South-central Norway Research Articles

Early-Holocene glacier fluctuations in Krundalen, south central Norway: palaeoglacier dynamics and palaeoclimate

Krundalen, a valley occupied by three eastern outlet glaciers of the Jostedalsbre ice cap, contains three groups of moraines, two of which are outside the dated neoglacial (`Little Ice Age', LIA) limits. Exposures in the outermost moraine ridge display three sedimentary units. Detailed sedimentological analyses reveal that the lower two units formed during a temporary stillstand of the ice margin inferred to have occurred because of a topographically controlled stabilization of the ice margin during glacier retreat following the Younger Dryas. A climatically controlled readvance during which the upper unit was deposited, partly eroding pre-existing sediments, followed. Continuation of this readvance led to the whole sequence being pushed up to form the present moraine. The sedimentological results including clast shape measurements imply a temperate glacier thermal regime at the time of moraine formation. The glacial palaeoenvironment was characterized by frequent oscillations and an abundant supply of glaciogenic sediment. The age of this landform can at present not be determined by numerical dating. However, the moraine is likely to have been formed in the early Holocene, during Jondal Event 2 (JE) from c. 10 550—10 450 cal. yr BP. The average equilibrium-line altitude lowering calculated for this event is c. 440 m, 340 m for the Erdalen Event 1 (EE, 10 100—10 050 cal. yr BP) moraines and c. 190 m for the LIA moraines farther upvalley. Precipitation calculated for these stages compared with present values is 160—175% (JE), 165—175% (EE) and 110% (LIA). Summer air temperatures were slightly higher than today's during the JE, much higher during the EE and are indistinguishable from present values during the LIA. The existence of a potential JE-equivalent and the extent of the EE are reported and used for glacier reconstruction for the first time in Krundalen. The sedimentological data implies that the JE did not simply consist of a single readvance but was more complex. It is argued that glacial sedimentology linked with methods of glacier reconstruction provides a powerful tool to gain insights into the dynamics and functioning of formerly glaciated areas.

Capercaillie Tetrao urogallus Lek Formation in Young Forest

Abstract Capercaillie Tetrao urogallus leks have repeatedly been reported to be located in old forest. However, two conditions may have biased this widely held view. First, leks are known to be continuously used over several decades, and therefore might have been established when forest stands were younger. Second, stand-replacement logging (clearcutting) was not widely applied until the 1950s, leaving even-aged regenerating stands too young for leks to have been established in the latter part of the 20th century. Here we report eight cases of lek formation in young plantations from south-central Norway. Stand age ranged within 26-46 years when display activity started. At six of the sites, we confirmed that females were regularly feeding on pine trees in winter prior to lek establishment, and at four of these sites displaying males were observed courting the females in late winter. These findings support the hotspot model of lek formation put forward by Gjerde et al. (2000), and it offers promising optio...

Reindeer (Rangifer tarandus) avoidance of a highway as revealed by lichen measurements

Reindeer and caribou Rangifer tarandus are reported to avoid human infrastructure such as roads, high-voltage power lines, pipelines, and tourist resorts. Lichens are important forage for reindeer during winter, and their relatively slow growth rates make them vulnerable to overgrazing. Height and volume of lichens are often used as an indicator of grazing pressure by reindeer and, thus, as an indirect measure of Rangifer avoidance of human infrastructure. We sampled lichen height in Cetraria nivalis-dominated communities along 4 and 3 parallel transects located on two parallel mountain ridges in Hardangervidda, south central Norway. The lichen measurements were analyzed in relation to altitude and the distance from four tourist cabins in the area and a highway (Rv7) running perpendicular to the 7 transects. The mountain ridge with 4 transects is part of a much used migratory corridor for wild reindeer R. tarandus tarandus. Along the nonmigratory ridge, lichen height decreased 35% over an 8-km distance from Rv7 and a tourist cabin, indicating reindeer aversion toward Rv7 and/or a tourist cabin. No similar relationship was found for the migration ridge in relation to distance from Rv7 or the tourist cabins. Our results suggest that avoidance of human infrastructure by wild reindeer might be limited where reindeer use of winter pastures is influenced by herd traditions and/or motivation to follow established migration corridors. This has important implications for addressing the use of similar pasture measurements when testing for Rangifer aversion toward human disturbances.

