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  • 1.
    Nemchin, A.A.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Humayun, M.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Hewins, R.H.
    Lorand, J.-P.
    Kennedy, A.
    Grange, M.
    Zanda, B.
    Fieni, C.
    Deldicque, D.
    Record of the ancient martian hydrosphere and atmosphere preserved in zircon from a martian meteorite2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, p. 638-642Article in journal (Refereed)
    Abstract [en]

    Mars exhibits ample evidence for an ancient surfacehydrosphere. The oxygen isotope compositions of carbonateminerals and alteration products in martian meteoritessuggest that this ancient hydrosphere was not in isotopicequilibrium with the martian lithosphere1–4. Martian meteoriteNWA 7533 is composed of regolith breccia from the heavilycratered terrains of ancient Mars and contains zircon grainsfor which U–Pb ages have been reported5. Here we reportvariations between the oxygen isotopic compositions offour zircon grains from NWA 7533. We propose that thesevariations can be explained if the mantle melts from whichthe zircon crystallized approximately 4.43Gyr ago hadassimiliated 17O-enriched regolith materials, and that someof the zircon grains, while in a metamict state, were lateraltered by low-temperature fluids near the surface less than1.7Gyr ago. Enrichment of the martian regolith in 17O beforethe zircon crystallized, presumably through exchange withthe 17O-enriched atmosphere or hydrosphere during surfacealteration, suggests that the thick primary atmosphere ofMars was lost within the first 120Myr after accretion. Weconclude that the observed variation of 17O anomalies in zirconfrom NWA 7533 points to prolonged interaction between themartian regolith, atmosphere and hydrosphere.

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  • 2.
    Slater, Sam M
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Twitchett, Richard J.
    The Natural History Museum, London.
    Danise, Silvia
    Università degli Studi di Firenze.
    Vajda, Vivi
    Swedish Museum of Natural History, Department of Paleobiology. Department of Geology, Lund University, Sweden.
    Substantial vegetation response to Early Jurassicglobal warming with impacts on oceanic anoxia2019In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 12, p. 462-467Article in journal (Refereed)
    Abstract [en]

    Rapid global warming and oceanic oxygen deficiency during the Early Jurassic Toarcian Oceanic Anoxic Event at around 183 Ma is associated with a major turnover of marine biota linked to volcanic activity. The impact of the event on land-based ecosystems and the processes that led to oceanic anoxia remain poorly understood. Here we present analyses of spore–pollen assemblages from Pliensbachian–Toarcian rock samples that record marked changes on land during the Toarcian Oceanic Anoxic Event. Vegetation shifted from a high-diversity mixture of conifers, seed ferns, wet-adapted ferns and lycophytes to a low-diversity assemblage dominated by cheirolepid conifers, cycads and Cerebropollenites-producers, which were able to survive in warm, drought-like conditions. Despite the rapid recovery of floras after Toarcian global warming, the overall community composition remained notably different after the event. In shelf seas, eutrophication continued throughout the Toarcian event. This is reflected in the overwhelming dominance of algae, which contributed to reduced oxygen conditions and to a marked decline in dinoflagellates. The substantial initial vegetation response across the Pliensbachian/Toarcian boundary compared with the relatively minor marine response highlights that the impacts of the early stages of volcanogenic global warming were more severe for continental ecosystems than marine ecosystems.

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