Benton, M.J., Cook, E. & Turner, P. 2002. Permian and Triassic Red Beds and the Penarth Group of Great Britain. Geological Conservation Review Series, No. 24, JNCC, Peterborough, ISBN 1 86 107 493 X. The original source material for these web pages has been made available by the JNCC under the Open Government Licence 3.0. Full details in the JNCC Open Data Policy
Colwick railway section, Nottinghamshire
Introduction
This site shows the Sherwood Sandstone–Mercia Mudstone group boundary with the Sneinton Formation, a unit of mudstones, siltstones, and thin sandstones arranged in fining-upwards units, resting unconformably on the Nottingham Castle Formation. Sedimentary structures present include ripple marks, wavy bedding, pseudomorphs after halite, and abundant desiccation cracks and suggest a marine intertidal depositional environment. The age of the formation is probably Anisian, and it correlates with other former 'Waterstones' units across Central England. The locality illustrates aspects of the initial Mercia Mudstone Group sedimentation in eastern England.
Key references on the Sneinton Formation include Irving (1874), Lamplugh et al. (1908), Smith (1910, 1912), Swinnerton (1918), Elliott (1961), Smith and Warrington (1971), Charsley (1989), and Lowe et al. (1990).
Description
This site is a cliff alongside a working railway, and access is restricted. The western end of the cliff lies a few metres from the tracks, but the central section is close to the tracks; the eastern end of the section is lower than the rest.
The Colwick railway section is close to the type locality for the 'Colwick Formation' (a quarry at
In the railway section some 23 m of the Sneinton Formation are exposed, overlying the Nottingham Castle Formation. The beds generally dip 30° to the ESE. Charsley (1989) gives a detailed section, reproduced in Lowe et al. (1990), which is summarized here:
| Thickness (m) | |
| Sneinton Formation | |
| Sandstone units, yellow-brown and yellow, very fine-grained, with subordinate, red-brown, silty mudstones | 2.76 |
| Succession of yellow, fine-grained sandstone units, each 0.2–1.1 m thick, ripple marks in the lowest sandstone unit | c. 6.70 |
| Gap | c. 2.45 |
| Sandstone– mudstone couplet, resting on an erosion surface and grading up from a pale orange, fine- to medium-grained sandstone, with dominantly rounded grains, red-brown mud flakes, through a very fine-grained, pale yellow to red-brown sandstone interbedded with red-brown mudstone, and terminating in a dark red-brown silty mudstone | c. 3.00 |
| Mudstone, red-brown and grey-green, silty, with subordinate green-yellow sandstone and siltstone laminae | 4.10 |
| Sandstone, yellow, very fine-grained, with red-brown mudstone partings, and, at the base, subangular to sub-rounded pebbles and overlying an erosion surface in places | 1.24 |
| Nottingham Castle Formation | |
| Sandstone, pale yellow and pale red-brown, fine- to medium-grained, with rare pebbles | 2.45 |
Elliott (1961) reported a range of sedimentary structures in the Sneinton Formation in the Colwick railway section and neighbouring locations; these include parallel bedding planes, ripple-marks in micaceous fine-grained sandstones and siltstones, mudcracks, and pseudomorphs after halite. Fossils from the Colwick area include remains of fishes, vertebrate tracks, and a cast of a possible Equisetites (horsetail) stem from Colwick Wood (although the latter may be an artefact, Elliott, 1961, p. 216). In some locations, the Sneinton Formation sediments are dolomitized and contain gypsum.
Interpretation
The Sneinton Formation sediments indicate intertidal conditions, with terrestrial input, but with strong indications of marine influence (pseudomorphs after halite and, farther north, (Rose and Kent, 1955) the brachiopod Lingula). The dolomitization and the occurrence of gypsum confirm marine influence, and provide important links eastwards to the Dowsing Formation, a lateral equivalent of the German Muschelkalk in. the SNSB (Rhys, 1974;
The Sneinton Formation is dated as Anisian on the basis of palynological evidence from surrounding areas, and from cross-country correlations using geophysical marker horizons (Warrington et al., 1980). The unit had long been treated as part of the 'Lower Keuper Sandstones', and was formerly equated with the German Upper Triassic succession, although Irving (1874, p. 317) was remarkably prescient when he noted, with respect to the Waterstones' at Colwick and around Nottingham: 'May not these be homotaxial with part of the Muschelkalk?'.
Conclusions
The Colwick railway section provides a good exposure in the lowest formation of the Mercia Mudstone Group in the Nottingham area and shows its contact with the Sherwood Sandstone Group. Colwick is the type location for the Sneinton Formation, a unit of fine-grained sandstones and mudstones, that was deposited in intertidal, marginal marine environments. The site is important for an understanding of part of the stratigraphy of the western part of the Southern North Sea Basin, and the palaeogeography of the region.