Viser treff 241-260 av 729

    • Evolution of ultrapotassic volcanism on the Kaapvaal craton: deepening the orangeite versus lamproite debate 

      Tappe, Sebastian; Shaikh, Azhar M.; Wilson, Allan H.; Stracke, Andreas (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-02)
      Orangeites are a significant source of diamonds, yet ambiguity surrounds their status among groups of mantle-derived potassic rocks. This study reports mineralogical and geochemical data for a c. 140 Ma orangeite dyke swarm that intersects the Bushveld Complex on the Kaapvaal craton in South Africa. The dykes comprise distinctive petrographic varieties that are linked principally by olivine ...
    • Proximal to distal grain-size distribution of basin-floor lobes: A study from the Battfjellet Formation, Central Tertiary Basin, Svalbard 

      Spychala, Yvonne T.; Ramaaker, Thymen A. B.; Eggenhuisen, Joris T.; Grundvåg, Sten-Andreas; Pohl, Florian; Wróblewska, Sara (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-09)
      The grain-size distribution of sediment particles is an important aspect of the architecture of submarine fans and lobes. It governs depositional sand quality and reflects distribution of particulate organic carbon and pollutants. Documenting the grain-size distribution of these deep-marine sedimentary bodies can also offer us an insight into the flows that deposited them. Submarine lobes ...
    • Rapid Atlantification along the Fram Strait at the beginning of the 20th century 

      Tesi, Tommaso; Muschitiello, Francesco; Mollenhauer, Gesine; Miserocchi, Stefano; Langone, Leonardo; Ceccarelli, Chiara; Panieri, Giuliana; Chiggiato, Jacopo; Nogarotto, Alessio; Hefter, Jens; Ingrosso, Gianmarco; Giglio, Federico; Giordano, Patrizia; Capotondi, Lucilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-24)
      The recent expansion of Atlantic waters into the Arctic Ocean represents undisputable evidence of the rapid changes occurring in this region. Understanding the past variability of this “Atlantification” is thus crucial in providing a longer perspective on the modern Arctic changes. Here, we reconstruct the history of Atlantification along the eastern Fram Strait during the past 800 years using ...
    • Putative fossils of chemotrophic microbes preserved in seep carbonates from Vestnesa Ridge, off northwest Svalbard, Norway 

      Himmler, Tobias; Cremiere, Antoine; Birgel, Daniel; Wirth, Richard; Orphan, Victoria J.; Kirsimae, Kalle; Knies, Jochen; Peckmann, Jörn; Lepland, Aivo (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-20)
      The microbial key players at methane seeps are methanotrophic archaea and sulfate-reducing bacteria. They form spherical aggregates and jointly mediate the sulfate-dependent anaerobic oxidation of methane (SD–AOM: CH4 + SO42– → HCO3– + HS– + H2O), thereby inducing the precipitation of authigenic seep carbonates. While seep carbonates constitute valuable archives for molecular fossils of SD–AOM-mediating ...
    • Sources and sinks of methane in sea ice: Insights from stable isotopes 

      Jacques, Caroline; Sapart, Celia J.; Fripiat, François; Carnat, Gauthier; Zhou, Jiayun; Delille, Bruno; Röckmann, Thomas; van der Veen, Carina; Niemann, Helge; Haskell, Tim; Tison, Jean-Louis (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-27)
      We report on methane (CH<sub>4)</sub> stable isotope (d<sup>13</sup>C and d<sup>2</sup> H) measurements from landfast sea ice collected near Barrow (Utqiagvik, Alaska) and Cape Evans (Antarctica) over the winter-to-spring transition. These measurements provide novel insights into pathways of CH<sub>4</sub> production and consumption in sea ice. We found substantial differences between the two ...
    • Microstructure and fluid flow in the vicinity of basin bounding faults in rifts – The Dombjerg Fault, NE Greenland rift system 

      Salomon, Eric; Rotevatn, Atle; Kristensen, Thomas Berg; Grundvåg, Sten-Andreas; Henstra, Gijs Allard (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-14)
      Faults commonly form loci for high fluid flux in sedimentary basins, where fluids, rocks and deformation processes frequently interact. Here, we elucidate the interaction of fluid flow, diagenesis and deformation near basin-bounding faults in sedimentary basins through a study in the vicinity (0–3.5 km) of the Dombjerg Fault in the NE Greenland rift system. Due to fault-controlled fluid circulation, ...
    • Distinct methane-dependent biogeochemical states in Arctic seafloor gas hydrate mounds 