Effects of a power line on migration and range use of wild reindeer

Linear infrastructures such as roads, pipelines and power lines can hinder Rangifer migration and reduce the total amount of area available for foraging. We studied the barrier and aversion effect of a 66 kV power line transecting the range of wild reindeer in North Ottadalen, south central Norway using aerial surveys of reindeer distribution (direct measurement of reindeer use) and lichen measurements (indirect measurement of reindeer use) at varying distances from both sides of the power line. We present a clear definition of the expected barrier and aversion effects, and present specific hypotheses and predictions based on these two terms that are often used unclearly in the literature. The aerial surveys and ground observations showed that reindeer crossed underneath and grazed under and on both sides of the power line during 14 out of the 22 years (63.6%) surveys were conducted over the last 31 years. This behaviour was confirmed by the lichen measurements, indicating a higher use of lichen pastures along ridges close to and under the power line compared to those at increasing distances and up to 3 km from both sides of the power line. This winter grazing pattern probably reflects the topographical channeling of reindeer to the ridges along an 8 km wide topographical corridor encompassing the power line and cannot be attributed to the power line itself. We found that direct measurement data (visual observations such as ours or GPS/telemetry tracking) provide less ambiguous information for testing barrier and aversion effects than indirect measurement data (pasture/lichen measurements) that are likely influenced by numerous uncontrollable environmental variables independent of reindeer grazing. Our results contrast with recent studies indicating strong barrier and aversion effects of similar power lines for Rangifer migration and grazing behaviour in alpine terrain.

Impacts of increased nitrogen supply on Norwegian lichen-rich alpine communities: a 10-year experiment

Summary 1 Species cover was tested during a 10-year fertilization experiment in the low-alpine Cetrarietum nivalis community and the middle-alpine Phyllodoco-Juncetum trifidi community in the Dovre mountains of south-central Norway. Nitrogen was added at 7, 35 and 70 kg N ha−1 year−1, with the highest dose corresponding to approximately 3.5 times the annual deposition in south-west Norway. 2 Both communities are dominated by lichens (Cladonia spp. and Cetraria spp., respectively), have a patchy structure and are ‘conservative’ as regards species content. 3 Lichens, which showed a decrease in cover and size, and after some years developed discoloured thalli, are the best organisms for monitoring changes in alpine vegetation that is exposed to increased nitrogen deposition. The most sensitive species in Cetrarietum nivalis appeared to be Alectoria nigricans and Cetraria ericetorum, but more abundant species (Cladonia mitis, C. stellaris and Cetraria nivalis) are likely to be more reliable indicators. Cetraria delisei seems to be a reliable indicator species for monitoring in Phyllodoco-Juncetum trifidi. 4 Fertilization had no significant effect on the vascular plants (dwarf shrubs and a few graminoids) in either community, except for Festuca ovina, the cover of which increased slightly. 5 Nitrogen pollution may affect oligotrophic, alpine communities differently, depending on their species composition and horizontal structure (patchiness). 6 It is suggested that other factors, such as climate, soil properties and community structure, may be more important than long-range nitrogen pollution for determining species composition and species cover in many of the oligotrophic, alpine communities in southern Norway. However, in lichen-rich communities, critical loads have already been exceeded in the most polluted areas of south-west Norway.

