The multiple regional stratigraphic and correlation schemes are contradictive because of various interpretations of the stratigraphic position and rank of the Middle Pleistocene glacial horizons. To solve the problem the authors have jointly performed an integrated study of the Middle Pleistocene till composition in the North-East and in the Center of the Russian Plain using a uniform methodology and criteria developed according to the paleogeographic concept of glacial lithogenesis (Sudakova, 1990).

The presented solution of the problem of inter-regional lithological correlation of marker tills is suggested based on provenances of the glaciated area (Andreicheva et al., 1997). The rhythmostratigraphic principle of subdivision of the glacial sedimentary complex has also been employed. To increase objectivity of the correlations special attention has been paid to spatial and temporal regularities of lithogenesis. Formal rules for latitudinal and meridional correlations of tills of different age have been introduced and used.

In the Middle Pleistocene composite succession of the central Russian Plain the Dnieper (310-270 kyr BP - isotope stage 8) and Moscow (220-150 kyr BP - isotope stage 6) glacial horizons with contrasting characteristics of the constituting tills are distinguished using integrated geological, geomorphological, lithological and biostratigraphical data controlled by paleomagnetic and geochronological parameters (Sudakova, 1990, 2005). The distinct features of the mineralogic-petrographic composition are due to the sharp reorganization of stream pattern, ice sheet regime and general change of the ice flow direction. The analysis of lithological features of the tills of different age in the area stretching from the upper Oka and Volga up to the rivers Vychegda and Pechora suggest the correlation between the Dnieper and Pechora horizons, and between the Moscow and Vychegda horizons. This correlation is based on similarity of indicator minerals, of petrographic composition and isorientation of pebbles, of ratio erratic/local fragments (Andreicheva, 2002; Andreicheva et al, 1997).

A Middle Pleistocene age of the glacial complex has been reliably established by biostratigraphy in a series of key sections. In the central area these are Chekalin, Rybinsk, Zagorsk and others, in north-east - Rodionovo, Seida, Laya, etc. New palynological evidence of interglacial environments between the Dnieper and Moscow glaciations have been received in the Satino polygon (Rychagov et al, 2005), which allows to correlate these deposits with the Rodionovo horizon of the northeastern Russian Plain.

Thus, the collateral biostratigraphical data and specifics of lithological composition unequivocally testify to different conditions of sedimentation and, therefore, to independence of these glaciations. The obtained integrated evidence for distinguishing and inter-regional correlation of the marker horizons of the Middle Pleistocene is an argument for updating the stratigraphic schemes of the Russian Plain. In the existing schemes, in particular, an early Middle Pleistocene glacial horizon (the Dnieper, the Pechora - isotope stage 8) is erroneously replaced by its hypothetical counterpart corresponding to a short Kaluga cooling observable solely in the Chekalin section.

Reference:

Andreicheva L.N., Sudakova N.G. Problems of correlation of the Middle Pleistocene events in the northeastern and central Russian Plain as related to modernization of the regional stratigraphic schemes. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 6.