given for the Nantois loess). It is              interesting to observe that the deposition of the coarser clays              occurred earlier in the stratigraphic column which supports the              weakening wind explanation.              c/ On the contrary, the low              concentrations in clay observed below (mainly expressed by the              0.2 micron clay – j arrows, Figure 7) suggests stronger winds              and thus a slightly cooler period.              d/ The maximum calcium concentration              just fall front of the maximum concentration of shells. But here              again this maximum is more likely related with a downward              migration of calcium than to the enrichment in shells, this is              supported by the very few shells found at this level.              e/ The lower concentration in calcium              observe below (l arrows, Figure 7) fits with a coarser              granulometric level and thus with the presence of a higher              amount of non-calcareous sand grains.                                                Rapid comparison with other loess deposits          known in a few adjacent areas                      Southern England            In southern England the Late Pleistocene (Late            Devensian, MIS 2) loess is widespread and may reach maximum            thicknesses of about 4 m. So far as the age is concerned and just            to give two well studied examples: at Pegwell Bay site (East Kent)            and Skipsea Till site (Yorkshire) loess have been dated between            18.8 and 14.6 Ka by TL methods (Madgett and Catt, 1978; Wintle,            1981; Parks and Rendell, 1992; Bateman, 1998; Antoine et al., 2003).            In this area the loess deposits attributed to            the MIS 6 stage are thin and discontinuous and represent the            remnants of an originally more extensive covers (Parks and            Rendell, 1992; Antoine et al., 2003).                                Northern and Northeastern France            In northern and northeastern France Late            Pleistocene loess is widespread and reaches up to 12 m in            thickness. The typical calcareous loess known in this region is            attributed to the Late Weichselian and dated between 15 and 25 ka            (Antoine et al., 2003). The molluscs            characteristic of the Late Pleistocene cold climates are known in            several sites in Brittany, Normandy and the Channel Islands (Keen,            1982, 1986 a and b; Keen et al., 1997;            Danukalova et al., 2013). The malacofauna            is usually poor and includes the species Pupilla            muscorum, Trichia hispida, Succinella            oblonga, and Columella columella. A            list of the sites where the Weichselian deposits contain mollusc            fauna can be found in Moine (2008).            The loess of the late Middle Pleistocene of            northern and northeastern France is usually restricted to fluvial            and marine terraces exposed to the east and northeast. This loess            is represented by more sandy facies originating in local fluvial            beds (Sommé, 1980; Lautridou, 1985; Antoine, 1990; Lebret and            Lautridou, 1991; Antoine et al., 2003).            Middle Pleistocene loess is known at St-Pierre-les-Elbeuf,            Garenne, Mautort, Grâce and some other sites in Normandy and in            the Somme River basin (Lautridou and Puissegur, 1977; Haesaerts            and Dupuis, 1986; Balescu, 1988; Antoine, 1994; Antoine et al., 1998, 2000, 2003).            Closer to the site we studied, Monnier (1973,            1974) found very small remnants of late Middle Pleistocene loess            equivalent to the upper part of the Nantois Formation, in the            Saint Brieuc Bay (Northern Brittany – France). They are known in            the sites of Piégu and Les Vallées and were studied for malacology            by Keen et al. (1997), there the fauna is            dominated by P. muscorum.                                6. Conclusion        Study of the physical, chemical and environmental        parameters of Nantois loess shows that the Middle and Late Pleistocene        loesses were deposited in different conditions even if they display a        few common characteristics.        The upper part of the Middle and Late Pleistocene        loess are both characterized by the complete absence of molluscs. This        can be explained by the influence of the soils which covered both        loess and reworked their upper layers. They also evidence the presence        of thin clay deposits just before the head formation corresponding        with a weakening of the cold winds coming from the North and thus the        beginning of a warming episode. At last, they both show on top the        existence of gley horizons which suggests the presence of open        habitats (tundra?) with cold grassy vegetation.        The older loess (Nantois Formation) which is about        5 meters thick is well sorted and partly made of silty carbonates        which explain many carbonate concretions found in some levels. The        quartz of the silty part is made of a mixture angular grains + micas        probably coming from the hill slope and of smoothed grains coming from        the neighboring beach. A thin clay deposit that may come from the        littoral marshes covers all the grains. The top of the formation is        affected by a head (warming) showing that solifluxion restarted. The        beginning of the warming episode, starting before the top of the        loess, is shown by the deposition of very thin clay particles related        with the weakening of the winds. This formation ends by an illuvial        pedogenesis called the “double stripped loam”. There is no clear        evidence of any pergelisoil. This loess is reworking foraminiferous or        coccoliths coming from the chalk of the English Channel and shells and        pieces of shells. This older loess is characterized by a rather large        variety of mollusc species. The analysis of the mollusc distribution        indicates for the first time three moderate climatic phases during the        sedimentation.        