SAMPLES DATED: DESCRIPTION, RESULTS AND DISCUSSION
5.2.4. Aschersleben 1. Introduction
The Ascherslebener Depression ( ^ 51° 4 7 ' N Lat, 11° 25' E Long) is situated in the northern Harz foreland between the rivers Selke and Eine, tributaries of the river Elbe, at an altitude of 108 m. Here a rather complete series of sediments ranging f r o m the Last Interglacial through the Weichselian Glacial t o the Holocene has been preserved. It has been studied by Mania (1967) in large exposures provided by a brown coal pit.
5.2.4.2. Stratigraphy
On deposits o f the Elster Glacial and the Tertiary, showing a distinct denudation surface, a series of sediments has been f o u n d , 20 to 25 m thick and belonging to the Last Interglacial, the Last Glacial and the Holocene. The sediments are composed of eleven sequels of sedimentation, which are an expression of the same number of climatic micro-cycles. This division has been made by Mania (1967). It is based among others on the grain size, the organic content, and the fauna of ostracodes and molluscs of the sediments.
One complete climatic micro-cycle consists of:
(i) a denudation phase (especially deflation) during a cold and dry climate.
(ii) a phase of fluviatile deposits corresponding to a gradual improvement of climate (warmer and more rain),
(iii) a phase of finely grained limnic sediments caused by a further increase of temperature and rainfall leading to a closed vegetation.
H i H 2 E U3 W h ^ 5 B 9e • D s H 9 H 1 0 H n H 1 2 B i 3 D M H i s •
Fig. 5.5. Generalized stratigraphy and periodicity for the Ascherslebener See.
1 — denudation surface, 2 — sandy gravel, 3 — sand with gravel, sand, 4 — sand and silt, 5 — clay, 6 — calcareous ooze, 7 — peat, 8 — solifluction deposit, 9 — cryo-turbatic involutions, 10 — cryoturbation and frost wedges, 11 — medium coarse gravel ( > 6 mm), 12 — fine gravel (6—2 mm), 13 — coarse grained sand (2—0.6 mm), 14 — medium grained sand (0.6—0.2 mm), 15 — fine sand (0.2—0.06 mm), 16 — silt and clay ( < 0.06 mm), a — warm stenothermous species, b — thermophilous species, c — species of spring-time, d — eurythermous persistent species, e — cold stenothermous species.
(iv) a phase of periglacial deposits and d r y i n g of t h e lake connected w i t h a decrease of t e m p e r a t u r e and rainfall.
T h e eleven micro-cycles together f o r m one macro-cycle starting w i t h clearly inter-glacial c o n d i t i o n s at the b o t t o m , passing a cold inter-glacial phase and ending again w i t h (the present) interglacial c o n d i t i o n s .
A t y p i c a l e x a m p l e of the p r o f i l e f o u n d (c.f. M a n i a , 1 9 6 7 , figs. 3 9 and 4 0 ) is given in f i g . 5 . 5 . T h e stratification has been m a d e i n d e p e n d e n t l y of C dates. T h e d i f f e r e n t c l i m a t i c cycles and their relatively more or less favourable c l i m a t e can clearly be recognized. Also the interglacial climatic c o n d i t i o n s give rise t o sufficient differences to be identified as such.
108m a.s.l.
VI
IV
III
lb
la,
o» 9 <* <*
Q . •
C
FR45 1750±100 FR32 8460 ±125
FR17: GrN-7078:
(peat)
49 200 "4100 -2700
FR 16 >40000
GrN-5423: 41000 ± 1275 GrN-7108: 3 7 2 0 0 * ] ™
60100 •1400
•1200
T
peat
calcareous coze sand, silt, clay
sand and coarse grained sand solifluction deposit
volcanic ash ( Laacher See) denudation surface cryoturbation surface frost wedge
middle palaeolithic artefacts C sample
Fig. 5.6. Stratigraphy of the sam-pled profile Aschers-leben.
5.2.4.3. Radiocarbon Dates
The new radiocarbon dates for the samples indicated in fig. 5.6 are presented in table 5.5.
The unmeasurably low radiocarbon activity of the t w o fractions of the alkali extract shows that the material used for the enrichment probably was uncontami-nated. The stratigraphy indicates that the sample FR 15 should be attributed to the second (Br^rup) Interstadial of the Last Glacial (Mania, 1967). The date obtained corresponds to an early phase of the third (Odderade) Interstadial as measured at Amersfoort and Odderade. In view of the measuring uncertainty and the possibility of sample contamination it cannot be excluded that the sample belongs to a de-veloped phase of the Br0rup Interstadial. It is of special importance because the sample was associated with middle-palaeolithic artefacts (Mania, 1967).
