Browsing by Subject "grain-size determination"

Subsurface sediments were investigated by radar acquisition campaigns and sedimentological investigations in Kersilö area, Sodankylä, central Finnish Lapland, in order to provide information about the sedimentology and stratigraphy of the area, and to construct the succession of events related to the glacial and postglacial development of the subsurface sediments. The study area covers an about 150 km2 area around Kitinen river. The subsurface is controlled by unconsolidated coarse-grained sediments with a mean grain-size ranging from sand to gravel. Typical thickness of the overburden varies from 5 to 15 metres, exceeding 20 metres in places. Eastern part of the study area is covered by Holocene peat of Viiankiaapa mire, underlain by clastic sorted sediments and till. Eastern river bank is characterized by sorted sediments interpreted to represent an ancient braided-river environment. Western side of the river presents extensive sorted sediment deposits, interpreted to represent extramarginal-outwash and braided-river sediments. Till beds are more dominant in the western side of the river. Stratigraphy of the Kärväsniemi test site comprises three sandy till beds, estimated to represent Early, Middle and Late Weichselian glaciations. The till units are interbedded by more sorted fluvial sediments, estimated to have Early and Middle Weichselian and Holocene origin. Absolute age determinations from the middle sorted sediment assemblage suggests Odderade Interstadial between the Early and Middle Weichselian glaciations. Ground penetrating radar, utilising 50 MHz and 100 MHz antennas, proves its suitability for investigation of fluvial deposits of a proglacial environment, with abundant coarse-grained sediments. Quality of the data enables identification of lithological interfaces within and between sediment units. Seven radar facies and facies associations are identified, and classified as organic, glacial and fluvial sediments. Fluvial sediments include five radar facies and facies associations characteristic of fluvial deposits. The sediments indicate a succession where glacial deposits alternate with fluvial sorted sediments indicating ice-free events. Fluvial activity is estimated to have been repetitious and especially intensive during the last deglaciation, possibly causing partial erosion of the till beds. Formation of organic peat started in the area after the final retreat of the Scandinavian Ice Sheet. Clastic surface sediments indicating deglacial to Holocene origin have experienced partial reworking by wind and floodwaters.