8th International Nannoplankton Association Conference


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David Jutson, K. Dybkjær:
Composite biostratigraphy of the Ryazanian - Hauterivian succession in the Iris-1 (5604/30b1) well, Danish Sector, North Sea

The Iris-1 well from the Tail End Graben, a subbasin of the Danish Central Graben, is one of the few wells in this area to have been drilled in a basinal setting. The well penetrated a thick interval of marine claystones and sandy claystones of Ryazanian to Hauterivian age (Biozones BC1-BC8 of Rutledge & Bown in Bown et al., 1998), including a Lower Valanginian section of 960'. An Upper Valanginian section was identified in the original description of this well but this was not encountered in this work, there being an unconformity with Lower Hauterivian lying directly over Lower Valanginian. The interval investigated represents the lower part of the Valhall Formation, as described by Jensen et al. (1986).

A three-discipline biostratigraphic analysis (nannofossils, palynology and microfauna) has been undertaken on the Ryazanian to Hauterivian succession in order to produce a composite biostratigraphy which has affinities to schemes from both England and northern Germany. The analysis also showed that there was significant reworking of material into the basin due to downslope movement, probably small turbidites.


Bown, P., Rutledge, D., Crux, J.A. & Gallagher, L.T. 1998. Lower Cretaceous. In: P. Bown (Ed.). Calcareous Nannofossil Biostratigraphy. Chapman & Hall: 86-131.

Jensen, T.F., Holm, L., Frandsen, N., & Michelsen, O. 1986. Jurassic-Lower Cretaceous lithostratigraphic nomenclature for the Danish Central Trough. Geological Survey of Denmark (DGU) Series A, Nr.12: 65pp.


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