Holocene environmental history and climate of R�t�sj�en, a low-alpine lake in south-central Norway

The Holocene environmental history and climate are reconstructed for Ratasjoen, a low-alpine lake in south-central Norway. The reconstructions are based on chironomids, diatoms, pollen, plant macrofossils, and sediment characteristics. From plant macrofossil evidence, birch trees (Betula pubescens) immigrated ca. 10,000 cal BP. The chironomid-inferred mean July air temperature was high, but may be unreliable during the early stages of the lake’s history due to the high abundance of Chironomus anthracinus type, a taxon that may include several species. From ca. 9000 cal BP the inferred mean July temperature was lower (ca. 9 °C). Temperatures increased towards 8000 cal BP and pine (Pinus sylvestris) reached its upper limit near the lake. July temperature may have become a significant factor controlling long-term pH in the lake, starting shortly after 8000 cal BP. High pH values were associated with periods of warm summers and lower pH values occurred during periods of colder summers. Alkalinity processes within the lake and/or the catchment are possible factors controlling this relationship. A temperature decline at ca. 5400 cal BP separated two 10.6 °C temperature maxima around 6400 and 4500 cal BP. The 1.5 °C decline in July air temperatures from ca. 4400 cal BP was paralleled by a decrease of pH from 7.2 to 6.8. Following the temperature drop, first pine and then birch trees declined and disappeared from the catchment and organic accumulation in the lake increased. The increased organic accumulation rate had a positive effect on diatom production. At ca. 2700 cal BP the temperature reached a minimum (ca. 9.2 °C) and correspondingly a second pH minimum was reached. Temperature decreased again slightly at ca. 400 cal BP during the ‘Little Ice Age’, before increasing by about 0.5 °C towards the present. Percentage organic carbon as estimated by loss-on-ignition appears to be better correlated with chironomid-inferred July temperatures than organic accumulation rates, at least for the last 9000 years. Accumulation rates of organic sediments are more coupled with catchment-related processes, such as erosion and major changes in vegetation, than is percentage organic carbon.

Assessment of combined glacier and tree-ring studies to constrain latitudinal climate forcing of Scandinavian glacier mass balances

AbstractAssessing climate change and its effects on the cryosphere is important, and individual proxies are commonly used for such assessments. We have investigated the possibility of combining glacier mass balance and tree-ring data to better understand regional climate variability in Scandinavia. There are substantial differences between climate information in mass-balance and tree-ring data. Summer balance (bS) is strongly related to summer temperature, while winter balance (bW) is less readily interpreted in terms of a climate signal. Tree rings are good summer temperature proxies, but due to the complexity of tree growth factors (e.g. the effect of the previous winter’s climate) tree-ring records do not exclusively represent summer temperatures. Combining bS and tree-ring records will not likely yield additional summer climate information. The relationship of mass balance with the Arctic Oscillation is stronger than with the North Atlantic Oscillation, especially for northernmost Sweden, whereas no such correlations were found for tree-ring data. The agreement between bN records from both maritime south-central Norway and continental northernmost Sweden and tree-ring data from Jämtland, in a maritime/continental climate transition zone, suggests possibilities to combine mass-balance and tree-ring data to provide information about climate over the entire year on interannual timescales.

Models to predict time since death of Picea abies Snags

Number of years since death was estimated by dendrochronological cross-dating of 107 standing dead trees (snags) of Norway spruce [Picea abies (L.) Karst.] in a submountainous old-growth forest in south–central Norway. Snag characteristics (size, bark cover, branch order present and variables derived from tree-ring analyses) were used in stepwise linear regression procedures to identify variables that explained time since death. Number of branch orders present (where branches growing directly on the stem were branch order 1, branches growing on order 1 branches were order 2, and so on) explained two-thirds of the variation in time since death. Adding other significant variables, such as diameter, relative height of snags, percentage bark cover and average tree-ring width in the final years before death, increased model precision only moderately. The models were validated by the PRESS statistic, which showed that new observations were predicted fairly well with 65–69% of the variation explained.

