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VALENTIN BURKI LOUISE HANSEN OLA FREDIN THORBJØRN A. ANDERSEN ACHIM A. BEYLICH MICHEL JABOYEDOFF EILIV LARSEN JAN‐FREDERIK TØNNESEN 《Boreas: An International Journal of Quaternary Research》2010,39(3):551-566
Burki, V., Hansen, L., Fredin, O., Andersen, T. A., Beylich, A. A., Jaboyedoff, M., Larsen, E. & Tønnesen, J.‐ F. 2009: Little Ice Age advance and retreat sediment budgets for an outlet glacier in western Norway. Boreas, Vol. 39, pp. 551–566. 10.1111/j.1502‐3885.2009.00133.x. ISSN 0300‐9483 Bødalsbreen is an outlet glacier of the Jostedalsbreen Ice Field in western Norway. Nine moraine ridges formed during and after the maximum extent of the Little Ice Age (LIA). The stratigraphy of proglacial sediments in the Bødalen basin inside the LIA moraines is examined, and corresponding sediment volumes are calculated based on georadar surveys and seismic profiling. The total erosion rates (etot) by the glacier are determined for the periods AD 1650–1930 and AD 1930–2005 as 0.8 ± 0.4 mm/yr and 0.7 ± 0.3 mm/yr, respectively. These rates are based on the total amount of sediment delivered to the glacier margin. The values are almost one order of magnitude higher than total erosion rates previously calculated for Norwegian glaciers. This is explained by the large amount of pre‐existing sediment that was recycled by Bødalsbreen. Thus, the total erosion rate must be considered as a composite of eroded bedrock and of removed pre‐existing sediments. The total erosion rate is likely to vary with time owing to a decreasing volume of easily erodible, unconsolidated sediment and till under the glacier. A slight increase in the subglacial bedrock erosion is expected owing to the gradually increasing bedrock surface area exposed to subglacial erosion. 相似文献
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BRADLEY W. GOODFELLOW OLA FREDIN MARC-HENRI DERRON ARJEN P. STROEVEN 《Boreas: An International Journal of Quaternary Research》2009,38(2):379-398
The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigated through an examination of fine matrix and clasts from two pits excavated across ridge-top sorted circles; one on a summit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorly crystallized Al- and Fe-oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occurs in the saddle. In both locations, volumes of clay-sized matrix are low, mass balance calculations indicate only minor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). In addition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sorted circles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix-rich circle centres, and some rind development, which increases in frequency in the clast-rich rings. The dominance of physical weathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicate that the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developing during interglacials, interstadials and the Holocene, primarily through subsurface weathering processes. 相似文献
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ASTRID LYSÅ MARIA A. JENSEN EILIV LARSEN OLA FREDIN IGOR N. DEMIDOV 《Boreas: An International Journal of Quaternary Research》2011,40(3):481-497
Lyså, A., Jensen, M. A., Larsen, E., Fredin, O. & Demidov, I. N.* 2010: Ice‐distal landscape and sediment signatures evidencing damming and drainage of large pro‐glacial lakes, northwest Russia. Boreas, Vol. 40, pp. 481–497. 10.1111/j.1502‐3885.2010.00197.x. ISSN 0300‐9483. Sediments from river sections and the morphology of the upper reaches of Severnaya Dvina and Vychegda in northwest Russia show evidence of the existence of large ice‐dammed lakes in the area twice during the Weichselian. During the Late Weichselian, three separate ice‐dammed lakes (LGM lake(s)) existed, the largest one at about 135 m a.s.l. having a volume of about 1510 km3. Stepwise and rapid lake drainage is suggested to have taken place within less than 1000 years. The locations of various passpoints controlled the drainage, and when the lake was at its maximum level water spilled southeastwards into the Volga basin. Later, but before the lake water finally drained into the White Sea, water was routed northeastwards into the southeastern part of the Barents Sea. The oldest lake, the White Sea lake, existed around 67–57 ka ago, slightly in conflict with earlier palaeogeographic reconstructions regarding the chronology. The extent of the lake was constrained by, in addition to the Barents Sea ice‐sheet margin in the north, thresholds in the drainage basin. Later, one threshold was eroded and lowered during the LGM lake drainage. Given a lake level of about 115 m a.s.l., a lake area of about 2.5 × 104 km3 and a water volume of about 4800 km3, the lake drainage northwards and into the ocean probably impacted the ocean circulation. 相似文献
