Recent drilling at Muhos, northern Finland has revealed an exceptionally thick Quaternary sediment cover, overlying the unmetamorphosed Neoproterozoic Muhos Siltstone Formation in the Oulujoki River Valley. Here we report preliminary petrographical, geochemical and heavy mineral results from four till units from the Muhos drill-core. The drilling site is located at 27 m asl, c. 1 km south of Oulujoki River and 30 km SE from the city of Oulu and the present shore of the Bothnian Bay of the Baltic Sea. The drilling at this site was performed with a GM 200 GTT drilling platform using 1 -m long sample tubes (HDPV, diameter 5 cm) inside the stainless steel cover tubes. The coring penetrated down to the siltstone bedrock 54 m below the ground surface and the sediment core recovery was over 75%. The sedimentary sequence from the ground surface down to the local siltstone bedrock consists of four till units interbedded with sand/silt/clay beds. The upper two till beds, Mu-1 and Mu-2, are interpreted as being deposited during the Weichselian Glaciation between 115 000–10 000 years ago, the third till bed Mu-3 during the Saalian and the lowest till bed, Mu-4, during the Saalian or pre-Saalian glaciations, i.e. till beds Mu-3 and Mu-4 prior to c. 130 000 years ago. Petrography of the coarse fraction, geochemistry of the fine fraction and heavy minerals of the sand fraction were studied from all four till units and the Muhos siltstone samples. Coarse and fine fractions were separated by dry-sieving. The fine fraction was analysed by XRF and AAS. The mineralogical composition of the heavy fraction was studied by FESEM+EDS and SEM+EDS. The lowest till bed Mu-4 can be divided into three subunits. On the basis of clast content, geochemistry of till fines the ice movement direction was from the NW or NNW during the deposition of the lowermost brown and red till units. The composition of the upper grey unit of till bed Mu-4 shows that the ice flow direction was from the WNW. Petrographical composition of till beds Mu-3 and Mu-2 indicates that the ice flow again was from the NW whereas the petrographical composition of the uppermost till bed Mu-1 suggests that the ice flow during this deposition phase was from the WNW. Younger till beds studied have in part also some reworked and re-deposited material from the older till beds. Supplementary material: The percentages of the rock types in pebble and gravel fraction, XRF and AAS analysis of the samples and identified mineral species of the heavy sand fraction are available at: http://www.geolsoc.org.uk/SUP18659
The SIS (Scandinavian Ice Sheet) became divided into several active, semi-independent ice lobes during the last deglaciation ca 13 000-10 000 years ago. The largest of them, the North Karelian/Oulu Ice Lobe (NKIL/OIL), covered vast areas in central Finland and in northwest Russian Karelia. This paper studies the behaviour and subglacial conditions of the NKIL/OIL with the inversion modelling method. The method is based on the identification and interpretation of mapped glacigenic streamlined lineations, formed during active flow stages of the NKIL/OIL. DEM and LiDAR data on lineations was obtained from seven subsets in different zones of the NKIL/OIL. Results indicate that the NKIL/OIL dynamics were strongly affected by pre-existing Quaternary sediment thickness, bedrock lithology, structures and topography. Due to these factors, the NKIL/ OIL operated through several flow corridors and had several retreat and re-advance cycles throughout its life span.
Glaciofluvial ice-contact deltas were mapped and altitudes of the highest shorelines defined in the eastern arc of the Salpausselkä zone, southern Finland, using Light Detection and Ranging (LiDAR)-based digital elevation models and GIS tools. Mapping of deltas and the highest shorelines in the Salpausselkä zone were undertaken in order to calculate and define the glacio-isostatic uplift palaeo-isobases, uplift gradients and equidistant diagrams (distance diagrams) for the Salpausselkä zone. The results indicate that the glacio-isostatic uplift palaeo-isobases were orientated NE-SW (50°-230°) and the uplift gradients for both the First and the Second Salpausselkä in the eastern arc, are virtually the same, namely 0.6 mkm-1. This suggests that both Salpausselkä ridge complexes, which were originally laid down in front of the Finnish Lake District Ice Lobe (FLDIL) in relatively shallow water, were deposited within a short time period during the Late Weichselian Younger Dryas Stadial. The results also suggest that the Baltic Ice Lake water level regressed 7.5 metres from Baltic Ice Lake level B I to level B III as the ice retreated in its eastern arc from the First to the Second Salpausselkä.
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