Showing papers by "Geological Survey of Denmark and Greenland published in 1999"
TL;DR: In this article, a shallow aquifer was studied for Fe-oxide reduction, sulfate reduction, and methanogenesis, with the main focus on sulfate reducing, and the results showed that the resulting sulfide forms framboidal pyrite via a FeS precursor, with elemental sulfur as an intermediate.
258 citations
TL;DR: It is suggested that estimates of relative pollen productivity should be used to guide the pollen sum on which pollen-type richness is estimated by rarefaction techniques and this approach is illustrated using a paired site study of late Holocene diversity dynamics.
Abstract: Summary
Quaternary pollen records may contribute uniquely to the understanding of present plant diversity. Pollen assemblages can reflect diversity at community and landscape scales but the time resolution of most studies does not match that of modern ecological studies. Because of the complicating effects of differential pollen productivity and dispersal, pollen records do not directly reflect equitability aspects of vegetation diversity. Vegetation diversity indices other than S (the total number of taxa) are therefore not appropriate for pollen assemblages. As a measure of the species richness palynological richness is biased by the lack of taxonomic precision, by a possible interference on pollen dispersal from vegetation structure and by pollen representation. The nonlinear relationship between species richness and pollen-taxa richness may be used in attempts to estimate past floristic richness from fossil pollen assemblages. Using a hypothetical example the strong effect of cover shifts in the vegetation affecting taxa with different representation (Rrel) values on observed palynological richness is demonstrated. It is suggested that estimates of relative pollen productivity should be used to guide the pollen sum on which pollen-type richness is estimated by rarefaction techniques and this approach is illustrated using a paired site study of late Holocene diversity dynamics. The need for a modern training set relating pollen-type richness to species richness, pollen productivity and vegetation structure is emphasized.
222 citations
TL;DR: Surface-sediment assemblages of subfossil chironomid head capsules from fifty-four primarily shallow and nutrient-rich Danish lakes were analysed using multivariate numerical techniques and can be used in the assessment and reconstruction of lake trophic state for long-term monitoring and palaeoecological investigations of shallow, temperate lakes in the mesotrophic to hypertrophic nutrient range.
Abstract: 1. Surface-sediment assemblages of subfossil chironomid head capsules from fifty-four primarily shallow and nutrient-rich Danish lakes were analysed using multivariate numerical techniques. The species data, comprising forty-one chironomid taxa, were compared to environmental monitoring data in order to establish a relationship between chironomid faunal composition and lake trophic state.
2. The subfossil assemblages were compared to the chironomid bathymetric distributions along transects from four lakes. Correspondence analysis and similarity coefficients showed that the subfossil assemblages, sampled in the lake centre, reflect the chironomid communities in the littoral at a depth of 2–7 m.
3. Two-way indicator species analysis (TWINSPAN) was used to classify the Danish lakes into five groups defined by trophic state, lake depth and pH. Eighteen chironomid taxa showed significant differences in abundance among the five groups. Canonical correspondence analysis (CCA) showed the chlorophyll a concentration ([Chl a]) and Secchi depth to be the variables best correlated to the faunal data, and fourteen taxa were significantly correlated to [Chl a].
4. The strong correlation between chironomid data and the ln-transformed ([Chl a]) was used to create a weighted averaging (WA) model to infer lake trophic state. Several models were tested by cross validation (leave-one-out jack-knifing), and a simple WA model using inverse de-shrinking had a RMSEPjack of 0.65 (ln units) and a r2jack of 0.67.
5. The results can be used in the assessment and reconstruction of lake trophic state for long-term monitoring and palaeoecological investigations of shallow, temperate lakes in the mesotrophic to hypertrophic nutrient range.
157 citations
TL;DR: In this paper, a procedure for structural investigations by X-ray diffraction of mixed-layer structures incorporating swelling layers has been developed, which includes I-S minerals from Kazachstan (a rectorite), Dolna Ves in Slovakia, Kinnekulle in Sweden, the North Sea, and Scania in Sweden.
