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Early Middle Pleistocene sequences in the Upper Don Basin, Russia and their significance for correlations in Western Europe.

Charles Turner1
1 Department of Geography, University of Cambridge

Plenary 1 in Plenar Vorträge

18.09.2012, 13:10-13:50, H8

The Upper Don Basin is a broad lowland basin of western Central Russia, centred on an area equidistant from Moscow and the Black Sea. A basin of tectonic origin, going back at least to Miocene times, it is traversed by the valleys of the River Don and its tributaries, which have changed course substantially at times. Within the basin a rich variety of Pliocene and Pleistocene occur and have been investigated over many years. In particular these consist of: -

1) Fluvial aggradations, mostly of Pliocene to early Middle Pleistocene age. These consist mostly of fine to coarse sands and beds of silt, occurring as scattered outcrops or as marked terrace features. The preservation of deposits from such a long age range suggests gentle tectonic sinking of parts of the basin over that period, but followed by later uplift which has enabled downcutting by rivers to expose these earlier sediments, which can now be seen or excavated in river cliffs and the slopes of smaller valleys;

2) Sequences with alternating loess and paleosol deposits, preserved on interfluves, where they can be seen when exposed by the incision of dry valley systems (‘balkas’), or else emplaced above older fluvial deposits;

3) Tills of the Don Glaciation (MIS 16) deposited when the most extensive of the glaciations of the Russian Plain, poorly represented in Western Europe, filled the basin with a huge lobe of ice, extending down to about latitude 49 o N. This till horizon, visible interrupting both fluvial and loessic sequences, serves as a major chronostratigraphic horizon. Later glaciations such as the Oka (MIS 12) and Dnieper (MIS 6) did not directly impinge on the Upper Don basin;

4) Lacustrine deposits, laid down in hollows and valleys on the surface of the Don Till. These provide records of the ensuing interglacial complex and, exceptionally in one case, of most of the remainder of the early Middle Pleistocene. Occasionally thin beds of fine-grained, slightly organic lacustrine deposits, formed in meander lakes, are found within the fluvial aggradations, including those below the Don Till.

 

The onset of the early Middle Pleistocene, marked by the Brunhes-Matuyama palaeomagnetic boundary is recorded in at least two sequences. Certain kinds of biostratigraphical evidence are abundant from the early Middle Pleistocene (and also older) deposits. In particular the sandy fluvial deposits are exceptionally rich not only in fossil remains of freshwater and occasionally land mollucs, ostracods and fish, but also in a wide variety of small vertebrates – much more so than most Pleistocene fluvial deposits in Western Europe. Some of these fossil taxa are critical biostratigraphic indicator species, particularly the rodents, which have been well studied. The lacustrine deposits have yielded a variety of pollen diagrams, some extending over more than one temperate interval, and recording the changing environments between cold and warm stages of the early Middle Pleistocene in an area today close to the ecotone between steppe and temperate forest biomes.

 

Whereas the early Middle Pleistocene sequences of Western Europe, particularly of eastern England, the Netherlands and Germany are regarded as “classic”, they are notoriously fragmentary and have been the subject of repeated re-interpretation. The Don and adjacent Eastern European sequences can provide a fuller reference with biostratigraphic records that can be used to order and assist correlation of those of Western Europe.



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Letzte Änderung 14.08.2012