Relief and saprolites through time on the Baltic Shield

Lidmar‐Bergström, Karna

doi:10.1016/0169-555x(94)00076-4

Cited by 113 publications

(87 citation statements)

References 23 publications

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“…The cored section of 16/3-6 is thus believed to represent the lower part of an ancient weathering profile, where the upper part of the weathering profile has partially been removed and remnants are preserved mainly along fracture zones. This is comparable to the interpretation by Olesen et al (2006) and Lidmar-Bergström (1995) from preserved Triassic/Jurassic weathering profiles in southern Norway and Sweden.…”

Section: Pre-upper Jurassicsupporting

confidence: 79%

Altered basement rocks on the Utsira High and its surroundings, Norwegian North Sea

Riber¹,

Dypvik²,

Sørlie³

2015

NJG

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As part of the recent discoveries on the Utsira High (Edvard Grieg and Johan Sverdrup fields), altered and fractured basement rocks were for the first time shown to act as a reservoir and possible migration paths for commercial hydrocarbon deposits on the Norwegian Continental Shelf. Altered basement rocks are underlying the main Upper Jurassic reservoir rocks in Johan Sverdrup and the main Cretaceous, Jurassic and Triassic reservoir rocks in Edvard Grieg. In the present study, eighteen basement cores from the Utsira High have been classified and investigated for signs of alteration, including subaerial weathering. The results show highly variable basement composition, including metasandstones, phyllites, granites, granodiorites and gabbroic rocks. In core view most of the basement rocks show signs of a medium to high degree of fracturing. Alteration has taken place in most of the cores, ranging from slight discoloration to disintegration along fractures, and to total fragmentation of the rock. The fragmentation of the rock is commonly associated with the dissolution of primary minerals and precipitation of secondary clays in the newly formed pore space. The upwards increasing disintegration and increasing amount of clay observed in the basement rocks from two of the wells (16/3-4 and 16/1-15) indicate that subaerial weathering was the main alteration agent.

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Section: Pre-upper Jurassicsupporting

confidence: 79%

Altered basement rocks on the Utsira High and its surroundings, Norwegian North Sea

Riber¹,

Dypvik²,

Sørlie³

2015

NJG

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“…Streamlined hills are separated by linear valleys of varying depth and width, described below. appear to follow single joints, but narrower than the joint-bounded valleys or fissure valleys reported by Rudberg (1973) and Lidmar-Bergström (1995). North-south trending linear valleys, oriented at high angles to ice flow (Fig.…”

Section: Streamlined Hillsmentioning

confidence: 78%

“…In light of the above, we propose that much of the cnoc-and-lochan landscape in NW Scotland corresponds approximately to the pre-glacial weathering front, similar to that described in southern Sweden (Johansson et al, 2001a, b;Lidmar-Bergström, 1995Olvmo et al, 2005;Olvmo and Johansson, 2002). Stripping of saprolite would most likely have occurred during the first major glacial cycle(s) in the early Pleistocene.…”

Section: Variability Of Glacial Modificationmentioning

confidence: 95%

“…In contrast, the etch surface that has appeared from beneath Cretaceous cover sediments has a relative relief of up to 50 m, with locally thick saprolite remnants (Johansson, 1999;Lidmar-Bergström, 1989;. The depth of a weathering mantle and the roughness of the weathering front prior to Pleistocene glaciation depends on a range of factors including lithology, fracture zone density, climate, vegetation, atmospheric chemistry, time of exposure and whether or not a weathering mantle was removed previously and/or covered by other rocks (Kroonenberg and Melitz, 1983;Lidmar-Bergström, 1995;Ollier, 1984;Twidale, 2002). Little is known or understood about weathering processes during the Precambrian but it appears that the mechanisms of producing and retaining Precambrian weathering mantles was very different from Phanerozoic weathering due to lack of terrestrial vegetation and other factors (e.g.…”

Section: Implications For Sub-glacial Bed Roughness Under Modern Ice mentioning

confidence: 99%

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Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

