The reliability of methods of distant lithological correlation of tills is especially important due to the known spatial limitations of climatic stratigraphic reconstructions and problems of interregional correlations. It is reasonable to put forward mineralogical analysis as essential for studies of glacial horizons of different age, since it is widely used for stratigraphical subdivision of glacial sequences and for spatial correlation of marker horizons. The many years of study of terrigenous and clay mineral components of tills from the formerly glaciated terrains of the Central and Northern Russian Plain and generalization of the obtained materials allow to identify certain trends in spatial and temporal variations of mineralogical indices as related to the ice stream structure and provenances. The established regularities in radial, zonal and provincial variations of the spectra formed the basis for understanding possibilities and limitations in interregional lithological correlation of tills of different age.

In order to lithologically correlate tills from different regions we propose to use maps of lithological-paleogeographical zonation of a territory according to the type of ice sheet alimentation, structure and dynamics. The base of lithological correlation is the system of lithological regions. The main principles of the lithological-mineralogical correlation are as follows: i) consideration of the balanced influence of distant, transit and local provenances; ii) integrated analysis of associations of terrigeneous, autigenous and clay minerals; iii) consideration of the spatial and temporal variability of mineralogical indices. The following criteria are shown to be the most significant: minerals-indicators of distant areas of glacial erosion, their correlation with the local minerals, and sustainable mineral associations.

In accordance with the paleogeographical concept of the glacial lithogenesis the rules for distant lithological correlation have been recommended. Radial correlation of tills within a single sector is based on zonal variations of unresistant components in the distal direction. Sub-latitudinal correlation of markers from different ice streams is more complicated since the objects are influenced by various distant, transit and local provenances. In this case the variability of tills within sectors should be considered.

The efficient use of the methodology helps reliable tracing of the markers till of different age by their composition. It is necessary to correct for some changes in till mineral spectra: the west-east decrease in content of minerals-indicators of Scandinavian origin (hornblende, garnet, illite) compensated by an increase of epidote, smektite and other components of the Northern Urals area in the same direction.

The further elaboration of the methods of distant correlation of tills will make the lithological approach a more reliable constituent of climatic and stratigraphical reconstructions.

Reference:

Sudakova N.G., Nemtsova G.M. Methodological approaches and perspectives in the interregional lithological correlation of tills. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 98.