Upper part of the young loesses (Dunaújváros-Tápiósüly series)
The most complete known section of the young loesses is ca. 10 m thick and mostly consists of layers of sandy loess and loessy sand. There are only two intercalated, poorly developed'soils (or humous loess horizons) (hi, Ьг - Fig. 4).
In the top part of the first humic layer in the Tápiósüly profile Pinus cembra and Larix charcoal remnants occur. Their radiocarbon age is 16,730 ± 400 years. In the loess, (h) above the humic layer (hi) there are abundant though sporadically distributed reindeer bone remnants. This loess horizon with reindeer remnants appears in similar stratigraphic positions in several profiles.
Dating the charcoals found in the Dunaújváros profile, the age of the older humic soil (Ьг) was determined as 22,000-20,000 radiocarbon years (Fig. 4). The lower sandy loess (Ь) frequently contains mammoth bones.
Judging from the texture of the layers, in the accumulation of the upper part of the young loess series in Hungary — in addition to falling dust — wind-blown sand movements and solifluction caused by meltwater flow also played a part.
The analysis of the profiles indicated that during the period of formation of the upperyoung loesses (ca. 26-12 ka) three sandy loess layers (li, I2’, I2” ) developed which are separated from one another by two humic loess horizons (hi, Ьг) as well as by layers of loessy sand with dell fill (h) and sandy loess (b). Both humic loess horizons (hi = 16-17 ka and h2 = 20-21 ka) are considered products of arctic soil formation. Before their formation the processes of dell deepening (slight erosion) and then dell filling (sparse vegetation and solifluction) took place.
Tentative dating of the lower young loesses (Mende-Basaharc loess series)
This series of three or four major loess layers and four paleosols is about 15-20 m thick (Fig. 4). In some cases the paleosols are overlain by pedosediments or loessy semipedolite.
The Mende Upper (MF) paleosol is usually a double layer. The top part (MFi) is poorly developed chernozem with animal burrows and charcoal remnants. Their radio
carbon age is 29,000-28,000 years and this dating has been confirmed by TL analyses.
The lower part is a well-developed forest steppe soil (MF2).
The paleosol Basaharc Double (BD) comprises two forest steppe soils. Previously these were dated — from the rate of sedimentation in young loess — to 40-44 ka.
According to TL investigations by Y. LU and L. ZÖLLER, in the Paks profile (Fig.
6) the paleosol BDi is located between loess horizons of 114 ka and 144 ka old.
In the Mende-Basaharc series the Basaharc Lower (BA) paleosol is the oldest fossil forest steppe soil. The upper part of BA is mostly soil sediment, redeposited by solifluc- tion over the slope. In the Cca horizon of the paleosol loess concretions in vertical orientation occur.
Based upon the earlier investigations and datings by M. PÉCSI it is assumed that the paleosol BA was formed in the lower part of last glacial period during a prolonged interstadial phase.
On the basis of recent TL dating in the environs of the Basaharc Double paleosol (Fig. 6) we can assume that BA paleosol may be the product of the R1-R2 interstadial and divides the two loess pockets (I5 and Ц) of the penultimate glaciation.
The Mende Base soil complex (MB) consists of two paleosols. The upper member (MBi) is 80-100 cm thick, chernozem-type soil, while the lower member (80 cm) is a well-developed brown forest soil (MB2). The formation of this double soil had been placed into the last interglacial stage (PÉCSI, M. 1965, 1975; BORSY, Z. et al. 1979).
The paleosol MB is one of the best-developed soil complexes in Hungary, a marker horizon, which had been previously referred into the R1-R2 interstadial (BULLA, В. 1934;
ZEBERA, K. 1954). K. ZEBERA regarded it of M-R interglacial age.
If we arrange the paleosols and loess horizons in a stratigraphic order or according to a chronological scheme (the MILANKOVITCH and BACSÁK climatic calendar or the isotopic stratigraphy), we certainly oversimplify reality; nevertheless, the paleosol MB can correlate with the Mindel-Riss interglacial period (see Fig. 2).
