Occurrences of group tops in wells
Elsewhere within the group thick local sandstones and conglomerates occur (Brennand and Siri, 1975), which are not given any formal status in this report. They are described from the Magnus area by De' Ath and Schuyleman (1981) and from the Brae area by Harms et al. (1980, 1981).
The name "Humber Group" was first proposed by Rhys (1974) for the Middle-Late Jurassic claystones in the Southern North Sea. Deegan and Scull (1977) extended the usage to the Northern North Sea where three formations were recognised, namely the Heather, Kimmeridge Clay and Piper Formations. The Piper Formation is restricted to the area around the Piper Field, while the two other formations are widely distributed.
Recognition of three Middle Jurassic to earliest Cretaceous "claystone" formations in the Central Graben area, none of which can alone be referred to the Heather Formation has led us to restrict the Heather Formation to the part of the North Sea north of 58°N (e.g. Ofstad 1983, and this report). We have further recommended restriction of the term "Kimmeridge Clay Formation" to the area south of the Mid-North Sea High and its replacement by local nomenclature in both the Central Graben and the Northern North Sea (see "Remarks" on the Draupne Formation).
The differences in mode of subdivision which exist between the Northern North Sea, the Central Graben and the type area of
the Southern North Sea would, perhaps, not alone constitute grounds for replacement of the Humber Group with more localized
group names. However, there is a major conceptual difference between the northern and southern Norwegian North Sea in the way
the "group" is defined. In the north, the practise of Deegan and Scull of including the marginal sands (e.g. Piper Formation)
in the group has been continued with units such as the Sognefjord Formation. In the south it was found to be practical and convenient to separate out the marginal sands as the Vestland Group. This suggested to the subcommittees the desirability of erecting locally defined units (Viking and Tyne Groups) to replace the Humber Group, a term which was in any case becoming unwieldy and virtually a synonym for the Upper Jurassic. We nevertheless recognise the unifying concept of an "Upper Jurassic claystone" suite throughout the North Sea, reflecting the general transgressive nature of the epoch. This overall character could perhaps be expressed as a "Humber Supergroup", although we have not for the present made this a formal proposal.