Palynostratigraphy of the last interglacial/glacial cycle in Germany

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  • Quaternary International, Vols 3/4, pp. 69-79, 1989. 1040-6182/89 $0.00 + .50 Printed in Great Britain. All rights reserved. O 1990 INQUA/Pergamon Press plc

    P A L Y N O S T R A T I G R A P H Y O F T H E L A S T I N T E R G L A C I A L / G L A C I A L C Y C L E IN G E R M A N Y

    Eberhard Grfiger Universitiit GOttingen, Institut fiir Palynologie und Quartiirwissenschaften, Wilhelm Weber-Strafle 2,

    D-3400 GOttingen, F.R. G.

    The last interglacial/glacial cycle comprises the Eemian and the Weichselian (in the area of the Scandinavian Glaciation), respectively the Riss/Wtirm and the Wiirm (in southern Germany). Drastic changes of the vegetation have occurred several times during this period in Europe. The best known in Germany is the development of the forests of the last interglacial stage and of the two succeeding early-glacial interstadial phases, the Br~rup and the Odderade. Above the Odderade, sediments of two more (Middle Weichselian) interstadials, the Oerel and the Glinde, with a shrub-tundra vegetation have been found at one site in northern Germany. In southern Germany the palynological record ends somewhat earlier, i.e. with the equivalent of the Oerel interstadial, which here in the south had a forest vegetation. Numerous single occurrences of interstadial sediments of different age and vegetation have been studied, but unfortunately their stratigraphic position is most frequently unclear. Therefore a general survey can only rely on few, but long sequences. Their comparison shows that vegetational gradients of different steepness existed at different times, which mirror the changing climatic gradients of this period. The main points of the vegetational zonation as far as it is known from Germany for the cycle are summarized.

    INTRODUCTION

    The lectures presented at the symposium on 'The last interglacial-glacial cycle' (StrafAburg, 20-21.3.1989) have distinctly shown that this part of the Pleistocene was a period of repeated climatic, and consequently also vegetational changes. Sections of it have been studied at many places, but very often correlation and even relative dating remained uncertain. Reference sites with complete or at least long sequences and knowledge of large-scale vegetational gradients can help to overcome these difficulties.

    In Germany four or five profiles with long Upper Pleistocene sequences exist which have been studied by pollen analysis, but none of them covers the complete last interglacial/glacial cycle (Fig. 1). The most com- plete sequence is that of Oerel in Lower Saxony (Behre, 1989; Behre and Lade, 1986). It begins with Eemian sediments, contains four interstadial succes- sions, and ends during Middle Weichselian time. Other sites with long sequences are Rederstall and Odderade in Schleswig-Holstein (Menke and Tynni, 1984; Aver- dieck, 1967), Kittlitz in the German Democratic Republic (Erd, 1973), and Samerberg in Bavaria (Griiger, 1979a, b). At these sites only the oldest two or three interstadials have been found above the Eemian. There are no palynologically reliable records of the younger half of the Upper Weichselian until the beginning of the so-called late-glacial period, which is well documented at comparatively numerous sites.

    In the following, the vegetational development of the different forest phases of the last interglacial/glacial cycle in northern and southern Germany will be compared. It will be found that - - as an expression of steeper climatic gradients - - the vegetational zonation was different during the different interstadial phases, a

    fact which should be considered if correlation and datation of new, but incomplete sections is being tried.

    THE VEGETATIONAL DEVELOPMENT OF THE LAST INTERGLACIAL/GLACIAL CYCLE IN

    SOUTHERN GERMANY

    The Riss/W~irm Interglacial Stage The key-site, Samerberg/Bavaria, is situated at 600 m

    a.s.l, on the northern edge of the Alps. Its pollen record (Fig. 2) starts in Riss late-glacial sediments (Griiger, 1979a, b). The first forests of the Riss/Wiirm interglacial period were formed by Betula and Pinus. Deciduous species (e.g. Quercus, Ulmus) then spread, among them - - late appearing - - Corylus. The montane character of the vegetation at Samerberg is clearly expressed by the high pollen values which Picea gained from the very beginning after its early immigra- tion into the area. Following a period with a very pronounced peak of the Taxus curve, Abies and somewhat later Carpinus spread. At the end of the interglacial all these tree species vanished and Pinus again occupied the area.

    At less elevated sites such as Zeifen (427 m, Jung et al., 1972) the montane species Picea and Abies are much less represented, but deciduous tree species, above all Carpinus, dominated throughout.

