Stratigraphic architecture and infill history of a deglaciated bedrock valley based on georadar, seismic profiling and drilling     

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   

FINE SCALE VARIABILITY IN SOIL FROST DYNAMICS SURROUNDING CUSHIONS OF THE DOMINANT VASCULAR PLANT SPECIES (AZORELLA SELAGO) ON SUB‐ANTARCTIC MARION ISLAND     

NATALIE S. HAUSSMANN  JAN C. BOELHOUWERS  MELODIE A. McGEOCH 《Geografiska Annaler: Series A, Physical Geography》2009,91(4):257-268

Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation‐banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub‐Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winterthan soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winterthan on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, lee‐side snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above ?2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia.  相似文献   

Holocene shoreline displacement at Agardhbukta, eastern Spitsbergen, Svalbard     

OTTO SALVIGSEN  JAN MANGERUD 《Polar research》1991,9(1):1-7

An emergence curve based on nine radiocarbon dated samples of mosses, shells, whale bones and driftwood has been constructed for Agardhbukta. Beach sediments and delta deposits were found up to c. 50 m above sea level, and the oldest date goes back to about 10, 000 yrs BP. However, the possibility of a higher marine limit cannot be excluded. The Agardhbukta curve shows a nearly linear uplift during the entire Holocene. It differs from the western Spitsbergen curves, where a transgression occurs, and is more similar to curves from areas further east in the Svalbard archipelago.  相似文献   

Late Quaternary foraminiferal stratigraphy from western Svalbard     

ANNE KATRINE LYCKE  JAN MANGERUD  HANS PETTER SEJRUP 《Boreas: An International Journal of Quaternary Research》1992,21(3):271-288

In the lower part of sections at Skilvika and Linneelva, western Svalbard, marine silts and sands characterized by infinite radiocarbon ages (<40,000 BP) on shells are found. These sediments are covered by at least one basal till of Late Weichselian age. The till is overlain by marine sediments from the last deglaciation (12,800-10,000 BP) which contain shallow-water, subarctic foraminiferal assemblages, similar to modern near-glacial faunas from western Svalbard. The most common foraminifera in all zones in the sub-till sediments are Cassidulina reniforme, Astrononion gallowayi and/or Elphidium excavatum . The richest zones at both localities are found in the sub-till units and contain more than 20 foraminiferal species, including some boreal-arctic species. These faunal assemblages are similar to the living faunas on the west coast of Svalbard. Faunas from the postglacial climatic optimum are not yet described. We suggest that the foraminiferal assemblages in the sub-till sediment reflect Early or Middle Weichselian interstadial environments, although an Eemian interglacial cannot be excluded.  相似文献   

Former extension of the East Antarctic Ice Sheet     

JAN LUNDQVIST 《Polar research》1989,7(2):109-117

Knowledge about the Quarternary geology of the Australian sector of Antarctica is very incomplete. Scattered observations of glacial deposits in that area, made during the ANARE 6 expedition in 1987, indicate that the inland ice had formerly a considerably wider extension than today. The ice was more than 200 m thicker, probably of the order 1, 000m. This maximum stage cannot yet be dated, but conditions seem to favour a late Wisconsin-Weichselian maximum age. However, a much higher age cannot be excluded.  相似文献   

Thermal hysteresis antifreeze agents in fishes from Spitsbergen waters     

JOHN-PEDER DENSTAD  TORE AUNAAS  JAN FREDRIK BORSETH  ARNE VOLLAN AARSET  KARL ERIK ZACHARIASSEN 《Polar research》1987,5(2):171-174