Old loess series and paleosols
In the exposures of the bluffs along the Danube river the old loesses — almost 25 m thick — were named under the term Paks series (PÉCSI, M. 1975; PÉCSI, M. et al. 1977). Based upon their lithological properties they are subdivided into two parts by their lithological properties (Figs. 1 and 5).
Upper part of old loess (Paks I series)
The upper part of the Paks series contains several erosional hiatuses (Fig. 1). Based on lithostratigraphical, paleopedological and paleontological considerations, the fluvial sand and silt Si, under old loess L2, had been referred to the Mindel-Riss interglacial (ÁDÁM, L. - MAROSI, S. - SZILÁRD, J. 1954; KRIVÁN, P. 1955; PÉCSI, M. 1975;
PÉCSI, M. & PEVZNER, M.A. 1974). It is probable that the fluvial sand S2 was deposited in an earlier interglacial (G/M) and during its accumulation part of the old loess could have been eroded (Fig. 1). Thus, the upper part of the Paks series may not represent the complete stratigraphic sequence of the Middle Pleistocene (but only that of the Mindéi glaciation, Fig. 2).
40
Fig. 6. Chronological subdivision o f loess profiles at Paks, Mende and Basaharc with paleomagnetic, TL and 14C data (by PÉCSI, M. 1990). Different TL methods o f dating resulted in extremely diverse ages.Segments o f profiles b, d and f were been investigated three times and showed normal polarity each time (analyses
Lower part of the old loess (Paks II series) and the Brunhes-Matuyama boundary (0.7 Ma)
This 15 m thick series comprises three old loess horizons (L4-L6) and three brownish red paleosols (Fig. 1). The Paks Double soil complex is comprised of two soils that are almost equally well-developed, 1.5 m thick, brownish red, compact and have medium clay content (PDi and PD2). These paleosols are separated by a 2 m thick loess horizon (L4). They may be the remnants of well-developed forest steppe soils of Mediterranean-type formed under dry conditions. The old loess (Lé’, Lé” ) that forms a layer of several metre thickness at the base of the Paks-Dunakömlód paleosol (PDK) represent the lower stratigraphic limit of the Paks series.
The lower part o f the Paks series can be dated first of all by the position of the Brunhes-Matuyama paleomagnetic boundary (0.73 Ma). In addition, in the pink sandy sediment below the old loess series of Dunaföld vár probably thtJaram illo paleomagnetic interval is observable which is of 0.9 Ma absolute age (Figs. 1 and 5, PÉCSI, M. &
PEVZNER, M.A. 1974). Relying on the investigations carried out so far, we believe that the oldest loess horizon known from the Carpathian Basin (Lé in the Paks brickyard profile
— Fig. 1) could have formed during the first glaciation with loess formation, i.e., during the Donau glacial period. On the basis of the paleomagnetic analyses of the Paks and Dunaföldvár profiles, the lowermost loess horizons seem to be older than 0.73 Ma and younger than 0.9 Ma (PÉCSI, M. & PEVZNER, M.A. 1974; MÁRTON, P. 1979; PÉCSI, M. 1984).
Subaerial formation below loess
Old loesses are underlain by subaerial formations of considerable thickness parts of which (sandy silt, sandy clay) were classed, also in Hungary, with loess-like deposits in their broader sense. Recently, the series of mostly red soils, red clays and gleyed clays
— briefly summarized as ’variegated clay’ series — was grouped with non-loessy terrestrial sediments. This series, located beneath the old loesses, is known partly from exposures but mainly from boreholes. First it was revealed by the soil mechanical boreholes of the Danubian bluff and was named ’Dunaföldvár series’ (PÉCSI, M.T975, 1985a; PÉCSI, M. et al. 1979b — Fig. 5).
