Bradák, B., Kiss, K., Barta, G., Varga, Gy., Szeberényi, J., Józsa, S., Novothny, Á., Kovács, J., Markó, A., Mészáros, E., Szalai, Z. (2014). Different paleoenvironments of Late Pleistocene age identified in Verőce outcrop, Hungary: Preliminary results. Quaternary International 319. pp. 119–136.
Complex geomorphological, geological, palaeopedological and chronometrical investigations were started to reveal the development of the alluvial section and the loess/paleosol sequence containing remnants of a Late Palaeolithic site near Verőce, Hungary.
Different palaeoenvironments were identified in the profiles of the abandoned brickyard influenced by different facies in the margin of fluvial-alluvial (Palaeo-Danube) and proluvial (South East pediment of Börzsöny Mountain) area and the environments affected by the climate fluctuation of Late Pleistocene (loess/paleosol sequence overlaying the base of alluvial materials).
Sediments possibly deposited by Palaeo-Danube were identified in a basal section of abandoned brickyard. The alluvial facies was indicated by sand, aleurite and clay layers in the sediment sequence. Some parts of the alluvial sediments were covered by loess in the glacial periods intercalated by four paleosol horizons formed during interglacial or interstadial periods. The sedimentation of loess and the forming of paleosols were finished by pedimentation processes (sheet wash, redeposition) indicated by the fine layered material at the top of each paleosol horizon.
Another complex fluvial-alluvial section was identified at a different part of the brickyard possibly developed parallel with the loess/paleosol sequence in the Late Pleistocene.
Based on the different kind of dating methods (e.g. archaeological, 14C and luminescence dating) the development of the loess/paleosol sequence started in marine isotope stage 6 (MIS6) and the youngest layer dated back to MIS2.
Samples were taken
from all main stratigraphic units of the outcrop for grain size analysis. The
grain-size distribution of collected loess, paleosol and loess-like samples
were measured in the laboratory of the Geographical Institute of the University
of Pécs by using a Fritsch Analysette 22 Compact laser grain-size analyser,
with 0.3–300 μm measurement ranges in 62 channels. Grain-size measurements by
laser particle sizers provide more accurate results than the previously applied
pipette and sieve methods (Konert and Vandenberghe, 1997; Blott and Pye, 2006).
The chemical
extraction procedure described by Konert and Vandenberghe (1997) was applied
before the measurements to sequentially remove the organic material and
carbonate content by treating the samples (3 g) with H2O2
(10 ml, 30%) and HCl (10 ml, 10%). After desiccation of samples, sodium
hexametaphosphate ((NaPO3)6) was added in order to
disperse the particles.
Mineral particles of the samples are generally
falling into clay, fine and coarse silt ranges, occasionally with minor fine sand
components (Fig. 3). Most of the measured loess grain-size distribution curves
(from L1–5) have very similar shape patterns with definite positive skewness
(asymmetry into the direction of coarse fractions), unimodality (or weakly
developed bimodality) and leptokurtic kurtosis. Paleosols (P1–4) have more
diverse granulometric profile; for instance, curves of red pedogene horizons of
P4 units have almost the same characteristics as the underlying loess deposits
with a slightly more finer components, while grain-size distributions of
brownish and especially blackish levels shift into the direction of clay and
very fine silt fractions occasionally without any coarse silt particles,
mesokurtic kurtosis and negative skewness. Redeposited loess-like (L1r–L4r) and
aleurite samples (A1) show more various properties with bi- or trimodal
distributions, moderate kurtosis and normal or negative skewness. Samples from
section B contain lot of coarse silt- and sand-sized aggregates of sedimentary
clay and fine silt particles. Presumably, these aggregates are connected to
post-depositional processes and/or have been formed by redeposition. According
to Mason et al. (2003, 2011) and Qiang et al. (2010), the genetic explanation
of aggregates is highly uncertain.
Deposits, described as loess (e.g. B1-11; C1-15;
D2-10,11) during the fieldworks were confirmed by the grain-size analysis. The
granulometric profile with a pronounced maximum in medium and coarse silt
fraction and a tail or shoulder in the clay and fine silt components indicate a
primary aeolian depositional environment (Nugteren et al., 2004; Vriend and
Prins, M.A. 2005, Vandenberghe et al., 2006; Sun et al., 2008; Novothny et al.,
2011; Varga et al., 2012). General characteristics of grain-size distribution
curves represent a similar sedimentary origin of the analysed samples; however
they differ largely from fluvial, lacustrine or other hydraulic deposits.
The loess-like and aleurite
deposits can be regarded as typical redeposited sediments due to their layered
deposition, multimodal grain-size distribution and poor sortness.
The L5 loess and the overlying P4 paleosol
levels of the different sections could be well correlated. The granulometric
profile (lower average and modal grain-size, higher clay-content, slightly
modest skewness and kurtosis compared to underlying loess) and stratigraphic
position of red paleosol horizons of P4 paleosols are indicating an in-situ origin
of the paleosol. These strata were formed from the L5 loess deposits. (Similar
stratigraphic connection among loess and other, younger pedogene horizons (e.g.
P2, P3) could not be identified in the sections.) The investigation of the
pedogenesis of upper levels of P4 is much more complicated based on the grain-size
analysis; probably mass movements, redeposition and sheet wash processes played
more significant role in formation of these brownish and reddish horizons.
Especially, in the case of black soil-layers (B1-7; C1-13; D2-4), the fairly
high clay-content and the almost totally missing coarser fractions are
indicating well the redeposited origin. After the pedogenic
phase dust accumulation became dominant again due to the changing climatic
conditions. During dust settlement the microecosystem of the soil remained
still active and tried to keep pace with the accumulation rates. This ensured
the presence of pedogenic processes in the dust accumulation phase as well (Catt 1990, Becze-Deák et al. 1997). The
SDI shows similar value to the P4 paleosol identified in the B profile.
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