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  • 1
    Publication Date: 2016-04-15
    Description: The impact of an asteroid at the end of the Cretaceous caused mass extinctions in the oceans. A rapid collapse in surface to deep-ocean carbon isotope gradients suggests that transfer of organic matter to the deep sea via the biological pump was severely perturbed. However, this view has been challenged by the survival of deep-sea benthic organisms dependent on surface-derived food and uncertainties regarding isotopic fractionation in planktic foraminifera used as tracers. Here we present new stable carbon ( 13 C) and oxygen ( 18 O) isotope data measured on carefully selected planktic and benthic foraminifera from an orbitally dated deep-sea sequence in the southeast Atlantic. Our approach uniquely combines 18 O evidence for habitat depth of foraminiferal tracer species with species-specific 13 C eco-adjustments, and compares isotopic patterns with corresponding benthic assemblage data. Our results show that changes in ocean circulation and foraminiferal vital effects contribute to but cannot explain all of the observed collapse in surface to deep-ocean foraminiferal 13 C gradient. We conclude that the biological pump was weakened as a consequence of marine extinctions, but less severely and for a shorter duration (maximum of 1.77 m.y.) than has previously been suggested.
    Keywords: GSA Open Access Journal Content
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 2
    Publication Date: 2017-04-04
    Description: We present a new Danian correlation framework between the land-based Zumaia and Sopelana sections from the Basque Basin and marine-based sections drilled during ODP Legs 198 (Shatsky Rise, North Pacific) and 208 (Walvis Ridge, South Atlantic) that reconciles magnetostratigraphy and the short and long eccentricity cycle patterns among the records. A new whole-rock d13C isotope record at Zumaia is compared to that of Site 1262. This allows the question of whether the Danian consists of 10 or 11 consecutive 405-kyr eccentricity cycles to be tested. The new consistent stratigraphic framework enables accurate estimates to be made of ages for magnetostratigraphic boundaries, bioevents, and sedimentation rates. Low sedimentation rates appear common in all records in the mid-Danian interval along the upper part of chron C28n, including conspicuous condensed intervals in some of the oceanic records that in the past have hampered the proper identification of cycles. Notably, we challenge the correlation to the Pacific Sites 1209–1210 that were offset by as much as one 405-kyr cycle in previous interpretations (i.e., the Fasciculithus spp. LO, which approximates the Danian–Selandian boundary, and the TC27n event were at odds between oceans in the interpretation of Hilgen et al. 2010). Finally, we envisage that the Zumaia section, which already hosts the Selandian GSSP, could serve as the global Danian stratotype.
    Description: Published
    Description: Lisbona
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: restricted
    Keywords: Orbital tuning ; Magnetostratigraphy ; Cyclostratigraphy ; ODP ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Extended abstract
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