End of the last interglacial in the loess record

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  • QUATERNARY RESEARCH 2, 374-383 (1972)

    End of the Last Interglacial in the Loess Record 1

    GEORGE J. KUKLA ' AND ALOIS KoCf 3

    Received July 15, 1972

    In the loess series of Central Europe the last interglacial is recorded by the para- brownearth soil accompanied by land snails and pollen of thermophilous deciduous forests. The termination of forest environment is marked by restricted eolian sedi- mentation and development of chernozemic steppe soil, followed in turn by rapid depo- sition of calcareous air-borne silt in the so called Marker horizon. Hillwash loams and loess interrupted by the weak rendzina-type soil Blf were then formed. The sequence is overlain by the interstadial soil complex which is correlated with the Barbados II Terrace because of its stratigraphic position and warmth-loving snail fauna. Through most of the section bracketed by the interglacial and interstadial soils, the sediments display the reversed declination but positive inclination. The top of the reversed interval is here informally called the Brno magnetostratigraphic horizon. It correlates reasonably well with the upper boundary of the Blake event estimated to be 108,000 yr old.

    The vertebrate and the snail faunas of chernozemic soil and of the loess together with the pedogenetic character of strata point to the harsh continental climate with the large temperature variation, dry seasons and partly, with torrential summer rains.

    If the remarkably periodic deposition of loess series has to continue, following the pattern observed through the last 350,000 yr or so, then the shift to expressed continental climate in this part of Europe is to be expected soon.

    INTRODUCTION

    In the neighborhood of Prague and Brno, Czechoslovakia, the richly subdivided se- quences of alternating windblown loess, hill- wash loams and different soils cover the flanks of river valleys. The climatostrati- graphic information is obtained from the changes in lithology and pedogenesis, from the land snail assemblages, pollen and verte-

    1 Lamont Doherty Geological Observatory con- tribution No. 1837.

    2 Czechoslovak Academy of Sciences, Geological Institute, Trojanova 13, Praha 2, Czechoslovakia. At present : Lamont-Doherty Geological Observa- tory, Palisades, N.Y. 10964.

    3 Czechoslovak Academy of Sciences, Geophysi- cal Institute, Bdni II, Praha-Spoiilov, Czecho- slovakia.

    brate finds. Chronostratigraphic control is achieved by radiocarbon dates and paleo- magnetic horizons (cf. Demek-Kukla, 1969 ; Kukla, 1970).

    As this part of Central Europe was never glaciated, the semicontinuous depositional records reach deep into the past. The oldest soils at Cervenf Kopec in Brno are of Jaramillo age (about 1 million YBP) and the system could have been extended up to the top of Olduvai event (about 1.7 million YBP) in neighboring Krems, Austria.

    The purpose of this article is to review shortly the basic facts about the last cycle in loesses and then to analyse in detail the interval which immediately followed the dis- appearance of interglacial deciduous forests from the area.

    374

    Al? % f Co yri ht 0 1972 by Academic Press, Inc.

    ng ts o reproduction in any form reserved.

  • END OF INTERGLACIAL IN LOESS 375

    STRATIGRAPHY OF THE LAST

    GLACIAL CYCLE

    In Fig. 3. the stratigraphic sequence of the last glacial cycle is plotted against the time scale. Similar sequence of strata, with few locally missing minor soils at some sites, was observed in more than 30 localities in the western half of Czechoslovakia. The principal locality where the radiometric determination and the depth plots in our diagram come from is Vestonice (location in Fig. 1, detailed description in Klima et al., 1962). The rich snail assemblages serve as sensitive indicators of vegetational and climatic changes throughout the shown in- terval. They are most completely studied in Kutna Hora (KH) and Vestonice (Loiek, 1964). The paleontologic independent check supports the paleoclimatic reconstructions obtained from soil micromorphology (Smoli- kovi, 1967, 1968a) and lithology (Kukla, 1961a). Additional climatostratigraphic cri- terion is provided by palynology. Even that the probability of redeposition of pollen grains in this type of sediments is very high, the well-expressed abundance peak of ther-

    mophilous broadleaf arboreal elements in the oldest soil of the glacial cycle demonstrates its synchroneity with the interglacial ,environ- ments (Frenzel, 1964).

    The sequence shown in Fig. 3 illustrates also the principles of the stratigraphic sub- division of the loess series.