Below the 50-60 m loess series ca. 30-40 m thick ’variegated clays’ and sandy silts follow. The lowermost variegated clay and red clay layers of this ’Dunaföldvár series’
belong to the Pliocene (PÉCSI, M. 1985a). In its base also Upper Miocene (Pannonian) sediment is found. In our opinion, the ’Dunaföldvár series’ can correlate with the ’stony loess’ of Central Asia and the Wucheng loess of the Chinese Loess Plateau and the underlying red clays (PÉCSI, M. 1987a).
An entirely different subaerial sequence is recorded in the parts o f the basin which underwent gradual subsidence during the Pliocene and the Pleistocene. The thickness
of basin deposits in the Hungarian Plain locally exceeds 500-1,500 m below the flood- plains of rivers. In the most intensively subsiding basins red soils and red clays are repeated 6-10 times between 600 and 1,000 m depths. With the preponderant flood-plain, meadow and chernozem soils, the swamp forests also allowed the formation of lignite.
The boreholes did not reach the sequence of the Upper Miocene (Pannonian) inland sea to 1,200 m depth. The paleomagnetic study of the cores and paleontological data cover the whole of the Quaternary and extend to most of the Pliocene (5.25 million years B.P.;
COOKE, H.B.S. et al. 1979; RÓNAI, A. 1977, 1985). In the Pliocene sequence 50-60 and in the Quaternary ca. 50 paleosol horizons are detected. Such a long Late Cainozoic geological record of subaerial sediment is only known to date from the exploration boreholes in the Hungarian Plain by A. RÓNAI (1985).
Long-term terrestrial records of the Middle Danubian Basin
In the Middle Danube Basin, loess and loess-like deposits cover various morpho- tectonic levels in ca. 150,000 km2 total area, basin types of various elevation and size are predominant.
Under different geomorphological or morphotectonic conditions — over an iden
tical time interval — the variation in the rate of basin subsidence produces various litho-and chronostratigraphical sequences.
The subaerial sequence of basins affected by prolonged subsidence in the Quater
nary is subdivided by paleosols of larger number than the loess-paleosol sequence of basins, elevated plateaus or watersheds which underwent more moderate subsidence during the Quaternary.
1. Young loess mantles of small intermountain basins and mountain slopes (at 150-400 m above sea level). In the mantle of slope loess maximum 3 or 4 loess/paleosols and 2 or 3 slope debris layers overlie one another. Their age is < 25,000 years B.P.
2. Low-lying terraces and alluvial fans, flood-plain loess. The thickness of the loess series of the subsided alluvial fan is 40-50 m; it is of Pleistocene age and partly eroded. Flood-plain loesses are 2-5 m thick, occasionally subdivided by 1 or 2 paleosols.
Their age is < 25,000 years B.P.
3. Loess-paleosol-sand sequences on pediments (100-150 m above sea level). In the loess-paleosol-sand sequences of 50-100 m thickness ca. 12 loess, 10 sand and silt layers and 20-30 paleosols are present. The age of these profiles with hiatuses is Pliocene-Pleistocene.
4. Loess-paleosol-sand sequences on alluvial fans and terraces (10-100 m relative heights). The loess sequence is 40-60 m thick and subdivided by 10-12 loess horizons, 10-12 paleosols and 5 or 6 sand layers; LTR — Pliocene-Pleistocene.
5. Subaerial basin sediment locally of 500-1,500 m thickness. The surface of the basin is a flood-plain at 90-100 m above sea level. In the basin sediments the number of paleosols — mostly forest steppe and meadow steppe soils — may reach one hundred.
In several boreholes there are 6-12 red soils or red clays between 600 m and 1,000 m.
12-16 intercalated sand layers are observed. The age of this almost complete sequence is 5.2-5Л million years B.P. In the most intensively subsiding basins sedimentation was almost continuous; during Pliocene ca. 50-60 and in the Pleistocene ca. 50 soils developed (RÓNAI, A. 1985; PÉCSI, M. & SCHWEITZER, F. 1991).
In contrast on the non-subsiding foothills only 20-30 soils formed during the Pliocene and Pleistocene and several gaps are detected in the sequence.