    The Early (=Lower) and Middle Wiirm Glacial Substages

    The Samerberg profile continues with a stadial phase (Fig. 2, zone 13), which marks the start of the WOrm glacial period (Chaline and Jerz, 1984). (The site is the type locality for the beginning of the Wtirm glacial period.) No forests existed in the area during this stadial phase (zone 13) until reforestation started with

    69

  • 70 E. Griiger

    FIG. 1. Sites with sediments of the last interglacial/glacial cycle (modified from Behre, 1989).

    the appearance of Juniperus and Betula during the first Early Wiirm interstadial phase. Later Pinus and Picea spread. Abies and deciduous species were unimportant, if present at all.

    Of special interest is the course of the Picea curve. Picea started to spread, but before it reached maximal values it was displaced again by Pinus (zone 17) and only sometime later could it finally spread.

    This Picea decline can only have been caused by a climatic deterioration. This climatic event can be recognized at other places, too. For ecological reasons one finds it usually better revealed at places close to the boundary of the area of distribution of the reacting species and less well recognizable towards its center. This climatic deterioration is characteristic of the first interstadial which follows the Eemian, i.e. the Brorup interstadial phase.

    Further up in the profile (Fig. 3) two more inter- stadials follow, which are separated by treeless stadiai periods. Both interstadials had a simple vegetational development leading to Picea forests only at Samer- berg.

    The interstadial following the Br0rup is the equiva- lent of the Odderade interstadial, the youngest one can be compared with the Dfirnten interstadial as described by Welten (1981) in Switzerland or Glinde in Northern Germany (Behre and Lade, 1986).

    The Middle Wiirm starts with the stadial following the Odderade interstadial (zone 26). Its beginning has been defined by the Subcommission on European Quaternary Stratigraphy of INQUA at the type locality Samerberg (Chaline and Jerz, 1984).

    Summarizing, at Samerberg a series of three inter- stadials follows the Eemian; the first of them, the BrOrup interstadial, comprises a period of climatic deterioration.

    THE VEGETATIONAL DEVELOPMENT OF THE LAST INTERGLACIAL/GLACIAL CYCLE IN

    NORTHERN GERMANY

    The Eemian Interglacial Stage The development of the vegetation during the last

    interglacial period, the Eemian, was basically the same

  • Palynostratigraphy in Germany

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    7 1

    as in the south The same species formed the forests and even the sequence of spreading was on the whole the same. Pollen diagrams of profiles in northern Germany (Fig. 4; for sites see: Menke and Tynni, 1984) show the fol lowing development: First, pioneers such as Juniperus, Betula and Pinus spread. They were fol lowed by deciduous tree genera such as Ulmus,

    Quercus, Fraxinus and others As in the south, Corylus spread late compared with its behaviour during the Postglacial. Taxus was an important constituent of the forests somet ime before the shade-tolerating Carpinus spread and started to dominate the Late-Eemian forests Picea and Abies immigrated very late. Their pollen is found in quantities, which prove their pre-

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    sence in the north. (Both genera did not reach northernmost Germany during the Postglacial. The area of distribution of Picea ended at the northern edge of the Central German Uplands and Abies stayed even further in the south. In contrast to the Postglacial, Fagus did not occur either in the south or in the north of Germany during the last interglacial period.)

    Menke (1980, 1984) pointed out that pollen of

    Hedera and llex was rather common from about the time of the spreading of Corylus to the end of the Carpinus phase. Also, some pollen of Viscum has been found. During Postglacial times Viscum reached as high values as during the Eemian, but the percentages of Hedera and llex were much higher during the Eemian than in Postglacial times. Since Iversen's classical studies (1944) the thermal requirements of Hedera and

  • Palynostratigraphy in Germany 73

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    llex in Denmark are known, and thus the characteristic differences indicate that winters were milder during the Eemian. Summers were probably as warm as during the Postglacial. Botanical evidence regarding the moisture conditions is deficient if not lacking, but sedimento- logical and pedological observations indicate that the climate was rather more humid than dry during the Eemian.

    The Eemian interglacial stage lasted approximately 11 ka (MOiler, 1974). This value is based on counts of annual laminations and on estimations of the duration of sedimentation in the unlaminated upper part of the profile. It corresponds well with datas of the Eemian deep-sea equivalent, Substage 5e, which according to a commonly used time-scale lasted from 127 to about 115 ka BP (Woillard and Mook, 1982, and others).

