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11.
A total of 138 walruses ( Odobenus rosmarus rosmarus ), including 21 cow/calf pairs, were observed during a ship-board survey in the southeastern Barents and Pechora seas 5-17 February 1993. The observations confirm these areas as wintering and nursery grounds for the species. 相似文献
12.
The 456 ± 4 Ma Skattøra migmatite complex in thenorth Norwegian Caledonides consists of migmatitic nepheline-normativemetagabbros and amphibolites that are net-veined by numerousnepheline-normative anorthositic and leucodioritic dykes. Plagioclase(An20–50) is the dominant mineral (85–100%) in thedykes and the leucosome, but amphibole is generally presentin amounts up to 15%. The following observations strongly suggestformation of the anorthositic magma by anatexis of the surroundinggabbro in the presence of an H2O-bearing fluid phase: (1) themigmatites have plagioclase-rich (anorthositic) leucosomes andamphibole-rich restites; (2) crystallization of amphibole inthe anorthositic and leucodioritic dykes suggests high H2O activity;(3) the presence of coarse-grained to pegmatitic dykes and miaroliticcavities indicates a fluid-rich magma; (4) hydration zones thatsurround many anorthosite dykes suggest that the magma probablyexpelled H2O-rich fluids during crystallization. Water-saturatedmelting experiments at 0·5–1·5 GPa and temperaturesfrom 800 to 1000°C have been performed on a nepheline-normativegabbro to test the proposed petrogenesis of the Skattøraanorthosites. The glasses produced close to the solidus aretonalitic in composition, but they become richer in plagioclaseat higher temperatures. At and below 1·0 GPa, the residuesare composed of amphibole. Experiments above 1·0 GPaproduced residual garnet and/or zoisite in addition to amphibole,suggesting that the anorthositic dykes in the Skattøramigmatite complex formed below 1·25 GPa. The experimentsshow that the high Na2O content of the anorthosite dykes canonly be produced if Na is added to the charges. The glass thatbest fits the composition of the Skattøra dykes was producedat 1·0 GPa and 900°C with 2 wt % Na(OH) added. KEY WORDS: anorthosite; dyke swarm; anatexis; experimental petrology 相似文献
13.
HELENE BERGSTEN KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1992,21(3):223-252
From stratigraphic investigations of 38 piston and vibro cores, four fine-grained Late Weichselian sediment units can be defined in the southern Kattegat. A continuous stratigraphic record of the Late Weichselian sediments cannot be established from single cores due to the uneven distribution of the units, but by compilation of relative stratigraphies a composite record can be determined for sediments deposited between approximately 13,500 and 10,000 BP. The sediments contain both lithological and biostratigraphical evidence that the Baltic Ice Lake was suddenly drained through the Öresund Strait at about 12,700 BP. This drainage route appears to have been unchanged until about 10,300 BP when a passage opened in south central Sweden through which the final drainage of the Baltic Ice Lake took place. The Younger Dryas cold event appears to have had only marginal effects on the marine benthic life in the region. The data also indicate that drainage of fresh Baltic water through the Öresund Strait was the driving force for an inflow of marine water from the Skagerrak North Atlantic Ocean into the southern Kattegat, as occurring at the present. This paper is a contribution to IGCP 253, Termination of the Pleistocene . 相似文献
14.
STEFAN MAJORAN KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1997,26(3):181-200
The ostracods in three vibro cores (representing the time between c . 13000 and 12000 BP) from southern Kattegat were studied to further elucidate palaeoenvironmental conditjons in an area interpreted to be influenced by a Late Weichselian drainage of the Baltic Ice Lake via the Öresund Strait. This time represents an extremely important phase of the deglaciation of the northern hemisphere. It is characterized by rapid climatic change and enormous amounts of meltwater that are drained into the ocean. The ostracod assemblages identified are characterized by a peculiar mixture of marine (arctic and temperate) and freshwater species believed to characterize environments ranging from the tidal zone of an outer estuary (or delta) to fully marine sublittoral conditions in a subarctic climate. Dominant species display autochthonous population structures typical of in situ elements of such environments. Indications of very shallow conditions are, however, difficult to reconcile with palaeobathymetrical inferences from earlier studies of shore-level displacements. It is, therefore, possible that the present assemblages are mainly death assemblages deposited offshore by postmortem meltwater discharge. Rare pre-Quaternary ostracods similar to Mesozoic species previously reported from the Öresund Strait (drill holes) and the Swedish west coast may have been redeposited by outflowing meltwater. 相似文献
15.
