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-

  • 7 2 E. Grfiger

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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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    FIG. 5. Simplified and slightly modified pollen diagram of the Brorup interstadial phase at Oerel (from Behre and Lade, 1986).

  • 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 ar...

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