      Klasek, Scott A.; Hong, Wei-Li; Torres, Marta E.; Ross, Stella; Hostetler, Katelyn; Portnov, Alexey; Gründger, Friederike; Colwell, Frederick S. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-02)
      Archaea mediating anaerobic methane oxidation are key in preventing methane produced in marine sediments from reaching the hydrosphere; however, a complete understanding of how microbial communities in natural settings respond to changes in the flux of methane remains largely uncharacterized. We investigate microbial communities in gas hydrate-bearing seafloor mounds at Storfjordrenna, offshore ...
    • The origin of driftwood on eastern and south-western Svalbard 

      Linderholm, Hans W.; Gunnarson, Björn E.; Fuentes, Mauricio; Büntgen, Ulf; Hormes, Anne (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-02)
      The Arctic is one of the regions where the effect of global change is most evident. Associated with warming are changes in snow, sea ice and hydroclimate, all which have significant impacts on environments and society. However, due to short observational records, it is difficult to set the current climate in a long-term context. Arctic driftwood (DW), available throughout the Holocene, is a paleoclimate ...
    • The Storfjorden, Svalbard, earthquake sequence 2008-2020: Transtensional tectonics in an arctic intraplate region 

      Ottemöller, Lars; Kim, Won-Young; Waldhauser, Felix; Tjåland, Norunn; Dallmann, Winfried (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-12)
      An earthquake sequence in the Storfjorden offshore area southwest of Spitsbergen in the Svalbard archipelago initiated with a 21 February 2008 magnitude <i><b>M</i></b><sub><b>w</sub></b> 6.1 event. This area had previously not produced any significant earthquakes, but between 2008 and 2020, a total of ∼<b>2800</b> earthquakes were detected, with ∼<b>16</b> of them being of moderate size ...
    • Distribution and Abundances of Planktic Foraminifera and Shelled Pteropods During the Polar Night in the Sea-Ice Covered Northern Barents Sea 

      Zamelczyk, Katarzyna; Fransson, Agneta; Chierici, Melissa; Jones, Elizabeth Marie; Meilland, Julie; Anglada-Ortiz, Griselda; Hodal Lødemel, Helene (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-22)
      Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ...
    • Microbial activity, methane production, and carbon storage in Early Holocene North Sea peats 

      Lippmann, Tanya J. R.; 't Zandt, Michiel H. in; Van der Putten, Nathalie N. L.; Busschers, Freek S.; Hijma, Marc P.; van der Velden, Pieter; de Groot, Tim; van Aalderen, Zicarlo; Meisel, Ove H.; Slomp, Caroline P.; Niemann, Helge; Jetten, Mike S. M.; Dolman, Han A. J.; Welte, Cornelia U. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-11)
      <p>Northern latitude peatlands act as important carbon sources and sinks, but little is known about the greenhouse gas (GHG) budgets of peatlands that were submerged beneath the North Sea during the last glacial–interglacial transition. <p>We found that whilst peat formation was diachronous, commencing between 13 680 and 8360 calibrated years before the present, stratigraphic layering and local ...
    • The Billefjorden Fault Zone north of Spitsbergen: a major terrane boundary? 

      Koehl, Jean-Baptiste P.; Allaart, Lis (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-13)
      The Billefjorden Fault Zone is a major terrane boundary in the Norwegian Arctic. The fault separates basement rocks of Svalbard’s north-eastern and north-western terranes that recorded discrete Precambrian tectonothermal histories and were accreted, intensely deformed and metamorphosed during the Caledonian Orogeny. Although the fault represents a major, crustal-scale tectonic boundary, its north-ward ...
    • Teaching with digital geology in the high Arctic: opportunities and challenges 

      Senger, Kim; Betlem, Peter; Grundvåg, Sten-Andreas; Horota, Rafael Kenji; Buckley, Simon John; Smyrak-Sikora, Aleksandra; Jochmann, Malte Michel; Birchall, Thomas; Janocha, Julian; Ogata, Kei; Kuckero, Lilith; Johannessen, Rakul Maria; Lecomte, Isabelle Christine; Cohen, Sarah M.; Olaussen, Snorre (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-28)
      <p>The Covid-19 pandemic occurred at a time of major revolution in the geosciences – the era of digital geology. Digital outcrop models (DOMs) acquired from consumer drones, processed using user-friendly photogrammetric software and shared with the wider audience through online platforms are a cornerstone of this digital geological revolution. Integration of DOMs with other geoscientific data, such ...
    • The role of Ediacaran synkinematic anatectic rocks and the late-orogenic charnockitic rocks in the development of the hot Araçuaí belt 

