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1.
  • Abel, I, et al. (författare)
  • Overview of the JET results with the ITER-like wall
  • 2013
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
  • Tidskriftsartikel (refereegranskat)abstract
    • Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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2.
  • Aguirre-Palafox, Erick Luis, et al. (författare)
  • Zircon provenance analysis from Lower Paleocene pelagic limestones of the Bottaccione section at Gubbio (Umbria-Marche basin, Italy)
  • 2019
  • Ingår i: Geological Society of America. Special Papers. - : Geological Society of America. - 0072-1077. ; 542
  • Tidskriftsartikel (refereegranskat)abstract
    • Dating detrital zircon grains from sands and sandstones has become an important geological technique for determining sediment provenance and dispersal patterns. Here, we report what we believe to be the first provenance study of zircon grains extracted by dissolving large samples of pelagic limestone. Our samples come from the Paleocene section of the Umbria-Marche Apennines, Italy. Recovery of these zircon grains was a fortunate by-product of a study on chromite grains aimed to determine the kinds of meteorites that have fallen on Earth through time. The zircons we recovered included both euhedral crystals interpreted as airborne ash from volcanic eruptions of the same age as the sediment in which they were found, and rounded grains interpreted as windblown detrital material with a history of sediment transport, probably derived from desert regions. This study focuses on the rounded grains, to provide constraints on the source region from which they came.Samples from five levels in the 12 m immediately above the Cretaceous-Paleogene boundary at Gubbio, Italy, yielded detrital zircon grains with ages clustered in eight bands extending back to the Neoarchean. A previous study of this outcrop using proxies for the noncarbonate detrital content had suggested a source region for this dust either in North Africa or in Central Asia. A comparison of our dates from the actual dust grains to geochronological studies from the literature suggests source regions in North Africa and/or the Iberian Peninsula, rather than in Central Asia. In reaching this conclusion, we considered the orogenic events that may have produced each of the eight age bands, the specific source regions that may have supplied zircons from each age group, and the implications for paleoclimate (especially aridity) and paleowind conditions for the few million years just after the Cretaceous-Paleogene boundary.
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4.
  • Ahlberg, Per, et al. (författare)
  • Maurits Lindström 1932-2009
  • 2011
  • Ingår i: Kungliga Fysiografiska Sällskapet i Lund Årsbok 2009-2010. - 1402-1277. ; 2009-2010, s. 138-140
  • Bokkapitel (refereegranskat)
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5.
  • Albanesi, Guillermo L., et al. (författare)
  • Darriwilian (Middle Ordovician) delta C-13(carb) chemostratigraphy in the Precordillera of Argentina: Documentation of the middle Darriwilian Isotope Carbon Excursion (MDICE) and its use for intercontinental correlation
  • 2013
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 389, s. 48-63
  • Tidskriftsartikel (refereegranskat)abstract
    • Although documented from Estonia, Latvia, Sweden, eastern North America, and China, the Middle Ordovician (Darriwilian) positive delta C-13 excursion known as the MDICE has previously not been recognized with certainty in South America. The most promising region in South America for detailed Middle Ordovician carbon isotope research is the Precordillera of western Argentina, where there are many excellent exposures of biostratigraphically well-dated carbonate successions spaning the Tremadocian through Sandbian stratigraphic interval. For this project, we collected numerous isotope and conodont samples from the middle Darriwilian Las Chacritas and Aguaditas formations at their type localities, which yielded important biostratigraphic data as well as informative delta C-13(carb) values. In the E. pseudoplanus Zone in the upper half of the Las Chacritas Formation, there is a relatively modest but distinct delta C-13(carb) excursion. Because its stratigraphic position and magnitude closely agree with the MDICE in other parts of the world, we recognize it as the first firm record of this excursion in South America. The fact that the delta C-13(carb) curve from the Las Aguaditas Formation shows no such excursion is due to the existence of a stratigraphic gap between the Lower and Middle Members of this formation that cuts out the excursion interval. The Precordilleran MDICE is used for detailed long-range correlations with successions in Baltoscandia, Newfoundland, and China illustrating the usefulness of also this delta C-13(carb) excursion as a global stratigraphic tool. A recent proposal of a greatly extended chronostratigraphic range of the Table Head Group on Newfoundland is rejected based on well-established biostratigraphic evidence. (C) 2013 Elsevier B.V. All rights reserved.
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6.
  • Alwmark, Carl, et al. (författare)
  • A 3-D study of mineral inclusions in chromite from ordinary chondrites using synchrotron radiation X-ray tomographic microscopy-Method and applications
  • 2011
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379. ; 46:8, s. 1071-1081
  • Tidskriftsartikel (refereegranskat)abstract
    • A method is described for imaging in 3-D the interiors of meteoritic chromite grains and their inclusions using synchrotron radiation X-ray tomographic microscopy. In ordinary chondrites, chromite is the only common mineral that survives long-term weathering on Earth. Information about the silicate matrix of the original meteorite, however, can be derived from mineral inclusions preserved in the protecting chromite. The inclusions are crucial in the classification of fossil meteorites as well as sediment-dispersed chromite grains from decomposed meteorites and larger impacts, as these are used for characterizing the past influx of material to Earth, but have previously been difficult to locate. The method is non-destructive and time efficient for locating inclusions. The method allowed quantitative and morphological studies of both host chromite grains and inclusions in three dimensions. The study of 385 chromite grains from eight chondrites (H4-6, L4-6, LL4, LL6) reveals that inclusions are abundant and equally common in all samples. Almost two-thirds of all chromite grains contain inclusions, regardless of group and type. The study also shows that the size of the inclusions and the host chromite grains, as well as the number of inclusions, within the host chromite grains vary with petrographic type. Thus, the petrographic type of the host of a suite of chromite grains can be determined based solely on inclusion content. The study also revealed that the amount of fractures in the host chromite can be correlated to previously assigned shock stages for the various chondrites. The study has thus shown that the features and inclusions of fossil chromite grains can give similar information about a former host meteorite as do studies of an unweathered whole meteorite, meaning that this technique is essential in the studies of ancient meteorite flux to Earth.
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7.
  • Alwmark, Carl, et al. (författare)
  • A global rain of micrometeorites following breakup of the L-chondrite parent body-Evidence from solar wind-implanted Ne in fossil extraterrestrial chromite grains from China
  • 2012
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379. ; 47:8, s. 1297-1304
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous studies of limestone beds of mid-Ordovician age from both Sweden and China show that the Earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 Ma, following the disruption of an L-chondrite parent body in the asteroid belt. Recovered extraterrestrial material consists of fossil meteorites and sediment-dispersed extraterrestrial chromite (SEC) grains, both with L-chondritic origin. Ne isotope analysis of SEC grains from one of the Swedish limestone sections revealed that the vast majority of the grains were delivered to Earth as micrometeorites. In this study, we extend the previous work, both in time and geographically, by measuring concentrations and isotopic ratios of Ne in individual SEC grains (60120 mu m in diameter) from three different beds from a contemporary Middle Ordovician limestone section in China. All of the Chinese SEC grains, 44 in total, contain surface-implanted Ne of fractionated solar wind composition, implying that these grains were, as in the case of the Swedish SEC grains, delivered to Earth as micrometeorites. This gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the L-chondrite parent body was indeed a global event. The rain of micrometeorites prevailed for at least 2 Myr (the estimated time of the deposition of the topmost Chinese bed) after the breakup event.
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8.
  • Alwmark, Carl, et al. (författare)
  • Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne crater, central Sweden
  • 2007
  • Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 253, s. 291-303
  • Tidskriftsartikel (refereegranskat)abstract
    • The distribution of extraterrestrial chromite grains (> 63 mu m) has been studied in the resurge deposit of the early Late Ordovician (458 Ma) Lockne impact structure in central Sweden. A 1-kg-sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite. In total the sample contains > 125 chromium spinel grains kg(-1), most grains being chromite. Due to post-depositional alterations, the origin of several of the grains is dubious, although it is clear that the major part of the chromites is of extraterrestrial origin (> 75 grains kg(-1)), most likely derived from the impactor. The alterations are primarily due to the hydrothermal system induced by the impactor, with zinc enrichment in the chromites as the most common characteristic. The element chemistry of the least altered chromite grains indicates that the impactor was an ordinary L chondrite. This concurs with a suggested increase in the flux of L chondritic asteroids to Earth, following the disruption of the L chondrite parent body at ca. 470 Ma. More than 170 impact craters are known from around the Earth, but only few of the impactors have been identified, mainly due to the low survival rate of projectile material. Further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the Lockne structure. (c) 2006 Elsevier B.V. All rights reserved.