Abstract: A procedure for structural investigations by X-ray diffraction of mixed-layer structures incorporating swelling layers has been developed. For each sample, specimens saturated with different cations (Na, Mg, and Ca), are analyzed both as air-dried and as glycolated. One structural model fitting all the observed patterns then provides the structure of the sample. Samples tested include: Illite-smectite (I-S) minerals from Kazachstan (a rectorite), Dolna Ves in Slovakia, Kinnekulle in Sweden, the North Sea, and Scania in Sweden. The fitting of the patterns of the Kazachstan rectorite demonstrated that the instrumental parameters applied in the modeling were correct. For the I-S minerals from Slovakia and Kinnekulle the observed patterns were fitted with one two-component I-S model. However, the Ca-saturated and air-dried specimen of the Kinnekulle bentonites had two types of swelling interlayers. For the Slovakian I-S with Reichweite = 2, an alternative two-phase I-S plus I-V (V = vermiculite) model fitted the experimental X-ray diffraction patterns equally well. The I-S mineral from Scania is in fact a three-component I-T-S (T = tobelite) and the North Sea sample is a four-component I-S-V-V', one type of the swelling layers having swelling characteristics intermediately between smectite and vermiculite. In addition to layer types and distribution, interlayer compositions, such as the amount of interlayer glycol and water and of fixed and exchangeable cations, were determined.
136 citations
TL;DR: In this article, chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous Palaeogene flood basalts in the Faeroe Islands and in the Nansen Fjord area in East Greenland are presented.
Abstract: Before continental break-up in the NE Atlantic, the Faeroe Islands and central East Greenland were within a distance of 100–120 km. Chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous Palaeogene flood basalts in the Faeroe Islands and in the Nansen Fjord area in East Greenland show very similar basalt compositions and evolution patterns with time. The Faeroes lower basalt formation and the equivalent Nansen Fjord Formation in East Greenland form a pre-break-up succession overlain by a sediment horizon. A syn-break-up succession consists of the Faeroes middle and upper basalt formations and the equivalent Milne Land Formation in East Greenland in which five intervals can be correlated with a compositional evolution from Ti-rich magnesian basalts and picrites at the base to a dominance of MORB -like low-Ti basalts at the top. The successions were generated in the same mantle melting column beneath a thinning continent with a rift zone that eventually ruptured the continent. The evolution pattern is very similar to that seen on the SE Greenland margin, but spreading according to the Palmason model of 1973 was not yet established. The pre- and syn-break-up successions formed volcanic megasystems stretching across the rift zone with areal extents of 70 000 and 220 000 km 2 and volumes of 120 000 and 250 000 km 3 . Rocks from the pre- and syn-break-up successions can be discriminated based on a simple major-element plot. The overlying succession was 3–3.5 km thick in E Greenland but was thin or absent in the Faeroes; the energy source for the melting appears to have been concentrated on the Greenland side.
128 citations
TL;DR: In the Nuussuaq Basin, central West Greenland, the first revision in 30 years of their understanding of the structure was made by as mentioned in this paper, based on the interpretation of seismic and magnetic data, forward modelling of gravity profiles and a reappraisal of all available data on faults onshore.
116 citations
TL;DR: In this paper, the authors show that the transition between the associated types of fjord-glaciations moved north-south in response to past climate change, and that local melt-out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of IRD.
Abstract: Calving of icebergs is the dominant ablation mechanism for large outlet glaciers from the Greenland ice sheet except in northernmost Greenland where bottom melting from floating glaciers dominates. This difference is controlled by present climate conditions. Glacial geological evidence indicates that the transition between the associated types of fjord-glaciations moved north-south in response to past climate change. In cold periods, local melt-out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of IRD. Thus, the marine IRD signal of Greenland origin is not a simple cold climate signal. Our findings are discussed in the context of the ongoing debate about the kind of ice transporting IRD - icebergs or sea ice.
113 citations
TL;DR: In this article, the existence of 12 regionally correlative depositional sequences that range from the Danian to the Pleistocene in age using foraminifera, dinoflagellates, miospores, land mammals and other macrofauna, magnetostratigraphy, and various radio-metric methods.
