Identification and characterisation of the Oligocene–Miocene boundary (base Neogene) in the eastern North Sea Basin — based on dinocyst stratigraphy, micropalaeontology and δ13C-isotope data

Abstract

For the first time a combined palynological and δ13C-isotope study has identified the Oligocene–Miocene boundary — and thus the base of the Neogene — within the North Sea Basin. The type section, the Lemme–Carrosio section in northern Italy, is correlated with the Frida-1 well in the eastern (Danish) part of the North Sea Basin using a combination of data from a previous dinocyst stratigraphic study and new δ13C-isotope data. The results show that the Oligocene–Miocene boundary is located at a depth of 1440m in the Frida-1 well. The Frida-1 δ13C-isotope curve further reflects the Mi-1 glaciation event also recorded in the Lemme–Carrosio section.The dinocyst events bracketing the boundary in Frida-1 are; the last occurrence (LO) of Distatodinium biffii at 1630m, below the boundary, the LO of Chiropteridium spp. at 1370m and first occurrence (FO) of Ectosphaeropsis burdigalensis at 1330m, both above the boundary. An influx of Deflandrea phosphoritica is found in an interval immediately below the boundary (1532–1490m), while the genus Homotryblium occurs abundantly in a broader interval (1650–1330m) encompassing the boundary.Hitherto unpublished data combined with new data provide a series of stratigraphically important nanno- and micropalaeontological events that frame/characterise the Oligocene–Miocene boundary within the North Sea Basin; an almost monospecific assemblage of Reticulofenestra bisecta at 1630m, the LO of Elphidium subnodosum at 1625m, the LO of Aulacodiscus insignis quadrata (Diatom sp. 3 of King, 1983) at 1610m, the LO of Karreriella seigliei at 1580m and the LO of Pararotalia canui at 1570m, all below the boundary, and the FO of Aulacodiscus aemulans (Diatom sp. 5 of King, 1983) at 1410m and the LO of Aulacodiscus aemulans at 1250m, both above the boundary.The dinocyst, nanno- and micropalaeontological studies thus provide a series of bioevents and abundance variations which can be used to locate and to correlate the Oligocene–Miocene boundary within the eastern North Sea Basin more precisely than was previously possible.