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10.
  • Alwmark, Carl, et al. (författare)
  • Relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material
  • 2009
  • Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 73:5, s. 1472-1486
  • Tidskriftsartikel (refereegranskat)abstract
    • Chromite is the only common meteoritic mineral surviving long-term exposure on Earth, however, the present study of relict chromite from numerous Ordovician (470 Ma) fossil meteorites and micrometeorites from Sweden, reveals that when encapsulated in chromite, other minerals can survive for hundreds of millions of years maintaining their primary composition. The most common minerals identified, in the form of small (<1-10 mu m) anhedral inclusions, are olivine and pyroxene. In addition, sporadic merrillite and plagioclase were found. Analyses of recent meteorites, holding both inclusions in chromite and corresponding matrix minerals, show that for olivine and pyroxene inclusions, sub-solidus re-equilibration between inclusion and host chromite during entrapment has led to an increase in chromium in the former. In the case of olivine, the re-equilibration has also affected the fayalite (Fa) content, lowering it with an average of 14% in inclusions. For Ca-poor pyroxene the ferrosilite (Fs) content is more or less identical in inclusions and matrix. By these studies an analogue to the commonly applied classification system for ordinary chondritic matrix, based on Fa in olivine and Fs in Ca-poor pyroxene, can be established also for inclusions in chromite. All olivine and Ca-poor pyroxene inclusions (>1.5 mu m) in chromite from the Ordovician fossil chondritic material plot within the L-chondrite field, which is in accordance with previous classifications. The concordance in classification together with the fact that inclusions are relatively common makes them an accurate and useful tool in the classification of extraterrestrial material that lacks matrix silicates, such as fossil meteorites and sediment-dispersed chromite grains originating primarily from decomposed micrometeorites but also from larger impacts. (C) 2008 Elsevier Ltd. All rights reserved.
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11.
  • Alwmark, Carl, et al. (författare)
  • The mid-Ordovician Osmussaar breccia in Estonia linked to the disruption of the L-chondrite parent body in the asteroid belt
  • 2010
  • Ingår i: Geological Society of America Bulletin. - 0016-7606. ; 122:7-8, s. 1039-1046
  • Tidskriftsartikel (refereegranskat)abstract
    • The Middle Ordovician (466 Ma) Osmussaar breccia, situated along the northwestern coast of Estonia, is rich in angular chromite grains of extraterrestrial origin (>13 grains kg(-1)) and shocked quartz. The angularity of the chromite grains implies that they have not been transported or reworked to any large extent, connoting that the brecciation is the result of a contemporary impactor, either as a direct consequence of the impact or as a result of an earthquake triggered by the impact, and thus is not, as previously suggested, redeposited material from the nearby similar to 70 m.y. older Neugrund impact structure. The chemical composition of the chromite indicates that the impactor was an ordinary chondrite of L-type, which concurs well with the hypothesis that the influx of large bodies to Earth increased during this period due to the breakup of the L-chondrite parent body. This in turn gives support to the recent suggestion that abundant coeval mega-breccias worldwide are impact triggered. The presence of extraterrestrial chromite also strengthens the theory that physical pieces of a large celestial body can survive upon impact with Earth.
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12.
  • Alwmark, Carl, et al. (författare)
  • The origin of the Brunflo fossil meteorite and extraterrestrial chromite in mid-Ordovician limestone from the Garde quarry (Jamtland, central Sweden)
  • 2009
  • Ingår i: Meteoritics and Planetary Science. - 1086-9379. ; 44:1, s. 95-106
  • Tidskriftsartikel (refereegranskat)abstract
    • The Brunflo fossil meteorite was found in the 1950s in mid-Ordovician marine limestone in the Garde quarry in Jamtland. It originates from strata that are about 5 million years younger than similar limestone that more recently has yielded >50 fossil meteorites in the Thorsberg quarry at Kinnekulle, 600 km to the south. Based primarily on the low TiO2 content (about 1.8 wt%) of its relict chromite the Brunflo meteorite had been tentatively classified as an H chondrite. The meteorite hence appears to be an anomaly in relation to the Kinnekulle meteorites, in which chromite composition, chondrule mean diameter and oxygen isotopic composition all indicate an L-chondritic origin, reflecting an enhanced flux of meteorites to Earth following the disruption of the L chondrite parent body 470 Ma. New chondrule-size measurements for the Brunflo meteorite indicate that it too is an L chondrite, related to the same parent-body breakup. Chromite maximum diameters and well-defined chondrule structures further show that Brunflo belongs to the L4 or L5 type. Chromites in recently fallen L4 chondrites commonly have low TiO2 contents similar to the Brunflo chromites, adding support for Brunflo being an L4 chondrite. The limestone in the Circle quarry is relatively rich (about 0.45 grain kg(-1)) in sediment-dispersed extraterrestrial chromite grains (>63 mu m) with chemical composition similar to those in L chondrites and the limestone (1-3 grains kg(-1)) at Kinnekulle, suggesting that the enhanced flux of L chondrites prevailed, although somewhat diminished, at the time when the Brunflo meteorite fell.
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13.
  • Alwmark, Sanna, et al. (författare)
  • Shock barometry of the Siljan impact structure, Sweden
  • 2011
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379. ; 46:12, s. 1888-1909
  • Tidskriftsartikel (refereegranskat)abstract
    • The Siljan impact structure in Sweden is the largest confirmed impact structure in Western Europe. Despite this, the structure has been poorly studied in the past, and detailed studies of shock metamorphic features in the target lithologies are missing. Here, we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at Siljan. At 21 localities from an area approximately 20 km in diameter located centrally in the structure, the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured. Observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter. The most strongly shocked samples, recording pressures of up to 20 GPa, occur at the very central part of the structure, and locally in these samples, higher pressures causing melting conditions in the affected rocks were reached. Pressures recorded in the studied samples decrease outwards from the center of the structure, forming roughly circular envelopes around the proposed shock center. Based on the distribution pattern of shocked quartz at Siljan, the original transient cavity can be estimated at approximately 3238 km in diameter. After correcting for erosion, we conclude that the original rim to rim diameter of the Siljan crater was somewhere in the size range 5090 km.
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14.
  • Arenillas, I, et al. (författare)
  • Foraminiferal and δ13C isotopic event-stratigraphy across the Danian–Selandian transition at Zumaya (northern Spain): chronostratigraphic implications
  • 2008
  • Ingår i: Terra Nova: the European journal of geosciences. - : Wiley. - 0954-4879. ; 20:1, s. 38-44
  • Tidskriftsartikel (refereegranskat)abstract
    • The Zumaya section, northern Spain, is a suitable candidate to define the Global Stratotype Section and Point for the base of the Selandian Stage (Palaeocene) because of its excellent accessibility, exposure and stratigraphic continuity. Uncertainties exist, however, with regard to the stratigraphic horizon where to place the Danian/Selandian (D/S) boundary. Five potential stratigraphic horizons (HDS1 to HDS5) to define the D/S boundary have been identified at Zumaya, based on integrated stratigraphic studies that include quantitative planktic and benthic foraminiferal results, as well as delta C-13 isotopic and lithological data. Two of these horizons (HDS2 and HDS4) placed in Zone C26r appear to have particularly good potential for serving as the D/S boundary marker, because they may represent significant global palaeoceanographic, palaeoclimatic and eustatic events.
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15.
  • Aubry, Marie-Pierre, et al. (författare)
  • The First Radiation Of The Fasciculiths: Morphologic Adaptations Of The Coccolithophores To Oligotrophy
  • 2012
  • Ingår i: Austrian Journal of Earth Sciences. - 2072-7151. ; 105:1, s. 29-38
  • Tidskriftsartikel (refereegranskat)abstract
    • The Qreiya section (Upper Egypt) contains a well-preserved record of the first radiation of the fasciculiths, an evolutionary event that affected the coccolithophores of the Order Discoasterales during the late Danian. At Qreiya it unfolds across the so-called Neo-Duwi Event. We describe the morphostructural changes that affected coccoliths and document a trend towards increased surface area of the coccoliths of the Order Discoasterales. Our isotopic data do not support earlier interpretation(s) that the Neo-Duwi Event may correspond to a Paleocene hyperthermal. We interpret the first radiation of the fasciculiths as an adaptive response to increased oceanic oligotrophy through the appearance of coccoliths adapted to food collection in nutrient-poor oceanic waters.
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17.