How long do Norway spruce snags stand? Evaluating four estimation methods

We estimated time from death to fall (standing time) of Norway spruce (Picea abies (L.) Karst.) snags in a submountainous old-growth forest in south-central Norway, applying four calculation methods to 124 dendro chrono logically cross-dated still-standing snags and 64 fallen logs. The calculation methods consistently estimated expected standing time of snags at 26–34 years, with a median of 16–21 years and 20% of snags standing for >48–58 years. The survival function from all methods took the approximate form of a negative exponential, with a 3%–4% annual fall rate for snags. In the distribution of time since death, a small peak in dead trees 20–30 years ago (late 1970s) coincides with a historic epidemic of bark beetles. The method using only time since death of still-standing snags appears to be the most feasible for estimating total standing time of snags in old-growth forests with constant tree mortality.

EFFECTS OF INFRASTRUCTURE ON MIGRATION AND RANGE USE OF WILD REINDEER

Abstract We studied reindeer (Rangifer tarandus tarandus) distribution in relation to possible travel barriers (roads and power lines) in south-central Norway, 1997–2000, using lichen biomass as an indicator of reindeer use. We recorded lichen cover on both sides of potential barriers within comparable habitat in 42 sites for 3 different reindeer herds. We used cover–biomass regressions to assess the relationship between lichen cover and biomass. In 2 of the regions, lichen biomass was 5.3 times and 2.8 times higher in areas isolated by 2 parallel power lines and an adjacent winter-closed road compared to biomass on the other side of the potential barrier. In a third region, lichen biomass did not vary significantly between areas on either side of a single winter-closed road. Lichen biomass data suggested that wild reindeer used both sides of a closed road in winter, whereas 2 parallel power lines and a winter-closed road in combination reduced reindeer migration and resulted in very different grazing pre...

Provenance characteristics of Mesoproterozoic metasedimentary rocks from Telemark, South Norway: a Nd-isotope mass-balance model

Abstract Whole-rock Nd isotope data on stratigraphically constrained samples of metasedimentary rocks from the ca. 1.50 to ca. 1.12 Ga Telemark supracrustal sequence in central South Norway define a linear array with a meaningless, late Archean apparent age; this is a mixing-line defined by two distinct endmembers, characterised by 147 Sm / 144 Nd=ca. 0.09 and ca. 0.13; and present-day 143 Nd / 144 Nd=0.5116 and 0.5122, respectively. From published SIMS and new LAM-ICPMS U–Pb ages of detrital zircon populations, ca. 1.8 Ga, ca. 1.5 Ga and ca. 1.15 Ga source components can be identified. The initial Nd isotope composition of sediments varies with stratigraphic level and geographic position within the basins, reflecting competition between juvenile volcanic sources and Paleoproterozoic granitoids throughout the ca. 400 Ma depositional period of the sediments. Given adequate external constraints, a normal whole-rock Sm–Nd analysis of a (meta)sedimentary rock can in principle be used to determine the relative contributions of up to four provenance components. The REE concentrations in the sedimentary rocks are controlled by source characteristics and differentiation processes acting during transport and deposition, which for most units have not affected the Sm/Nd ratio of the sediment. Initial Nd isotopic compositions and model ages are inherited from the source components, and are not significantly controlled by syn- or post-depositional differentiation processes. A (semi)quantitative model of sedimentary mass balance indicates that variations in volcanogenic input are erratic in the ca. 1.4 Ga Vindeggen group and the 1.15 Ga Lifjell group (both previously assigned to the obsolete Seljord group), reflecting changes in provenance with time as well as laterally. During deposition of the 1.15 Ga and younger Oftefjell and Hoydalsmo groups (parts of the obsolete Bandak group), the accumulated volcanogenic input increased with time, as a result of Sveconorwegian volcanism. The present findings support the presence of Paleoproterozoic (1.7–1.9 Ga) source terranes in central South Norway.

