Microtexture and provenance signatures for oscillations of the late Pleistocene Scandinavian Ice Sheet in Rautuvaara, north-western Finland

In order to understand sedimentary processes and dynamics of ice sheet oscillations on the eastern flank of the Scandinavian Ice Sheet (SIS) near its glaciation centre, we carried out quartz grain surface microtextural, and heavy mineral studies from the Rautuvaara section in north-western Finland which has widely considered as the stratotype for the northern Fennoscandian Late Pleistocene. We investigated the two uppermost Middle-Late Weichselian tills and the interbedded fine sediments, which, according to published age constraints, were deposited during the late Pleistocene Marine Isotope Stages (MIS) 3 and 2. The purpose of this study is to use varietal heavy mineral analysis to better constrain sediment sources for studied sediments and to test a theory of ice flow origin in this area. Microtextural study is used to identify first cycle subglacial processes from multiple transport processes during deglaciations. At the stratigraphically lowest studied till bed, the sediment grain characteristics indicate that primary transport processes were subglacial and the SIS advanced from SSW across the area during the Middle Weichselian (MIS 3) as skarn and iron ore minerals are dominant heavy minerals. The upper part of the till bed bears an imprint of some longer distance transport processes from NW granitoid dominant provenance. The grain surface microtextures of the overlying sandy diamicton bed do not show any specific transport signature, suggesting that this bed consist of supra- or englacial debris deposited by a retreating ice front through mass flow. Subsequent layers of interbedded horizontal to rippled and massive sand and silt are characteristic of glaciofluvial transport processes representing shallow to deepening water conditions and gradually basin filling in a glaciolacustrine setting. The occurrence of highly stable detrital minerals in sand, like epidotite, garnet and zircon indicate clear reworking of earlier materials. The uppermost massive till represents Late Weichselian (MIS 2) glacial advance phase again dominantly from SW including reworked Rautuvaara iron ore indicative heavy minerals and showing multiple transport histories in quartz sand grains microtextures, being affected by some chemical abrasion.