GLACIOTECTONIC DEFORMATION PATTERN IN ESTONIA

A set of glaciotectonic deformations in Estonia have been described in connection with different substratum lithology; a) bedrock dislocations associated with a rigid environment, and b) soft bed deformations associated with unconsolidated drift masses. Glaciotectonic features have been classified in five main categories. (1) Ridges, hills and composite massifs built of disturbed Quaternary substratum, which have clear topographical expression. Composite massifs are a system of individual glaciotectonic landforms and composed largely of unconsolidated Quaternary strata. Ice-shoved hills and ridges (push moraines, cupola hills, drumlins) are created at or near ice margins during ice-lobe advance or readvance denoting ice marginal positions of different stadials or oscillations. (2) Point samples of buried disturbed sediments are described in connection with buried dislocated interglacial (Holsteinian and Eemian) deposits. They have no morphologic expression in relief. (3) Point samples of disturbed pre-Quaternary substratum include bedrock dislocations, fracture disturbances, folds and fissures with no morphological expression. (4) Large glacial rafts, mostly with morphological evidence, are allochthonous masses of dislocated bedrock or Quaternary substratum. (5) Glacial depressions as typical ice scooped landforms are associated with concealed glaciotectonic deformations initiated by lateral pressure of the surged glacier near the outline of depressions. Glaciotectonic disturbances in hard rock appear due to pre-existing tectonic dislocations. Tectonically loosened bedrock blocks can easily be incorporated into the glacier sole and transported subglacially by shearing or proglacially by pushing. Glaciotectonically folded sequences with number of faults in poorly consonsolidated bedrock have a subglacial origin with thin deformed layer in till/sandstone continuum. Deformation in soft drift sediments are formed proglacially by compressive deformation represented by push moraines, either by subglacial ductile deformation by shearing movements represented by drumlins and hummocky moraine.