A new stratigraphic framework for the Miocene – Lower Pliocene deposits offshore Scandinavia: A multiscale approach

• Published in: Geological journal (Chichester, England) Vol. 56; no. 3; pp. 1699 - 1725
• Main Authors: Dybkjær, Karen, Rasmussen, Erik Skovbjerg, Eidvin, Tor, Grøsfjeld, Kari, Riis, Fridtjof, Piasecki, Stefan, Śliwińska, Kasia K.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.03.2021; Wiley Subscription Services, Inc
• Subjects: Continental shelves; Correlation; Cysts; Dinoflagellate cyst zonation; Dinoflagellates; Ecological succession; Eustatic changes; Miocene; Molo Formation; Multiscale analysis; Neogene; North Sea; Norwegian Sea shelf; Offshore; Oligocene; Palynology; Pleistocene; Pliocene; Seismic data; sequence stratigraphy; Stratigraphy; Unconformity; Zonation; Norwegian Sea; North Sea
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.3982

Here, we present an updated stratigraphic subdivision of the Oligocene to Pleistocene succession (880–610 m) in the newly proposed type well for the Molo Formation, the industrial 6407/9‐5 well, located on the continental shelf in the eastern Norwegian Sea. Furthermore, new data from the Danish North Sea wells Nora‐1, Vagn‐2, and Tove‐1 are presented. The studied succession in the 6407/9‐5 well is composed of five sedimentary units separated by hiati. The dating of these five units is based on correlation to the stratigraphically more complete Neogene succession in the (Danish) central North Sea area. In this study, a robust stratigraphic framework of these five units, based on a combination of dinoflagellate cysts (dinocyst) stratigraphy and seismic data, is established. The Oligocene succession is referred to the NSO zonation of Van Simaeys et al., Review of Palaeobotany and Palynology, 2005, 134, 105–128, while the Miocene–Pliocene succession is referred to the dinocyst zonation of Dybkjær and Piasecki, Review of Palaeobotany and Palynology, 2010, 161, 1–29. In well 6407/9‐5 the two lowermost units, located below the Molo Formation, comprise a Rupelian (Lower Oligocene) succession up to 803 m, and an Aquitanian/Burdigalian (Lower Miocene) succession from 803 to 787 m, respectively. Both of these units are referred to the Brygge Formation. The Molo Formation is separated from the underlying Brygge Formation by an unconformity. Furthermore, and in contrast to previous studies, our study shows that the Molo Formation (787–703 m) has an unconformity within it. The lower part of the formation (787–724 m) is dated to late Tortonian (Late Miocene), and referred to the Hystrichosphaeropsis obscura dinocyst Zone. The upper part (724–703 m) is dated to Zanclean (Early Pliocene), and referred to the Melitasphaeridium choanophorum dinocyst Zone. The uppermost unit studied (703–670 m) in the well is referred to the Gelasian (Lower Pleistocene) and is included in the Naust Formation. The regional correlation of this stratigraphy with the complete succession in the Danish North Sea reveals that the hiati found in the Miocene succession on the Norwegian Sea shelf are controlled by tectonism, while the internal depositional patterns of the Molo Formation were controlled by eustatic sea‐level changes. A multiscale stratigraphic framework (combined dinocyst stratigraphy, sequence stratigraphy, and seismic stratigraphy) for the Neogene succession in the Danish North Sea area is presented. Based on this framework, an updated stratigraphic subdivision of the more fragmentary Neogene succession in the well 6407/9‐5 (Norwegian Sea shelf), proposed as the type well for the Molo Formation, is presented. The Molo Formation in the 6407/9‐5 well consists of two units separated by an unconformity; a late Tortonian (Late Miocene) unit referred to the Hystrichosphaeropsis obscura dinocyst Zone from 787 to 724 m and a Zanclean (Early Pliocene) unit referred to the Melitasphaeridium choanophorum dinocyst Zone from 724 to 703 m.