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

Karen Dybkjær,Erik Skovbjerg Rasmussen

doi:10.1144/jm.26.1.1

Abstract

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.

Highlights

The Global Stratotype Section and Point (GSSP) for the base of the Neogene System, and for the Oligocene–Miocene boundary, is defined in the Lemme–Carrosio section in northern Italy (Steininger et al, 1997)
The purpose of the present study is: (1) to document the dinocyst assemblages in an expanded Upper Oligocene–Lower Miocene succession in the eastern North Sea Basin, exemplified by the Frida-1 Well; (2) to testify the age of the sequences defined onshore and the proposed hiati by correlating the onshore succession with the stratigraphically more complete succession in Frida-1; (3) to subdivide the succession in Frida-1 using the sequence stratigraphic model defined onshore; and (4) to try to locate the Mi-1 glaciation event and the Oligocene–Miocene boundary within the succession in the Danish North Sea sector
The Frida-1 Well, located in the basinal parts of the eastern North Sea Basin, penetrates an unusually thick (>800 m) and probably complete succession spanning the Upper Oligocene– Lower Miocene, comprising marine sediments deposited in a basinal setting

Summary

Introduction

The Global Stratotype Section and Point (GSSP) for the base of the Neogene System, and for the Oligocene–Miocene boundary, is defined in the Lemme–Carrosio section in northern Italy (Steininger et al, 1997). The final ratification of the GSSP in 1996 initiated a series of studies The understanding of the Upper Oligocene–Lower Miocene succession onshore Denmark, in Jylland (Fig. 1) has improved considerably during the last couple of years due to a series of new boreholes, new seismic data and studies of outcrops. A sequence stratigraphic model (Dybkjær, 2004a; Rasmussen, 2004a; Rasmussen & Dybkjær, 2005) has been built up by correlating a number of boreholes and outcrops, using a combination of organic-walled dinoflagellate cyst (dinocyst) stratigraphy, log correlations and a few seismic lines. The model indicates the presence of several minor and major hiati and the dating of the stratigraphically incomplete succession is somewhat problematic in places

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