EYSTEIN JANSEN KJELL R. BJORKLUND 《Boreas: An International Journal of Quaternary Research》1985,14(3):243-257
Quantitative studies of foraminifera and radiolaria, semi-quantitative analyses of diatoms and coccoliths, and the distribution of ice-rafted sediments have been performed on cores from the southeastern Norwegian Sea. The results document large variations in sea-surface temperatures and ocean circulation, showing a strong correlation between oceanic data and palaeoclimatic data from the neighbouring coastal areas of Norway. For the first time the Allerød – Younger Dryas climatic fluctuations and the Holocene climatic optimum are shown in records from the Norwegian Sea. Starting at about 13,000 B.P. the sea surface became seasonally ice-free with productive seasons. During the Allerød a narrow wedge of temperate Atlantic water flowed into the southeastern Norwegian Sea. In Younger Dryas time the surface waters cooled by several degrees. Holocene surface conditions were relatively constant, with somewhat higher temperatures in a period possibly corresponding with Atlantic time. 相似文献
16.
HELENE BERGSTEN KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1993,22(4):311-318
Foraminifera, pollen, lithology and radiocarbon dates from a core in the southern Kattegat provide a rare opportunity to obtain data relating to environmental conditions during the Middle Weichselian in the offshore Kattegat. This core is also correlated with an adjacent second core. Redeposited Eemian foraminifera and pollen occur in the Middle Weichselian sediments. This is interpreted as a result of reworking by an active Middle Weichselian ice present in, or advancing from, a northeasterly to easterly direction. During a second phase the Middle Weichselian sediments were compacted, probably a result of overriding by an ice from the northeast during the Middle Weichselian and/or the Late Weichselian Maximum. The Middle Weichselian sequence is overlain by a Holocene sequence which, in turn, is overlain by an admixture of Middle Weichselian and Holocene sediments. This mixing may be a result of tectonic activity some time between 7300 and 1000 BP. The core ends in Holocene fine sediments representing the last c. 1000 years. 相似文献
17.
Solution-collapse breccias of the Minkinfjellet and Wordiekammen Formations, Central Spitsbergen, Svalbard: a large gypsum palaeokarst system 总被引：3，自引：0，他引：3
Large volumes of carbonate breccia occur in the late syn-rift and early post-rift deposits of the Billefjorden Trough, Central Spitsbergen. Breccias are developed throughout the Moscovian Minkinfjellet Formation and in basal parts of the Kazimovian Wordiekammen Formation. Breccias can be divided into two categories: (i) thick, cross-cutting breccia-bodies up to 200 m thick that are associated with breccia pipes and large V-structures, and (ii) horizontal stratabound breccia beds interbedded with undeformed carbonate and siliciclastic rocks. The thick breccias occur in the central part of the basin, whereas the stratabound breccia beds have a much wider areal extent towards the basin margins. The breccias were formed by gravitational collapse into cavities formed by dissolution of gypsum and anhydrite beds in the Minkinfjellet Formation. Several dissolution fronts have been discovered, demonstrating the genetic relationship between dissolution of gypsum and brecciation. Textures and structures typical of collapse breccias such as inverse grading, a sharp flat base, breccia pipes (collapse dolines) and V-structures (cave roof collapse) are also observed. The breccias are cemented by calcite cements of pre-compaction, shallow burial origin. Primary fluid inclusions in the calcite are dominantly single phase containing fresh water (final melting points are ca 0 °C), suggesting that breccia diagenesis occurred in meteoric waters. Cathodoluminescence (CL) zoning of the cements shows a consistent pattern of three cement stages, but the abundance of each stage varies stratigraphically and laterally. δ18O values of breccia cements are more negative relative to marine limestones and meteoric cements developed in unbrecciated Minkinfjellet limestones. There is a clear relationship between δ18O values and the abundance of the different cement generations detected by CL. Paragenetically, later cements have lower δ18O values recording increased temperatures during their precipitation. Carbon isotope values of the cements are primarily rock-buffered although a weak trend towards more negative values with increasing burial depth is observed. The timing of gypsum dissolution and brecciation was most likely related to major intervals of exposure of the carbonate platform during Gzhelian and/or Asselian/Sakmarian times. These intervals of exposure occurred shortly after deposition of the brecciated units and before deep burial of the sediments. 相似文献
18.