Abstract: Evidence is reviewed in this paper for the existence, on the polar margin of Canada and Greenland, of 12 regionally correlative depositional sequences that range from the Danian to the Pleistocene in age. Sequences are dated using foraminifera, dinoflagellates, miospores, land mammals and other macrofauna, magnetostratigraphy, and various radio-metric methods. However, the present resolution of biostratigraphic schemes generally falls short of that provided by low latitude localities of similar age. The last seven cycles of the Cenozoic, those younger than 47 Ma, have been profoundly influenced by global climate variation. No such climate effect is recognizable in the earlier five sequences (65 to 47 Ma) for which a tectonic explanation is invoked. Rift-related deformation has affected depositional patterns for the later Cretaceous and Danian of the Labrador Sea and Baffin Bay region. This rift system is also inferred to have developed across the eastern Arctic Islands and to have included coeval volcanics and dyke swarms of northernmost Ellesmere Island and North Greenland. The Eurekan Orogeny evolved through various phases from the early Late Paleocene (Selandian) to at least the end of the Eocene. These phases involved the simultaneous emplacement of one or several plumes from a migrating hotspot, first beneath West Greenland, later beneath East Greenland, and finally beneath the North Atlantic and ancestral Iceland. The eastward migration of the plume jet is matched in time by the apparently diachronous westward expansion of the Eurekan Orogen and progressive rotation of tectonic transport directions; from northeasterly- and northerly-directed in the mid-Late Paleocene to northwesterly-directed in the latest Paleocene and Early Eocene, to westerly- and southwesterly-directed in the Middle and Late Eocene. A fundamental driving force for orogeny is considered to have been gravitational potential and spreading forces created by sublithospheric underplating and plume-induced regional uplift acting on the ancestral Greenland microplate. The orogenic transport directions of the Middle and Late Eocene are roughly parallel to those which acted to extend the eastern Arctic Islands and Baffin Bay region in the Cretaceous and Danian. Thus northwesterly-striking extension faults and northerly-striking sinistral faults, all active during the rifting phase, were converted into thrust inversion structures and dextral strike-slip faults, respectively, during the later stages of the Eurekan Orogeny. This conclusion, together with a presumed Late Paleocene and Early Eocene age for oceanic crust in northern Labrador Sea, promises to help resolve some of the long-standing issues surrounding the Nares Strait debate. Plume-head push acting on the Labrador and Baffin margins of North America, beginning at about 61 Ma, may also partly account for the simultaneous development of the Beaufort Foldbelt and other Laramide thrust belts of the North American Cordillera. End_Page 223------------------------ RESUME Des faits sont mis en evidence dans cet article pour montrer l'existence, sur la marge polaire du Canada et du Groenland, de 12 sequences de depot correlatives a l'echelle regionale, qui varient en age entre le Danien et le Pleistocene. Les sequences sont datees en utilisant les foraminiferes, les dinoflagelles, les miospores, les mammiferes terrestres et d'autres macrofaunes, la magnetostratigraphie, et diverses methodes radiometriques. Toutefois, la presente resolution des schemas biostratigraphiques n'est generalement pas aussi precise que celle fournie par les localites de basse latitude et d'age similaire. Les sept derniers cycles du Cenozoique, ceux plus jeunes que 47 Ma, ont ete profondement influences par les variations climatiques globales. Il n'y a pas d'effet climatique semblable reconnu dans les cinq sequences anterieures (65 a 47 Ma) pour lesquelles une explication tectonique est invoquee. Une deformation liee a un rift a affecte les patrons de depot pour la fin du Cretace et le Danien de la region de la mer du Labrador et de la baie de Baffin. Le systeme de rift est aussi infere s'etre developpe a travers les iles de l'Arctique Est et avoir inclut des volcanites contemporaines et des essaims de dyke de la partie extreme nord de l'ile d'Ellesmere et du Groenland Nord. L'orogenie Eurekeenne a evolue a travers diverses phases a partir du debut du Paleocene superieur (Selandien), jusqu'au moins la fin de l'Eocene. Ces phases impliquent l'emplacement simultane de un ou plusieurs panaches mag-matiques provenant d'un point chaud en migration, en premier lieu au Groenland Ouest, plus tard sous le Groenland Est, et finalement sous l'Atlantique Nord et l'Islande ancestrale. La migration vers l'est de ce panache-jet est apparente dans le temps par une expansion vers l'ouest, apparemment diachronique, de l'orogene Eurekeen et a la rotation progressive des