  • Bergstroem, Stig M., et al. (författare)
  • First documentation of the Ordovician Guttenberg delta C-13 excursion (GICE) in Asia: chemostratigraphy of the Pagoda and Yanwashan formations in southeastern China
  • 2009
  • Ingår i: Geological Magazine. - 0016-7568. ; 146:1, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • The only published VC data from the Ordovician of China are from the Lower and Upper Ordovician, and only the latter records include a significant excursion, namely the Hirnantian excursion (HICE). Our recent chemostratigraphic work on the Upper Ordovician (Sandbian-Katian) Pagoda and Yanwashan formations at several localities oil the Yangtze Platform and Chiangnan (Jiangnan) slope belt has resulted in the recognition of a positive delta C-13 excursion that has values of similar to+1.5 parts per thousand above baseline values. This excursion starts a few metres above a stratigraphic interval with B. alobatus Subzone conodonts as well as graptolites of the N. gracilis Zone. The distinctive conodonts Amorphognathus aff. Am. ventilatus and Hamarodus europaeus first occur at, or very near, the excursion interval. Because these conodonts appear in the stratigraphic interval of the Guttenberg VC excursion (GICE) in Estonia, we identify the Chinese excursion as the GICE. This is the first record of the GICE in the entire Asian continent. It confirms that GICE is a global excursion and provides an illustration of how VC chemostratigraphy, combined with new biostratigraphic data, solves the problem of the previously controversial age of the Pagoda Formation and how this classical stratigraphic unit correlates with the Baltoscandian and North American successions.
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18.
  • Bergstroem, Stig M., et al. (författare)
  • First record of the Hirnantian (Upper Ordovician) delta C-13 excursion in the North American Midcontinent and its regional implications
  • 2006
  • Ingår i: Geological Magazine. - 0016-7568. ; 143:5, s. 657-678
  • Forskningsöversikt (refereegranskat)abstract
    • The most prominent of the two major global delta C-13 excursions in the Ordovician, the Hirnantian delta C-13 excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated delta C-13 values of + 4 parts per thousand to + 5 parts per thousand. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes.
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19.
  • Bergstroem, Stig M., et al. (författare)
  • Global Upper Ordovician correlation by means of delta C-13 chemostratigraphy: implications of the discovery of the Guttenberg delta C-13 excursion (GICE) in Malaysia
  • 2010
  • Ingår i: Geological Magazine. - 0016-7568. ; 147:5, s. 641-651
  • Tidskriftsartikel (refereegranskat)abstract
    • Apart from a single study of the early Katian delta C-13 chemostratigraphy in two regions in China, no investigations of the Sandbian and Katian chemostratigraphy have been published from anywhere in Asia. A recent study of the conodont biostratigraphy of the classical Ordovician succession on Langkawi Islands, peninsular Malaysia, showed the presence there of strata coeval with those having the Guttenberg Carbon Excursion (GICE) on the Yangtze Platform. In an effort to establish for the first time the presence of this widespread delta C-13 excursion in southern Asia, a series of samples from the upper part of the Kaki Bukit Formation was isotopically analysed. This resulted in the discovery of a conspicuous delta C-13 excursion with peak values of similar to 2% above the baseline values. The excursion is located just above the Baltoniodus alobatus Subzone and near the level of the first appearance of Hamarodus europaeus, hence the same stratigraphic position as the GICE on the Yangtze Platform. Using the GICE, the Malaysian study interval is closely correlated with the GICE intervals at three localities representing an approximately 23 000 km long transect from Malaysia across Baltoscandia to central North America. This shows the usefulness of delta C-13 chemostratigraphy to clarify previously obscure stratigraphic relationships between geographically very widely separated localities.
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20.
  • Bergstroem, Stig M., et al. (författare)
  • Hirnantian (latest Ordovician) delta C-13 chemostratigraphy in southern Sweden and globally: a refined integration with the graptolite and conodont zone successions
  • 2014
  • Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 136:2, s. 355-386
  • Tidskriftsartikel (refereegranskat)abstract
    • The delta C-13(org) chemostratigraphy of the Hirnantian and lower Rhuddanian in the biostratigraphically well-controlled Rostanga-1 drillcore from west-central Scania is used for an improved integration of the Hirnantian Isotope Carbon Excursion (HICE) with the standard graptolite zonation. In this drillcore succession, the end of the HICE corresponds to the top of the range of Metabolograptus persculptus. Baseline delta C-13(org) values occur in the uppermost Hirnantian Avitograptus avitus Faunal Interval as well as in the Rhuddanian Akidograptus ascensus Zone, and the isotope curve is also tied to the Swedish uppermost Katian and Hirnantian trilobite zonation. Chemostratigraphic data from sections in Vastergotland confirm that the beginning of the HICE is at, or very close to, the base of the Skultorp Member of the Loka Formation. The biostratigraphically less precisely controlled end of the HICE is at least locally in the Upper Member of the same formation. The graptolite biostratigraphy in the Mt. Kinnekulle succession indicates that the lowermost Kallholn Formation, which has long been known as the Leonaspis (formerly Acidaspis) Shale, is of Hirnantian rather than earliest Silurian age which is consistent with the age of the lowermost Kallholn Formation in the Rostanga-1 drillcore. Comparisons with Hirnantian sections in the United Kingdom, North America and China make it possible to improve the calibration of the HICE with conodont and graptolite biostratigraphy and confirm the usefulness of delta C-13(org) chemostratigraphy for detailed correlations. The upper Katian carbon chemostratigraphy in key sections in North America and eastern Baltoscandia indicates that the Elkhorn and Paroveja excursions are the same. Available data are used for a new Hirnantian eustasy-climate-faunal evolution model.
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21.
  • Bergstroem, Stig M., et al. (författare)
  • Lower Katian (Upper Ordovician) delta(13)C chemostratigraphy, global correlation and sea-level changes in Baltoscandia
  • 2011
  • Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 133:1-2, s. 31-47
  • Tidskriftsartikel (refereegranskat)abstract
    • A long-standing problem in the Ordovician stratigraphy of south-eastern Norway has been to the relations between the Mjosa Formation in the Lake Mjosa region and coeval strata in the Oslo region. The recent discovery of the globally distributed Guttenberg delta(13)C excursion (Guttenberg Isotopic Carbon Excursion) in the Mjosa region provided the impetus to search for this excellent chemostratigraphic marker in the classical Oslo region succession, where it was found in the Frognerkilen Formation. Another positive delta(13)C excursion, which we identify as the Kope excursion, was discovered in the Solvang Formation. The new data show that the lower Katian delta(13)C chemostratigraphy in the Oslo region is closely similar to that from south-eastern and southern Estonia. This permits detailed correlations across Baltoscandia, which are useful for recognising the Baltic stage boundaries in the Oslo region succession. Both the Lake Mjosa and Oslo regions study successions can be chemostratigraphically correlated with those in North America and eastern Asia. The newly established stratigraphic relations in the Oslo region are also used for a re-assessment of lower Katian local and eustatic sea-level changes.
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22.
  • Bergstroem, Stig M., et al. (författare)
  • The delta C-13 chemostratigraphy of the Upper Ordovician Mjosa Formation at Furuberget near Hamar, southeastern Norway: Baltic, Trans-Atlantic, and Chinese relations
  • 2010
  • Ingår i: Norsk Geologisk Tidsskrift. - 1502-5322. ; 90:1-2, s. 65-78
  • Tidskriftsartikel (refereegranskat)abstract
    • Whereas no studies have previously been carried out on the delta C-13 chemostratigraphy of the Sandbian-Katian (Upper Ordovician) succession anywhere in Norway, such investigations in Sweden and the East Baltic region have made the delta C-13 chemostratigraphy of that interval well known. 1 an attempt to document for the first time the presence of the globally distributed and stratigraphically important Guttenberg Carbon Isotope Excursion (GICE), 45 samples were collected at 2 m intervals through the Furnesfjorden and Galas members of the Mjosa Formation from two sections at Furuberget in the Nes-Hamar District 70 km north of the City of Oslo. Relatively high delta C-13 values, which are interpreted to represent the GICE, were obtained throughout the Galls Member. The presence of this delta C-13 excursion in the middle part of the Mjosa Formation, combined with biostratigraphic and other evidence, are used for detailed correlations of the Mjosa Formation with other successions in Baltoscandia, North America, and on the Yangtze Platform in southern China.
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23.
