Organic-walled dinoflagellate cyst stratigraphy in an expanded Oligocene–Miocene boundary section in the eastern North Sea Basin (Frida-1 Well, Denmark) and correlation from basinal to marginal areas

Abstract. The organic-walled dinoflagellate cyst (dinocyst) assemblages in an unusually thick (>800m) Oligocene–Miocene boundary succession from the eastern North Sea Basin (the Frida-1 Well) were studied. Six successive dinocyst assemblages are described: the Wetzeliella gochtii Assemblage (early Chattian), the Distatodinium biffii Assemblage (Chattian), the Deflandrea phosphoritica Assemblage (latest Chattian), the Homotryblium spp. Assemblage (early Aquitanian), the Caligodinium amiculum Assemblage (Aquitanian) and the Cordosphaeridium cantharellus Assemblage (latest Aquitanian to early Burdigalian). The dinocyst assemblages are compared with informal dinocyst zonations proposed for the southern North Sea Basin (Germany, Belgium and the Netherlands).

A correlation of the expanded basinal succession in Frida-1 with the marginal marine succession found onshore Jylland, based on the dinocyst stratigraphy combined with well logs and seismic data, is proposed. This correlation confirms earlier proposed datings of the onshore deposits and the presence of several hiati. Furthermore, the correlation made it possible to subdivide the succession in Frida-1 into the sequences A–C, as defined onshore. The Mi-1 glaciation event and thus the Oligocene–Miocene boundary are proposed to correlate to the boundary between sequences A and B.