extended abstracts - Geomorphic Processes and Geoarchaeology

Geomorphic processes and geoarchaeology
In the central Russian Plain, typical for river valleys is a 8-12- m terrace called
«first terrace». It is believed to have been formed about Last Glacial Maximum (LGM)
when rivers had low discharges but were overloaded with sediments. Rivers are thought
to have incised at the Pleistocene/Holocene border, which gave start to formation of
floodplains and their occupation by ancient humans. In spite of wide acceptance of this
traditional view, several archaeological sites exist that strongly contradict it. One of them
is the Avdeevo Upper Paleolithic site on River Seim, 51º 41.3' N, 35º 48.5' E. It is located
at the confluence of the Seim and Rogozna rivers on a gentle hill rising only 0.5-1.0 m
above surrounding floodplain [1, 2]. Cultural layer with evidences of stationary human
occupation is found at the depths of 1-1.5 m, i.e. 5.5-6 m above the present-day water
level of river Seim (about the height of modern highest floods). Series of radiocarbon
dates of cultural layer (mostly on bone charcoal) group in several periods of human
occupation which in total cover the interval between 17-23 14 C ka BP [2], or 20-
28 ka BP cal. During this period river floods must have been lower than 5-6 m above the
modern river, which may indicate deep river incision before and at the time of LGM. This
study is aimed at establishing chronology of the Seim River terraces and its
incision/infilling cycles to assess the conditions of the Avdeevo site occupation and its
survival in a changeable riverine landscape.
The Seim river valley is situated in extraglacial part of central Russian Plane
between the cities of Kursk and Kurchatov. A set of low terraces of the Seim river valley
(fig. 1) was studied between the Malutino village on the left riverbank and the Avdeevo
village on the right bank.
The following set of methods was used to reconstruct the Seim river valley
development: DGPS topographic profiling (Leica Smart Station), examination of terrace
sediments in exposures and cores, subsurface exploration (ground penetration radar
(GPR) Zond 12e), laboratory study of sedimentary sections (granulometric, spore-pollen),
sediment absolute dating (radiocarbon – 14 C, optically stimulated luminescence – OSL).
Archaeological data have also been taken into account.
Several terrace levels were detected based on the results of GPS-survey (fig. 2):
Holocene floodplain (h=2-4 m); terrace T0 with heights 5-8,5 m (levels T0a 5-6 m, T0b
6-7 m, T0c 7-8 m); terrace T1 with heights 12-16 m (levels T1a 12-13 m, T1b 13-14 m,
T1c 15-16 m).
Terrace T1 (h=12-16 m) correlates with the so-called «first terrace» in river
valleys of Russian Plane. The lower level of this terrace (T1a) was studied in a sand pit
(section ML-1). According to OSL dating, alluvium of terrace T1a was accumulated
about 45-55 ka ago. It lies on an older alluvial basement dated to ca 70-80 ka. The upper
3.7 m of the section is represented by two units of thin-bedded aeolian sands divided by a
0.8- m thick layer of deluvial loam. The upper aeolian unit was dated at ca 20-23 ka [3].
Terrace T0 (h=5-8,5 m) can be correlated with the so-called «intermediate terrace»
that was distinguished by some scientists in other river valleys of Russian Plane (the
Volga River valley – A.I. Moskvitin, the Oka River basin – A.A. Aseev, N.I. Kriger).
This terrace rises only 1-2 m above the modern inundation level. According to GPR data,
the upper level of this terrace (T0c) is composed predominantly by sands. Two lower
levels (T0b and T0a) have different composition which was studied at river bank
exposures (sections ML-2 and ML-3 respectively).
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