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1.
Holocene history of Lake Soldatskoje (Kola Peninsula, Russia) inferred from sedimentary diatom assemblages 总被引：3，自引：0，他引：3
TUULIKKI GRÖNLUND TOMMI KAUPPILA 《Boreas: An International Journal of Quaternary Research》2002,31(3):273-284
A sediment core from Lake Soldatskoje, a small tundra lake located in the northern coastal area of the Kola Peninsula and surrounded by numerous archaeological dwelling sites, was analysed for diatom species. The core covers the entire Holocene, i.e. 10000 radiocarbon years. The diatom record has similarities with studies made earlier from tundra lakes of northern Russia and from Arctic lakes in general. The genus Fragilaria was dominant and many other small, benthic, nordic, cold-water diatom species typical of Arctic lakes were common, including Achnanthes minutissima Kützing, A. pusilla (Grunow) De Toni, Cyclotella tripartita Håkansson and Navicula absoluta Hustedt. Multivariable ordinations were used to characterize the changes in the diatom flora. Diatom-based pH and total phosphorus inferences indicate that the lake has become progressively more acidic and poorer in nutrients. Disturbances in the diatom stratigraphy of Lake Soldatskoje around 4000–5500 14 C yr BP may be related to human activity. 相似文献
2.
VELI-PEKKA SALONEN BRITA ERIKSSON TUULIKKI GRÖNLUND 《Boreas: An International Journal of Quaternary Research》1992,21(3):253-270
Seventy-four meters of a 95-m-long drill core recovered from the Lappäjarvi crater, a meteoritic impact site in western Finland, consisted of Pleistocene sediments. These sediments refer to two events of glacial deposition (Saalian and Weichselian) interrupted by non-glacigenic freshwater sedimentation. The sediments contain abundant redeposited Holsteinian and Tertiary microfossils, and possibly represent a pre-Weichselian interstadial not described from elsewhere in Finland. The pollen flora indicates a mixed primary arctic to subarctic succession that followed deglaciation, i.e. the beginning of an interglacial or interstadial event. The secondary pollen component derives from an eroded interglacial deposit that can be interpreted as Holsteinian, or possibly Eemian, in age. The vegetation succession interpreted from the primary pollen flora reflects a transition from arctic conditions to subarctic birch forests. The diatom flora indicates a primary succession that can be observed clearly in the uppermost gyttja layer in which the rich alkaliphilous diatom flora refers to more or less eutrophic conditions. The diatom flora of sediments below the gyttja layer is composed of a primary component and a secondary, redeposited or relict component. The diatoms encountered are interglacial or Tertiary in origin. The results show that meteorite craters can provide long, representative stratigraphic sequences in glacially eroded Precambrian shield areas such as Finland. 相似文献
3.
Phenomena associated with small ice cap instability (SICI) are investigated using a general circulation model (GCM: NCAR Community Climate Model version 0) and a noise-forced nonlinear energy balance model (EBM). Both make use of idealized boundary conditions consisting of an all-land planet without topography and mean annual insolation. Ice is prescribed to exist on surface areas for which the instantaneous temperature lies below freezing. The adjustable parameters of the EBM were chosen to match the GCM solutions. For the regions in parameter space where SICI might occur we do not find the corresponding icefree steady state solution with the GCM. Our simulations with the EBM show that SICI phenomena in the presence of fluctuations are strongly dependent on the amplitude of the noise forcing. When the strength of noise forcing is adjusted to match the fluctuations in the GCM, we do not find a SICI in the EBM. With weaker levels of forcing the SICI reappears. In all cases steady stable ice caps smaller than a critical size are not found to exist. 相似文献
4.
