Sedimentary record of a Scandinavian Ice Sheet drainage system and till deposition over subglacial obstacles promoting basal sliding (an example from southern Poland)

摘要: Abstract Subglacial obstacles occurring in the path of advancing ice sheets generally generate higher longitudinal compression and frictional drag than a flat substrate. However, case soft sediment substratum, they can have very different effect on sheet behaviour. This study concerns substrate composed fine-grained sediments with low permeability. The relationship between subglacial overriding Scandinavian Ice Sheet was studied an area southern Poland where small intervalley Neogene clay ridge (40 m high) present. Based sedimentological structural analysis till gravelly–sandy sediments, basal depositional processes conditions their influence behaviour were analysed. related deposits within reflecting high water pressure lack glacitectonic deformations indicate that did not much resistance against sheet, but instead favoured slip: impermeable substratum weakened ice/bed coupling promoted detachment from substratum. Gravelly sandy inclusions at till/clay contact during first stage overriding, canal drainage system developed ice/substrate interface. Varied geometry, size location sorted suggest periodic instability system, which could lead to its transformation initially uniform being conduits sizes. During later stages traction deposited occasional through film sufficient evacuate meltwater. resulting change character probably variations gradient progressive advance.