updated to follow: Stratigraphic Guide to the Cromer Knoll, Shetland and Chalk Groups of the North Sea and Norwegian Sea. Felix M. Gradstein & Colin C. Waters (editors), Mike Charnock, Dirk Munsterman, Michelle Hollerbach, Harald Brunstad, Øyvind Hammer & Luis Vergara (contributors). Newsletter on Stratigraphy, vol 49/1 pp71-280, 2016
Cromer Knoll Group
Ran was the wife of the sea god Gir in Norse mythology. She liked to drag sailors down to the depths with her net.
The colour of the sandstones ranges from white to light grey, green and brown to reddish-brown. The sandstones are generally argillaceous, sometimes calcareous and glauconitic, and usually do not represent potential reservoir rocks in these wells.
The gross sandstone thickness varies from a few metres up to approximately 100 m. The gross thickness in the reference wells are 48 m (2/7-15), 16 m (7/3-1) and 35 m (17/11-2). Up to 130 m (gross) of Aptian-Albian sandstone sequences are penetrated in block 16/27 in the UK Sector (see Remarks below).
The upper boundary can usually be identified as an upward increase in the gamma-ray readings (Figure 22 in Isaksen & Tonstad (1989)) and generally by a slight decrease in the sonic velocity as it passes up into Rødby Formation.
The various sandstone bodies may be in stratigrapic contact with the Åsgard, Tuxen, Sola and Rødby Formations (Figures 4, 7, 8 and 9 in Isaksen & Tonstad (1989)). Their lower boundaries are generally defined as the base of an upward decrease in the gamma-ray response when passing into the sandstone units (Figures 22 and 23 of Isaksen & Tonstad (1989)).The gamma-ray readings in the calcareous marlstones and chalks of the Tuxen Formation, especially its upper part, and the Mime Formation may be similar to those in the sandstones. The velocity curve is often less suitable, for defining the lower boundary.
Hesjedal & Hamar (1983) recognised scattered sandstone sequences, which they described as the Kopervik and Klepp Formations in the Central Trough and Norwegian-Danish Basin, and the Florø Formation in the Agat Field in blocks 35/3 and 36/1. The Kopervik and Klepp Formations are here described as the Ran Member. Since the units consist of several isolated sandstone bodies they should not have been given formation status; also, the names did not conform with existing recommendations. The Florø Formation is formally defined as the Agat Formation in this study.
In the UK Sector (the Andrew Field), just south of the Andrew Ridge and Fladen Ground Spur (Figure 4.2), Aptian-Albian sandstone bodies (Bosun Sandstone Member) are encountered in many wells, among others UK wells 16/27-1 and 16/27a-2 (100-130 m gross), 16/28-1 (50 m gross) and 16/28-6 (90 m gross). The Devil's Hole Sandstone Member (UK well 29/25-1) and the Scapa Sandstone Member (UK well 14/20-5) in the UK Sector are comparable to the Ran Member.