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LOUISE HANSEN ACHIM BEYLICH VALENTIN BURKI† RAYMOND S. EILERTSEN‡ OLA FREDIN EILIV LARSEN ASTRID LYSÅ ATLE NESJE† KNUT STALSBERG JAN F. TØNNESEN Associate Editor – Nick Eyles 《Sedimentology》2009,56(6):1751-1773
The sediment fill of a silled bedrock valley in Western Norway has been investigated with respect to stratigraphy and infill history using a combination of mapping, georadar, seismic profiling and drilling. A small outlet glacier occupies the head of the valley that displays a stepwise down-valley profile and terminates in a lake at 29 m above sea-level. The valley is surrounded by high, steep bedrock slopes and is characterized by a series of filled basins each limited by sills of bedrock or moraine accumulations. Till, glacial outwash and/or rockslide deposits fill in the lower half of the two larger basins. (Fan) delta deposits fringed by the deposits of alluvial fans and colluvial cones dominate the upper fill of most basins. (Fan) delta deposits interfinger downstream with lake sediments in the larger basins and fluvial deposits comprise the top fill. The overall infill pattern was controlled by deglaciation as well as basin size and shape. An overall decreasing sediment supply following deglaciation is shown in the fill of a larger basin down-valley, whereas a recently increasing sediment supply during glacier growth is reflected primarily in an upstream basin. Only the lowermost basin was exposed to a sea-level drop from 75 m above sea-level to the present lake level associated with incision and river migration. This observation is in contrast to the basins above marine influence where incision has been limited due to fixed downstream sills resulting in insignificant erosion except for some fan-head entrenchment. It follows that the fills of these small valley basins display progradational and aggradational trends of deposition and paraglacial reworking has been limited. Additionally, the study demonstrates that georadar profiling, combined with other methods, is very useful for comprehensive investigation of valley basins. 相似文献
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LEIF KULLMAN OLA ENGELMARK 《Boreas: An International Journal of Quaternary Research》1990,19(4):323-331
Radiocarbon dates of subfossil pines found on dry ground above the present-day tree-limit are reported from northern Sweden. The uppermost and oldest specimen germinated c. AD 300–600. During some shorter part of this interval the tree-limit might have been 235 m higher than it was at the turn of the last century. Based on a current adiabatic lapse rate of 0.7°C per 100m, it may be tentatively deduced that the summers were at least 1.6°C warmer. The pine tree-limit and upper pine populations are inferred to have declined substantially shortly after AD 600. The tree-limit reached a low at the end of the Little Ice Age. In parallel with the warming of c. 1°C during the first half of the 20th century the tree-limit advanced 110m altitudinally. Spruce forest dominance seems to have increased at the study site during the first half of the 19th century, when thermal and hygric conditions may have been optimally balanced. Although basically a direct climatic response, it can be hypothesized that the spruce expansion was facilitated by the pine demise during the Little Ice Age. 相似文献
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OLA EIKEN 《Polar research》1985,3(2):167-176
The status of seismic exploration work mapping the post-Caledonian strata in the Svalbard area is presented. Compressional wave velocities are very high throughout the area, around 4km/s in the Tertiary and Mesozoic layers. In the Permian section velocities exceed 5 km/s, with refraction velocities > 6 km/s in the calcareous rocks of the Gipsdalen Group (early Permian/Late Carboniferous). Apart from correlation with carbonate and chert lithology, high velocities reflect the high degree of consolidation and the low porosities of shales and sandstones in the post-Caledonian strata in Svalbard. In van Mijenfjorden seismic reflection events are observed down to 3–4 km depth and associated with Carboniferous and younger strata. The thickness of the Mesozoic layers in this part of the central Spitsbergen syncline seems to be greater than previously suggested, and there is an apparent eastward divergence between the Jurassic and the Triassic reflectors. In south-western Storfjorden, reflections interpreted to originate from Carboniferous and Permian strata might represent the seaward extension of the central Spitsbergen syncline. In the northern part of Storfjorden, carbonate layers within the Gipsdalen Group are interpreted to lie about one kilometre below the sea floor. A prominent fault zone in this area trends NNW-SSE, like the main structural elements on Spitsbergen. It shows block-faulting, presumably caused by extensional movement in late Devonian-Carboniferous time. 相似文献
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