directions de transport tectonique, ayant une direction nord-est et vers le nord au mi-Paleocene superieur, a une direction vers le nord-ouest a la fin du Paleocene et le l'Eocene inferieur, a une direction vers l'ouest et vers le sud-ouest a l'Eocene moyen et superieur. Le potentiel gravitationnel et les forces d'expansion creees par le sous-plaquage sub-lithospherique et le soulevement regional induit par le panache magmatique agissant sur la micro-plaque Groenland ancestrale sont considerees avoir ete la force motrice fondamentale de l'orogenie. Les directions de transport tectonique de l'Eocene moyen et superieur sont grossierement paralleles a celles qui ont agit pour etirer la region de l'est des iles de l'Arctique et de la baie de Baffin au Cretace au et Danien. Donc, les failles d'extension orientees vers le nord-ouest et les failles senestres orientees vers le nord, toutes actives durant la phase de rift, furent converties respectivement en des structures d'inversion par chevauchement et en failles de decrochement dextre durant les etapes finales de l'orogenie Eurekeenne. Cette conclusion, alliee a un age presume Paleocene superieur et Eocene inferieur pour la croute oceanique du nord de la mer du Labrador, promet d'aider a resoudre quelques-unes des questions de longue date concernant le debat du detroit de Nares. La poussee de la tete d'un panache magmatique agissant sur les marges du Labrador et de Baffin de l'Amerique du Nord, debutant a environ 61 Ma, peut aussi rendre compte du developpement simultane de la ceinture de plissement de Beaufort et d'autres ceintures de chevauchement de Laramide dans la Cordillere de l'Amerique du Nord. Traduit par Lynn Gagnon
112 citations
TL;DR: In this article, the authors present detailed information from the Darss Sill threshold area as well as the adjacent basins, i.e. the Mecklenburg Bay and Arkona Basin located in the southwesternmost Baltic.
Abstract: One of the most discussed stages in the history of the Baltic Sea is the Ancylus Lake phase. This paper presents detailed information from the Darss Sill threshold area as well as the adjacent basins, i.e. the Mecklenburg Bay and Arkona Basin located in the southwesternmost Baltic. The threshold area was transgressed at the Baltic Ice Lake maximum phase and during the following regression about 10.3 ka BP a river valley was incised in the Darss Sill to a level of 23–24 m below present sea level (b.s.l.). Preboreal sediments in the study area show lowstand basin deposition in the Arkona Basin and the existence of a local lake in Mecklenburg Bay. The lowstand system is followed by the Ancylus Lake transgression that reached a maximum level of 19 m b.s.l. Thus, at the maximum level the water depth was about 5 m over the threshold, and the shore level fall during the Ancylus Lake regression must be in the same range. The Darss Sill area is the key area for drainage of the Ancylus Lake, and if the previously suggested regression of 8–10 m in southeastern Sweden is to be achieved, isostatic rebound must also play a role. The existence of the so-called Dana River in the Darss Sill area cannot be supported by our investigations. We observed no signs of progressive erosion of the Darss Sill area in the Early Holocene, and there are no prograding systems in Mecklenburg Bay that can be related to the Ancylus Lake regression. On the contrary, local lakes developed in Mecklenburg Bay and in the Darss Sill threshold area. In the Darss Sill area, marl was deposited in a lake in the valley that developed after the final drainage of the Baltic Ice Lake. Studies of diatoms and macrofossils, combined with seismic interpretation and radiocarbon dating, provide detailed information about the chronology and the relative shore level of these lake phases as well as about environmental conditions in the lakes.
96 citations
TL;DR: In this article, a series of 23 AMS 14C dates defines the chronology of the postglacial sequence, which records a succession from a pioneer grass- and Oxyria-dominated tundra between 10.4 and 8.4
91 citations
TL;DR: In this paper, the authors have shown that amphibolite facies gneiss is the dominant contaminant at low stratigraphic levels, whereas contamination with granulite facia-gneiss prevails in the upper part of the lava succession.
TL;DR: This is the first use of PCR for quantification of indigenous bacteria in more than one sample of soil and targets 16S ribosomal DNA using competitive PCR for specific detection of indigenous Pseudomonas DNA in soil hot spots.
Abstract: We used a quantitative PCR method targeting 16S ribosomal DNA using competitive PCR for specific detection of indigenous Pseudomonas DNA in soil hot spots. The amount of Pseudomonas DNA corresponded to the number of culturable Pseudomonas bacteria on Gould's S1 agar. This represents the first use of PCR for quantification of indigenous bacteria in more than one sample of soil.