    The Cyclic Subdivision of the Loess Series

    The striking feature of the loess series is their cyclic development. The first order Glacial cycles and second order Stadial cycles were recognized as early as 1960 and form the basis of the local lithostrati- graphic subdivisions (Kukla, 1961). Only later it was found that eight glacial cycles were completed within the Brunhes paleo- magnetic epoch (Bucha et al., 1969), same as in the deep-sea sediments (Kukla, 1970).

    The cyclic units form the frame of the lithostratigraphic subdivision of the loess se- ries. The principal boundaries and units are recognized as follows :

    Marklines : The principal lithostrati- graphic boundaries, separating the individual glacial cycles are called Marklines. They are defined as the boundaries between the

    POLAND

    FIG. 1. Location of sites discussed in text. Full circle : localities ModiYce (M), Sedlec (S), Chabry (CH), Kutni Hora (KH), V&tonice (V), No& Mesto (NM). Open circle : towns Praha (P), Brno (B) and Bratislava (BR). Areas of calcareous loesses dotted.

  • thick layer of the cold type windblown loess and the hillwash loam occurring closely below the level of the deciduous forest soil (Kukla : in Demek and Kukla, 1969). This boundary could be recognized even when masked by the subsequent development of decalcified forest soil (cf. Fig. 2). Mark- lines are labeled ML and numbered consecu- tively backwards with roman numerals.

    The last Markline (ML-I) in the de- scribed region is about 10,000 yr old. The dating was indirectly obtained by tracing the

    TIME

    I IIIlImPm

    ? GI M - ML

    FIG. 2. Development of the soil complex in loess areas shown schematically in six subsequent stages. The major lithostratigraphic boundary, Markline, could be precisely fixed only in stages II-V. l- Windblown loess, Z-hillwash, 3-Ca-horizon on the base of decalcified soil, 4-decalcified forest soil with preserved loess fabric, 5-ditto, with hillwash fabric. In upper part of that horizon the original structure could be destroyed by clay movement, &-eolian dust with small stones (skellet of older soil), 7-biogenic soil high in humus. Stones moved to the base by the burrowing of worms and rodents. ML-Markline. In the upper horizontal band (SED.), the prevailing type of sedimentation is shown. By full dots : eolian loess ; fine dots: eolian fine dust; thick wavy line: hill- wash deposition; fine wavy line: slow hillwash deposition. In the lower horizontal band (VEG.), the inferred type of vegetation is schematically shown.

    last marks of loess deposition in l-ate Paleo- lithic Nagdalenian sites (cf. lYalocll, 1968). There is no doubt that the Narklines are the exln-ession of the same rallid environ-

    mental change at the end of a glacial, which produced the Terminations in the deep- sea sediments (Broecker and Van Donk, 1970) and that the Marklines and Termina- tions in a broad sense timely correlate.

    Sub-marklines: These are defined as boundaries between the windblown loess of any kind and the hillwash loam or soil of at least interstadial character (including brown earth and chernosem) .

    Glacial &e: This is the unit delimited defined by Marklines. Starts with hillwash sediments and soils related to the interglacial climate (similar to present conditions) and ends with the potent loess member, which contains arctic-type f rost-gley soils and cold- resistant snails of Collumella collunzella and Pupilla n4uscoYu~ group.

    Glacial cycles are labeled from the present backwards with the capital letters A to R. Present glacial cycle (first of the Holocene age) is labeled A, the last one completed is labeled B. In the intercorrelations with the systems from outside the loess region, the prefix L- should be used to distinguish the loess units from similarly labeled other strata (e.g., L-B for the last glacial cycle).

    Stadial cycle (also subcycle) : It is the unit delimited by Sub-marklines. It starts with hillwash sediments and soils related to the interstadial climate and ends with the deposition of the windblown loess related to either cold or mild climate of continentaj

    We. The stadial cycles are labeled by majus..

    cules referring to the corresponding glacial cycle and by number. Originally (Kukla, 1961) only three stadial cycles, namely Bl, B2, B3, were distinguished within the last glacial cycle B. However, it is now possible and useful to subdivide further the unit 32 into three units BZI, 322 and BZ3.

  • END OF INTERGLACIAL IN LOESS 377

    The recognked strata: On the localities described in detail (e.g., Klima et al., 1962 ; Kukla et al., 1962) all recognized layers were designated by small letters.

    More frequently only soils are separately recognized. This is done by a symbol con- sisting of the designation of the stadial cycle with the suffixed small latin letters.

    As miscorrelations within the loess area are locally possible, the complete reference to any given soil should include a prefix which refers to the corresponding locality (cf. Kukla : in Demek and Kukla, 1969).

    The Chronostratigraphic Correlations

    The sedimenta