Ground‐penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries. This article reports the results of an integrated study performed on an Upper Jurassic outcrop from the south‐east Paris basin, where coral bioherms laterally change into prograding depositional sequences. Ground‐penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop. A ground‐penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled. The excellent penetration depths of the ground‐penetrating radar (20 m with a monostatic 200 MHz antenna) images the carbonate platform geometries, ranging between outcrop workscale (a few metres) and seismic scale (several hundreds of metres). This study supports recent evidence of icehouse conditions and induced sea‐level fluctuations controlling the Upper Jurassic carbonate production. 相似文献
5.
The Valanginian is a period of global environmental change as illustrated by sedimentary, palaeontological, geochemical and climatic perturbations. A production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions. During the same time interval, a major positive excursion in δ13C, the Weissert Event, suggests perturbations of the carbon cycle from the latest Early Valanginian to the Early Hauterivian. In order to better understand the link between these changes, sea‐level fluctuations have been reconstructed in detail from the Middle Berriasian to the earliest Hauterivian. Sections from the Peri‐Vocontian Zone (South‐east France) have been investigated because of the good quality of outcrops on the carbonate platforms, their margins and in the Vocontian Basin. Sections ranging from the most proximal zone (Swiss Jura) to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy, and correlated at high resolutions. Using the identified small, medium and large‐scale sequences as well as depositional geometries, sea‐level fluctuations were reconstructed. Two main trends are evidenced during the studied interval: (i) the peak amplitude (magnitude) of the sea‐level fluctuations increased gradually from the Middle Berriasian to the Early Valanginian, and reached a maximum (more than 50 m) from the middle Early Valanginian to the Valanginian/Hauterivian boundary; and (ii) sea‐level variations were quite symmetrical during the Late Berriasian, slightly asymmetrical during the Early Valanginian and strongly asymmetrical (fast sea‐level rise, slow fall) from the latest Early Valanginian to the earliest Hauterivian. Moreover, three orders of sea‐level fluctuations were recognized in the sedimentary rocks of the Peri‐Vocontian Zone. Platform‐basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea‐level variations, mainly by the two eccentricity cycles of 100 and 400 kyr. The increase in the amplitude of the sea‐level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the Early Valanginian. Fast transgressions followed by slower regressions would correspond to waxing and waning of high‐latitudinal ice during most of the Valanginian, especially from the latest Early Valanginian to the latest Late Valanginian. Glacio‐eustatic sea‐level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the Valanginian. 相似文献
6.
准噶尔盆地南缘新生代构造特征及其与砂岩型铀矿成矿作用初析 总被引：5，自引：0，他引：5
准噶尔盆地南缘盆山结合部中新生界沉积巨厚,新生代变形强烈,是研究新盆山耦合的理想场所,也是我国砂岩型铀矿找矿的远景区段。本文在综合前人资料和野外观测分析基础上,根据新生代构造活动特征,将准噶尔盆地南缘划分为博格达山前和西部断褶带两个构造分区,博格达山前以强烈的逆冲推覆为特征,发育多条活动的逆冲推覆断裂; 乌鲁木齐以西至乌苏南的西部断褶带则发育三-四排的褶皱-逆冲断裂构造带。对采自博格达山前逆冲推覆断裂带内的方解石和断层泥,利用电子自旋共振测年手段,推测博格达山前的富康-吉木萨尔断裂带和北三台断裂带分别在0.7~1Ma和0.25Ma期间,经历了一期重要的逆冲推覆作用。结合盆地南缘砂岩型铀矿的展布规律及其成矿条件的分析,探讨了新生代构造运动对砂岩型铀矿成矿的控制作用,认为西部断褶带的第一排构造带具有较好的成矿前景,而博格达山前由于新生代构造活动强烈而相对成矿不利,为此提出了准噶尔盆地南缘砂岩型铀矿成矿“构造优先权”的构造控矿模式,进而指出了区域找矿的优选区段。 相似文献
7.