  • Bergstrom, Stig M., et al. (författare)
  • High-resolution δ13Corg chemostratigraphy links the Decorah impact structure and Winneshiek Konservat-Lagerstätte to the Darriwilian (Middle Ordovician) global peak influx of meteorites
  • 2018
  • Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 51:4, s. 504-512
  • Tidskriftsartikel (refereegranskat)abstract
    • The precise age of the Winneshiek Shale, a recently discovered Konservat-Lagerstätte located in a very unusual depositional setting inside the Decorah impact structure, has remained uncertain in the absence of biostratigraphically highly diagnostic fossils. This chemostratigraphical study, based on δ13Corg data from 36 drill core samples through the shale, shows that the age ranges from the upper part of a small unnamed δ13C excursion in the Dw1 Stage Slice of the Darriwilian Global Stage to the lower part of the MDICE excursion in Stage Slice Dw2 of the same stage. This Dw1-Dw2 interval has an isotopic age of ~464-467 Ma. The gradational contact between the Winneshiek Shale and the underlying, rapidly deposited, impact breccia indicates minimal time difference between the impact event and the Winneshiek Shale. New age data show that the Decorah impact event was coeval with the early Darriwilian abnormally high influx of micrometeorites and meteorites recorded in sections in Baltoscandia, Russia and China and that the Decorah crater can be included among the unusually large number of meteorite craters formed during Middle and early Late Ordovician time. As is commonly the case in black shale deposits, the partly uniquely preserved Winneshiek Shale crater fauna is impoverished taxonomically and adds numerically relatively little to the conspicuous and much discussed Darriwilian global biodiversification increase.
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24.
  • Bergstrom, Stig M., et al. (författare)
  • Katian (Upper Ordovician) delta C-13 chemostratigraphy and sequence stratigraphy in the United States and Baltoscandia: A regional comparison
  • 2010
  • Ingår i: Early Palaeozoic sea level and climate - Selected papers presented at the IGCP 503 closing meeting in Lille (France), 23-31 August 2008 (Palaeogeography, Palaeoclimatology, Palaeoecology). - : Elsevier BV. - 1872-616X .- 0031-0182. ; 296:3-4, s. 217-234
  • Konferensbidrag (refereegranskat)abstract
    • delta C-13 values of numerous limestone samples from Katian (Upper Ordovician) successions in Oklahoma and the Upper Mississippi Valley document the presence of at least three of the four positive excursions that have been recognized in the lower-middle Katian interval in the Cincinnati region in Ohio. Kentucky, and Indiana. A comparison with Estonia reveals that five out of the six positive excursions now recorded through the Katian succession in the Cincinnati region are present in the coeval stratigraphic intervals in Estonia, which suggests that these represent global perturbations in the carbon cycle A study of the relations between flooding events and delta C-13 excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence, this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level Part of a previously published attempt to use Upper Ordovician sequence stratigraphy for trans-Atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy Several of the sequences recognized in the Cincinnati region do not appear to have counterparts in Estonia, which suggests that they do not reflect eustatic, but local, conditions (C) 2010 Elsevier B V All rights reserved.
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25.
  • Bergstrom, Stig M., et al. (författare)
  • Late Ordovician-Early Silurian delta C-13 chemostratigraphy in the Upper Mississippi Valley: implications for chronostratigraphy and depositional interpretations
  • 2011
  • Ingår i: Earth and Environmental Science Transactions of the Royal Society of Edinburgh. - 1755-6929. ; 102, s. 159-178
  • Tidskriftsartikel (refereegranskat)abstract
    • A pioneer study of the previously unknown delta C-13 chemostratigraphy in the Ordovician/Silurian boundary interval in eastern Iowa and northeastern Illinois resulted in the discovery of the Hirnantian Isotope Carbon Excursion (HICE). The presence of this major isotope excursion in the Mosalem Formation in Iowa and the Wilhelmi Formation in Illinois, which indicates that the excursion interval in these units is of Hirnantian (latest Ordovician) rather than Early Silurian age, necessitates a revised chronostratigraphic classification of these units. Although the precise level of the Ordovician/Silurian boundary remains somewhat uncertain in the absence of the diagnostic graptolites, it is herein placed in the upper part, but well below the top, of the Mosalem Formation and at the top of the Wilhelmi Formation. During a major regression following the deposition of the Maquoketa Shale, the upper part of the latter elastic unit was in some places deeply eroded, resulting in a topographically dissected landscape with upland areas separated by wide incised valleys. During a subsequent late Hirnantian transgression, these palaeovalleys were gradually filled with marine sediments, but the upland areas were not transgressed until earliest Silurian times. The new chemostratigraphical evidence is in good agreement with the available biostratigraphical data, especially from corals, conodonts, and brachiopods. A preliminary chemostratigraphical study of the presumably coeval Edgewood Group successions in Pike County, northeastern Missouri failed to document any heavy delta C-13 values characteristic of the HICE and some, or all, of the Hirnantian values obtained there may be diagenetically overprinted.
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26.
  • Bergstrom, Stig M., et al. (författare)
  • Revision of the position of the Ordovician-Silurian boundary in southern Ontario: regional chronostratigraphic implications of delta C-13 chemostratigraphy of the Manitoulin Formation and associated strata
  • 2011
  • Ingår i: Canadian Journal of Earth Sciences. - 0008-4077. ; 48:11, s. 1447-1470
  • Tidskriftsartikel (refereegranskat)abstract
    • delta C-13 values of 142 samples from the Manitoulin Formation and subjacent strata collected from 14 exposures and two drill-cores on Manitoulin Island, Bruce Peninsula, and the region south of Georgian Bay suggest that the Manitoulin Formation is latest Ordovician (Hirnantian) rather than earliest Silurian in age. A delta C-13 excursion identified as the Hirnantian isotope carbon excursion (HICE), which has a magnitude of nearly 2.5 parts per thousand above baseline values, is present in an interval from the upper Queenston Formation to the lower to middle part of the Manitoulin Formation in most of Bruce Peninsula and in the area south of Georgian Bay, whereas on Manitoulin Island the RICE appears to be absent. This indicates that a significant part of the Manitoulin Formation is older on the Bruce Peninsula and in its adjacent region than on Manitoulin Island. The chemostratigraphically based conclusions are consistent with biostratigraphic data from conodonts and brachiopods. The Hirnantian delta C-13 curve from Anticosti Island, Quebec is closely similar to those of southern Ontario. Traditionally, the Ordovician-Silurian boundary has been placed at the base of the Manitoulin Formation, but the new results suggest that it is more likely to be at, or near, the base of the overlying Cabot Head Formation. These new results have major implications For the interpretation of the geologic history and marine depositional patterns of the latest Ordovician of a large part of the North American Midcontinent.
  •  
27.
  • Bergström, Stig M., et al. (författare)
  • Local and trans-Atlantic chemostratigraphic significance of new δ13Ccarb data from the Sandbian and Katian Stages (Middle–Upper Ordovician) of the Oslo region, Norway
  • 2017
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 139:4, s. 289-300
  • Tidskriftsartikel (refereegranskat)abstract
    • Late Sandbian to early Katian δ13Ccarb chemostratigraphy has in Norway been described in only two previous reports that dealt with two geographically rather widely separated areas, namely the Oslo-Asker district and the Nes-Hamar district. No data have been available from the Ordovician outcrop areas between these districts that could help clarify the partly unclear regional stratigraphic relations across the Oslo region. A chemostratigraphic study of the classical road section at Tønnerud in the northwestern Hadeland district about halfway between the previously investigated districts resulted in the recognition of two δ13C excursions, namely one in the uppermost Furuberget Formation tentatively identified as the Guttenberg Isotopic Carbon Excursion and one in the lower Solvang Formation that is classified as the KOPE (RAKVERE) excursion. Based on these results, the Furuberget and Solvang formations are interpreted to be separated by a significant gap in the study area corresponding to the Oandu and lower Rakvere regional Baltoscandic stages. This suggests that the Tønnerud succession is less complete stratigraphically than those in the Oslo-Asker district. Similar gaps are not uncommon in this interval in Baltoscandia and in North America and probably reflect both eustatic and local epeirogenetic movements that make it difficult to establish a regionally applicable sequence stratigraphy.
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28.
  • Bergström, Stig M., et al. (författare)
  • Obituary Lennart Jeppsson 1940-2015
  • 2015
  • Ingår i: The Palaeontological Association Newsletter. - 0954-9900. ; 89, s. 103-105
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
  •  
29.
