Új tanulmány az utolsó interglaciális talajformáló mechanizmusainak kérdéseiről

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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