Smolting in anadromous and landlocked strains of Atlantic salmon (Salmo salar)

Abstract Juvenile Atlantic salmon from a landlocked population (‘Blege’, lake Byglandsfjord, south–central Norway) and an anadromous population (river Vosso, southwestern Norway) were reared in freshwater on simulated natural photoperiod (60°25′N) between December 2000 and June 2001. Fish from the Blege (mean length: 13.4 cm) and Vosso (mean length: 13.9 cm) strains were transferred to seawater tanks in late May for studies of long-term post-smolt performance. Condition factor of fish from the Blege strain increased throughout the study, whereas in the anadromous Vosso strain condition factor increased until April followed by a decrease between April and June. Smolts from the Vosso strain showed all the morphological characteristics of smolting, whereas smolt-sized fish from the landlocked population obtained a lower degree of silvering, and distinct parr-marks and red dots in the skin prevailed. Gill Na + ,K + -ATPase activity remained low in both strains in January and March, with a significant increase in the Vosso strain in April and May to peak levels of approximately 17 μmol ADP/mg protein/h. In contrast, only a slight increase was seen in the Blege strain in May, with peak level of approximately 8 μmol ADP/mg protein/h. In mid-June Na + ,K + -ATPase activity was down to parr levels. Improved short-term hypoosmoregulatory ability (seawater challenge tests, 34‰, 96 h) was observed in both strains; however, the Vosso strain showed better seawater tolerance than the Blege strain in March and April. There was no mortality among the smolt-sized fish of the Vosso strain transferred to seawater in late May, whereas high mortalities (40%) were observed in the Blege strain during the 2 weeks of seawater rearing. Our findings show that landlocked Atlantic salmon, represented here by the Blege population, having been isolated from the sea for approximately 9000 years, may have abandoned key elements of the parr–smolt transformation associated with marine life. Our results further emphasize the importance of the gill Na + ,K + -ATPase for long-term seawater performance.

The influence of scale and species pool on the relationship between vascular plant species richness and cover in an alpine area in Norway

Recent studies emphasise the potential importance of scale and species pool on the humped-back or unimodal relationship between species richness and productivity. We use a classic phytosociological data-set from Rondane, central south Norway, to evaluate the relative importance of these factors in an alpine area. The effect of species pool is assessed using plot scores from a Correspondence Analysis (CA) of the data. Generalised Additive Models (GAM) are used to relate vascular plant species richness to cover of vascular plants, CA plot scores, and plot area in different combinations. Species richness of vascular plants is unimodally related to total vascular plant cover. Plot scores of the first three CA axes (representing the effect of species pool) have a complex relationship with species richness, but explain a large fraction of the total deviance in richness. A humped relationship between richness and cover remains after accounting for CA plot scores in the model, i.e. the relationship is independent of species pool. The results suggest that the relationship between richness and cover changes from one vegetation type to another, as evaluated statistically through the importance of the interaction between cover and CA scores in explaining variation in richness. Plot area also influences the relationship. A unimodal relationship is only evident when small plot sizes are used, whereas a monotonically increasing relationship is found at large plot sizes. Plot area has the strongest effect on the unimodal relationship between richness and cover, whereas vegetation type has only a minor effect on this relationship.

Holocene climatic change and tree-line response in Leirdalen, central Jotunheimen, south central Norway

The provisional results of pollen analysis of a small mire (Leirdalen 5) provide evidence for long-term changes in forest composition and extent at and around the present day altitudinal tree-line in Leirdalen valley, south central Norway. Following deglaciation c. 10,115cal.yrbp, dense pine forest migrated into the area c. 9785cal.yrbp, replacing vegetation dominated formerly by birch. The pollen evidence suggests that Pinus sylvestris then expanded significantly in response to a warmer climate with summer temperatures ca. 1.5–2.0°C higher than present. This climatic optimum was probably interrupted by climatic deterioration c. 8380cal.yrbp (the Finse event), that caused woodland around Leirdalen 5 to retreat to lower altitudes. A sudden shift from dense pine forest to birch woodland with Pinus sylvestris and Alnus in conjunction with the development of a sub-alpine Betula belt is postulated to have occurred c. 6870cal.yrbp Since c. 4850cal.yrbp a general decrease in woodland extent due to further climatic deterioration and increased human impact is evident.