TL;DR: While ice-free areas (refugias) were present, it is concluded that only hardy, cold-adapted species could have survived, which explains why so few clearly endemic species are present in Greenland.
Abstract: In the light of data from the Greenland ice sheet concerning the ice-age climate, and palaeoecological studies of interglacial and Early Holocene deposits, the concept that a large proportion of Greenland's plants and animals may have survived during the ice ages is evaluated. While ice-free areas (refugias) were present, it is concluded that only hardy, cold-adapted species could have survived, which also explains why so few clearly endemic species are present in Greenland. Most members of the present biota are considered to be postglacial immigrants. Some species came to Greenland by walking or flying, but most arrived by passive, long-distance, chance dispersal, carried by wind, sea currents, and, in particular, birds. Transport by birds may explain why so many species arrived from Europe, because vast numbers of geese in particular migrate from northwest Europe to Greenland.
TL;DR: In this paper, a theory that the giant deer were sufficiently abundant to convert juniper scrub communities into open grassland at a regional scale was proposed. But this theory was not supported by the geological record from the Eemian interglacial in Denmark, where the presence of elephant and rhinoceros did not create widespread openings in forest cover.
TL;DR: Gould's S1 agar is suggested to be used for isolation of Pseudomonas because the results are reproducible, specific and give the most diverse recovery and the least work.
Abstract: King's B and Gould's S1 agar were compared with regard to the isolation of Pseudomonas from four environmental samples. In all samples, King's B gave the highest number of colony-forming units, and in some environments, there were more fluorescent colony-forming units on King's B as well. However, almost all types grew on Gould's S1, which enabled us to isolate a greater variety of groups than with King's B, fluorescent as well as non-fluorescent members of Pseudomonas. The Pseudomonas isolates were comparatively typed by repetitive extragenic palindromic-polymerase chain reaction and Fourier transform infrared spectroscopy, not previously used for environmental Pseudomonas. The two typing methods were similar in resolution, thus Fourier transform infrared spectroscopy proved fast and reproducible and is a good method for discrimination at subspecies level. Representative strains were identified by partial 16S rDNA sequencing. Thus, we suggest Gould's S1 agar be used for isolation of Pseudomonas because the results are reproducible, specific and give the most diverse recovery and the least work.
TL;DR: In the southern marginal zone of the Palaeoproterozoic Nagssugtoqidian orogen and its foreland (West Greenland), Archaean gneisses were intruded by the syn-kinematic Kangâmiut dyke swarm.
TL;DR: In this article, the causal relationship between the Cenozoic sequence development in the southeastern North Sea Basin and sea-level changes, climatic fluctuations and tectonic events is unravelled by relating variations in the relative sea level and base level, based on interpretations of seismic surveys, to published δ 18 O variations and eustatic changes.
Abstract: The causal relationship between the Cenozoic sequence development in the southeastern North Sea Basin and sea-level changes, climatic fluctuations and tectonic events is unravelled by relating variations in the relative sea level and base level, based on interpretations of seismic surveys, to published δ 18 O variations and eustatic changes. The latter curve is based on the Earth9s orbital forcing, and here informally termed as the GSI curve. The analysis shows that the Cenozoic sequence development in the southeastern North Sea was influenced by climatically and tectonically induced sea-level changes. The major Cenozoic sequence stratigraphic boundaries (lower order) are highly influenced by tectonic events, e.g. uplift of Fennoscandia and increased subsidence rates in the basin centre. Reactivation of Mesozoic fault zones controlled the deposition of minor sand bodies transported to the centre of the basin during the Late Palaeocene by mass flows. The location of an Oligocene mound structure, which constitutes part of a sequence, is controlled by the overall palaeotopography of the basin and local fault-related depressions. Correlation between (i) the ages of our sequences and the δ 18 O variations in the Oligocene succession, and (ii) the GSI curve and the base-level fluctuations of the late Miocene and younger sequences, show that the generation of the higher order sequence boundaries were driven by glacio-eustatic sea-level changes. A climatic control of the sequence formation due to glacio-eustatic sea level changes is therefore suggested for the Oligocene and Pliocene sequences, and probably also for the Upper Miocene sequences.
