Abstract

BRONGER, Arnt  and  SMOLIKOVA, Libuše. Quaternary loess-paleosol sequences in East and Central Asia in comparison with Central Europe - micromorphological and paleoclimatological conclusions. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.1, pp.65-92. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n1a5.

Detailed knowledge of the genesis of paleosols is needed to establish loess-paleosol stratigraphies that can be used for paleoclimatic reconstruction. Most paleosols, however, are truncated and largely recalcified from overlying loess. Micromorphological studies allow e.g. primary and secondary carbonates to be distinguished and provide unequivocal evidence of clay illuviation. This enables the recognition of typical loess, weathered loess and the recognition of different genetic soil horizons, such as CB, BC, Ah, Bw and Bt horizons. For the Brunhes epoch, the sequence at Karamaydan, Tadjikitan, is more detailed than the corresponding section in Luochuan, China and even more than in the Carpathian Basin except for the last glaciation, however, similar to the pedocomplexes of the composite section in Czechia. The very good correlation with the deep-sea oxygen isotope record, which includes the development of an accurate astronomical time scale, allows a detailed chronostratigraphical subdivision of the loess-paleosol sequence in Karamaydan down to the substage level, which therefore should be regarded as a key sequence in the temperate climatic belt of the Northern Hemisphere for reconstructing the climate history of the Brunhes epoch. An example of the incompleteness of the loess-paleosol sequence in the Carpathian Basin is the very strongly developed F6 paleosol, a rubefied earthy Braunlehm (-Lessivé) in the sense of Kubiena in Stari Slankamen (Serbia) with a distinct Ckm horizon. This soil was earlier (1976) thought to be a soil of the “subtropical soil province” according to Kubiena. Later the F6 soil was correlated with the three soils of the S5 pedocomplex in Luochuan (1989) and therefore with the 5-6 soils in the two pedocomplexes PKVI and PKV at Karmaydan (1998), which were formed over a period of about 140 ka, although pedogenesis was interrupted several times by loess deposition. The F6 soil is therefore an example of a welded or multistory paleosol. Loess paleosol sequences of the early Würm period in the Central Asian Kashmir Basin are well comparable with those in Central Europe. For most of the Matuyama epoch, the central and lower parts of the sequence at Chashmanigar/Tadjikistan show more pronounced paleosols (about twenty) than the equivalent parts at Luochuan. In the Carpatian Basin only at Stari Slankamen are three strongly developed though truncated rubefied braunlehms (F9-F11) above Neogene sediments. In Lower Austria, however, many paleosols, mostly classified as Braunlehms, rubefied Braunlehms and Rotlehms, are exposed, especially in Stranzendorf and Krems-shooting range. Mineralogical investigations of the silt and clay subfractions show that there is little difference in the type and amount of pedogenic clay mineral formation between the Holocene soils and the paleosols of the Brunhes epoch at Karamaydan and of the Matuyama epoch at Chashmanigar. This suggests that the interglacial climates represented by the B or Bt horizons of the buried paleosols of late, middle, and early Pleistocene age were roughly similar to that of the Holocene. Therefore, the partly rubefied Braunlehms of middle and early Pleistocene age in the Carpathian Basin and in Lower Austria must be regarded as multistory paleosols.

Keywords : loess-paleosol sequences; multistory paleosols; paleoclimate.

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