  • Bergström, Stig M., et al. (författare)
  • The age of the Middle Ordovician Winneshiek Shale : reply to a critical review by Lindskog & Young (2019) of a paper by Bergström et al. (2018a)
  • 2020
  • Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 53:1, s. 1-4
  • Tidskriftsartikel (refereegranskat)abstract
    • A recent review by Lindskog & Young (2019) of a paper published in Lethaia by Bergström et al. (2018a) contains many errors, misleading statements and unsupported opinions. Their review claims that we did not consider biostratigraphy in our efforts to chemostratigraphically date the Winneshiek Shale. That this is incorrect is shown by the fact that Liu et al. (2017), which contains a two-page review of all fossil evidence that has a bearing on the age of the Winneshiek Shale and was written by Bergström, was cited in Bergström et al. (2018a) and used extensively in our chemostratigraphical age assessment of the unit. Interestingly, recent research provides support for our conclusion regarding the age of the Winneshiek Shale, indicating that at least its upper part is coeval with the Nicholsonograptus fasciculatus Graptolite Zone and the Eoplacognathus pseudoplanus Conodont Zone. In constructing their arguments, Lindskog & Young (2019) provide no alternative interpretations or corrections of scientific value.
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30.
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31.
  • Bergström, Stig M., et al. (författare)
  • The δ13C chemostratigraphy of Ordovician global stage stratotypes : geochemical data from the Floian and Sandbian GSSPs in Sweden
  • 2020
  • Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:1, s. 23-32
  • Tidskriftsartikel (refereegranskat)abstract
    • The δ13C chemostratigraphy of five of the seven Ordovician global stages has been published previously but no such data have been available from the Floian GSSP and most of the Sandbian GSSP in Sweden. This lack of information has now been remedied by isotope data obtained from series of closely spaced shale samples collected from the Floian stratotype at Diabasbrottet in Västergötland and the Sandbian stratotype at Fågelsång in Scania. Although the bases of these stages cannot be precisely tied to levels of conspicuous δ13C excursions, that of the Floian Stage, which is marked by the appearance of the graptolite Tetragraptus approximatus, is between the closely spaced excursions named LTNICE and BFICE. The base of the Sandbian Stage, which is defined as the appearance level of the graptolite Nemagraptus gracilis, is just below a negative excursion previously known as the “Upper Kukruse Low”, which is nowadays known as the LSNICE. The relations between chemostratigraphy and graptolite and conodont biostratigraphy in the Swedish GSSPs and some coeval key sections in Baltoscandia, China, and America are briefly discussed. It is concluded that the data at hand indicate that there is good regional agreement in these relations.
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32.
  • Bergström, Stig M., et al. (författare)
  • Upper Ordovician δ13Corg chemostratigraphy, K-bentonite stratigraphy, and biostratigraphy in southern Scandinavia : A reappraisal
  • 2016
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 454, s. 175-188
  • Tidskriftsartikel (refereegranskat)abstract
    • A pioneer δ13Corg study through the upper Sandbian and Katian (Upper Ordovician) succession in the Röstånga 1 drill core in the classical geological outcrop area at Röstånga in southernmost Sweden produced a wealth of new carbon isotope data which are useful for local and regional correlations. Among the Upper Ordovician positive δ13C excursions, the Guttenberg (GICE), Waynesville (Saunja), Whitewater (Moe), Paroveja, and Hirnantian (HICE) isotopic carbon excursions are recognized but the Kope (Rakvere) δ13C excursion is missing, suggesting a stratigraphic gap. All these isotopic excursions are tied closely to biostratigraphy, especially graptolite biostratigraphy, and in the case of the Waynesville (Saunja) and Whitewater (Moe) excursions, for the first time anywhere in the world. The Röstånga GICE δ13Corg curve from the upper Sularp Shale shows a striking similarity to that of the Katian GSSP in Oklahoma, suggesting the potential of trans-Atlantic correlation. Based on a projection from the Katian GSSP, the previously poorly constrained position of the base of the Katian in southern Sweden appears to be in the uppermost Sularp Shale in strata of the upper Diplograptus foliaceus Zone. Previous interpretations of the relations between K-bentonite successions in southern Scandinavia are somewhat revised and the Kinnekulle K-bentonite is recognized for the first time in Scania. Based on new radiometric dates, this very prominent and widespread ash bed appears to be slightly older than the Deicke and Millbrig K-bentonites in eastern North America.
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33.
  • Bjärnborg, Karolina, et al. (författare)
  • Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes
  • 2013
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379. ; 48:2, s. 180-194
  • Tidskriftsartikel (refereegranskat)abstract
    • By dissolving 30400kg of marine limestone in HCl and HF acid, our group has previously recovered common relict chromite grains (approximately 63250m) from ordinary chondritic micrometeorites that fell on ancient sea floors, up to 500Myr old. Here, we evaluate if CM group carbonaceous chondritic material, which makes up an important fraction of the micrometeorite flux today, contains analogous grains that can be searched for in acid residues. We dissolved 8g of CM2 meteorite Acfer 331 in HF, which yielded a characteristic assemblage of both transparent Mg-Al- and opaque Cr-spinels >28m. We find on average 4.6 and 130 Mg-Al-spinel grains per gram in the 63250 and 2863m size fractions, respectively. These grains are mostly pink or colorless, and often characterized by heterogeneous Cr-content. Black, opaque Cr-spinel grains are absent from the >63m fraction, but in the 2863m fraction we find approximately 65 such grains per gram meteorite. The individual grains have a characteristic composition, with heterogeneous major element compositions (e.g., 44.461.7wt% Cr2O3), but narrow ranges for maximum TiO2 (0.61.6wt%) and V2O3 (0.51.0wt%) concentrations. The content of spinel grains in the 2863m fraction of CM meteorites appears comparable at the order of magnitude level with the content of >63m sized chromite grains in fossil L-chondrites from Ordovician limestone. Our approach of recovering meteoritic spinel from sediment may thus be extended to include CM meteorites, but the smaller size fraction of the acid residues should be searched.
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34.
  • Boschi, Samuele, et al. (författare)
  • Distribution of chrome-spinel grains across the 3He anomaly of the Tortonian Stage at the Monte dei Corvi section, Italy
  • 2019
  • Ingår i: 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco. - : Geological Society of America. - 0072-1077. ; 542, s. 383-391
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • The present-day ocean-climate system configuration took shape during the Miocene Epoch. Toward the end of the epoch, in the late Tortonian at ca. 8.5 Ma, there was an exceptional event: collisional disruption of an >150-km-diameter asteroid, which created the Veritas family of asteroids in the asteroid belt. This event increased the flux of interplanetary dust particles rich in 3He to Earth and probably caused a period of increased dust in the atmosphere, with consequent alteration of global and local environmental conditions. A late Miocene 3He anomaly likely related to the Veritas event has been registered in deep-sea sediments from Ocean Drilling Program (ODP) Site 926 (Atlantic Ocean), ODP Site 757 (Indian Ocean), and in the late Tortonian–early Messinian Monte dei Corvi section near Ancona, Italy. Here, we report the results of a study in the Monte dei Corvi section aimed to recover extraterrestrial chrome-spinel grains across the 3He anomaly interval, as has been done for the similar late Eocene 3He anomaly in the nearby Massignano section. In this study, three ~100 kg samples were collected from the Monte dei Corvi section: two within the 3He peak interval and one outside the anomaly interval as a background reference sample. In total, 1151 chrome-spinel grains (>63 µm) were recovered, but based on chemical composition, none of the grains has a clear extraterrestrial origin. This supports the inference that the 3He anomaly is indeed related to the Veritas event and not to an approximately coeval breakup of a smaller H-chondritic body in the asteroid belt, an event registered in meteoritic cosmic-ray exposure ages. Spectral studies of the Veritas asteroids indicate that they are made up of carbonaceous chondritic material. Such meteorites generally have very low chrome-spinel concentrations in the grain-size range considered here, contrary to the very chromite-rich ordinary chondrites. The terrestrial grains recovered were classified, and their composition showed that all the grains have an ophiolitic origin with no substantial compositional and distributional change through the section. The source area of the terrestrial grains was probably the Dinarides orogen.
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35.
