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      Integrated biomagnetochronology for the Palaeogene of ODP Hole 647A: implications for correlating palaeoceanographic events from high to low latitudes

      1 , 2 , 3 , 4 , 5 , 6
      Geological Society, London, Special Publications
      Geological Society of London

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          Abstract

          Lower Eocene to Oligocene microfossil-rich hemipelagic sediments in ODP Hole 647A, southern Labrador Sea, provide a strategic section for resolving the early history of high North Atlantic climates and ocean circulation, and for correlating with carbonate-poor lower Cenozoic sediments in the Arctic and Nordic seas. Our new, integrated palaeomagneto- and multigroup biostratigraphy (63 dinoflagellate cyst, calcareous nannofossil, planktonic foraminifer and diatom datums) significantly improves Site 647 chronostratigraphy and provides a framework for future studies. This new age model, coupled with provisional δ 18O analyses, provides greater confidence in the location of significant ocean-climate events at this site, including the Eocene–Oligocene transition and the Middle Eocene Climatic Optimum. Early Eocene hyperthermals may also be present near the base of the section. Palaeomagnetic age control is significantly improved in the Eocene, but not in the Oligocene. Revised estimates of sedimentation and biogenic flux indicate changes in supply and preservation that may be climatically controlled. A Lower to Middle Eocene hiatus is more precisely constrained, with a c. 4 million year duration. Age and depth errors quantify the age uncertainties throughout the section. Our revised age model will play an important role in stratigraphic correlation between very high latitude and lower latitude sites.

          Supplementary material:

          All tables with ages and age-derived calculations based on the Gradstein et al. (2004) timescale used herein are reproduced as supplementary tables using both the Gradstein et al. (2004) and the Cande & Kent (1995) timescales (Tables DS1–DS6). Discrete sample and shipboard pass-through cryomagnetometer palaeomagnetic data, planktonic foraminifer and fine fraction (<20 µm) stable isotope data, raw and processed core GRA density data, and specifications and results of GRA density spectral analyses are also provided as supplementary tables (Tables DS7–DS11). These tables are available at www.geolsoc.org.uk/SUP18546.

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          The least-squares line and plane and the analysis of palaeomagnetic data

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            A REVISED CENOZOIC GEOCHRONOLOGY AND CHRONOSTRATIGRAPHY

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              Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean.

              The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth. At present, this depth is approximately 4,500 m, with some variation between and within ocean basins. The calcite compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate. Geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (approximately 34 million years ago) when significant permanent ice sheets first appeared on Antarctica, but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning, by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.
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                Author and article information

                Journal
                Geological Society, London, Special Publications
                Geological Society, London, Special Publications
                Geological Society of London
                0305-8719
                2041-4927
                July 02 2013
                2013
                2013
                October 01 2012
                : 373
                : 1
                : 29-78
                Affiliations
                [1 ]Integrated Ocean Drilling Program, 1000 Discovery Drive, College Station, TX 77845, USA
                [2 ]Shell Exploration and Production Inc., 3737 Bellaire Boulevard, PO Box 481, Houston, TX 77001-0481, USA
                [3 ]University of Southampton, National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK
                [4 ]School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, UK
                [5 ]Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
                [6 ]Present address: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
                Article
                10.1144/SP373.9
                e624443d-0fdf-4a69-870a-8385b87938a2
                © 2012
                History

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