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
The Wick Sandstone Formation was proposed by Johnson & Lott (1993) for a thick unit of mass-flow sandstones, interbedded with siltstones and mudstones, in the Inner Moray Firth. These strata were not included in the formal nomenclature of Deegan & Scull (1977), although they were informally assigned to the ‘Valhall Formation’ or as the ‘Wick Member of the Valhall Formation’ in some oil company reports. ‘Devil's Hole Formation’ was used as an informal term in the Beatrice Field by Stevens (1991) for sandstones present between the Kimmeridge Clay and Valhall formations.
From the Caithness town on the northeast coast of Scotland.
The Wick Sandstone Formation comprises mainly sandstones with interbedded siltstones and mudstones. The sandstones are very fine- to coarse-grained, pebbly, generally poorly consolidated, locally argillaceous and poorly sorted. They are pale grey to grey brown, dominantly quartz sandstones. Glauconite grains, carbonaceous debris and lignite are widespread and calcareous concretions are common (Johnson & Lott, 1993).
The Mudstones and siltstones are similar to those of the Valhall Formation. They are generally calcareous, medium to dark grey, occasionally pale grey, grey-brown, red-brown and grey-green. They are micromicaceous, pyritic, glauconitic and blocky. Sporadic, thin, white to tan, argillaceous, microcrystalline limestones occur.
The Wick Sandstone Formation is thickest on the downthrown side of the Wick Fault, with 1400 m recorded in 13/11-1 (Johnson & Lott, 1993).
The Wick Sandstone Formation is present in the Inner Moray Firth and extreme northwestern margins of the Halibut Shelf and Halibut Horst (North Sea Quadrants 11-14 and 17). It is limited to the north by the Wick Fault.
|13/12-1: 1045.5-2144 m (3430-7034ft)||Lat. 58º 31’ 51”N||Long. 01º 44’ 26”W|
The top of the formation is usually taken at a downward change from argillaceous lithologies (Carrack Formation) to sandstones with interbedded siltstones and mudstones (Wick Sandstone Formation). It does not necessarily coincide with the top of the highest thin sandstone in the Cromer Knoll Group, but is placed at the top of the sandstone-rich section. Where the Wick Sandstone Formation is divisible into members a vertical succession of up to three formation tops are possible where strata of the Carrack or Valhall formations overlie the sandstone of the three members (Johnson & Lott, 1993).Where the formation is undivided or where the Captain Sandstone Member (the highest member) is present, the top is normally taken at a downward change from dark grey, non-calcareous to slightly calcareous, low-velocity mudstone (Carrack Formation) to sandstones and interbedded mudstones (e.g. Well 12/30-1 and 13/11-1, Johnson & Lott, 1993). Locally, however, the Captain's Member is overlain by the Valhall Formation (e.g. Well 13/13-1 and 13/14-1, Johnson & Lott, 1993). Where the Captain Sandstone Member is absent, the Valhall Formation rests on the Wick Sandstone Formation (e.g. Well 13/29-2, Johnson & Lott, 1993).
The Wick Sandstone Formation displays both blocky and serrated signatures on wireline logs, reflecting the massive sandstones units and thinly interbedded sandstones and mudstones units, respectively. Calcareous concretions give high velocity spikes on wireline logs. On wireline logs the lower boundary is marked by a downward increase in average gamma-ray values and a decrease in average velocity and the upper boundary is taken at a sharp downward decrease in gamma-ray values and an increase in velocity (Johnson & Lott, 1993).
The microbiotas in the proximal area may be abundant compared to those in the distal parts of the unit (Johnson & Lott, 1993). Calcareous nannofossils are found throughout and the following biomarkers have been identified: Micrantholithus hoschulzii / Micrantholithus obtusus and Rhagodiscus asper (acme), Nannoconus abundans, N. borealis, Stradnerlithus comptus, Tegulalithus septentrionalis, Tegulalithus septentrionalis (acme), Cruciellipsis cuvillier, Corolithion silvaradion, Eprolithus antiquus, Micrantholithus speetonensis, Sollasites arcuatus and Nannoconus sp. (discs) (Johnson & Lott, 1993). Dinoflagellate cyst biomarkers include Subtilisphaera perlucida, Cerbia tabulate, Ctenidodinium elegantulum, Heslertonia heslertonensis, Hystrichodinium ramoides, Batioladinium longicornutum, Pseudoceratium anaphrissum, Kleithriasphaeridium corrugatum, Hystrichodinium furcatum, Canningia duxburyi, Nematosphaeropsis scala, Batioladinium varigranosum, Lagenorhytis delicatula, Tubotuberella apatela, Endoscrinium pharo and Dingodinium spinosum (Johnson & Lott, 1993). Foraminifera are often patchily distributed and reworking is a problem in some cases. Biomarkers that have been recognized include Globigerinelloides gyroidinaeformis, Verneuilinoides chapmani, Hedbergella infracretacea, Gavellinella barremiana, Falsogaudryinella moesiana and Trocholina infragranulata.
Boote & Gustav (1987) interpreted Lower Cretaceous sandstones in the Inner Moray Firth as laterally extensive turbidites that were largely unconfined by fault topography within the rift. On the basis of the benthic fauna present in the mudstones, Linsley et al. (1980) suggested that the Valanginian sandstones in the Beatrice Field (Block 11/30) were deposited in moderately deep water marine channels. In contrast, Bird et al. (1987) used seismic profiles to delineate a mound-shaped, southwest-trending, fault-controlled, Lower Cretaceous channel deposit in the Beatrice Field and postulated that this broadened to the southwest into a fan-delta.