  • Boschi, Samuele, et al. (författare)
  • Late Eocene 3He and Ir anomalies associated with ordinary chondritic spinels
  • 2017
  • Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 204, s. 205-218
  • Tidskriftsartikel (refereegranskat)abstract
    • During the late Eocene there was an enigmatic enhancement in the flux of extraterrestrial material to Earth. Evidence comes from sedimentary 3He records indicating an increased flux of interplanetary dust during ca. 2 Myr, as well as two very large impact structures, Popigai (100 km diameter) and Chesapeake Bay (40–85 km), that formed within 10–20 kyr at the peak of the 3He delivery. The Massignano section in Italy has one of the best sedimentary records of these events, including a well-defined 3He record, an Ir-rich ejecta bed related to the Popigai impact event, and two smaller Ir anomalies. Recently we showed that the Popigai ejecta is associated with a significant enrichment of chromite grains (>63 μm) with an H-chondritic elemental composition (17 grains in 100 kg of rock). Most likely these grains are unmelted fragments from the impactor. Slightly higher up (ca. 20 cm) in the section, where a small Ir anomaly possibly related to the Chesapeake Bay impact has been measured, we found a weak enrichment in L-chondritic grains (8 grains in 208 kg of rock). Here we report an extended data set increasing the total amount of sediment dissolved in acid and searched for extraterrestrial chromite grains from 658 to 1168 kg. In altogether 760 kg of background sediment from 17 levels over 14 m of strata outside the interval corresponding to the Popigai and Chesapeake Bay impacts, we only found 2 extraterrestrial chromite grains. Both grains have L-chondritic compositions and were found in a 100 kg sample from the ca. 10.25 m level in the section where the second of the smaller Ir anomalies has been reported. A correlation appears to exist between Ir, 3He and chromite from ordinary chondrites. We also report oxygen three-isotope measurements of the extraterrestrial chromite grains associated with the Popigai ejecta and confirm an H-chondritic composition. The new results strengthen our scenario that the upper Eocene 3He and Ir enrichments originate from the asteroid belt rather than the Oort cloud as originally proposed when the 3He anomaly was discovered. The generally low background concentrations of extraterrestrial chromite through the section speak against any major single asteroid breakup event such as in the mid-Ordovician after the break-up of the L-chondrite parent body. Instead the data reconcile with a small, possibly a factor of 2–3, increase in the flux of extraterrestrial material to Earth, but of both H- and L-chondritic composition. We also report the composition of all the 2310 terrestrial chrome spinel grains recovered, and show that their chemical composition indicates a dominantly regional ophiolitic source. Four anomalous chrome spinel grains with high Ti and V concentrations were found in the Popigai ejecta. These grains originate from Siberian Traps basalts in the Popigai crater at the time of impact.
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36.
  • Boschi, Samuele, et al. (författare)
  • Popigai impact ejecta layer and extraterrestrial spinels recovered in a new Italian location—The Monte Vaccaro section (Marche Apennines, Italy)
  • 2019
  • Ingår i: 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco. - : Geological Society of America. - 0072-1077. ; 542, s. 355-367
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • The Popigai (100 km in diameter) and the Chesapeake Bay (40–85 km diameter) impact structures formed within ~10–20 k.y. in the late Eocene during a 2 m.y. period with enhanced flux of 3He-rich interplanetary dust to Earth. Ejecta from the Siberian Popigai impact structure have been found in late Eocene marine sediments at numerous deep-sea drilling sites around the globe and also in a few marine sections outcropped on land, like the Massignano section near Ancona in Italy. In the Massignano section, the Popigai layer is associated with an iridium anomaly, shocked quartz, and abundant clinopyroxene-bearing (cpx) spherules, altered to smectite and flattened to “pancake spherules.” The ejecta are also associated with a significant enrichment of H-chondritic chromite grains (>63 µm), likely representing unmelted fragments of the impactor. The Massignano section also contains abundant terrestrial chrome-spinel grains, making reconstructions of the micrometeorite flux very difficult. We therefore searched for an alternative section that would be more useful for these types of studies. Here, we report the discovery of such a section, and also the first discovery of the Popigai ejecta in another locality in Italy, the Monte Vaccaro section, 90 km west of Ancona. The Monte Vaccaro section biostratigraphy was established based on calcareous nannoplankton, which allowed the identification of a sequence of distinct bioevents showing a good correlation with the Massignano section. In both the Monte Vaccaro and Massignano sections, the Popigai ejecta layer occurs in calcareous nannofossil zone CNE 19. The ejecta layer in the Monte Vaccaro section contains shocked quartz, abundant pancake spherules, and an iridium anomaly of 700 ppt, which is three times higher than the peak Ir measured in the ejecta layer at Massignano. In a 105-kg-size sample from just above the ejecta layer at Monte Vaccaro, we also found an enrichment of H-chondritic chromite grains. Because of its condensed nature and low content of terrestrial spinel grains, the Monte Vaccaro section holds great potential for reconstructions of the micrometeorite flux to Earth during the late Eocene using spinels.
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37.
  • Boschi, Samuele, et al. (författare)
  • The micrometeorite flux to Earth during the earliest Paleogene reconstructed in the Bottaccione section (Umbrian Apennines), Italy
  • 2020
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379 .- 1945-5100. ; 55:7, s. 1615-1628
  • Tidskriftsartikel (refereegranskat)abstract
    • Based on sediment-dispersed extraterrestrial spinel grains in the Bottaccione limestone section in Italy, we reconstructed the micrometeorite flux to Earth during the early Paleocene. From a total of 843 kg of limestone, 86 extraterrestrial spinel grains (12 grains > 63 μm, and 74 in the 32–63 μm fraction) have been recovered. Our results indicate that the micrometeorite flux was not elevated during the early Paleocene. Ordinary chondrites dominated over achondritic meteorites similar to the recent flux, but H chondrites dominated over L and LL chondrites (69%, 22%, and 9%, respectively). This H-chondrite dominance is similar to that recorded within an enigmatic 3He anomaly (70, 27, and 3%) in the Turonian, but different from just before this 3He anomaly and in the early Cretaceous, where ratios are similar to the recent flux (~45%, 45%, and 10%). The K-Ar isotopic ages of recently fallen H chondrites indicate a small impact event on the H-chondrite parent body ~50 to 100 Ma ago. We tentatively suggest that this event is recorded by the Turonian 3He anomaly, resulting in an H-chondrite dominance up to the Paleocene. Our sample spanning the 20 cm above the Cretaceous–Paleogene (K–Pg) boundary did not yield any spinel grains related to the K–Pg boundary impactor.
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38.
  • Bredberg, Anders, et al. (författare)
  • Human cancer, the naked mole rat and faunal turnovers
  • 2019
  • Ingår i: Cancer Medicine. - : Wiley. - 2045-7634. ; 8:4, s. 1652-1654
  • Tidskriftsartikel (refereegranskat)abstract
    • We argue that the human evolutionary heritage with frequent adaptations through geological time to environmental change has affected a trade-off between offspring variability and cancer resistance, and thus favored cancer-prone individuals. We turn the attention to a factor setting the highly cancer-resistant naked mole rat apart from most other mammals: it has remained phenotypically largely unchanged since 30-50 million years ago. Research focusing on DNA stability mechanisms in ‘living fossil’ animals may help us find tools for cancer prevention and treatment.
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39.
  • Bridges, J. C., et al. (författare)
  • Petrographic classification of middle ordovician fossil meteorites from Sweden
  • 2007
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379 .- 1945-5100. ; 42:10, s. 1781-1789
  • Tidskriftsartikel (refereegranskat)abstract
    • The maximum diameter of chromite (FeCr2O4) grains within L chondrites reflects the petrographic type of the sample. On the basis of our measurements of nine recent L chondrites, L3 chromite D-mac = 34-50 mu m, L4 = 87-150 mu m, L5 = 76-158 mu m, and L6 = 253-638 mu m. This variation reflects the crystallization of the chromite grains during parent body thermal metamorphism.We use this calibration to classify six fossil meteorites from the Middle Ordovician in Sweden as type 3 (or 4) to 6. The high flux of L chondrites at 470 Ma contained a range of petrographic types and may have had a higher proportion of lower petrographic type meteorites than are found in recent L chondrite falls. The fossil meteorites have in places preserved recognizable chondrule textures, including porphyritic olivine, barred olivine, and radiating pyroxene. A large relict clast and fusion crust have also been tentatively identified in one fossil meteorite. Apart from chromite, all of the original meteorite minerals have been replaced by carbonate (and sheet silicate and sulfate) during diagenesis within the limestone host. The preservation of chondrule definition has allowed us to measure the mean diameters of relict chondrules. The range (0.4-0.6 mm) is consistent with measurements made in the same way on recent L chondrites.
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40.
