Integrated biomagnetochronology for the Palaeogene of ODP Hole 647A: implications for correlating palaeoceanographic events from high to low latitudes
J. V. Firth, J. S. Eldrett, I. C. Harding, H. K. Coxall, B. S. Wade, 2013. "Integrated biomagnetochronology for the Palaeogene of ODP Hole 647A: implications for correlating palaeoceanographic events from high to low latitudes", Magnetic Methods and the Timing of Geological Processes, L. Jovane, E. Herrero-Bervera, L.A. Hinnov, B. Housen
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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 δ18O 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.
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 http://www.geolsoc.org.uk/SUP18546.
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Magnetostratigraphy is best known as a technique that employs correlation among different stratigraphic sections using the magnetic directions defining geomagnetic polarity reversals as marker horizons. The ages of the polarity reversals provide common tie points among the sections, allowing accurate time correlation. Recently, studies of magnetic methods and the timing of geological processes have acquired a broader meaning, now referring to many types of magnetic measurements within a stratigraphic sequence. Many of these measurements provide correlation and age control not only for the older and younger boundaries of a polarity interval, but also within intervals. Thus, magnetostratigraphy no longer represents a dating tool based only on geomagnetic polarity reversals, but comprises a set of techniques that includes measurements of geomagnetic field parameters, environmental magnetism, rock-magnetic properties, radiometric dating and astronomically forced palaeoclimatic change recorded in sedimentary rocks, and key corrections to magnetic directions related to geodynamics, palaeocurrents, tectonics and diagenetic processes.