Tyne Group (new)
(From NPD Bulletin no. 3)
Name
From the River Tyne in north-eastern England. It includes sediments
formerly assigned to the Humber Group by Deegan and Scull (1977).
For further discussion, see "remarks" under the
Viking Group.
Type area
The group is found in the Central Graben and the Southern Vestland Arch.
Its northern limit is defined approximately by 58° N. The Tyne Group is
illustrated in the Norwegian sector by wells
2/7-3 (Phillips)
and 7/12-2 (BP).
Thickness
The Tyne Group is thickest in the axial regions of the Central Graben,
where more than 800 m of the group have been penetrated. The group thins,
locally to only a few metres, over intrabasinal highs and the Southern
Vestland Arch.
The thicknesses in the above selected wells are 839 m (2/7-3) and 116.5 m
(7/12-2).
Lithology
Claystone is the dominant lithology of the Tyne Group sediments. These range
in colour from grey to brownish black and contain frequent silty, sandy and
calcareous horizons. The Tyne Group also includes a thicker, discrete sand
unit occuring locally in the Central Graben which is named the
Eldfisk Formation.
Boundaries
In wells situated in the axial portion of the Central Graben the base of the
Tyne Group is not penetrated except where the group is underlain by diapiric
Zechstein salt (e.g. 2/7-3). On the south-western flank of the Southern
Vestland Arch the Tyne Group overlies sands of the the
Vestland Group or may locally rest with unconformity
on Triassic or Lower Jurassic sediments. In most cases the lower boundary is
marked by a downward break to lower gamma ray and generally higher sonic
log velocities.
The upper boundary is picked where the exceptionally high gamma ray response
and low sonic velocity of the Mandal Formation
(the uppermost formation of the group) gives way to the lower gamma ray,
and higher sonic velocity values of the Lower Cretaceous Cromer Knoll Group.
Distribution
The Tyne Group is distributed throughout the Central Graben and over the
Southern Vestland Arch. It passes northwards (in the Viking Graben) into
the Viking Group. Due to the overall transgressive
nature of the unit the higher formations of the group are more widely
distributed.
Age
The group ranges in age from Callovian to Ryazanian.
Subdivision
Four formations are recognised within the Tyne Group, namely the
Haugesund, Eldfisk,
Farsund and Mandal
Formations. The lowermost is the Haugesund Formation, which is generally
overlain by the Farsund Formation. Locally in the Central Graben the two
formations are separated by the Eldfisk Formation. The uppermost and most
widespread unit is the Mandal Formation.
