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Palaeosurfaces and palaeovalleys on North Atlantic previously glaciated passive margins: reference forms for conclusions on uplift and erosion
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: Institutionen för naturgeografi och kvartärgeologi , 2004. , 17 p.
Series
Avhandling i geografi med naturgeografisk inriktning, ISSN 1650-4992 ; 30
Keyword [en]
palaeosurface, palaeovalley, uplift, valley, incision, glacial erosion, weathering, Neogene, southern Norway, West Greenland
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-136ISBN: 91-7265-876-2 (print)OAI: oai:DiVA.org:su-136DiVA: diva2:189953
Public defence
2004-05-28, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2009-06-01Bibliographically approved
List of papers
1. Palaeosurfaces and major valleys in the area of Kjølen Mountains, southern Norway: consequences of uplift and climatic change
Open this publication in new window or tab >>Palaeosurfaces and major valleys in the area of Kjølen Mountains, southern Norway: consequences of uplift and climatic change
2003 (English)In: Norsk Geografisk Tidsskrift, ISSN 0029-1951, E-ISSN 1502-5292, Vol. 57, no 2, 83-101 p.Article in journal (Refereed) Published
National Category
Physical Geography Geology
Identifiers
urn:nbn:se:su:diva-23035 (URN)10.1080/00291950310001360 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved
2. Re-exposed basement landforms in the Disko region, West Greenland: disregarded data for estimation of glacial erosion and uplift modelling
Open this publication in new window or tab >>Re-exposed basement landforms in the Disko region, West Greenland: disregarded data for estimation of glacial erosion and uplift modelling
2005 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 74, no 1-4, 106-127 p.Article in journal (Refereed) Published
Abstract [en]

Classifications of large-scale landscapes in Greenland have traditionally been based on type and intensity of glacial erosion, with the general idea that present landforms are mainly the result of erosion from ice sheets and glaciers. However, on southern Disko and in areas offshore in Disko Bugt, a basement surface has preserved remnants of weathered gneiss and pre-Paleocene landforms, recently exhumed from Paleocene basalt. Isolated hills and lineaments have been mapped in a digital terrain model and aerial photographs. Offshore have hills been mapped from seismic lines. The medium size bedrock forms on southern Disko as tors, clefts and roche moutonées have been studied in the field. Remnant saprolites were inventoried, sampled and analysed according to grain size and clay mineralogy. The basement surface retains saprolites up to 8 m thick in close relation to the cover rocks. The landforms in the basement rocks belong essentially to an etched surface only slightly remodelled by glacial erosion and, below the highest coastline, also by wave action. The outline of hills is governed by two lineament directions, ENE–WSW representing the schistocity of the gneiss and NW–SE fracture zones. These structures are thus interpreted to have been exploited by the deep weathering while the frequent N–S lineaments have not and thus might be younger. Main ice-flow has been from the NE and has resulted in plucking of SW facing lee sides, however the resulting bedrock forms are mainly controlled by structures and orientation of joints. The identification of re-exposed sub-Paleocene etch forms on Disko and the hills of similar size offshore, forming a hilly relief, have implications for identification of a hilly relief south of Disko Bugt, its relation to younger planation surfaces as well as for conclusions of uplift events.

Keyword
Etch surface, Glacial erosion, Kaolin, Landforms, Weathering, West Greenland
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-23036 (URN)10.1016/j.geomorph.2005.05.006 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved
3. Cenozoic uplift of Nuussuaq and Disko, West Greenland: elevated erosion surfaces as uplift markers of a passive margin
Open this publication in new window or tab >>Cenozoic uplift of Nuussuaq and Disko, West Greenland: elevated erosion surfaces as uplift markers of a passive margin
Show others...
2006 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 80, no 3-4, 325-337 p.Article in journal (Refereed) Published
Abstract [en]

Remnants of a high plateau have been identified on Nuussuaq and Disko, central West Greenland. We interpret the plateau as an erosion surface (the summit erosion surface) formed mainly by a fluvial system and graded close to its former base level and subsequently uplifted to its present elevation. It extends over 150 km east–west, being of low relative relief, broken along faults, tilted westwards in the west and eastwards in the east, and having a maximum elevation of ca. 2 km in central Nuussuaq and Disko. The summit erosion surface cuts across Precambrian basement rocks and Paleocene–Eocene lavas, constraining its age to being substantially younger than the last rift event in the Nuussuaq Basin, which took place during the late Maastrichtian and Danian. The geological record shows that the Nuussuaq Basin was subjected to subsidence of several kilometres during Paleocene–Eocene volcanism and was transgressed by the sea later during the Eocene. By comparing with results from apatite fission track analysis and vitrinite reflectance maturity data, it is suggested that formation of the erosion surface was probably triggered by an uplift and erosion event starting between 40 and 30 Ma. Surface formation was completed prior to an uplift event that started between 11 and 10 Ma and caused valley incision. This generation of valleys graded to the new base level and formed a lower erosion surface, at most 1 km below the summit erosion surface, thus indicating the magnitude of its uplift. Formation of this generation of valleys was interrupted by a third uplift event also with a magnitude of 1 km that lifted the landscape to near its present position. Correlation with the fission-track record suggests that this uplift event started between 7 and 2 Ma. Uplift must have been caused initially by tectonism. Isostatic compensation due to erosion and loading and unloading of ice sheets has added to the magnitude of uplift but have not significantly altered the configuration of the surface. It is concluded that the elevations of palaeosurfaces (surfaces not in accordance with present climate or tectonic conditions) on West Greenland's passive margin can be used to define the magnitude and lateral variations of Neogene uplift events. The striking similarity between the landforms in West Greenland and those on many other passive margins is also noted.

Keyword
Landform analysis, Erosion surface, Glaciation, Neogene, Passive continental margin, Uplift, West Greenland
National Category
Physical Geography Geology
Identifiers
urn:nbn:se:su:diva-23037 (URN)10.1016/j.geomorph.2006.03.006 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved
4. Palaeosurfaces in central West Greenland as reference for identification of tectonic movements and estimations of glacial erosion
Open this publication in new window or tab >>Palaeosurfaces in central West Greenland as reference for identification of tectonic movements and estimations of glacial erosion
2006 (English)In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 50, no 3-4, 161-183 p.Article in journal (Refereed) 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.

Keyword
palaeosurface, West Greenland, uplift, tectonic movements, differential erosion, Neogene, planation surface, etch surface, hilly relief, Landform analysis
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-23038 (URN)10.1016/j.gloplacha.2005.12.011 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved

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