Wild reindeer: impacts of progressive infrastructure development on distribution and range use

We investigated the distribution of wild reindeer (Rangifer tarandus tarandus) from aerial surveys in 1986–1998 in 622 contiguous 4-km2 grid squares in relation to density of power lines, roads and ski trails in the Nordfjella region, south-central Norway. Density of reindeer was significantly lower in developed quadrats compared to undeveloped quadrats and decreased with increasing density of development. No reindeer were observed in areas exceeding 1.3 km/km2 of linear structures and only 1.1% of the reindeer were observed in areas exceeding 0.8 km/km2 of linear structures, an area constituting 17% of the study area. The results imply that development, and also the degree of development, affect the availability of range for wild reindeer. Furthermore, the results suggest that reindeer may abandon areas once disturbance exceeds a critical level. We conclude that there is a need for cumulative impact assessments of the overall development in Norwegian mountain regions, to preserve the last remaining wild reindeer populations in Europe.

Response of Norwegian alpine communities to nitrogen

The effect of nitrogen pollution on species cover was tested in the Dovre mountains, south-central Norway, through a three-year fertilisation experiment in a low-alpine community and a two-year one in a middle-alpine community, both dominated by lichens. The doses used were 0.7, 3.5 and 7 g N/m2, the highest doses corresponding to 1.75 and 3.5 times the annual deposition of nitrogen in southwestern Norway. The results were tested using the SAS/STAT/MIXED procedure. Using the Bonferroni correction, the procedure did not confirm a change in the cover of single species due to increased nitrogen supply, but there seemed to be a general tendency for an increase in cover in the low-alpine Cetrarietum nivalis community. When less rigorous tests were applied, Arctostaphylos uva-ursi, Vaccinium vitis-idaea, Polytrichum piliferum, Cetraria nivalis and Cladonia mitis in Cetrarietum nivalis, and Cladonia coccifera in Phyllodoco-Juncetum trifidi seemed to indicate that nitrogen had some effect on these communities. The lack of a clear response in single species may be due to the application of low doses over a short time-span in an environment characterised by large interannual variations in climate, the deficiency of other important nutrients, dryness, the low growth potential of the species involved, and, to some extent, the community structure.

Modelling ecological half‐lives for radiocaesium in Norwegian brown trout populations

Summary 1. Models of ecological half‐life may be valuable and cost‐effective predictive tools for authorities setting restrictions on human consumption of freshwater fish after environmental releases of radioactivity. This work aimed to validate such a model for radioactive caesium (134Cs and 137Cs) in brown trout Salmo trutta populations. Data were drawn from lakes with a wide variability in abiotic and biotic factors and initial caesium load. 2. In Norway, the highest fallout (more than 150 kBq m–2 of 137Cs) from the Chernobyl accident occurred in Oppland county, in south central Norway. Radioactivity was measured in more than 1800 samples of brown trout in nearly 100 localities in this region during 1986–95. 3. The back‐calculated maximum initial radioactivity on 1 January 1987 showed a strong regional variability (range 443–13 370; average 3855 Bq kg–1). Large variation in initial radioactivity was also recorded on a local scale (within 50 km). 4. The ecological half‐life model for caesium in brown trout populations for 1987–94/95 gave a close fit to real data from all localities with sufficient time series. Predicted half‐lives ranged from 1·2 to 4·2 years (average 2·5) but 95% confidence limits were narrow (2·7 and 2·3 years). 5. The overall variability in radioactivity levels over time was almost entirely related to the initial load and, with few exceptions, 88% of the changes in radioactivity was explained by the simple regression model. Modest variability in ecological half‐life was not correlated with initial activity, and no clear effects of water quality or season could be detected. For most lakes, levels of radioactivity in brown trout appeared to be predictable, with high accuracy after a fallout event, without extensive information on population ecology and water quality. However, more detailed work may be required to assess patterns within individual lakes.

