Sedimentary environments of glaciofluvial uplands and glaciofluvial crevasse fillings against the general background of other glacioaqueous environments
Abstract
Środowisko sedymentacyjne wysoczyzn glacjofluwialnych i glacjofluwialnych form szczelinowych na tle innych środowisk lodowcowo-wodnych
Glaciofluvial uplands have been recently characterized by the writer. They are mainly built of glaciofluvial stratified gravels and sands which in many places are interbedded and/or capped by comparatively thin and discontinuous beds of flow till. These uplands most probably represent features accumulated upon dead ice areas with prevailing braided system of glaciofluvial discharge coexisting with the glacial sensu stricto deposition from the protruding debris bands. Glaciofluvial crevasse fillings - very vaguely defined in the literature - are described here as originated from ice-slope-washing processes within crevasses in glacial ice, which (crevasses) were not steadily occupied either by running or by ponded water. This is revealed by very differentiated kinds of sediments, ranging from (flow) tills and poorly stratified gravels to laminated fine sands with silt. These sediments, however, do not show any regular pattern except that the coarse material was supplied from both sides of crevasse, and that it was suppliedd more abundantly in a final stage of deposition. Attention is drawn to the fact that “undulated” top surface of some eskers may have been a result of (final) changing from typical esker (running water) environment into a crevasse-filling environment described in the paper. A genetic subdivision of glaciofluvial features is also proposesd, with their sedimentary environments - running water, ice-slope-washing, dammed water - used by the writer as main criteria. Zones of deposition asssociated with the ice body - i.e. englacial, proglacial, ice-marginal—which until now have been used as main criteria, are treated here as subordinate ones. Very conscise remarks on sedimentaiy environments of glaciofluvial features, subdivided according to the mentioned criteria, are given as a background of the more detailed characteristics of glaciofluvial uplands and crevasse fillings.
Glaciofluvial uplands have been recently characterized by the writer. They are mainly built of glaciofluvial stratified gravels and sands which in many places are interbedded and/or capped by comparatively thin and discontinuous beds of flow till. These uplands most probably represent features accumulated upon dead ice areas with prevailing braided system of glaciofluvial discharge coexisting with the glacial sensu stricto deposition from the protruding debris bands. Glaciofluvial crevasse fillings - very vaguely defined in the literature - are described here as originated from ice-slope-washing processes within crevasses in glacial ice, which (crevasses) were not steadily occupied either by running or by ponded water. This is revealed by very differentiated kinds of sediments, ranging from (flow) tills and poorly stratified gravels to laminated fine sands with silt. These sediments, however, do not show any regular pattern except that the coarse material was supplied from both sides of crevasse, and that it was suppliedd more abundantly in a final stage of deposition. Attention is drawn to the fact that “undulated” top surface of some eskers may have been a result of (final) changing from typical esker (running water) environment into a crevasse-filling environment described in the paper. A genetic subdivision of glaciofluvial features is also proposesd, with their sedimentary environments - running water, ice-slope-washing, dammed water - used by the writer as main criteria. Zones of deposition asssociated with the ice body - i.e. englacial, proglacial, ice-marginal—which until now have been used as main criteria, are treated here as subordinate ones. Very conscise remarks on sedimentaiy environments of glaciofluvial features, subdivided according to the mentioned criteria, are given as a background of the more detailed characteristics of glaciofluvial uplands and crevasse fillings.