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Multi-phase development of a glaciated inselberg landscape
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
School of GeoSciences, University of Edinburgh, Edinburgh, UK.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
(English)Manuscript (preprint) (Refereed)
Abstract [en]

We investigate the evolution of a glaciated inselberg landscape in northern Sweden since the late Mesozoic, c. 65 million years ago. The study area is part of the Fennoscandian shield and has been stripped of cover rocks and also largely of weathering mantles by preglacial and glacial erosion to leave low relief inselberg plains, with a thin cover of Quaternary deposits. We use these inselbergs as the basis for study of the impact of glacial and preglacial erosion on the shield landscape. GIS-analyses of digital elevation models (DEMs) enable us to identify the morphometry of the inselbergs. Field mapping and mechanical excavations of inselberg margins allow links to be explored between dome-like granite inselbergs and sheet structures and to examine till and saprolite mantles. Very low glacial erosion in the Parkajoki area allows the final stages of preglacial relief development to be reconstructed for the Late Neogene. The hypsometry of the study area, in combination with inselberg elevation and distribution, allows four palaeosurfaces to be identified.

 

The effects of glacial erosion on the bedrock forms of the inselbergs of the study area were generally restricted to inselberg streamlining by steepening of inselberg flanks. The inselberg landscape relief was enhanced by the removal of saprolite mantles during the Quaternary glaciations. The saprolites formed during the late Neogene, thin or absent close to the inselberg summits and of 10-20 m thickness at the inselberg feet and on the plains. The inselbergs are much older features, however, and deep kaolinization and soft ores are evidence for development by etching from a Mesozoic base level surface. Eocene marine clays on the continuation of the inselberg plains in northern Finland at around 260 m a.s.l. indicate that the inselberg plains above the Pakko palaeosurface generation predate the Paleogene-Eocene thermal maximum. Erosion rates, calculated for two reconstructed summit envelope surfaces, range between 1.5m/Myr and 4.8m/Myr since the late Mesozoic. The inselberg plains of northern Sweden are therefore directly comparable to other shield landscapes in extra-glacial areas that have experienced episodes of deposition of thin cover rocks, long periods of weathering and very low long term rates of erosion.

Keyword [en]
Inselbergs; shield area; DEM-analysis; glacial erosion; weathering and stripping
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-30851OAI: oai:DiVA.org:su-30851DiVA: diva2:274404
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Cenozoic landscape evolution in northern Sweden: Geomorphological interpretation within a GIS-framework
Open this publication in new window or tab >>Cenozoic landscape evolution in northern Sweden: Geomorphological interpretation within a GIS-framework
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The large-scale bedrock landscape in northern Sweden has a complex evolution history of planation, uplift, transgression, burial, weathering, and erosion. The aim of this thesis is to examine the long-term development of the area.

Terms for base-level surfaces in the area are defined. A combination of GIS-analyses of digital elevation models and field work is used to explore landform characteristics and formation. Inselbergs east of the northern Scandes in northern Sweden are used as a basis for describing landscape development.

In total, 794 inselbergs are identified in the study area. The inselbergs are classified according to their degree of glacial erosion. The Parkajoki area, with low glacially modified inselbergs, tors, boulder fields and saprolites, has been shown to have largely escaped Quaternary glacial erosion and is taken as a type area to describe the late-Neogene landscape development prior to glaciation. The removal of Neogene saprolite mantles at the inselberg feet in areas of glacial erosion increased inselberg relief during the Quaternary by 10-20 m. For landscape evolution further back in time, beyond the Neogene, the hypsography of the study areas shows at least two palaeosurface generations in the northern Scandes and at least four palaeosurface generations on the inselberg plains. The distribution of inselbergs in relation to palaeosurface generations in the same elevation intervals suggests land uplift with a tilt towards the SE-ESE. Eocene marine diatom findings at 260 m a.s.l. in Finland, 200 km east of the study area, indicate a pre-Eocene age of the inselberg plains above this elevation.

The development of today’s inselberg plains likely started in the late Mesozoic, with a sub-Mesozic etch surface that was subjected to land uplift at the late Mesozoic-Paleocene transition during breakup of the Atlantic. The great antiquity of the northern Swedish bedrock landscape stands as an analogy for shield areas in for example Australia and Africa.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2009. 23 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 19
Keyword
Long-term geomorphology, northern Sweden, base-level surface, inselbergs, digital elevation models, field observations
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-30711 (URN)978-91-7155-966-1 (ISBN)
Public defence
2009-12-04, De Geersalen, Geovetenskapens Hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defence, the following papers were unpublished and had a status as follows: Paper 2: In press. Paper 3: Manuscript. Paper 4. Manuscript. Available from: 2009-11-12 Created: 2009-10-23 Last updated: 2010-04-22Bibliographically approved

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