  • Burman, Johan, 1966, et al. (författare)
  • A simplified method of preparing phosphoric acid for stable isotope analyses of carbonates
  • 2005
  • Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 19:21, s. 3086-3088
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to produce CO2 for stable isotope analyses (delta(18)O and delta(13)C), carbonate samples are commonly digested in phosphoric acid. The acid recipe here presented is based on phase shifting crystalline orthophosphoric acid of pro-analysis quality to a liquid state through heating, followed by pre-vacuum treatment during a start-up procedure before mass analyses for common acid bath preparation, or adding a small amount of phosphoric pentoxide for single drop equipments, respectively. This methodology results in a final acid concentration of 104%. Copyright (C) 2005 John Wiley & Sons, Ltd.
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41.
  • Burman, Johan, 1966, et al. (författare)
  • Periwinkle (Littorina littorea) intrashell delta O-18 and delta C-13 records from the mid-Holocene Limfjord region, Denmark: a new high-resolution palaeoenvironmental proxy approach
  • 2005
  • Ingår i: Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 15:4, s. 567-575
  • Tidskriftsartikel (refereegranskat)abstract
    • Shells of the common intertidal gastropod Littorina littorea both of recent and mid-Holocene origin were analysed along their growth spirals for seasonally induced variations in stable oxygen and carbon isotope compositions. The subfossil specimens are from the Stone Age kitchen midden in Ertebolle, northern Denmark, dated between 5970 +/- 95 and 5070 +/- 90 BP The recent specimens were collected along a west-east salinity gradient within the Limfjord. A Limfjord mixing line of 0.25 parts per thousand. change in delta(18)O (V-SMOW) for each salinity unit was determined. The recent Littorina periwinkles display a calcite relationship of - 0.22 parts per thousand change in shell delta(18)O per degrees C change in temperature, as derived from the Littorina equilibrium equation (versus V-PDB): delta(18)O((Littorina)) - delta(18)O((water)) = 5.250 - 0.224T (degrees C). By using this linearity together with maximum ('winter') isotopic results, we extracted a Littorina growth stop isotherm equivalent to a temperature of 3.7 +/- 1 degrees C. In order to constrain the climate and salinity in the Limfjord region during the mid-Holocene, we used this regression-derived growth stop isotherm as a boundary condition. The subfossil shells indicate a summer surface-water temperature close to 22 +/- 1 degrees C together with a salinity of 31 +/- 1 PSU. These results suggest a more pronounced water exchange between the central Limfjord and the North Sea during the late Atlantic time, and in terms of temperature they indicate 2-4 degrees C warmer conditions than today.
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42.
  • Calner, Mikael, et al. (författare)
  • A shoreline to deep basin correlation chart for the middle Silurian coupled extinction-stable isotopic event
  • 2006
  • Ingår i: GFF. - 2000-0863. ; 128, s. 79-84
  • Tidskriftsartikel (refereegranskat)abstract
    • A shoreline to deep basin correlation chart for the middle Silurian coupled extinction-stable isotopic event is presented. The chart is a first attempt to synthesise new stratigraphic, faunal and stable isotopic data, as well as diversity changes among organic-walled microplankton (acritarchs), from the Grotlingbo-1 and Hunninge-1 cores on Gotland (Sweden), along with previously published data from the Bartoszyce IG 1 core (Poland), the Grafenwarth section (Germany), and the Ruhnu (500) and Ohesaare cores (Estonia). Accordingly, the relative timing of biotic, sedimentary, and stable isotopic changes associated with the event can be studied in high stratigraphic resolution across a basin area of similar to 120 000 km(2) (in the epicontinental Baltic Basin) and further off the Silurian continental margin into the Rheic Ocean (Grafenwarth section). A graptolite biozonation is presented for the Late Wenlock of the Grotlingbo-1 core and the middle Silurian carbon isotope excursion (CIE) is for the first time detected in stratigraphically continuous sections on Gotland. It starts close above the LAD of Monograptus flemingii and peaks at delta C-13 values of 2.4 parts per thousand in the Grotlingbo-1 core and at 3.8 parts per thousand in the Hunninge-1 core. The correlation chart forms the basis for several important conclusions for the mid-Silurian event: (a) it is associated with major and synchronous sedimentary changes across the basin independent of palaeodepth, i.e., the entire marine realm, from shoreline to deep basin, was affected; (b) the onset of the CIE is within the latest part of a regressive systems tract and related to carbonate platform exposure and termination; (c) the CIE peak interval correlates with the early transgressive systems tract and the development of laminated strata in the deeper parts of epicontinental seas, as well as with increased accumulation of organic matter in even deeper basins; (d) the major diversity anomalies among planktonic and nektonic taxa precede or occur close to the onset of the CIE.
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43.
  • Caplan, Caroline E., et al. (författare)
  • The classification of relict extraterrestrial chrome spinels using STEM techniques on silicate inclusions
  • 2021
  • Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379 .- 1945-5100. ; 56:4, s. 700-722
  • Tidskriftsartikel (refereegranskat)abstract
    • Remnant extraterrestrial chrome spinels from terrestrial sediments provide information on how the mixture of meteoritic materials falling to Earth has changed over Earth’s history. The parent meteorite type of each grain can be identified by characteristic elemental and oxygen-isotope abundances. Some meteorite types can be difficult to classify because their chrome-spinel compositional ranges overlap. Silicate inclusions within chrome spinels of modern ordinary chondrites have been shown to have discriminating power among meteorite subclasses. We employed energy-dispersive X-ray spectroscopy in a scanning electron microscope (SEM) and in a (scanning) transmission electron microscope (S/TEM) to investigate inclusions in chrome-spinel grains from Ordovician and Jurassic sediments. Unaltered Ordovician inclusions allowed us to establish the size limits for reliable SEM analysis of inclusions. The Jurassic grains were more altered, but the use of STEM techniques on small inclusions (<3 μm diameter at their polished surfaces) allowed us to determine chemical compositions and mineral structures of inclusions in three chrome spinels. The parent meteorite type was determined for one Jurassic grain based on its inclusion compositions. Our study confirms that silicate inclusions can be used to classify parent meteorite types of chrome-spinel grains, but the size of the inclusions and the complex effects of terrestrial alteration must be taken into account. During our study, we also found some interesting exsolution phenomena in the host chrome-spinel grains.
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44.
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45.
  • Cronholm, Anders, et al. (författare)
  • Extraterrestrial chromite distribution across the mid-Ordovician Puxi River section, central China: Evidence for a global major spike in flux of L-chondritic matter
  • 2010
  • Ingår i: Icarus. - : Elsevier BV. - 0019-1035. ; 208:1, s. 36-48
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous studies of mid-Ordovician limestone in Sweden have shown that over a stratigraphic interval representing a few million years there is a two orders-of-magnitude enrichment in fossil L-chondritic meteorites (empty set = 1-21 cm) and sediment-dispersed extraterrestrial chromite (EC) grains (>63 mu m). This has been interpreted as a dramatic increase in the flux of L-chondritic matter to Earth following the breakup of the L-chondrite parent body, which based on Ar-Ar gas retention ages (470 +/- 6 Ma) of recently fallen meteorites occurred at about this time. Here we show that the general trend in the distribution of sediment-dispersed EC grains can be reproduced in the Puxi River section in central China. A total of 288 kg of limestone was searched for chrome spinels. In samples spanning the lower 8 m of the section, representing the Paroistodus originalis and Lenodus antivariabilis conodont zones, a total of 110 kg of limestone yielded only one EC grain. Similarly to the Swedish sections, EC grains begin to be common in the overlying L. variabilis Zone and remain common throughout the upper 9 m of the section, representing the L. variabilis, Yangtzeplacognathus crassus and L. pseudoplanus zones. In this part of the section 178 kg of limestone yielded 290 EC grains, with an average chemical composition very similar to chromite from recent L chondrites. In most of the beds over this interval one finds 1-4 EC grains per kilogram rock, a clear two orders-of-magnitude enrichment relative to the lower part of the section. Small bed-by-bed variations in the EC content over the upper interval most likely reflect small variations in sedimentation rates. The Puxi River section contains only very rare terrestrial chrome spinel grains, which can be distinguished already by their rounded, abraded appearance compared to the angular, pristine extraterrestrial spinels. In the mid-Ordovician, based on paleoplate reconstructions, the Puxi River site was positioned at mid-latitudes on the southern hemisphere a couple of thousand kilometers east of the Swedish sites. The prominent enrichment of EC grains over the same stratigraphic interval in China and Sweden is supporting evidence for a dramatic increase in the flux of L-chondritic matter to Earth shortly after the disruption of the L-chondrite parent body in the asteroid belt. (C) 2010 Elsevier Inc. All rights reserved.
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46.
