Mid‐Weichselian interstadial in Kolari, western Finnish Lapland

Abstract

Finnish Lapland is known as an area where numerous sites with sediments from Pleistocene glacial and interglacial periods occur. Recent sedimentological observations and dating call for reinterpretation of the record, which shows a complicated Mid-Weichselian ice-sheet evolution within the ice-divide zone. Here, a large, previously unstudied section from a former Hannukainen iron mine was investigated sedimentologically and dated with optically stimulated luminescence (OSL). Ten sedimentary units were identified displaying a variety of depositional environments (glacial, glaciolacustrine, fluvial and aeolian). They are all -except for the lowermost, deeply weathered till -interpreted to be of Mid-or Late Weichselian/Holocene age. Five OSL samples from fluvial sediments give ages ranging from 55 to 35 ka, indicating two MIS 3 ice-free intervals of unknown duration. The Mid-Weichselian interstadial was interrupted by a re-advance event, which occurred later than 35 ka and caused glaciotectonic deformation, folding and stacking of older sediments. This new evidence emphasizes the importance of the Kolari area when unravelling the complex Late Pleistocene glacial history of northern Finland and adjacent regions. -Pekka Salonen (veli-pekka.salonen@helsinki. Veli

A hydrostratigraphical approach to support environmentally safe siting of a mining waste facility at Rautuvaara, Finland

“…It hosts a complex Quaternary stratigraphy, as shown in previous studies by Hirvas (1991) and Lunkka et al (2014) at Rautuvaara, and Salonen et al (2014) at Hannukainen. Also, because of the historic prospecting and mining at Rautuvaara, the bedrock composition is well known.…”

“…However, a recent study by Lunkka et al (2014) has challenged this interpretation and has proposed that the Rautuvaara site comprises of sediments only from the Late Pleistocene, mostly representing glacial and non-glacial lacustrine sediments of Weichselian regional stage. This is supported by observations from the nearby Hannukainen locality, where Mid-and LateWeichselian sediments built up a sediment series with a considerable thickness of 20-30 metres (Salonen et al, 2014). However, it is also possible that pre-Weichselian sediments exist within the area, as demonstrated with the Sivakkapalo interglacial site (Hirvas, 1991;Johansson et al, 2005) about two kilometres south-east of Rautuvaara.…”

“…Based on the results presented here, previous publications from the Rautuvaara (Hirvas, 1991;Lunkka et al, 2014) and Hannukainen areas (Salonen et al, 2014), and percussion drillings related to mining activities in the area (Korvuo, 1981), it is possible to divide the examined strata into three main sedimentary successions each of which representing a glacial/ice-free cycle. The lowermost stratigraphical succession I consists of Mid-Weichselian sediments.…”

“…This event was followed by a second MidWeichselian ice-free period (Johansson et al 2011) with meltwater, fluvial activity (sands and gravels in Unit 4) and lacustrine conditions (Unit 5) dating back to around 36 ka. Thick Mid-Weichselian sand and gravel deposits are also reported from Hannukainen (Salonen et al, 2014), where they have been interpreted as delta foreset sediments, 35 to 39 ka old. Delta/outwash deposits in Sadinkangas and Aavahelukka are also of this age, and it is possible that the coarse-grained bar-like deposits in the centre of Niesajoki valley (TP15) are related to that icefree phase.…”

“…The lowermost stratigraphical succession I consists of Mid-Weichselian sediments. Till Unit 1 can be related to the first Mid-Weichselian glaciation (Johansson et al, 2011), which is overlain by thick, inter-glacial Mid-Weichselian fluvial sands, Unit 2 (Lunkka et al, 2014, Salonen et al, 2014 (Fig. 8).…”