Volume 17 (2011): Issue 2 (June 2011)

Structural and petrographic study applied to the gneisses from the eastern part of the Orlica-Śnieżnik Dome, indicate that two different types of gneiss are present. The Śnieżnik gneisses are porphyrithic granites, constricted and sheared into L-S tectonites, most commonly with augens; the Gierałtów gneisses are sheared migmatites, porphyroblastic gneisses and banded gneisses, with two sets of metamorphic foliation, intrafolial folds and lensoid leucosome aggregates or metamorphic porphyroblasts. Both lithologies were later zonally sheared and transformed into more or less deformationally advanced mylonites, difficult to be distinguished from one of the two types. Identification of the Śnieżnik and Gierałtów gneisses is possible only between zones of the late (Variscan) shearing, in which the original, pre-kinematic structures are preserved.

Danian and Selandian successions in western Siberia are rich in calcareous benthic foraminifers. The assemblages with a constant systematic composition that have the widest lateral occurrence are distinguished as foraminiferal zones. The Brotzenella praeacuta Zone was established in the low-carbonate, clayey beds that form the transition from the Gankinskaya Suite to the Talitskaya Suite. These transitional beds are assigned to the Danian. The calcareous benthic foraminifers in this zone occur mainly together with agglutinated forms. The zone is traced along the areas of the largest subsidence of the Mesozoic-Cenozoic basin, principally in depressions. The transition from the Cretaceous to the Palaeogene is represented by a continuous succession, in which the Danian deposits escaped from erosion and were found to contain the B. praeacuta assemblage. In Danian rocks with a shallow-marine facies (near Beryozovo and in the Ust'-Tym depression, Fig. 1), the Bathysiphon nodosarieformis - Glomospira charoides assemblage occurs. It is dominated by primitive forms in addition to more advanced tests (mainly Late Maastrichtian relic species).

The overlying Selandian (Middle Palaeocene) foraminiferal assemblages are assigned to the Talitskaya Suite. The Ammoscalaria friabilis assemblage is widely spread and is represented mainly by agglutinated quartz-siliceous forms. Beds with these species are attributed to the Ammoscalaria friabilis Zone, which can be correlated with beds in the East containing Cyclammina coksuvorovae. The Cibicidoides proprius assemblage is known from the lower and middle beds of the Talitskaya Suite in Transuralia, the Omsk Depression and more south-eastern areas; the species of this assemblage are characteristic of the Selandian.

The lithology, structure and geophysical characteristics of the glaciolacustrine clays deposited in the Wierzchowo proglacial lake were determined using static penetration tests (CPTU) in combination with standard lithological measurements. The deposits are divided into four lithological units (R1 to R4) on the basis of overconsolidation. Units R3 and R4 are separated by mass-flow deposits.

The depositional conditions history of the lake result represent four phases: (1) an initial (low-energy) phase with the deposition of the rhythmically laminated sediments of units R1 and R2, which are divided by an erosional interval; (2) a phase of non-deposition with some desiccation structures and extended consolidation of sediments; (3) the main phase characterised by deposition of the rhythmically laminated sediments of unit R3; and finally, (4) the youngest phase, which represents alternations of deposition and erosion. The results show that sedimentation in the Wierzchowo proglacial lake was less continuous, and that the depositional processes were more complex than in the neighboring Złocieniec glacial lake.