      Cavalcante, Carolina; Meira, Vinicius T.; Magalhães, Nivea; Hollanda, Maria Helena B.M.; Oliveira, Eurídice (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-13)
      The orogenic evolution of the hot Araçuaí belt is characterized by continuous magmatic activity, with magmas of different compositions recording a long-lived (∼630 to ∼530 Ma) tectono-thermal evolution in response to convergence between the Congo and São Francisco continents during the West Gondwana amalgamation. Geochemical data from the Carlos Chagas domain (CCD) and the Nova Venécia Complex (NVC), ...
    • Linking facies variations, organic carbon richness and bulk bitumen content – A case study of the organic-rich Middle Triassic shales from eastern Svalbard 

      Wesenlund, Fredrik; Grundvåg, Sten-Andreas; Engelschiøn, Victoria Sjøholt; Thießen, Olaf; Pedersen, Jon Halvard (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-03)
      The organic-rich shales of the Middle Triassic Botneheia Formation in Svalbard and its correlative units offshore are considered important source rock intervals for oil and gas generation in the Norwegian Barents Shelf region. Detailed investigation of these intervals is essential to better understand the intra source rock variations and thus to improve exploration models. As source rocks are rarely ...
    • Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico 

      Portnov, Alexey; Cook, A.E.; Vadakkepuliyambatta, Sunil (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-12)
      In marine basins, gas hydrate systems are usually identified by a bottom simulating reflection (BSR) that parallels the seafloor and coincides with the base of the gas hydrate stability zone (GHSZ). We present a newly discovered gas hydrate system, Moby-Dick, located in the Ship Basin in the northern Gulf of Mexico. In the seismic data, we observe a channel-levee complex with a consistent phase ...
    • Glacial and environmental changes in northern Svalbard over the last 16.3 ka inferred from neodymium isotopes 

      Jang, Kwangchul; Ahn, Youngkyu; Joe, Young Jin; Braun, Carmen; Joo, Young Ji; Kim, Jung-Hyun; Bayon, Germain; Forwick, Matthias; Vogt, Christoph; Nam, Seung-Il (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-05)
      The reconstruction of past ice sheet extents and dynamics in polar regions is essential for understanding the global climate system and obtaining more reliable predictions of future climate change. Here, we present a multi-proxy dataset integrating the Nd isotopic compositions (εNd) of paired detrital and authigenic Fe oxide fractions, grain size distributions, organic geochemistry, and mineral ...
    • Resistivity of reservoir sandstones and organic rich shales on the Barents Shelf: Implications for interpreting CSEM data 

      Senger, Kim; Birchall, Thomas; Betlem, Peter; Ogata, Kei; Ohm, Sverre Ekrene; Olaussen, Snorre; Paulsen, Renate Strugstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-03)
      Marine controlled source electromagnetic (CSEM) data have been utilized in the past decade during petroleum exploration of the Barents Shelf, particularly for de-risking the highly porous sandstone reservoirs of the Upper Triassic to Middle Jurassic Realgrunnen Subgroup. In this contribution we compare the resistivity response from CSEM data to resistivity from wireline logs in both water- and ...
    • Crystal rotations and alignment in spatially varying magma flows: 2-D examples of common subvolcanic flow geometries 

      Vachon, Remi Elie Celestin; Bazargan, Mohsen; Hieronymus, Christoph F.; Ronchin, Erika; Almqvist, Bjarne (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-31)
      Elongate inclusions immersed in a viscous fluid generally rotate at a rate that is different from the local angular velocity of the flow. Often, a net alignment of the inclusions develops, and the resulting shape preferred orientation of the particle ensemble can then be used as a strain marker that allows reconstruction of the fluid’s velocity field. Much of the previous work on the dynamics of ...
    • Enhanced Arctic stratification in a warming scenario: Evidence from the mid pliocene warm Pperiod 

      Behera, Padmasini; Tiwari, Manish; Knies, Jochen (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-10)
      Global warming is most pronounced in the Arctic as evident from the massive sea ice loss during the past few decades. The Mid-Pliocene Warm Period (MPWP), 3.264 – 3.025 million years ago with similar CO2 levels, is the nearest analogue for understanding the impacts of future global warming. High-resolution studies of relative nutrient utilization and productivity from the Atlantic-Arctic Gateway ...