Integrated Quantitative Calcareous Plankton Bio-Magnetostratigraphy of the Early Miocene from IODP Leg 342, Hole U1406A, Newfoundland Ridge, NW Atlantic Ocean

Abstract

High-resolution quantitative analyses of the planktonic foraminifera and calcareous nannofossil content have been carried out on IODP Leg 342, Hole U1406A (Northwest Atlantic Ocean) in the core interval 10H2–2H4, plotting the abundance distributions of the biostratigraphically and quantitatively most significant species. Qualitative analyses have been used to identify the precise depth of marker bioevents. For almost the whole succession, relevant magnetostratigraphic data were provided by previous studies. All chrons and subchrons in the interval C6Cn–C6AAr were recognised in core interval 10H2–4H1 and calibrated to the GPTS 2012, but no magnetostratigraphic data are available for the highest portion (above 35 m). The investigated succession falls between Sphenolithus delphix FO (First Occurrence)—uppermost Chattian bioevent—in core 10H2 and the Sphenolithus belemnos LO (Last Occurrence)–Burdigalian bioevent – in core 2H5, embracing the Zone O7 (uppermost part)–M3 foraminiferal zone interval and the Zone CNO6– CNM5 calcareous nannofossil zone interval. A calcareous plankton biochronological framework has been produced integrating calcareous plankton and magnetostratigraphic data. Calculated ages for the most significant recognised bioevents are S. delphix FO 23.35 Ma, S. delphix LO 23.02 Ma, Paragloborotalia kugleri FO 23.00 Ma, Globoquadrina dehiscens FO 22.59 Ma, Sphenolitus disbelemnos FO 22.56 Ma, Helicosphaera carteri FCO (First Common Occurrence) 22.18 Ma, P. kugleri LO 21.23 Ma. Two hiatuses have been recognised within core 4H, whereas only one was recognised in previous studies. The first one in core 4H5 spans the interval 21.17–19.01 Ma and coincides with a phosphate-rich layer; the second in core 4H2 spans the interval from 18.87 to 18.21 Ma and corresponds to a glauconite-rich layer. The results obtained from Hole U1406A allow some considerations about potential reference bioevents concerning the still open issue of Burdigalian GSSP (Global Stratotype Section and Point).