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Palaeosurfaces in central West Greenland as reference for identification of tectonic movements and estimations of glacial erosion
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
2006 (engelsk)Inngår i: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 50, nr 3-4, s. 161-183Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Landform analysis of basement rocks has been undertaken with the aid of digital elevation data, aerial photographs and field observations in central West Greenland (69°15′N–66°00′N). Palaeosurfaces have been identified, dated relatively to each other, used to quantify uplift and fault movements and also used to estimate differential erosion. Two types of palaeosurfaces were mapped across the Precambrian basement: a surface at low elevation with distinct hills (hilly relief), and two planation surfaces formed across different types of basement rocks. The hilly relief surface emerges as an inclined surface from Cretaceous cover rocks in Disko Bugt and is interpreted as a stripped late Mesozoic etch surface. This surface is cut off towards the south by a less inclined planation surface, which is younger and thus of Cenozoic age. It is similar to the post-Eocene (Miocene?) planation surfaces identified on Disko and Nuussuaq in other studies. The planation surface splits in two southwards towards high areas around Nordre Isortoq and Sukkertoppen Ice Cap. The upper planation surface forms near-summit areas of tectonic blocks dipping in different directions and with different tilts. The uplift centres define the crests of two mega blocks, separated by the ‘Sisimiut Line’ which coincides with the Precambrian Ikertôq thrust zone. A partially developed lower planation surface indicates a first uplift of maximum 500 m followed by a second uplift of maximum 1000 m. We infer that these uplift events occurred during the late Neogene based on correlation with similar surfaces on Nuussuaq and the timing of exhumational events estimated from apatite fission track analyses of samples from a deep borehole on Nuussuaq (reported elsewhere). The difference between a reconstruction of the upper planation surface across the entire area and the present topography was used as an estimate of erosion of basement rock since the formation of the upper planation surface. The erosion is unevenly distributed and varies from almost none on the well-preserved planation surfaces to 800–1300 m along valleys, and even more in the fjords. Erosion is less within areas of gneiss in granulite facies, than in areas of gneiss in amphibolite facies.

sted, utgiver, år, opplag, sider
2006. Vol. 50, nr 3-4, s. 161-183
Emneord [en]
palaeosurface, West Greenland, uplift, tectonic movements, differential erosion, Neogene, planation surface, etch surface, hilly relief, Landform analysis
HSV kategori
Identifikatorer
URN: urn:nbn:se:su:diva-23038DOI: 10.1016/j.gloplacha.2005.12.011OAI: oai:DiVA.org:su-23038DiVA, id: diva2:189952
Tilgjengelig fra: 2004-05-06 Laget: 2004-05-06 Sist oppdatert: 2017-12-13bibliografisk kontrollert
Inngår i avhandling
1. Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins: reference forms for conclusions on uplift and erosion
Åpne denne publikasjonen i ny fane eller vindu >>Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins: reference forms for conclusions on uplift and erosion
2004 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Palaeosurfaces and palaeovalleys are landforms under destruction in the present climate and/or tectonic regime, and thus mainly reflect processes not active today. Uplifted palaeosurfaces exist along the formerly glaciated passive continental margins around the North Atlantic. Large-scale landform development has recently become a matter of interest also for geologists and geophysicists as the result of an increasing awareness that a thorough knowledge of uplift, erosion, deposition and development of landforms along continental margins can only be accomplished by combined studies using independent data from different scientific disciplines. The present study focuses on one of these above data sets; the landform record. Two uplifted areas, southern Norway and central West Greenland, were selected for landform analysis of high resolution digital elevation models, aerial photographs, relation between landforms in basement and cover rocks, offshore seismic lines and X-ray diffraction of clay minerals in saprolites.

In southern Norway, analysis of slope angles within the range of pediment slopes was combined with analysis of main valley incision. This resulted in the identification of three main planation surfaces in a stepped sequence formed along the main valleys as a consequence of tectonic uplift events, maybe in the Palaeogene, (in total >1000 m). Two phases of late uplift (~900 m), probably in the Neogene, triggered incision of deep fluvial valleys, later reshaped by glacial erosion (up to 300 m).

In central West Greenland palaeosurfaces were analysed in relation to cover rock of different age. An exhumed etch surface, characterized by a typical hilly relief, occurs on Disko and south of Disko Bugt, and are by the presence of cover rocks shown to be sub-Palaeocene in origin. To the north, a post-Eocene erosion surface on Nuussuaq, cuts across basement and basalt and was probably formed close to sea level. Uplift in two phases elevated this surface up to 2000 m above present sea level and broke it in differently tilted tectonic blocks. South of Disko Bugt, a planation surface, of probably the same age as the one on Nuussuaq, cuts the tilted etch surface, and also cuts across different bedrock types. The planation surface rises towards the south and splits in two surfaces, separated in altitude up to 300 m, within two highly elevated areas. The separation into two surfaces indicate two uplift events: A first minor event of a few hundred metres in the uplift centres resulted in incision of the lower planation surface. This event was later followed by a major uplift event amounting to >1000 m. Correlation with the offshore sedimentary record suggests that both uplift events occurred in the Neogene. The erosion pattern calculated from one reconstructed palaeosurface to present topography shows large spatial variations. This is interpreted as an effect of differential bedrock resistance and local variations of glacial erosion (400–1300 m in low areas).

The results presented in this thesis demonstrate the usefulness of palaeosurfaces and palaeovalleys as tools for deciphering magnitude of uplift events, establishing relative event chronologies and for calculation of erosion. Moreover integrated studies of palaeolandforms, offshore geology and thermal chronologies, are shown to be invaluable when used to solve the spatial and temporal patterns of uplift, erosion and deposition.

sted, utgiver, år, opplag, sider
Stockholm: Institutionen för naturgeografi och kvartärgeologi, 2004. s. 17
Serie
Avhandling i geografi med naturgeografisk inriktning, ISSN 1650-4992 ; 30
Emneord
palaeosurface, palaeovalley, uplift, valley, incision, glacial erosion, weathering, Neogene, southern Norway, West Greenland
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-136 (URN)91-7265-876-2 (ISBN)
Disputas
2004-05-28, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2004-05-06 Laget: 2004-05-06 Sist oppdatert: 2009-06-01bibliografisk kontrollert

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