The new loess (Late Pleistocene) is about 3 meters        thick. It is made of silty layers ending by homogeneous carbonated        loess. It is well sorted but coarser than the Upper Saalian loess. It        also incorporates foraminiferous and pieces of mollusc shells but with        a much smaller amount of species. At the end of the deposit, there are        more and more micas and pieces of organic matter with traces of leaves        and cryptogam crusts suggesting the end of an arctic climate. The rare        molluscs indicate severe climatic conditions during the deposit of the        loess particles. The pockets of thin sand terminating the formation a        little bit out of the sections (thermokarst) are no more carbonated.        They are typically eolian and contain heavy minerals (mainly        hornblend+epidote+garnet) identical to the heavy mineral sampled in        the central part of the English Channel. This formation is affected by        a small soil of hygromorph tundra. The main characteristic of this        section is the clear existence of well expressed permafrost.        Since we know that the winds transporting the loess        particles were coming from the North or the Northwest in Brittany        (Bigot, 1986; Lefort et al., 2013b), the        initial purpose of this study was to compare the various        characteristics of the two loess which constitute the Nantois cliff        and to check if their respective evolutions were controlled by a        different distance between Nantois and the maximum extension of the        Saalian and Weichselian British ice sheets (Ehlers et al., 2011, Figure 12). After our study it is        unlikely that the differences observed in the grain size, mollusc        faunas and climatic environments were related with the small        difference in latitude of the boundaries of these icesheets. This        limited difference in latitude cannot explain why a well expressed        permafrost (Loyer et al., 1995) developed in        the Weichselian and a very poorly expressed equivalent in the        Saalian.        Figure 12: Regional map showing the location of        the Nantois site respect with the southern limit of the Saalian and        Weichselian British ice sheets. The arrows show the wind direction.        Black: main reliefs known in Brittany and Normandy; grey: submerged        braided rivers of the English Сhannel; stipples: loess deposits        (partly after Ehlers et al., 2011) / Carte régionale montrant la localisation du site de        Nantois par rapport aux limites saaliennes et weichseliennes de la        calotte glaciaire britannique                Comparisons between two equivalent loess have been        already made in the Paris Basin (Locht et al.,        2003; Limondin-Lozouet and Gauthier, 2003). The dry and sever climatic        condition they observed in the Saalian and the variable but partly        warmer conditions they found during the Weichselien differ from our        observations. This maybe due to local conditions but also to the fact        that we were not able to study the continuous malacologic evolution of        the deposits in some parts of the Nantois sections because they were        completely decalcified.        It is not sure that the results of the QUEEN        Project (Colleoni, 2009) which suggest that the Eurasian ice-sheet was        substantially larger during the Late Saalian period (160-130 ka) than        during the entire Weichselian cycle (and especially during the Last        Glacial Maximum around 25-21 Ka) can be applied to Nantois region. At        a small scale, the discrepancy in the evolution of these two        ice-sheets has been correlated with the fact that the Late Saalian ice        sheet was extending more to the South and was consequently more        sensitive to the successive ice ablations. On the contrary, the LGM        Eurasian ice-sheet had a limited southward extent and was consequently        less sensitive to the changes occurring over Central Eurasia        (Colleoni, 2009). However, if we take account of the distances of        these two fronts respect with the studied area it is doubtful that the        differences observed between the Late Weichselian and the Saalian of        Nantois were directly controlled by the general behavior of these two        ice sheets.        The main difference which characterizes the old and        the new loess of the Nantois cliff is the presence of three warming        episodes during the Upper Saalian and the existence of a well        expressed permafrost during the Weichselian. This apparent discrepancy        is in fact artificial since the time spanning during the Upper Saalian        and Upper Weischelian loess deposition is very different. Upper        Saalian loess deposited during about 60 Ka while the Upper Weischelian        loess deposited only during 7 ka. If we accept the concept of        sub-Milankovitch cycles observed or calculated by different authors        (Berger, 1977; Gupta, 2009) showing that we cannot have any climatic        change during a period shorter than 11Ka, we better understand why no        warming evidences can be found during the studied Upper Weischelian.        Comparison between the maximum shell production during the Upper        Weischelian (13 individuals/2,5 kg of sediment, figure 7) and the        maximum shell production during the Upper Saalian (150 individuals/        for 2,5 kg of sediment, figure 6) support this interpretation.