    The Early Weichselian Substage The vegetation of the different stadial periods of the

    Weichselian glacial period was open and treeless, though tree pollen values are sometimes fairly high in stadial samples due to reworked older material, espe-

    cially if lake sediments are studied. Thus it can be difficult to decide where to draw the interglacial/glacial or interstadial/stadial boundaries in a pollen diagram. In such a case the beginning of curves of heliophytes such as Artemisia, Plantago, Armeria and of other species, which grow on mineral soils only, and a general rise of the number of nonarboreal pollen types are helpful indicators.

    The end of a stadial phase is indicated when tree species, generally Betula, immigrate and spread causing the upland heliophytes to disappear; climate might, however, have changed earlier. It must be added that it is not possible to distinguish the different stadial phases by their flora.

    The (concerning the interstadial phases) most com- plete Weichselian profile in Germany is that of Oerel (Behre, 1989; Behre and Lade, 1986). Here, four layers of lacustrine and telmatic sediments separated by more or less thick stadial sand layers have been found above the Eemian peats.

    The two Early Weichselian interstadial phases, the Brorup and the Odderade, are characterized by forest

  • 74 E. Griiger

    vegetation. Reforestation started with the spreading of tree-birches during the Br0rup (Fig. 5). After an apparently long period of Betula dominance, Larix and Picea reached the area and later Pinus spread and became the dominant tree species.

    Larix pollen is usually not well represented in the pollen spectra, but locally it reached extraordinarily high values (17.8% in Osterwanna, W of Hamburg; Behre, 1974; 18% in Keller, N of Hamburg; Menke, 1970, 1975). Numerous needles and other remains of Larix found at Osterwanna (Br0rup; Behre, 1974)

    indicate at least the local importance of this tree species, which is considered to be heavily underrepre- sented in the pollen rain.

    Picea pollen values differ at the different localities, but finds of needles prove the presence of this genus in northern Germany during the BrOrup. Needles of the two species Picea abies and Picea omorica have been known from several places since the beginning of this century (Mtiller and Weber, 1904; Behre, 1974). Picea omorica is found today in the Drina valley in Serbia only. A determination of its pollen in fossil material is

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  • Palynostratigraphy in Germany 75

    doubtful and leads to minimum values at the best. Thermophilous deciduous woody species such as

    Quercus, Ulmus, Corylus, Carpinus and others were missing in northern Germany throughout all of the Weichselian period. Continuous, though minor repre- sentation of their pollen in the peats of Oerel (Behre and Lade, 1986) and Odderade (Averdieck, 1967) makes their presence probable somewhere in the south, yet north of the Alps (Behre, 1974). The same would apply to the Odderade interstadial, whereas the occurr- ence of such species north of the Alps during the Middle and Upper Weichselian interstadial phases can be excluded.

    The Br~rup interstadial phase comprises a period of climatic deterioration, which allowed (for example) Juniperus and Artemisia and other heliophytes to spread again into the former Betula forests around Rederstall in the north (WFIIa2; Menke and Tynni, 1984). This is less recognizable in pollen diagrams from sites in the centre of the area of distribution of Betula (or any other reacting species), as here the changing climatic conditions could not that easily have fallen short of the ecologically effective boundary values as close to the limits of distribution of the species. In the pollen diagram from the more southern site Oerel, it is indicated by a weak decline of the Betula curve and somewhat higher Juniperus values only.

    In the Netherlands the climatic deterioration of the Br~rup interstadial phase caused a change of sedimen- tation, which gave reason to consider the two climati- cally more favourable parts before and after it as separate interstadials, called Amersfoort and Br~rup (Zagwijn, 1961). At Oerel the end of the Br~rup interstadial phase is not recorded, but at other sites its end is indicated by a gradual change to open treeless conditions.

    The Odderade interstadial development of the forests was simple (Fig. 6). Reforestation started as usual with the spread of tree-birches. Then Pinus immigrated and became the dominant tree species. Later Picea and Larix approached the area, Larix (at Oerel) apparently later than Picea. Thermophilous deciduous species were absent.

    A special feature of the Br~rup and the Odderade interstadials and of the intervening stadial phase is the occurrence of pollen of the Bruckenthalia pollen type. Br~rup-time sediments contain seeds of Bruckenthalia spiculiflora (Salisb.) Reichb. (Behre, 1974), which at present occurs only on peat bogs and other sites with acid soils in the montane zone of the Balkans and the Carpathians.

    Considering the similarity of their pollen floras it appears to be difficult to distinguish the Br~rup and the Odderade interstadial phases by their vegetational development. Behre and Lade (1986) emphasize the following differences:

    - - The Betula phase of the Br~rup lasted longer than that of the Odderade interstadial phase.

