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  • 1. Ge, Rongfeng
    et al.
    Wilde, Simon
    Nemchin, Alexander
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bellucci, Jeremy
    Swedish Museum of Natural History, Department of Geology.
    Erickson, Timmons
    Frew, Adam
    Thern, Eric
    A 4463 Ma apparent zircon age from the Jack Hills (Western Australia) resulting from ancient Pb mobilization2018In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, no 4, p. 303-306Article in journal (Refereed)
    Abstract [en]

    Hadean (≥4.0 Ga) zircon grains provide the only direct record of the first half-billion years of Earth’s history. Determining accurate and precise crystallization ages of these ancient zircons is a prerequisite for any interpretation of crustal evolution, surface environment, and geodynamics on the early Earth, but this may be compromised by mobilization of radiogenic Pb due to subsequent thermal overprinting. Here we report a detrital zircon from the Jack Hills (Western Australia) with 4486–4425 Ma concordant ion microprobe ages that yield a concordia age of 4463 ± 17 Ma (2σ), the oldest zircon age recorded from Earth. However, scanning ion imaging reveals that this >4.4 Ga apparent age resulted from incorporation of micrometer-scale patches of unsupported radiogenic Pb with extremely high 207Pb/206Pb ratios and >4.5 Ga 207Pb/206Pb ages. Isotopic modeling demonstrates that these patches likely resulted from redistribution of radiogenic Pb in a ca. 4.3 Ga zircon during a ca. 3.8 Ga or older event. This highlights that even a concordia age can be spurious and should be carefully evaluated before being interpreted as the crystallization age of ancient zircon.

  • 2.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Balz, B.S
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon.2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, p. 431-434Article in journal (Refereed)
    Abstract [en]

    Constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of Earth’s very early crust and Hadean geodynamics. Previous applications of the Ti-in-zircon thermometer to >4 Ga zircons have identified a population with relatively low crystallization temperatures () of ~685 °C. This could possibly indicate wet minimum-melting conditions producing granitic melts, implying very different Hadean terrestrial geology from other rocky planets. Here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated Sudbury impact melt sheet. The new zircon Ti contents and corresponding  fully overlap with those of the Hadean zircon population. Previous studies, which measured Ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true Ti content. It is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low  in zircons from the most evolved rocks. On Earth, melt sheet

  • 3.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kamber, B.S.
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon: Reply2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, article id e399Article in journal (Refereed)
  • 4.
    Kiel, Steffen
    Swedish Museum of Natural History, Department of Paleobiology.
    Using network analysis to trace the evolution of biogeography through geologic time: A case study2017In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 45, p. 711-714Article in journal (Refereed)
    Abstract [en]

    The biogeographic distribution of organisms has continuously changed through Earth’s

    history as plate tectonics changed the configurations of land masses, ocean basins, and climate

    zones. Yet, methods to investigate this dynamic through geologic time are limited. Here,

    network analysis is used to explore and to visualize the biogeographic history of brachiopods

    through the entire Triassic period. Many previously recognized biogeographic provinces are

    found, and in addition, the stratigraphic ranges of these provinces were identified. Provinces

    in the Tethys Ocean show the lowest degree of connectedness, which can be linked to higher

    evolutionary rates in this tropical ocean basin and possibly also to higher habitat heterogeneity.

    Stratigraphically, the Tethyan provinces are separated largely along the boundaries of

    the Early, Middle, and Late Triassic. This suggests that the events resulting in faunal changes

    among the index fossils used to define these sub-periods also affected the brachiopods. However,

    through the ~50 m.y. of the Triassic period, geographic proximity played a greater role

    in producing faunal similarity than proximity in geologic age. Thus network analysis is a

    viable tool to better understand the dynamic evolution of biogeography through geologic time.

  • 5.
    Kiel, Steffen
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Krystyn, Leopold
    Department of Palaeontology, Vienna University, 1090 Vienna, Austria.
    Demirtaş, Ferdi
    Department of Geological Engineering, Akdeniz University, 07058 Antalya, Turkey.
    Koşun, Erdal
    Department of Geological Engineering, Akdeniz University, 07058 Antalya, Turkey.
    Peckmann, Jörn
    Institute for Geology, Universität Hamburg, 20146 Hamburg, Germany.
    Late Triassic mollusk-dominated hydrocarbon-seep deposits from Turkey2017In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, p. 751-754Article in journal (Refereed)
    Abstract [en]

    Deep-sea hydrothermal vents and hydrocarbon seeps host unique ecosystems relying on geochemical energy rather than photosynthesis. Whereas the fossil and evolutionary history of these ecosystems is increasingly well known from the Cretaceous onward, their earlier history remains poorly understood and brachiopods are considered to have played a dominant role during the Paleozoic and Mesozoic. Here we report five new hydrocarbon-seep deposits from the Upper Triassic Kasımlar shales in southern Turkey. The pyritiferous seep limestones predominantly consist of 13C-depleted micrite with δ13C values as low as −10.4‰, and contain only sparse 13C-depleted rim cement (δ13C as low as −12.0‰), interpreted to result from the recrystallization of banded and botryoidal crystal aggregates of fibrous cement. The geologic ages of the studied seep deposits were determined as late Carnian and early Norian using conodonts. The associated fauna is dominated by modiomorphid and anomalodesmatan bivalves, and also includes a diversity of gastropods and the dimerelloid brachiopod Halorella. These faunal assemblages allow a comparison between seep faunas from the two major Triassic ocean basins—the present assemblages being from Tethys, and the only previously known examples being from eastern Panthalassa—and indicate that a cosmopolitan, seep-restricted fauna as in the present-day oceans has existed since the Late Triassic. With almost 20 species, the seep fauna of the Kasımlar shales approaches the diversity of Cretaceous to present-day seep faunas, further emphasizing the ecological similarity of seep faunas since the early Mesozoic. Our findings also highlight that brachiopods and bivalves had a more complex history of coexistence at seeps than currently appreciated.