The t w o conventional dates were intended as a check. If the correlation of FR 15 w i t h the Br^rup Interstadial is correct, the interstadial of cycle II (FR 16;c.f.
figs. 5.5 and 5.6) should correspond to the Odderade Interstadial and that of cycle III (FR 17) to the Moershoofd Interstadial as described in the Netherlands (Zag-w i j n , 1961). The result for FR 16 is obviously much too young. The sample must have been contaminated. Probably also the earlier value of GrN-5423 (41 000 ± 1275 yrs BP) was still influenced by contamination. The age of FR 17 seems quite reasonable for an early phase of the Moershoofd Interstadial. This result supports the one obtained on FR 15. Together the dates support the corre-lation made by Mania of the sedimentation cycles in the Ascherslebener See De-pression w i t h the pollen zonation in the Netherlands and North-west Germany.
A further discussion is given in sect. 5.3.
5.2.5. Samerberg
The Samerberg basin (47° 4 5 ' N Lat, 12° 12' E Long) is situated at an altitude of 600 m in the northern foothills of the Alps approximately 15 k m south-east of Rosenheim. During the Last Glaciation it was the tongue basin of a branch of the Inn glacier.
5.2.5.1. Lithostratigraphy (by E. Gruger)
A b o u t 19 m of pollen containing fine sands and silts belonging both to an inter-glacial and to the early part of a succeeding glaciation are lying on till f r o m an older glaciation. This sequence is covered by 2 to 3 m of till f r o m the Last Glaciation.
o
Table 5.5. Results from Aschersleben.
GrN
5.2.5.2. Pollen analysis (by E. Gruger)
The basal part of the sediments shows a complete interglacial vegetational cycle characterized by high values of mixed-oak forest and hazel, the early expansion of spruce, a Taxus phase and finally a fir, spruce, horn-bearr) phase. A similar vegeta-tional development was found in Zeifen and Eurach in the Alpine foreland of Bavaria (Jung et al., 1972; Beug, to be publ.). There it was attributed t o the Riss-Wurm Interglacial. The overlying early glacial sediments are approximately 18 m thick. They comprise three forest phases, which most likely represent three interstadials, and the corresponding stadial periods. Although the pollen flora of the
SAMERBERG (Exposure)
* Or or c? <£>
/ / //A*
y C <s Y V #
10
Fig. 5.7.
Pollen diagram for the second forest 20 30 40 50 60 70 80 90 100 5 5 7. phase at Samerberg.
stadials is very similar, the interstadials can be discerned on basis of their vege-tational development. The simplified pollen diagram of the middle forest phase is given in fig. 5.7.
After a rather long period w i t h open vegetation, characterized by relatively high values of NAP with regular occurrence of Artemisia, Hetianthemum, Thalictrum, Selaginella selaginoides etc., the forest vegetation in this area begins w i t h a slight increase of Betula and Juniperus values. During the f o l l o w i n g expansion of Pinus the NAP values decrease t o less than 5%. After this Picea becomes dominant. Apart from these conifers also pollen of Larix and the different species of the mixed-oak forest (especially Quercus) was found in small numbers. Abies pollen is completely missing. A subsequent increase of the NAP values above the 3 m level reflects the lowering of the tree-line and the beginning of a cool phase.
5.2.5.3. Dating (by E. Griiger)
From the position of the interstadial deposits on t o p of interglacial beds classified on good evidence to be of Riss-Wurm age and below Wurm till we can place these interstadials in the early part of the Last Glacial. If a direct correlation w i t h the North-west European Early Weichselian profiles is possible, this would mean that we have here the Amersfoort, the Br0rup and the Odderade Interstadials as found in Amersfoort (sect. 5.2.1). The wood collected for 1 C dating was obtained f r o m the second forest phase, probably the equivalent of the Br0rup Interstadial. A more detailed discussion of vegetational development and climate is given elsewhere (Griiger, to be publ.).
5.2.5.4. Radiocarbon Dates
The enrichment date obtained for a sample of Picea wood taken f r o m the lower 14
part of the middle forest phase (c.f. fig. 5.7) and the C result on the first alkali extract are given in table 5.6.
The measurable radiocarbon activity of the extract indicates that the sample con-tained some younger carbon. The fact that already in the first extract the activity was rather low indicates that the sample was not seriously contaminated.
The date obtained for the enriched sample is somewhat unexpected. From the pollenanalytical correlation and the dates obtained for the profiles at Amersfoort and Odderade an age between 60 000 and 65 000 years BP was expected.
A further discussion of the result is given in sect. 5.3.
Table 5.6. Results from Samerberg.
GrN
7275 7 4 1 5# #
Sample Code
F Il/A 226 F I I / A 2 2 6 1st alkali
extr.
Depth (m)
8.80*
Measured activity (cpm)
0.051 ± 0.020 0.117 ± 0.021
Enrichment
13.41 ± 0.27 Sample activity (pmc)
0.012 ± 0.005 0.270 ± 0.048
Age (yrs BP) 1a criterion
72 300 + 4 1 0 0
72 300 _ 2 7 Q 0 47 500 + 1 6 0° 4 / o u U _1 3 0 0
c13 IOI \
°PDB y ,00'
- 24.82 - 26.43
t*
* depth below Wiirm till
** counter G R A D A