TL;DR: The age of the Thule supergroup is quite poorly constrained, at the base by a 1268-Ma basaltic sill, and at the top by a basic dyke swarm with a K/Ar age range between 630 and 725 ǫ, that cuts the entire succession.
01 Jan 1999
TL;DR: The presence of oil seepage and staining commonly occur within vesicular lava flow top, and are often associated with mineral veins (mostly carbonates) in major fracture systems.
Abstract: Widespread oil seepage and staining are observed in lavas and hyaloclastites in the lower part of the volcanic succession on northwestern Disko and western Nuussuaq, central West Greenland. Chemical analyses suggest the existence of several petroleum systems in the underlying Cretaceous and Paleocene fluvio–deltaic to marine sediments. Seepage and staining commonly occur within vesicular lava flow tops, and are often associated with mineral veins (mostly carbonates) in major fracture systems. Organic geochemical analyses suggest the existence of at least five distinct oil types: (1) a waxy oil which, on the basis of the presence of abundant angiosperm biological markers, is interpreted as generated from Paleocene mudstones (the ‘Marraat type’); (2) a waxy oil, probably generated from coals and shales of the Cretaceous Atane Formation (the ‘Kuugannguaq type’); (3) a low to moderately waxy oil containing 28,30-bisnorhopane, and abundant C 27 -diasteranes and regular steranes (the ‘Itilli type’), possibly generated from presently unknown Cenomanian–Turonian marine mudstones; (4) a low wax oil of marine, possibly lagoonal/saline lacustrine origin, containing ring-A methylated steranes and a previously unknown series of extended 28-norhopanes (the ‘Eqalulik type’); (5) a waxy oil with biological marker characteristics different from both the Kuugannguaq and Marraat oil types (the ‘Niaqornaarsuk type’), probably generated from Campanian mudstones. The presence of widespread seepage and staining originating from several source rocks is encouraging for exploration in basins both on- and offshore western Greenland, where the existence of prolific source rocks has previously been the main exploration risk.
TL;DR: In this article, a review of the results of the exploration efforts so far shows that the distribution of potential source rocks and their time of hydrocarbon generation are the critical risks for finding commercial amounts of hydrocarbons.
TL;DR: In this article, the distribution of fractures and biopores in a clayey and sandy till aquitard was investigated in two excavations, on southem Zealand, Denmark, where a large number of fracture data were measured and quantitative fracture properties calculated.
Abstract: The distribution of fractures and biopores in a clayey and sandy till aquitard was investigated in two excavations, on southem Zealand, Denmark. A large number of fracture data were measured and quantitative fracture properties calculated. The formation of fractures can be related to the depositional history of the tills during two glacier-advances/retreats and subsequent climatic changes during the Quaternary. The fractures including faults are separated into four systems: 1) Large vertical/subvertical fractures related to the oldest glacier-advance or interstadial climatic influence. 2) Horizontal -subhorizontal fractures related to subglacial drag/shear during a glacial advance from northeast and in an initial stage of a younger glacier-advance from southeast. 3) Normal faults related to subglacial loading during a late stage of the youngest glacier-advance and, 4) Minor desiccation and freeze-thaw fractures related to post-glacial climatic influence. A conceptual macropore distribution model was developed that consists of three zones with different macropore characteristics.
TL;DR: Palynological analysis of two sections at Haumuri Bluff and Conway River (southern Marlborough, New Zealand), and three sections in the Waipara area (northern Canterbury, Australia) of the Piripauan-Haumurian age (late Cretaceous) as discussed by the authors showed that the Haumurians were deposited in a marginal marine nearshore environment, and the overlying Tarapuhi Grit, Conway Siltstone and Claverley Sandstone were mostly non-marine.
TL;DR: In this paper, fly ashes, bottom ashes, and deposits collected on air-cooled probes at a PF-fired boiler co-fired with coal and straw (0, 10%, and 20% straw on an energy basis) have been studied with respect to chemical composition, mineralogy, sintering, and melting.
