Petrographic composition of pebbles in Upper Pleistocene and partly Middle Pleistocene tills in the Polar Ural and Pai-Hoi has been studied in the course of geological mapping, quadrangles Q-41 and R-41, scale 1:1 000 000. The detected representative fragments of concrete formations and magmatic complexes allow to reconstruct directions of ice motion.

The pebble composition of Lower Valdai tills independently confirms the Kara Sea ice motion from Pai-Hoi southward into mountain valleys, as reconstructed by Astakhov, Mangerud, Svendsen and others (1998, 1999, 2004). In the area of Riphean volcanic rocks of the Bedamel Series in the core of the Malokarskaya anticline within river valleys of Bol. Kara and Mal. Kara there are up to 30% of limestone pebbles. Among them marbleized limestone of the Nyarminsky Reef, dark-grey limestones of the Tournaisian and Visean stages known from bedrock at 30-50 km to the west, Pai-Hoi jasper of the Gromashor formation, coaly-siliceous shales and loop-shaped limestones of the Harota and Oy-Yu formations have been identified.

The Harbei till pebbles to the south-west of Pai-Hoi persistently contain up to 30% of Carboniferous limestones of the Pai-Hoi Anticlinorium. Along its axis limestones are virtually absent in till pebbles. Polymict sandstones of Permian age from the Kara Depression, glauconitic sandstones of the Cretaceous, the allogenic breccias from the Kara Astrobleme dominate in pebbles of the northeastern slope of Pai-Hoi. All these facts indicate quite unambiguously an ice motion from the Kara shelf toward southwest, across the axial part of Pai-Hoi.

Glaciers, which moved westward from the axial part of the Polar Urals, coalesced into a piedmont lobe that covered an area с 400 sq. km. This Bol. Usa lobate system blocked a further southward advance of the Kara ice. The Bol. Usa till contains only local, Uralian rock fragments, namely, lilac and green quartzitic sandstones, and dolerites from a proximal side of the mountain range. The polymict gritstones of the Hoidyshor formation, occurring only in this area of the axial zone of the Urals, are easily recognizable. The Harota, Kechpel and Hoy la moraines are very similar. An Early Valdai age of these tills is firmly established based on the presence of two incised alluvial terraces (the Syr-Yaha and Yarvozh) in the valleys of Kara, Mal. Usa, Bol. Usa rivers, and also on the Paleolithic site (Pymva-Shor) dated by radiocarbon method (Mangerud et ah, 1999). Upper Valdai moraines are localized exclusively within alpine troughs of the Polar Urals. The pebble composition reflects the bedrock lithology in the accumulation area.

The fragmentary Middle Pleistocene tills have been studied in the intramontane depression of the Yenganepe Range and the western foothills of the Polar Urals. Numerous pebbles composed of biogenic limestone of the Carboniferous Sart-Yu formation have been identified in tills within the area of Pre-Paleozoic formations of the Bedamel Series on the Yenganepe. This limestone originates from the bedrock in the north, from the area of confluence of rivers Bol. and Mal. Usa. In the western foothills of the Polar Urals between rivers Kechpel and Bol. Hoyla boulders of pink and lilac quarzitic sandstones are ubiquitous. They belong to the Manita-Nyrd Series that makes bedrock far to the north. This indicates a Middle Pleistocene ice motion from the north along the main range down to the latitude of river Bol. Hoyla

However, Middle Pleistocene pebbles in the foothills of the Subpolar Urals demonstrate a predominance of fragments of local Uralian rocks originating in the axial zone of the mountain range. It suggests a divergent ice motion in both western and eastern directions.

Reference:

Shishkin M.A. Ice flow directions of Pleistocene glaciers on the Pai-Hoi and Polar Urals based on till pebbles provenance. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 84.