Pleistocene architecture and stratigraphy in the contact zone of ice streams and lobes in the south-eastern part of the Baltic Region

Autor: Bronislavas Karmaza, Violeta Pukelytė, Valentinas Baltrūnas, Danguolė Karmazienė
Rok vydání: 2019
Předmět:
Zdroj: Quaternary International. 501:21-32
ISSN: 1040-6182
DOI: 10.1016/j.quaint.2017.10.019
Popis: Rich material obtained during the glacigenic topography researches shows that the advance of the ice sheet and deglaciation of the area took place in a shape of ice streams, substreams and lobes. During the last glaciation, the south-eastern part of the Baltic Region had been covered by ice on a form of three ice streams, which, in its continental part, were dividing into smaller substreams and lobes differently named in the scientific literature. The goal of the present study is to discuss the glacial multilayerness of the Pleistocene strata in the SE Baltic Region as a phenomenon of palaeo-ice streams, substreams and lobes in the contact zone. The material of previous researches is analysed, as well as published data and new findings of the authors are used. The material available on the Middle Pleistocene Žemaitija till occurring at the depths from 10 to 175 m along the NW–SE distribution of the deposits shows differences in petrographic composition of gravel and pebble beds for the western and eastern sectors. The deposits of the Middle Pleistocene occurring at the surface the Ashmyany Upland and the Lida Plain in this region are thought to be a result of two different asynchronous ice substreams. In the area of the last (Nemunas) glaciation, the ice sheet of two stages – maximum Grūda and the younger Baltija – also formed tills differing in features and composition, thus, testifying the result of different ice streams and substreams. The statistical correlation analysis for the most widely occurring palaeosurfaces of tills in the South Lithuania revealed that the positive coefficient of adjacent surfaces was increasing with the occurrence depth. A conclusion is made that different dynamic activity of ice streams and substreams is a natural and objective phenomenon. Therefore an ice stream, substream or a lobe of the same glaciation but of different stages (phases) could move into a depression formed by another (adjacent) substream or lobe. The multilayered character of the Pleistocene strata in the South Lithuania can be explained by different manifestation of glacial till layers formed by ice streams, substreams or lobes of the same glaciation but of different stages (phases). Application of this conception makes easier the stratigraphic interpretation of the Pleistocene deposits in the region.
Databáze: OpenAIRE
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