The role of principles and methods in loess-paleosol investigations

In the process of loessification, the development of loess fabric, the role of zonal, regional and partly of local environmental factors is regarded decisive. In the loess sequences various genetic types of loess pockets and paleosols occur and reflect different climatic and paleogeographical conditions.As a consequence, even within a single profile the colour, grain size and mineral composition, CaCO₃ content, degree of weathering and fabric of loess may vary. Zonal, regional or even local variations in such loess properties may equally derive from syngenetic or postgenetic processes. For similar reasons, spatially and temporally different forms, types and subtypes of paleosol also developed.This way, loess and soil formation resulted in various spatial types in the same glacial, interstadial or interglacial phase in the various geographical zones and regions. Although there exist major loess regions where the interglacial soils (eg brown forest soils) are markedly distinct from interstadial steppe soils or from other types of humic soils, continental loess areas can also be observed where the paleosols developed under interglacial and interstadial conditions (eg steppe or forest steppe soils) cannot be referred into different genetic types. In such cases the changes in paleoenvironments are difficult and uncertain to reconstruct.The interregional correlation of paleosols is occasionally hindered by the various terminologies applied to denote them. In addition, there are uncertainties concerning the dating and identification of paleoenvironments of polygenetic soils and of soil complexes consisting of paleosol units: how many soil formation phases they represent and how long erosional gaps can be reckoned with between these phases.     

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The loess-paleosol and related subaereal sequence in Hungary

The loess of type localities is subdivided into 3 subseries on the basis of the paleosols allowing even an Eurasian comparison for their lithostratigraphy.

1. The upper young loess (8–10 m) is most widespread, characterized by 3 sandy loess and 2 intercalated humic loess horizons. The ages of the humic loess horizons H₁, H₂ are c. 16 ka and 20 ka BP, respectively.
2. The lower young loess (15–20 m) contains 4 loess packets and 3 chernozem-like paleosols, usually doubled soil complexes (designated MF, BD, BA). The MF paleosol complex, first member of lower young loess is c. 27–28 ka BP (C¹⁴ and TL dating). The lower young loess is underlain by a brown forest soil and chernozem-like paleosol-assemblage (MB), probably formed during the last interglacial (c. 105–125 ka BP).
3. The old loess (c. 20 m) is generally characterized by 6–7 loess, mainly brown forest soil and 2 interbedded fluvial sand layers. The lowermost old loess member and an ochre-red paleosol lie below the Brunhes-Matuyama boundary (0,73 Ma).
4. The loess is underlain by a subaerial non-loessic sequence (20–40 m) with 5–10 red soils, red clays mostly directly superimposed on and locally interbedded by sand and silty sand. At the base of this sequence of red paleosols usually Uppermost Miocene inland sea deposits are found.

It can be concluded that the reddish paleosol developed under climatic, and in general, ecological conditions (probably warm subhumid with rapid cyclical climatic changes) differing from the cold and semiarid or semidesert environments of typical loess formation. The former conditions were characteristic — from the Lower Pliocene to the Lower Pleistocene — on continental or global scales.     

Problems of loess chronology

Loess as a typically subaerial, loess deposit has long been regarded a Pleistocene sediment and its date of formation has been put to ca 600 ka BP. Recently, the beginning of the Pleistocene is identified in the official concord reached — at 1.6 Ma BP, while not infrequently others propose 2.4 Ma BP. Until the fifties the whole loess (loess-paleosol-sand) sequence could be referred into the shorter Pleistocene period, which —according to the climatic claendar by Milankovitch — consisted of nine cold and eight warm intervals. Some supporters of the longer Pleistocene chronology hold that the beginning of loess formation can be put as far back as 1.6 – 2.4 Ma BP. Loess formation intervals are usually correlated with the cold stages (nos 2, 4, 6 etc.) of the Emiliani oxygen isotope timescale, while soil formation is believed to correspond to the warm stages (nos 1, 3, 5, 7 etc.). The typical loess, i. e. loess proper, are not older than stage no 23 (Jaramillo event — 0.96 Ma BP). Previous to this date climatic conditions had not generally favoured loess formation and paleosols formed one above the other with clay, loam or carbonate intercalations.