Characterization of till units under glaciofluvial deposits in south western Lapland

This master’s thesis mainly aimed to characterize and compare till samples, collected in southwestern Finnish Lapland, through geological, chemical, and mineralogical analyses. The intent was to study their possible relationship with the underlying geological layers, mainly linked to the Central Lapland Granitoid Complex (CLGC) and the Peräpohja Belt (PeB), as well as with glacial flow directions during different glaciation periods. Till samples collected at various depths within the same borehole and at different boreholes were analyzed and compared, in order to identify mineralogical and chemical variations as functions of both depth and geographical location.

Three analytical approaches were employed. Firstly, the Grain Size Distribution (GSD) analysis was done, to determine the different grain size classes in the samples, from clays to large pebbles, constructing a GSD curve. GSD analysis included two techniques, according to the grain size: the dry sieving and the PSA (Particle Size Analyzer) method. Secondly, the chemical analysis was done using a portable XRF, which determined the elemental composition of the samples; the data was then converted to oxides for better interpretation. Finally, a mineralogical analysis was conducted through FE-SEM, which could identify the mineralogical composition of the samples. The mineralogical results were compared with the expected ones, based on the analysis of the extraction coordinates and correlation with the geological maps provided by the GTK. GSD curves findings demonstrated that there are notable variations in grain size dimensions with depth, an event related to reworking processes over time, like glacial flows. Chemical data from pXRF together with the mineralogical findings obtained from FE-SEM, allowed to identify the different lithologies from which the samples derived. Moreover, intra-borehole differences affirmed changes in glacial flow directions over time, while variations between boreholes highlighted interactions between glacial flows and lithological layers.

Overall, glacial tills and the relationship between geological substrates and glacial activity was successfully characterized by this study. The integration of three different analytical techniques was complete enough for a comprehensive understanding of till composition and the geological processes that characterized sedimentary events in southwestern Finnish Lapland.