  • 6.
    Mays, Chris
    et al.
    Swedish Museum of Natural History, Department of Paleobiology. Monash University.
    Cantrill, David
    Royal Botanic Gardens Victoria, Private Bag 2000, South Yarra, VIC 3141, Australia.
    Bevitt, Joseph J.
    Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.
    Polar wildfires and conifer serotiny during the Cretaceous globalhothouse2017In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 45, no 12, p. 1119-1122Article in journal (Refereed)
    Abstract [en]

    Several highly effective fire-adaptive traits first evolved among modern plants duringthe mid-Cretaceous, in response to the widespread wildfires promoted by anomalously highatmospheric oxygen (O2) and extreme temperatures. Serotiny, or long-term canopy seedstorage, is a fire-adaptive strategy common among plants living in fire-prone areas today,but evidence of this strategy has been lacking from the fossil record. Deposits of abundantfossil charcoal from sedimentary successions of the Chatham Islands, New Zealand, recordwildfires in the south polar regions (75°–80°S) during the mid-Cretaceous (ca. 99–90 Ma).Newly discovered fossil conifer reproductive structures were consistently associated withthese charcoal-rich deposits. The morphology and internal anatomy as revealed by neutrontomography exhibit a range of serotiny-associated characters. Numerous related fossils fromsimilar, contemporaneous deposits of the Northern Hemisphere suggest that serotiny was akey adaptive strategy during the high-fire world of the Cretaceous.

  • 7.
    Renne, Paul R
    et al.
    Berkeley Geochronology Center, Berkeley, California 94709, USA.
    Arenillas, Ignacio
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Arz, José A.
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Vajda, Vivi
    Swedish Museum of Natural History, Department of Paleobiology. Department of Geology, Lund University, Sweden.
    Gilabert, Vicente
    Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Universidad de Zaragoza, E-50009 Zaragoza, Spain.
    Bermúdez, Hermann D
    Grupo de Investigación Paleoexplorer, St. George, Vermont 05495, USA.
    Multi-proxy record of the Chicxulub impact at the Cretaceous-Paleogene boundary from Gorgonilla Island, Colombia2018In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, p. 547-550Article in journal (Refereed)
    Abstract [en]

    A 40 m stratigraphic section at Gorgonilla Island, Colombia, provides a unique deepmarine, low-latitude, Southern Hemisphere record of events related to the end-Cretaceous Chicxulub impact and the global Cretaceous/Paleogene boundary (KPB). The KPB is marked by a 20-mm-thick, densely packed spherule bed as defined by planktic foraminifera, in contrast to complex relationships found in high-energy, impact-proximal sites in the Gulf of Mexico and Caribbean basins. The absence of basal Danian foraminiferal Zone P0 may indicate a possible hiatus of <10 ka immediately above the spherule bed, but is most probably an artifact of deposition below the calcite compensation depth as suggested by the nearly complete absence of calcareous fossils for 20 m below the Zone Pα. A weighted mean 40Ar/39Ar age of 66.051 ± 0.031 Ma for 25 fresh glassy spherules unequivocally establishes both their derivation from Chicxulub, and the association between the impact and the KPB. The spherule bed, and Maastrichtian strata below it, display soft-sediment deformation features consistent with strong seismic motion, suggesting that seismic activity in the immediate aftermath of the Chicxulub impact continued for weeks. We discovered a fern-spike immediately above the spherule bed, representing the first record of this pioneer vegetation from the South American continent, and from a low-latitude (tropical) environment.

  • 8. Smit, Matthijs
    et al.
    Ratschbacher, Lothar
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Stearns, Michael
    Early evolution of the Pamir deep crust from Lu-Hf and U-Pb geochronology and garnet thermometry2014In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, no 12, p. 1047-1050Article in journal (Refereed)
    Abstract [en]

    Determining early orogenic processes within the Pamir-Tibet orogen represents a critical step toward constructing a comprehensive model on the tectonic evolution of the region. Here we investigate the timing and cause of prograde metamorphism of Cenozoic metamorphic rocks from the Pamir plateau through Lu-Hf geochronology, U-Pb rutile thermochronology, and garnet thermometry. Regional prograde metamorphism and heating to 750–830 °C, as constrained by thermometry, occurred between 37 and 27 Ma. Prograde growth of garnet first occurred in the South Pamir and spread to the Central Pamir during the following 10 m.y. The early metamorphism is attributed to high mantle heat flow following the ca. 45 Ma break-off of the Indian slab south of the Pamir. Our investigation confirms a long-lived thermal history of the Pamir deep crust before the Miocene, and provides a causal link between break-off, enhanced mantle heat flow, and prograde heating of the subduction hanging wall.

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