A revised lithostratigraphic scheme for the Eocene to Pleistocene succession on the Norwegian continental shelf

Abstract

Introduction and backgroundA formal lithostratigraphic nomenclature of the pre-Permian to the upper Miocene/lower Pliocene for the central and northern North Sea was published by Deegan & Scull (1977). A revision of the Cretaceous and Cenozoic parts of the nomenclature was established by Isaksen & Tonstad (1989). Dalland et al. (1988) introduced a lithostratigraphic nomenclature for the Triassic to Quaternary of the mid-and northern Norwegian continental shelf. A "Lithostratigraphy of the Paleogene-lower Neogene succession of the Danish North Sea" was published by Schiøler et al. (2007). Subsequently, Gradstein et al. (2010) have published an informal lithostratigraphic nomenclature for the Mesozoic and Cenozoic of the North Sea, Norwegian Sea, Barents Sea and Svalbard (stratigraphic database). However, they introduced no new formal lithostratigraphic units. The present publication presents a revision of the Eocene to Pleistocene lithostratigraphies of Isaksen & Tonstad (1989) and Dalland et al. (1988; see Figs. 1 and 2) for the Norwegian central and northern North Sea, the Norwegian Sea and the western part of the Barents Sea.When drilling exploration wells, the petroleum companies commonly sample the Eocene to Pleistocene sediments with drill cuttings. Generally, the post-Eocene deposits have been far less sampled and investigated than the older sediments, which have been the main target for hydrocarbon exploration. The sampling programme is usually considerably less dense than in the deeper sections, e.g., every ten metres compared to every three metres in reservoirs. Only a small number of wells have been sampled with sidewall cores and short conventional cores, and the number of cored shallow stratigraphic boreholes covering the Eocene to Pleistocene is limited. The conventional cores are used mainly for geotechnical investigations. Contracted biostratigraphical consultants usually execute routine investigations. However, the samples are commonly investigated with large spacing and limited effort

The Molo Formation and its ‘impossible’ correlation to the time-equivalent Kai Formation explained by strong coastal currents and occasional margin collapse

“…The exact age of the Molo Formation as well as the stratigraphic relationship between Kai, Molo and the Naust formations have been a subject of discussion since the time when the formation was first described. Eidvin et al (1998) placed it in the Oligocene based on palynomorphs from sidewall cores and drill cuttings, whereas Henriksen & Weimer (1996) placed it in the Lower Pliocene based on sequence-stratigraphic reasoning. A similar approach was made by Henriksen et al (2005) and .…”

“…A similar approach was made by Henriksen et al (2005) and . Eidvin et al (2007) gave a late Miocene to early Pliocene age to the Molo Formation mainly based on foraminiferal and dinoflagellate cysts correlation and Sr-isotope stratigraphy in well 6407/9-5 in the distal southwestern part of the Molo Formation. They suggested that the recorded Oligocene microfossils in well 6610/3-1 were reworked.…”

“…No new biostratigraphic and Sr-isotope datings were provided by Eidvin et al (2014), however they suggested that the Oligocene microfossils in well 6610/3-1 were not reworked and based on regional consideration they inferred that the Molo Formation started its progradation in the Oligocene and maintained a more or less continuous progradation throughout the Miocene and into the Lower Pliocene. These authors also view the Molo and Kai formations as time-equivalent deposits and proximal and distal parts of the same depositional system, respectively (Eidvin et al, 2007(Eidvin et al, , 2014. Løseth at al.…”

Simulations of the effect of smectite‐to‐illite transition in shales on permeability and overpressures using a stochastic approach, a Norwegian margin case study

“…The Brygge Formation of Early Eocene to Early Miocene age is deposited over most of the Halten Terrace and Dønna Terrace, in a mainly marine environment. On the Halten Terrace, it consists mostly of clay, while out in the Møre and Vøring basin, it consists mostly of ooze deposits (Chand et al, 2011; Eidvin et al, 2007). The fine‐grained sediments of the Kai Formation (Middle Miocene to Lower Pliocene) overlie the mid‐Miocene unconformity (Eidvin et al, 2007).…”

“…On the Halten Terrace, it consists mostly of clay, while out in the Møre and Vøring basin, it consists mostly of ooze deposits (Chand et al, 2011; Eidvin et al, 2007). The fine‐grained sediments of the Kai Formation (Middle Miocene to Lower Pliocene) overlie the mid‐Miocene unconformity (Eidvin et al, 2007). Depositional environment was generally marine, with sediments deposited on the outer and middle part of the margin.…”