  • Cronholm, Anders, et al. (författare)
  • Extraterrestrial chromite in latest Maastrichtian and Paleocene pelagic limestone at Gubbio, Italy: The flux of unmelted ordinary chondrites
  • 2007
  • Ingår i: Meteoritics and Planetary Science. - 1086-9379. ; 42:12, s. 2099-2109
  • Tidskriftsartikel (refereegranskat)abstract
    • The distribution of sediment-dispersed extraterrestrial (ordinary chondritic) chromite (EC) grains (>63 pm) has been studied across the latest Maastrichtian and Paleocene in the Bottaccione Gorge section at Gubbio, Italy. This section is ideal for determining the accumulation rate of EC because of its condensed nature and well-constrained sedimentation rates. In a total of 210 kg of limestone representing eight samples of 14-28 kg distributed across 24 m of the Bottaccione section, only 6 EC grains were found (an average of 0.03 EC grains kg(-1)). In addition, one probable pallasitic chromite grain was found. No EC grains could be found in two samples at the Cretaceous-Tertiary (K-T) boundary, which is consistent with the K-T boundary impactor being a carbonaceous chondrite or comet low in chromite. The average influx of EC to Earth is calculated to similar to 0.26 grain m(-2) kyr(-1). This corresponds to a total flux of similar to 200 tons of extraterrestrial matter per year, compared to similar to 30,000 tons per year, as estimated from Os isotopes in deep-sea sediments. The difference is explained by the EC grains representing only unmelted ordinary chondritic matter, predominantly in the size range from similar to 0.1 mm to a few centimeters in diameter. Sedimentary EC grains can thus give important information on the extent to which micrometeorites and small meteorites survive the passage through the atmosphere. The average of 0.03 EC grain kg(-1) in the Gubbio limestone contrasts with the up to similar to 3 EC grains kg(-1) in mid-Ordovician limestone that formed after the disruption of the L chondrite parent body in the asteroid belt at similar to 470 Ma. The two types of limestone were deposited at about the same rate, and the difference in EC abundance gives support for an increase by two orders of magnitude in the flux of chondritic matter directly after the asteroid breakup.
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47.
  • Dypvik, H., et al. (författare)
  • Impact structures and events - a Nordic perspective
  • 2008
  • Ingår i: Episodes. - 0705-3797. ; 31:1:SI, s. 107-114
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in UndeterminedImpact cratering is one of the fundamental processes in the formation of the Earth and our planetary system, as reflected, for example in the surfaces of Mars and the Moon. The Earth has been covered by a comparable number of impact scars, but due to active geological processes, weathering, sea floor spreading etc, the number of preserved and recognized impact craters on the Earth are limited. The study of impact structures is consequently of great importance in our understanding of the formation of the Earth and the planets, and one way we directly, on the Earth, can study planetary geology.The Nordic-Baltic area have about thirty confirmed impact structures which makes it one of the most densely crater populated terrains on Earth. The high density of identified craters is due to the level of research activity, coupled with a deterministic view of what we look for. In spite of these results, many Nordic structures are poorly understood due to the lack of 3D-geophysical interpretations, isotopeor other dating efforts and better knowledge of the amount of erosion and subsequent tectonic modifications.The Nordic and Baltic impact community is closely collaborating in several impact-related projects and the many researchers (about forty) and PhD students (some seventeen) promise that this level will continue for many more years. The main topics of research include geological, geophysical, and geochemical studies in combination with modeling and impact experiments. Moreover, the Nordic and Baltic crust contains some hundred suspect structures which call for detailed analysis to define their origin.New advanced methods of analyzing geophysical information in combination with detailed geochemical analyses and numerical modeling will be the future basic occupation of the impact scientists of the region. The unique Cretaceous/Tertiary boundary (K-T) occurrences in Denmark form an important source of information in explaining one of the major mass extinctions on Earth.
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48.
  • Egger, H, et al. (författare)
  • Early Eocene climatic, volcanic, and biotic events in the northwestern Tethyan Untersberg section, Austria
  • 2005
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 217:3-4, s. 243-264
  • Tidskriftsartikel (refereegranskat)abstract
    • The 40 in thick Untersberg section (Salzburg, Austria) of the Northern Calcareous Alps comprises the Palaeocene-Eocene transition and spans the upper part of calcareous nannoplankton zone NP9 and the lower part of zone NP10 (subzone NP10a). These zones are equivalent to planktonic foraminifera zone P5 and the lower part of zone P6 (sub-zone P6a). The succession was deposited in a lower bathyal slope environment at a palaeodepth of about 2000 in. Within the dominantly marlstone succession, a 5.5-m-thick intercalation of red and green claystone and marly claystone represents the global negative carbon isotope excursion (CIE) which is used to recognize the Palaeocene-Eocene boundary. The CIE was associated with a shallowing of the calcite compensation depth by at least 1 km. Throughout the section, clay mineral assemblages are dominated by smectite, indicating a seasonal climate with alternating wet and dry conditions. A 49% increase in detrital quartz and feldspar within the CIE-interval suggests enhanced continental run-off This was probably the result of the establishment of a monsoonal setting, in which vegetation was sparse, while periodic high rainfall caused pronounced sediment transport. The increased terrestrially derived input is associated with abundant radiolarian casts indicating high primary productivity. This suggests that seasonal nutrient pulses resulting from intensified precipitation during the wet season have caused high surface-water fertility. The benthic foraminifera faunas of the samples rich in siliceous plankton are strongly dominated by Glomospira spp., Nuttalides truempyii, Abyssamina poagi, Anomalinoides praeacutus, Anomalinoides nobilis, and Oridorsalis spp. We assume that the Glomospira-Nuttalides fauna consists of opportunistic species which quickly react to seasonally varying amounts of food. The calcareous nannoplankton assemblage of the CIE-interval is characterized by the first occurrences of the genus Rhomboaster and of Discoaster araneus and Discoaster mahmoudii, whereas Scapholithus apertus become extinct at the Palaeocene-Eocene boundary. Within nannoplankton sub-zone NP10a, a series of primarily basaltic ashes give evidence for a major episode of explosive volcanism which can be correlated with the positive ash-series of the Fur-Formation in northern Denmark. The wide dispersal distance of the tephras implies Plinian-scale eruptions and multiple ejections of large volumes of pyroclastic material.
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49.
  • Egger, H., et al. (författare)
  • From shelf to abyss: Record of the Paleocene/Eocene-boundary in the Eastern Alps (Austria)
  • 2009
  • Ingår i: Geologica Acta. - 1695-6133. ; 7:1-2, s. 215-227
  • Tidskriftsartikel (refereegranskat)abstract
    • In the Eastern Alps (Austria) several marine successions, which were deposited ranging from shallow shelf to bathyal slope and abyssal basin, provide detailed records across the Paleocene/Eocene-boundary. These records indicate a two-step event starting with a prominent sea-level fall and followed by climatic changes. At the northern and southern shelves that fringed the Penninic Basin, the shallow-water sedimentary records are incomplete across the Paleocene/Eocene transition. Erosional surfaces indicate a major sea-level drop, which was terminated by an early Eocene (Ypresian) transgression within calcareous nannoplankton Zone NP12. As a proxy for the onset of this sea-level fall a strong increase in the terrestrially-derived input into the Penninic Basin can be used. The abyssal Anthering section from the northern part of the basin comprises a complete succession from NP9 to the upper part of NP10 (upper Thanetian-lower Ypresian). The thickest turbidite beds of this 250 m thick succession appear just before the carbon isotope event in the upper part of zone NP9, which is used to recognize the Paleocene/Eocene-boundary. A major lithological change from a sandstone-dominated facies to a claystone-dominated facies occurs at the onset of the carbon isotope event. This might be the result of a climatic change, resulting in increased intra-annual humidity gradients and increased physical erosion of the hinterland. Consequently, mainly fine-grained suspended material would have come into the basin and caused an increase in hemipelagic sedimentation rates by about a factor of 6. A similar value has been calculated for the bathyal Untersberg section, which was deposited on the southern slope of the basin, where an increased input of siliciclastic material is associated with a carbonate dissolution event during the carbon isotope event. At the southern shelf, a stratigraphic gap within the Gosau Group in the Krappfeld area (Carinthia) comprises the Maastrichtian and Paleocene. After a sea-level rise nummulitic marlstone and limestone were deposited in the lower part of zone NP12. Since the northern and southern shelves of the Penninic Basin belonged to different tectonic domains, with different potentials of crustal subsidence, the temporal similarity of sea-level changes on both shelves in the latest Paleocene and earliest Eocene suggests that these sea level fluctuations were mainly eustatic in origin.
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50.
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