Krabbendam

Bradwell

2014

Quaternary Science Reviews

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Vast areas previously covered by Pleistocene ice sheets consist of rugged bedrock-dominated terrain of innumerable knolls and lake-filled rock basins -the 'cnoc-and-lochan' landscape or 'landscape of areal scour'. These landscapes typically form on gneissose or granitic lithologies and are interpreted (1) either to be the result of strong and widespread glacial erosion over numerous glacial cycles; or (2) formed by stripping of a saprolitic weathering mantle from an older, deeply weathered landscape.We analyse bedrock structure, erosional landforms and weathering remnants and within the 'cnoc-andlochan' gneiss terrain of a rough peneplain in NW Scotland and compare this with a geomorphologically similar gneiss terrain in a non-glacial, arid setting (Namaqualand, South Africa). We find that the topography of the gneiss landscapes in NW Scotland and Namaqualand closely follows the old bedrock-saprolite contact (weathering front). The roughness of the weathering front is caused by deep fracture zones providing a highly irregular surface area for weathering to proceed. The weathering front represents a significant change in bedrock physical properties. Glacial erosion (and aeolian erosion in Namaqualand) is an efficient way of stripping saprolite, but is far less effective in eroding hard, unweathered bedrock. Significant glacial erosion of hard gneiss probably only occurs beneath palaeo-ice streams.We conclude that the rough topography of glaciated 'cnoc-and-lochan' gneiss terrains is formed by a multistage process: 1) Long-term, pre-glacial chemical weathering, forming deep saprolite with an irregular weathering front;2) Stripping of weak saprolite by glacial erosion during the first glaciation(s), resulting in a rough land surface, broadly conforming to the pre-existing weathering front ('etch surface');3) Further modification of exposed hard bedrock by glacial erosion. In most areas, glacial erosion is limited, but can be significant beneath palaeo-ice stream. The roughness of glaciated gneiss terrains is crucial for modelling of the glacial dynamics of present-day ice sheets. This roughness is shown here to depend on the intensity of pre-glacial weathering as well as glacial erosion during successive glaciations.

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“…On the other hand, where it emerges from below Mesozoic cover rocks as on the west coast and in southern Sweden, the relief is hilly and joint-controlled. Remnants of kaolinitic saprolites Olvmo et al, 1999) suggest that the main relief features in the basement on the west coast of southwestern Sweden were etched out by deep weathering along structurally weakened zones during the Mesozoic (Lidmar-Bergström, 1995), with a possible later phase during the Neogene (Olvmo et al, 1999;Johansson et al, 2001). The relief type is labelled exhumed sub-Mesozoic etch surface due to the close connection to Mezozoic cover rocks (see Figure 2; cf.…”

Section: Introductionmentioning

confidence: 97%

The significance of rock structure, lithology and pre‐glacial deep weathering for the shape of intermediate‐scale glacial erosional landforms

Olvmo

Johansson

2002

Earth Surf Processes Landf

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The main landforms within the glacially scoured Precambrian rocks of the Swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes, probably during the Mesozoic and with a possible second period of etching during the Neogene. To explore the effect of multiple glacial erosion on the rock surfaces, an island with two different lithologies and with striae from different directions was selected for a detailed study, focusing on the shape of roches moutonnées. Air-photo interpretation of bedrock lineaments and roches moutonnées combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape. The study reveals a significant difference in shape between roches moutonnées in augen-granite and orthogneiss. Low elongated and streamlined roches moutonnées occur in the gneiss area, striated by a Late Weichselian ice flow from the NE. This ice flow is subparallel with both the local dominant trend of topographically well-expressed joints and the schistosity of the gneiss. Frequently, there are no signs of quarrying on the lee-sides of the gneiss roches moutonnées and hence they resemble the shape of whalebacks, or ruwares, as typically associated with the exposed basal weathering surface found in tropical areas. The granite roches moutonnées were formed by an older ice flow from the ESE, which closely followed the etched WNW-ESE joint system of the granite. Late Weichselian ice flow from the NE caused only minor changes of the landforms. On the contrary, marks of the early ESE ice flow are poorly preserved in the gneiss area, where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and, accordingly, also to the pre-glacial relief. The study demonstrates that coincidence between ice flow direction and pre-glacially etched structures is most likely to determine the effects of glacial erosion.

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Relief and saprolites through time on the Baltic Shield

Cited by 113 publications

References 23 publications

Altered basement rocks on the Utsira High and its surroundings, Norwegian North Sea

Altered basement rocks on the Utsira High and its surroundings, Norwegian North Sea

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

The significance of rock structure, lithology and pre‐glacial deep weathering for the shape of intermediate‐scale glacial erosional landforms

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