Struktury sedymentacyjne plejstoceńskich osadów wodnomorenowych a teoria struktur glacidynamicznych

Abstract

Polemiczna wypowiedź autora na temat teorii tzw. struktur glacidynamicznych jest oparta na wynikach badań sedymentologiczno-strukturalnych specyficznego typu osadów glacjalnych, tj. osadów wodnomorenowych. Podstawą do dyskusji jest podobieństwo zbadanych struktur sedymentacyjnych osadów wodnomorenowych i ich mutacji glacitektonicznych ze strukturami znanymi z literatury jako glacidynamiczne.SEDIMENTARY STRUCTORES IN WATERMORAINIC PLEISTOCENE DEPOSITS VERSUS THE THEORY OF GLAODYNAMIC STRUCTURESThe complexes of watermorainic, deposits are formed of flow tiils deposited by mudflows and stratified meltwater sediments deposited by meltwater. Watermorainic deposits originate during deglaciation at the surface of an icesheet, in its forefield, fissures and caverns inside and beneath icesheet, and melted-out passages between dead-ice blocks. They are represented by stratified complexes of flow tills, layers varying in lithology and without any stratigraphic value, interfinging lenses varying in size, as well as stratified complexes of meltwater sediments with flow-till lenses and blocks. Characteristic structures are those of the flow type, resulting from plastic flow and gradual stabilization of water-saturated rock material.A marked similarity of sedimentary and synsedimentary structures of watermorainic deposits and the same structures modified by glacitectonic processes to so-called glacidynamic structures is the basis of the objections raised by the author against the theory of glacidynamic structures.The objections raised against glacidynamic structures are mainly centred on the mechanism of gathering deposits from icesheet basement and their preservation in undisturbed form during transport in the icesheet. According to the author, several structures hitherto regarded as g1acidynamic display the nature of sedimentary structures or glacitectonic ones which disturb the sedimentary structures in watermorainic deposits.An appropriate genetic interpretation of individual structures in glacial deposits requires multidirectional studies which should primarily concern textural properties of the deposits (with refrence to results of analyses of grain-size distribution, roundness and petrographic composition of grains, and orientation of longer axes of boulders), geometry and interrelationships of structures, nature and vertical range of disturbances, and degree of involvement of individual sedimentary layers in disturbances.