    - - The Betula phase was the time of spreading of (first) Larix and (later) Picea during Br~rup times.

    - - Spreading time and spreading sequence were dif- ferent during the Odderade: Larix spread later than Picea, and both spread during the Pinus phase. - - Much higher Alnus values are recorded for the Br0rup than for the Odderade.

    The opinions concerning the general character of the Br0rup- and Odderade-time climates, especially the degree of continentality, diverge. Behre (1974) assumes cold winters as the interstadial forests did not contain so-called thermophilous species and warm summers as remains of warmth demanding aquatic plant species have been found. Menke (1975) claims that the recorded climatic indicators - - mainly water plants - - prove relatively mild winters. He argues that the short duration of the growing season did not allow deciduous tree species to live in the area as they need summers long enough to accumulate sufficient amounts of carbohydrates for dissimilation during the long mild winters and for the yearly formation of new foliage. Estimates allow a July mean temperature of 13-15C (Andersen, 1961) or even more (Behre, 1974).

    The Early (=Lower) Weichselian ends with the Odderade interstadial phase. The following stadial phase, the Schalkholz stadial of Menke and Tynni (1984) marks the beginning of the Middle Weichselian substage. This corresponds with the subdivision, which was recommended by the INQUA subcommission of European Quaternary stratigraphy for the region of the alpine WOrm glaciation.

    The Middle Weichselian Substage Pollen-bearing sediments of Middle Weichselian age

    are rare in northern Germany. At Oerel sands of this age are found above the Eemian and the Early Weichselian layers (Behre and Lade, 1986). These sands are free of autochthonous organic remains, a fact which is interpreted as reflecting a more or less total absence of vegetation during the time of sand deposi- tion. Intercalated into these sands two layers of peat and gyttja have been found, which contain the pollen flora of a shrub-tundra. These sediments must have been deposited during periods with more favourable climatic conditions, i.e. during interstadial phases. The older one is the Oerel, the younger the Glinde interstadial phase.

    The Oerel interstadial pollen spectra (Fig. 7) indicate an open vegetation without trees. Leaves, fruits and fruitscales of Betula nana occurring in the sediments suggest that dwarf birches produced the Betula pollen, which has been recorded. Salix was probably also represented by shrubby species. Another shrub species, Juniperus, spread later as its pollen curve rises to almost 10% in the upper part of the pollen diagram only. Dominating pollen types were first Poaceae and Cyperaceae, later Ericales, among them Empetrum nigrum, Arctostaphylos uva-ursi (seeds) and Calluna. Numerous nonarboreal pollen types of additional wetland and upland species are listed in the pollen diagram. Thus one must conclude that the site of Oerel was surrounded by a shrub-tundra during the time of

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  • Palynostratigraphy in Germany 77

    the Oerel interstadial phase. The site was a fen first, which later developed into a raised bog.

    The sediment of the Giinde interstadial phase is a sedge-peat, which is covered by a fine-detritus gyttja and sandy silt with humic layers, totalling only 30 cm thick (Fig. 7). Again a shrub-tundra with Betula nana and Salix is indicated by the plant remains. This shrub- tundra must have been of a more open type than that of the Oerel interstadial phase as upland heliophytes (Helianthemum, Armeria, Campanulaceae, Plantago, Selaginella selaginoides and others) are much better represented than previously. Juniperus was missing and Ericales (except Empetrum nigrum) unimportant. Tree pollen values - - low in samples of the preceding interstadial phase - - are less during the Glinde interstadial phase as the source areas for long-distance transported pollen were probably farther away during

    the Glinde than during the Oerel interstadial phases. Behre and Lade (1986) place the Oerel and the

    Glinde interstadials between the Odderade and the Moershoofd phases. Concerning the correlation of the Oerel interstadial phase they argue that the vegetation around Oerel consisted of much more Ericales and other shrubs and less heliophytes than that around the Dutch Middle Weichselian sites (e.g. Kolstrup and Wijmstra, 1977; Zagwijn, 1974). The opposite would be expected for a vegetation of the same age. Further, the climate permitted the growth of a raised bog near Oerel, but not in the Netherlands, where for that reason the climate seems to have been more continen- tal than farther to the east.

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  • 78 E. GrOger

    the Moershoofd interstadial phase. They argue that the degree of soil acidity, which due to cryoturbation, solifluction and other mixing or sedimentary processes decreased during pleniglacial times and which is corre- lated to also decreasing Ericales values, can be used to establish a relative chronology. The comparatively high Empetrum values at Oerel would then allow to place the Glinde before the Moershoofd interstadial phase.