Abstract: Fly ashes, bottom ashes, and deposits collected on air-cooled probes at a PF-fired boiler co-fired with coal and straw (0%, 10%, and 20% straw on an energy basis) have been studied with respect to chemical composition, mineralogy, sintering, and melting. The varying straw share was found not to influence the overall chemical composition of the fly ashes, which were quite alike on an oxide basis, whereas computer-controlled scanning electron microscopy data revealed a change in the species present, meaning that the more potassium that was available for reaction (i.e., the higher the straw share burned), the higher was the fraction of alumino-silicates having reacted to form potassium-alumino-silicates. Comparing compositions of fly ashes and deposits, it was found that K-, Ca-, Fe-rich silicates were concentrated in deposits, probably as an effect of relatively low viscosities of these particles. Based on simultaneous thermal analysis, STA, all ashes examined showed melting in the temperature range from 10...
TL;DR: In this paper, a study of interval velocities from almost a thousand wells reveals basinwide differences in physical properties of the Cenozoic deposits of the North Sea Basin.
Abstract: A study of interval velocities from almost a thousand wells reveals basinwide differences in physical properties of the Cenozoic deposits of the North Sea Basin. These differences relate primarily to the sediments below the mid-Miocene unconformity as testified by a subdivision of a subset of these wells. Velocity-depth anomalies are mapped relative to a constrained, normal velocity-depth trend derived for marine Jurassic shale: tt = 465.e (super -z/2435) +180, where tt is transit time in mu s m (super -1) , and z is depth in metres below sea bed. The upper Cenozoic deposits are close to normal compaction, whereas anomalies for the lower Cenozoic sediments outline a zone of undercompaction in the Central North Sea that corresponds to the overpressure in the Upper Cretaceous-Danian Chalk. The overpressure results from a balance between the load of the upper Cenozoic deposits, and the draining determined by the thickness and sealing quality of the lower Cenozoic sediments. The shale trend may be more widely applicable to marine shale dominated by smectite/illite. This suggestion is based on the observed correspondence between velocity anomalies and pressure data, and due to the match between trends for marine shale of different ages in the North Sea and in the US Gulf Coast area over a significant velocity range.
30 Dec 1999
TL;DR: In this paper, the development of the biological structure of these lakes over time should primarily reflect climate changes that have taken place since deglaciation, and these changes in lake species composition and their productivity are preserved in the lake sediments.
Abstract: The many lakes in south-western Greenland offer excellent opportunities for both limnological and palaeolimnological studies. The lack of any cultural disturbance means that these lakes are tightly and directly linked with their catchment areas and regional climate. As such, the development of the biological structure of these lakes over time should primarily reflect climate changes that have taken place since deglaciation. In turn, these changes in lake species composition and their productivity are preserved in the lake sediments. These lakes provide, therefore, excellent opportunities for studying the impact of past climatic changes on lake ecosystems. Similarly, the sediment records can also be used as proxies for palaeoclimatic changes. Clearly, however, to interpret sediment records in terms of fluctuating climate it is necessary to understand contemporary processes. The limnology of these lakes is not particularly well understood as only a few of the lakes have been studied, and then only infrequently, over the last 50 years (Williams 1991).
TL;DR: In this paper, the authors describe and interpret early Holocene floras and faunas and suggest that the majority of the extant flora of vascular plants of East Greenland arrived by long distance dispersal during the Holocene.
Abstract: Aim The aim of this paper is to describe and interpret early Holocene floras and faunas. Location The floras and faunas come from various localities in North-east Greenland. Methods Sediment samples were wet sieved, and macrofossils picked out and dated by the AMS radiocarbon-dating method. Results Sediments, dated to the first centuries after the last glacial stage came to an abrupt end, contain a macroflora of bryophytes and a few herbs, and we suggest that these plant remains represent a pioneer vegetation entirely without woody plants. The named species of herbs are either confined to the northern parts of Greenland at present, or they become increasingly more important towards the north. Crowberry is the oldest woody plant recovered; it was present at 10.4 cal. ka BP, and it appears to have been common during the early Holocene in East Greenland. Main conclusions We suggest that the majority of the extant flora of vascular plants of East Greenland arrived by long distance dispersal during the Holocene. Some species may also have arrived during the late-glacial, and a few hardy species that are adapted to low summer temperatures may have survived the last glacial stage in nonglaciated areas. Some hardy animals may also have survived, but the majority of the fauna are considered Holocene immigrants. We suggest that migrating birds and storms, perhaps in combination, are under-appreciated dispersal vectors.