Factors associated with wolverine Gulo gulo predation on domestic sheep

Summary 1. Following a long history of eradication campaigns against predators, wolverine Gulo gulo distribution and numbers became critically low in Norway in the 1960s. Consequently, wolverines were protected by law during the 1970s and 1980s. This led to an increase in wolverine numbers and re‐establishment in some formerly occupied habitats, resulting in increased depredation on domestic reindeer Rangifer tarandus and sheep Ovis aries. Wolverine control and licensed hunting have been used increasingly as tools to reduce the depredation since protection was introduced. However, the factors influencing the level of this depredation have not been studied. We therefore examined losses of domestic sheep grazing unattended on upland summer ranges in the Snøhetta plateau of south central Norway during 1979–94, in relation to wolverine population numbers, reproduction and control measures. This area was recently re‐occupied by wolverines and reproduction has been recorded regularly from the beginning of the study period. 2. The number of ewes and lambs recorded in organized grazing areas increased more than fivefold during the period, and losses increased proportionally with sheep numbers. The differences in losses among municipalities and grazing co‐operatives were probably related to sheep breeds and local variation in wolverine density. 3. The heavy Dala sheep breed was most at risk, whereas losses from the lighter Norwegian short‐tailed and Norwegian fur‐bearing breeds were lower than expected. 4. Killing of wolverines led to fewer lambs being lost in the same year that the wolverine killing took place, but the effect quickly declined, implying a rapid re‐establishment of wolverines in the local area. 5. Lambs were more vulnerable to wolverine predation than ewes, and losses were higher in wolverine cub‐rearing areas than in the area as a whole. 6. We conclude that: (i) control programmes for wolverines, as practised today, will have little long‐term effect in reducing sheep losses, unless wolverines are eradicated or severely reduced in numbers; (ii) the introduction of more agile sheep breeds will probably reduce losses; (iii) in areas where wolverine control to protect sheep is a threat towards wolverine conservation, the present sheep husbandry system of grazing unguarded sheep in the mountains should be replaced by alternative forms that provide the sheep with more protection. This is particularly important in wolverine denning areas.

Late Weichselian ice-flow directions in J ren, SW Norway; clast fabric and clast lithology evidence in the uppermost till

Late Weichselian ice-flow directions in southern Jæren, SW Norway, have been reconstructed through the applications of clast fabric and clast lithology in the uppermost till, and from glacial striations. Combined with previously published data, the results of the present investigation indicate three different ice-flow directions (phases). The earliest phase, towards the NW, is related to an ice stream along the Norwegian Channel. During the second phase, terrestrial ice from central south Norway moved towards the coast as the Norwegian Channel Ice Stream disintegrated. During the final deglaciation, part of the terrestrial ice became reactivated and advanced towards the SW in the northern part of the study area.

Permian and Mesozoic extensional faulting within the Caledonides of central south Norway

Palaeomagnetic data from fault rocks along major faults in the Laerdal-Gjende Fault System cutting the Caledonian structure in the Jotunheimen area of central south Norway reveals a multi-component remanence pattern. Sample and site-mean directions from the fault rocks obtained by thermal cleaning demonstrate a simple pattern of normal polarity low blocking components and reverse polarity high-blocking directions. The magnetic signature of the Laerdal-Gjende Fault System fault rocks is identical to that observed on breccias on late faults along the west coast of Norway. Based on available palaeomagnetic reference data, we assign ages of mid-late Permian and late Jurassic-early Cretaceous for important phases of faulting and breccia formation along the Laerdal–Gjende Fault System in central south Norway. Structural windows, partly exposing basement along the axis of the Caledonides in southern Norway were exhumed by footwall uplift on major faults in the Laerdal–Gjende Fault System. The consanguinity of fault rock data from the Laerdal–Gjende Fault System and fault rocks in western Norway, and comparison with displacement on the offshore continuation of the Laerdal–Gjende Fault System along the Hardangerfjorden Shear Zone, indicate that the main tectonic events responsible for the development of the North Sea basin also significantly affected the geology of central south Norway.