利用融合二氧化硅毛细管技术制作了纯H2O体系、纯CO2体系、H2O-NaCl体系和H2O-CO2体系的人工包裹体样品,并对样品进行了显微测温和激光拉曼光谱测试工作。实验结果显示毛细管样品中的流体成分具有代表性,而且常规的流体包裹体显微测温和显微激光拉曼光谱分析技术完全适于毛细管样品的测试。对样品的显微测温和拉曼光谱研究... 相似文献
8.
dr. phil. N. KINGO JACOBSEN CHR. BAY B. FREDSKILD B. GRøNNOW B. HOLM JAKOBSEN M. MELDGAARD 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):29-44
Jacobsen, N. Kingo, et.al. Report of activities at Tugtuligssuaq, Melville Bugt, 1978–79. Geografisk Tidsskrift 80: 29–44. Copenhagen, June 1980. A joint cooperative Greenland/Danish expedition to the Melville Bugt area, Tugtuligssuaq/Kap Seddon to throw light on the Eskimos' immigration routes to Greenland seen in relation to climatic fluctuations. Studies of geography, botany, zoology, archaeology, and ethnohistory have been carried out. 相似文献
9.
BRITA ERIKSSON TUULIKKI GRÖNLUND ANNELI UUTELA 《Boreas: An International Journal of Quaternary Research》1999,28(2):274-291
The till-covered clay and silt deposits at Mertuanoja, Pohjanmaa (Ostrobothnia), western Finland, have been investigated in great detail. The Eemian interglacial environment is reconstructed here on the basis of pollen, diatom and dinoflagellate analyses. The pollen stratigraphy shows an interglacial vegetational succession reflecting stable climatic conditions typical of the Eemian Stage in the Pohjanmaa area. The initial Betula forests were followed by Pinus-Betula forests with Quercus. The next successional phase was dominated by Betula, Pinus and Alnus; temperate deciduous trees and Corylus also grew in the area. Later, Picea advanced and temperate deciduous trees declined. Some Corylus was, however, still present and thermophilous Osmunda thrived in wet places. The diatom record indicates that the sediments were deposited first in a freshwater basin, then in the Eemian Baltic Sea, and finally in a freshwater basin once more. The presence of dinoflagellates demonstrates that the Eemian Baltic Sea, when at its maximum extent, was connected to the Atlantic Ocean, which brought northern cool-temperate surface waters to Finland as far north as Mertuanoja. Mertuanoja is the first interglacial site at which numerous dinoflagellate cysts were encountered in Finnish Quaternary sediments. 相似文献
10.
NICHOLSON HUGH; CONDOMINES MICHEL; FITTON J. GODFREY; FALLICK ANTHONY E.; GR?NVOLD KARL; ROGERS GRAEME 《Journal of Petrology》1991,32(5):1005-1020
The Krafla volcanic system consists of a central volcano andassociated fissure swarm in the NE axial rift zone of Iceland.Lavas spanning the whole of Krafla's exposed volcanic history(estimated to be 0-> 300 ka) have been analysed and rangein composition from olivine tholeiite to rhyolite. Major-elementcompositions suggest that fractional crystallization exertsthe main control over the differentiation process. However,K2O and the very incompatible trace elements, Rb, Th, and U,are all enriched beyond the extent expected by closed-systemfractional crystallization. Fractionation coupled with periodicreplenishment and tapping of the reservoir is unlikely to beresponsible for this enrichment, despite the geophysical evidencesuggesting a large number of inflations and deflations of ashallow magma reservoir (Tryggvason, 1986). Th- and O-isotope results confirm the work of previous authorsthat crustal assimilation is operating on a local scale beneathKrafla. A model is suggested, fitting both the Th- and O-isotopicdata, which involves the partial melting and incorporation ofa hydrothermally altered wall-rock contaminant during fractionalcrystallization (i. e., AFC processes). This process of partialmelting is likely to enhance the most highly incompatible elementconcentrations (e. g., increasing Rb/Zr) more than expectedby closed-system fractional crystallization. 相似文献