TL;DR: In this article, a small number of samples from the lowermost part of the East Greenland lava pile and the nearby Skaergaard intrusion were used to study the abundance and isotopic properties of the latter.
TL;DR: In the Palaeoproterozoic Ketilidian orogen of South Greenland, tabular intrusions of the rapakivi granite suite exposed at Graah Fjelde, Lindenow Fjord and Qernertoq, and a Mesopero-terrestrial syenite of the Gardar province exposed at Paatusoq, were emplaced by a combination of roof uplift and floor depression as discussed by the authors.
Abstract: In the Palaeoproterozoic Ketilidian orogen of South Greenland, tabular intrusions of the rapakivi granite suite exposed at Graah Fjelde, Lindenow Fjord and Qernertoq, and a Mesoproterozoic syenite of the Gardar province exposed at Paatusoq, were emplaced by a combination of roof uplift and floor depression. The strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere. Space for the emplacement of the rapakivi plutons was not created during regional extension on low-angle, ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening. The rapakivi granites post-date peak metamorphism in the orogen by 35–46 Ma and their contacts cross-cut and clearly post-date intense, flat-lying D1/D2 fabrics that formed by partitioning of deformation into arc-normal and arc-parallel components during oblique convergence.
TL;DR: In this article, a new conceptual palaeo-oceanographical model was proposed by using shifts in Hadley circulation caused by orbital variations, and the rotation rate of the Earth, to locate the position of the planetary oceanic low-and high-pressure systems, around which the planetary oceans surface currents flow.
Abstract: A new conceptual palaeo-oceanographical model is outlined in this paper. The model differs from previous models by using shifts in Hadley circulation caused by orbital variations, and the rotation rate of the Earth, to locate the position of the planetary oceanic low-and high-pressure systems, around which the planetary ocean surface currents flow. Adapting the model to the Arenig (early Ordovician) the temperate low pressure zones were found to be located at 50° latitude and the subtropical high pressure zones at 25° latitude.
Traditionally, most Palaeozoic palaeogeographical recon-structions are reconstructed using palaeomagnetic data supplemented with data from climate-sensitive lithofacies and palaeo-biogeographical distributions. However, as a new approach in palaeogeographical reconstructions, the con-ceptual palaeo-oceanographical model is combined with palaeobiogeographical data for the Arenig series, comple-menting the palaeomagnetic data, and resulting in a new, refined palaeogeographical reconstruction.
TL;DR: In this article, image analysis was used to digitize the grey-scale variations and to measure the varve thickness of 540 varves (476-1015 AD) from Lake Kassjon in northern Sweden.
Abstract: Varved lake sediments, with their annual to seasonal resolution, have a high potential for inferring past environmental and climatic conditions. To fully utilize the information present in varved records, high-resolution analyses, which often are time-consuming and difficult to perform, are desirable. The investigation reported here aims at (i) developing image analysis as a method for estimating annual accumulation rates of sediment components such as minerogenic matter, organic matter and biogenic silica, and (ii) assessing the relative importance of these components for changes in varve thickness. Image analysis was used to digitize the grey-scale variations and to measure the varve thickness of 540 varves (476-1015 AD) from Lake Kassjon in northern Sweden. From the 35 cm long digitized sediment sequence, 108 consecutive five-year samples were cut out quantitatively, and relationships between grey-scale variations and sediment dry mass and individual sediment components were assessed. There is a strong correlation between corrected grey-scale (i.e. the product of grey-scale and varve thickness) and the dry mass accumulation rate (r = 0.90, p < 0.001). With a stepwise multiple regression a significant model (R2 = 0.81) between corrected grey-scale and the accumulation rates of minerogenic matter (r = 0.90, p < 0.001) and biogenic silica (r 0.26, p < 0.012) was obtained. Considering the minor contribution and weak significance of biogenic silica, image analysis can be used as a fast and non-destructive method to infer past annual accumulation rates of dry mass and minerogenic matter in Kassibn. The model of the relationship between changes in varve thickness, and water content and accumulation rates of sediment components has little predictive power (R2 = 0.45). The result shows that the varve thickness in Kassjon, at least during the period 476-1015 AD, is not determined by a single sediment component but partly depends on interactions between the major sediment components.