Geochronology and paleothermometry of Neogene sediments from the Voering Plateau using Sr, C and O isotopes

The Neogene sediments from DSDP site 341 on the Voering Plateau, Norwegian Sea, contain a thin glauconitic pellet-bearing subunit, which separates underlying pelagic clays from overlying glacial-marine sediments. Oxygen isotope measurements of benthic foraminifera show a delta18O shift of +1per mille during deposition of this subunit, probably a combined effect of a drop in bottom water temperature and a rise in sea water delta18O. The chronology of this sedimentological and O isotope transition is, however, poorly constrained by fossil evidence. Rb-Sr dating of glauconitic pellets indicates that the lower part of the glauconitic subunit was deposited 11.6+-0.2 Ma ago. Further geochronological evidence, derived from the Sr and C isotopic compositions of foraminifera compared with known seawater-time variations, indicates that the lower pelagic clays are early to middle Miocene, deposited at a mean rate of proportional15 m/Ma. The glauconitic subunit contains part of the middle Miocene and probably all of the late Miocene in a condensed sequence with a very low mean depositonal rate (proportional0.2 m/Ma). The overlying glacial marine sediments are probably Pliocene, with a high mean rate of deposition, proportional45 m/Ma. This is the first application of C, O and Sr isotopic stratigraphy combined with Rb-Sr dating of glauconitic minerals, and it illustrates the applications of this integrated approach in geochronology. (orig.)