The occurrence of macromolecular antifreeze agents (so-called Thermal Hysteresis Factors) in blood plasma of fishes from Spitsbergen waters was investigated in August 1983, October 1984, and January 1986.
Thermal hysteresis was found in the plasma of three species of Spitsbergen fishes: shorthorn sculpin (Myoxocephalus scorpius) , polar cod (Boreogadus saida) , and sea snail (Liparis liparis) . This is the first time thermal hysteresis is reported from the sea snail. Seasonal changes in the amount of thermal hysteresis were observed in blood plasma of the shorthorn sculpin and the sea snail.
With the exception of the polar cod, blood plasma of deep water fishes displays no thermal hysteresis. The reason for this is probably that the polar cod also occurs in shallow ice laden sea water, where an'antifreeze'would be needed to protect against inoculative freezing.
No thermal hysteresis was observed in blood plasma of the saithe (Pollachius virens) , despite the fact that the saithe was observed swimming in ice laden sea water at a temperature of -1 to – 1.5°C under natural conditions, and was rapidly killed when it came into contact with ice in the laboratory. It is not known how the saithe survives in ice laden water under natural conditions.  相似文献   

Cave stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna     

EILIV LARSEN  STEINAR GULLIKSEN  STEIN-ERIK LAURITZEN  ROLF LIE  REIDAR LØVLIE  JAN MANGERUD 《Boreas: An International Journal of Quaternary Research》1987,16(3):267-292

Skjonghclleren is a marine-cut cave with 15–20. m thick pre-Holocene sediments. Corings and excavations reveal three beds of extremely fine-grained, laminated sediments alternating with blocky sediments. The laminated beds are interpreted as glaciolacustrine sediments deposited subglacially at times when ice sheets covered the area, suggesting at least three glaciations after the cave was formed. The blocky/diamictic sediments were formed by frost-shattered blocks from the roof of the cave during ice-free periods, and mixing with the fines through slow mass movements along the floor of the cave. In the diamictic sediment beneath the uppermost laminated bed, almost 7,000 bone and teeth fragments of birds, mammals and fish were found. Birds dominated, with little auk and brunnich's guillemot as the most frequently occurring species. Arctic fox was the dominating mammal. During climatic optimum of the interstadial, conditions seem to have been similar to present-day coastal Finnmark, with North Atlantic warm water entering the Norwegian Sea. Two radiocarbon dates on bones and three Uranium series dates on speleothems from this bed all cluster around 30,000 B.P., i.e., the end of the Ålesund interstadial. Above the uppermost laminated bed, bone fragments of birds, fish and mammals, deposited between c . 12,000 and c . 10,000 B.P., were found. Little auk dominate. The occurrence of squirrel is worth noting since it is limited mainly to areas with coniferous forest today. The beds below the 30,000B.P. bed are poorly dated or undated, but it is tentatively concluded that the entire sediment sequence was deposited during the Weichselian stage. It seems that the cave was formed at a high relative sea-level stand sometime during the Early Weichsclian. Two recorded palaeomagnetic excursions seem to correlate with the Laschamp/Olby and the Lake Mungo events, respectively.  相似文献   

Bedform migration and bed-load transport in some rivers and tidal environments     

JAN H. VAN DEN  BERG 《Sedimentology》1987,34(4):681-698

Reliable field data obtained by directly measuring bed-load transport of fine- to coarse-grained bed material are extremely scarce, mainly because of the difficulty of sampling accurately. Therefore, the verification of bed-load transport formulae is largely based on flume experiments, which refer to unrealistic shallow-water conditions. In this study, some bed-load transport formulae were tested against data from natural environments. As an alternative to ascertaining the bed-load transport rate by sampling the bed-load, the transport rate was deduced from data on bedform height and bedform celerity. For this purpose, 43 sets of data from rivers, representing a wide range of bed material, bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings. Two formulae were used for the prediction of the bed-load transport: the formula of Van Rijn (1981) and the Kalinske (1947) formula as approximated by Elzerman & Frijlink (1951) (and, in the present study, slightly modified for application to tidal waters). Both the bed-load function of Van Rijn and the modified formula of Kalinske-Frijlink require data which are easily obtained and that can be measured accurately. At those stages of the flow when bed-load transport was high the Van Rijn function tended to overestimate that transport. For flow stages when bed-load transport was low the opposite was true. The modified Kalinske-Frijlink function gave consistently good results: 86% of the transport rates predicted using the river data were within 0·5–2·0 times the values actually measured.  相似文献