Fluid-absent melting experiments on a zoisite- and phengite-bearingeclogite (omphacite, garnet, quartz, kyanite, zoisite, phengiteand rutile) were performed to constrain the melting relationsof these hydrous phases in natural assemblages, as well as themelt and mineral compositions produced by their breakdown. From1·0 to 3·2 GPa the solidus slopes positively from1·5 GPa at 850°C to 2·7 GPa at 1025°C,but bends back at higher pressures to 975°C at 3·2GPa. The melt fraction is always low and the melt compositionsalways felsic and become increasingly so with increasing pressure.The normative Ab–An–Or compositions of the initialmelts vary from tonalites at 1·0 GPa to tonalite–trondhjemitesat 1·5 GPa, adamellites at 2·1 and 2·7GPa, and to true granites at 3·2 GPa. At pressures < 相似文献
19.
Dehydration-melting experiments from 10 to 20 kbar were performedon a metavolcanoclastic rock containing (in vol. %) biotite(16), amphibole (15) and epidote (13) in addition to plagioclaseand quartz. At 10 and 12.5 kbar traces of biotite and epidoteremain at 850C, amphibole becomes more abundant, and the meltfraction is 5–10 vol. %. These relationships reflect thatthe thermal stability of biotite is lowered in the presenceof epidote through the dehydration-melting reaction biotite+epidote+quartz=amphibole+garnet+alkalifeldspar+melt. Amphibole dehydration-melting produces an additional25 vol. % melt between 875 and 925C. At 15 kbar and 875C themelt fraction is 22 vol. %, amphibole is present in trace amounts,and biotite constitutes 8 vol. %. These relationships suggestthat the curves marking biotite- and amphibole-out intersectclose to 15 kbar, and that the fertility of the rock increasesfrom 10 to 15 kbar at 850C. At 20 kbar the melt fraction isonly 5 vol. % at 850C, amphibole is transformed to omphaciteand biotite constitutes 5% of the mode. This result shows thatthe fertility decreases from 15 to 20 kbar at 850C, mainlybecause much Na is locked up in omphacite. Along active continentalmargins, intrusion of hot mantle-derived magmas is common, andmelting of metavolcanoclastic rocks may be an important granitoid-formingprocess. Intersection of the amphibole- and biotite-out reactionsbetween 12.5 and 15 kbar suggests that fusion of biotite- andhornblende-bearing rocks can produce magmas ranging in compositionfrom granitic (biotite dehydration-melting) to granodioritic(amphibole dehydration-melting) in either order depending onpressure. KEY WORDS: amphibole; biotite; dehydration-melting; epidote; metavolcanoclastic rock
*Corresponding author. 相似文献
20.
KJELL R. BJØRKLUND JØRN THIEDE HANS HOLTEDAHL 《Boreas: An International Journal of Quaternary Research》1979,8(2):133-135
In a region of generally thin Holocene sediment cover along the outer Norwegian continental margin, a 565 cm long piston core was taken, which contained more than 4 m of Holocene clayey silty sediments. A several decimetres thick sandy horizon separated the glacial marine clays with ice-dropped components and the fine-grained Holocene sediments which have bulk sedimentation rates of more than 40 cm/1000 years. The scarcity of biogenous sediment components in the glacial sediments and the increasing frequency of benthonic as well as planktonic fossils in the Holocene deposits points to important changes in the Norwegian Sea hydrography during the time of the Scandinavian deglaciation. 相似文献