Kettle holes ‐ stratigraphical archives for Weichselian geology and palaeoenvironment in northernmost Sweden

Abstract

An active search for pre‐Holocene organic deposits in stratigraphically well‐defined positions has proved to be a useful tool for reconstruction of glacial and non‐glacial Weichselian development in northernmost Sweden. The investigations have been concentrated to kettle holes connected to eskers belonging to a morphologically prominent northwesterly glacial system characterized by extensive drumlinization. Organic deposits, radiocarbon‐dated as older than the Holocene, have been found at some 25 localities. Some sites display two organic‐bearing sequences separated by a till bed. The pollen flora in the lowest organic bed reflects an interstadial vegetational development: Arctic shrub and herb tundra‐subarctic light birch forestherb tundra with ericaceous shrubs and dwarf birch. This interstadial is correlated with Peräpohjola in Finland. During the younger Tärendö Interstadial the vegetational development was similar, but a more continental climate is indicated hy high values of steppe plants, e.g. Artemisia and Chenopodiaceae. The Tärendö Interstadial, correlated with Odderade, wascharacterized by open, unstable soils due to periglacial processes such as cryoturbation and eolian activities. The Weichselian glaciation is divided into three glacial stades separated by ice‐free interstadials in the area studied. Except for a zone with S‐SW drumlinization the impact of the two later ice sheets is insignificant.

Patterns of Quaternary ice sheet erosion and deposition in Fennoscandia and a theoretical framework for explanation

“…Since it is a depositional feature, a comprehensive understanding of its stratigraphy would, in principle, yield its formation history through the Quaternary. However, although numerous sites with complex stratigraphies and relict tills are known from the region, and especially from its northern parts (Lundqvist, 1969;Lagerbäck, 1988;Lagerbäck and Robertsson, 1988;Andrén, 1990;Helmens et al, 2000), neither the density of observations, nor the depth of observations in relation to till thickness and achieved dating control are sufficient to yield a clear picture based on direct stratigraphical observation. There are also reasons to believe that tills in this region have been recycled multiple times, thus further complicating the analysis.…”

Unequal ice-sheet erosional impacts across low-relief shield terrain in northern Fennoscandia

“…This ice flow of ice likely prevailed during the majority of Quaternary glaciations (Hättestrand et al, 2004). During the last glacial cycle, ice flow from the northwest dominated this transect in the early Weichselian, while ice flow from the west and south-west dominated during the Late Weichselian deglaciation (Lagerbäck and Robertsson, 1988;Kleman et al, 1992Hättestrand, 1998;Hättestrand et al, 1999). Flow conditions in the northern transect are complex, with till fabrics indicating dominant flow towards the N and NE along its northern boundary but towards the E and SE along its southern boundary (Hirvas, 1991).…”

Morphometry and pattern of a large sample (>20,000) of Canadian eskers and implications for subglacial drainage beneath ice sheets

“…This suggests that eskers have a low potential for preservation beneath dynamic ice sheets, and/or that they form very close to final deglaciation. Elsewhere, eskers have been shown to survive entire glaciations beneath frozen beds (Lagerb€ ack and Robertsson, 1988;Kleman, 1994) and frozen beds have been inferred beneath parts of the LIS (Kleman and H€ attestrand, 1999;Kleman and Glasser, 2007), although the subglacial thermal regime changes through time to almost entirely warm-based (e.g. Marshall and Clark, 2002).…”