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 term Spilsby Sandstone Formation was introduced by Rhys (1974) for a unit of fine grained marine sandstones that lay between the Speeton Clay Formation (Cretaceous: now renamed Valhall Formation) calcareous mudstones above and Kimmeridge Clay Formation (Jurassic) variably calcareous mudstones below.
From the village of Spilsby in Lincolnshire (Rhys 1974).
The formation is generally thin (<50 m) over most of its subcrop area of the Southern North Sea but thickens substantially along the western margin of the Sole Pit Inversion (Dowsing Fault zone) to >250 m (e.g. 53/2-5, Lott & Knox, 1994). Onshore, the formation has a maximum thickness of 200 m on the East Midlands Shelf and onto the Anglo-Brabant Massif (Cameron et al., 1992).
The Spilsby Sandstone Formation is largely restricted to the southwestern margins of the Southern North Sea basin over the East Midlands Shelf and onto the northern flank of the London-Brabant Massif. Isolated occurrences of basal Cretaceous sandstones have been proved further eastwards in wells 50/16-1 and 54/1-2 (Lott & Knox, 1994).
WGS84 coordinates: Lat. 53º 15’ 39.5”N Long. 01º 22’35”E (Rhys, 1974, pp. 79, fig. 7, table 5)
UTM zone: 31
Drilling operator name: BP Exploration Operating Company Limited
Completion date: 28.01.1968
Status: P & A
Interval of type section & thickness in type well: 417-435 m (13681427ft- amended depths by Lott & Knox, 1994)
|Southern North Sea (Lott & Knox, 1994)|
|14/17a-2: 661-792 m (21702600ft)
48/23-1: 769-905.5 m (25232971ft)
53/2-5: 836-1104 m (27443622ft)
|Lat. 53º 24’ 35.90”N
Lat. 53º 12’ 57”N
Lat. 52º 52’ 58.193”N
|Long. 01º 22’31.19”E
Long. 01º 3’ 03”E
Long. 02º 14’ 27.706”E
The upper boundary of the Spilsby Sandstone Formation is defined by a marked downward change from calcareous mudstone of the Valhall Formation to sandstone lithologies (Lott & Knox, 1994).
Biostratigraphic data suggests that the lower part of the formation may span the Jurassic/Cretaceous boundary, as occurs in the equivalent onshore sandstone sequences of eastern England (Lott & Knox, 1994). The Spilsby Sandstone Formation yields variably abundant dinoflagellate cyst assemblages. The Rotosphaeropsis thula biomarker occurs within the formation (Lott & Knox, 1994).
The Spilsby Sandstone Formation equates, at least in part, with the sandy Spilsby and Sandringham formations of eastern England (Rawson et al. 1978) which range from Tithonian (Ryazanian) to Valanginian in age. In the UK Sector of the Central North Sea area partly equivalent basal Cretaceous sandstone developments are termed the Devil's Hole Sandstone Member of the Valhall Formation (Johnson & Lott 1993).
The Spilsby Sandstone Formation was deposited on the southern fringes of a well-oxygenated shallow marine shelf (Cameron et al., 1992; Lott & Knox, 1994).
An informal subdivision into two units is possible with the lower unit (SP1) containing more mudstone interbeds than the upper, massive sandstone interval (SP2) (e.g. 48/17a-2, Lott & Knox, 1994).