    The Upper Weichselian Substage The Upper Wiirm as defined in the area of the alpine

    glaciation (Chaline and Jerz, 1984) started with the deposition of glacial advance gravels ('VorstoBschot- ter') about 25 ka BP and ended at 10 ka BP with the beginning of the Holocene. Though not yet formally defined, the Upper Weichselian will cover about the same span of time. Thus it includes the classical 'Late Glacial', during which reforestation began anew in Middle Europe. The most demanding forests of this period were those of the AllerOd time. They were formed by Betula and Pinus. The climatic deterioration of the Younger Dryas time let Pinus disappear from northern Germany, but not from the south. The further development of the forests is beyond the scope of this review as it is of Holocene age.

    CONCLUSIONS

    The vegetation of the last interglacial/glacial cycle was not always the same in the north of Germany as in the south. Vegetational gradients of different steepness existed during the different periods. Especially, the interstadial vegetation was different, and the differ-

    ences increased from one interstadial to the following one. The steepest vegetational gradient known hitherto from this period in Middle Europe - - with Picea forests in the foreland of the Alps and shrub tundra in northern Germany - - is that of the Oerel interstadial phase. No or only little floristic differences seem to have existed during the last interglacial period, though there are some in the present interglacial, the Post- glacial. Table 1 summarizes the findings. The vegeta- tional differences mirror climatic gradients if periods long enough to permit the immigration of suitable species are considered. Knowledge of such gradients is necessary when trying to date interstadial floras of unknown age.

    This sketch of changing vegetational zonations can be extended regardless of the type of vegetation to more remote areas. Long-distance correlation of se- quences from Germany with profiles of far distant sites is possible thanks to the distinct climatic development during the last interglacial/glacial cycle, which is characterized by the sequence of one interglacial, one bipartite interstadial and further 'simple' interstadials. The same climatic pattern is known from sites in Poland (Zgierz-Rudunki: Jastrzebska-Mamelka, 1985), Austria (Mondsee: Klaus, 1987), Switzerland (Sulz- berg, Dtirnten: Welten, 1981, 1982; Gondiswil: Weg- miiller, 1986), northeastern France (Grande Pile: Woillard, 1975, 1978), southern France (Les Echets: de Beaulieu and Reille, 1984), southern Spain (Padui: Florschiitz et al., 1971), central Italy (Castiglione: Follieri et al., 1986) and northern Greece (Tenaghi Philippon: Wijmstra, 1969). Besides proving the simul- taneousness of the different periods in these regions

    TABLE 1. Upper Quaternary Vegetational Gradients

    Northern Germany Southern Germany

    Postglacial Fagus Fagus (Abies, Picea) Flandrian

    10 ka BP

    Upper Weichselian

    25 ka BP

    Middle Weichselian

    73 ka BP

    L o w e r

    Weichselian

    115 ka BP

    Eemian

    127 ka BP

    Weichsel B. etula ( Pinus ) Pinus, Betula late-glacial

    (Denekamp) NAP (Hengelo) NAP (Moershoofd) NAP

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    Glinde ( Ericales ) Betula nana

    Ebersdorf Oerel Ericales, B. nana, Juniperus Picea ( Pinus)

    Schalkholz NAP

    Odderade Rederstall

    Pinus ( Picea) Picea (Pinus) NAP NAP

    t Pinus, Betula (Picea) Picea (Pinus) Br6rup IIa2 ~ Betula, Juniperus, Artemisia Pinus

    { Betula Pinus, Picea Herning NAP NAP

    Eem Quercus . . Corylus . . Taxus . . Carpinus . . Picea . . Abies

    10 ka BP

    Upper WOrm

    25 ka BP

    Middle WOrm

    73 ka BP

    Lower WOrm

    115 ka BP

    Riss/WOrm

    127 ka BP

  • Palynostratigraphy in Germany 79

    this typ ica l c l ima t i c d e v e l o p m e n t a l lows t h e f o r m e r

    v e g e t a t i o n a l a n d c l ima t i c g r a d i e n t s to be e s t i m a t e d ,

    w h i c h s h o u l d be c o n s i d e r e d w h e n a c o r r e l a t i o n o f n e w

    s e q u e n c e s is b e i n g t r i ed . A n e w l y f o u n d fossi l f l o r a

    m u s t fit i n t o t he o v e r a l l p i c t u r e o f t h e v e g e t a t i o n a l

    z o n a t i o n o f t ha t p a r t i c u l a r p e r i o d . I f it d o e s n o t , its

    d a t i n g is m o s t l ike ly w r o n g .

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