WAJ Rutter (UK) and HC Costigan (UK)
This article is about the geology and geomorphology of the Levisham Bottoms and Newtondale area of Yorkshire. This is an interesting strip of virtually level land, which forms a shelf at about 150m above sea level, between Levisham Moor and the bottom of Newtondale. It is a fascinating geological region that allows a visitor to see exposures of Middle Jurassic rocks and Quaternary deposits from the Ice Age, together with examples of interesting glacial geomorphology. There are many noteworthy features, including features within the solid bedrock indicating the depositional environment of the Middle Jurassic strata, and the drift geology of ice-age deposits, including erratics. The aim of this article is to allow the reader to understand the geological processes and features at this locality.
The strata of Levisham Bottoms comprises of Middle Jurassic, fluvio-deltaic rocks and Upper Jurassic marine deposits. The beds dip at an angle of approximately 5° due south, and contain no faulting, folds or crush zones (Robinson, 2010). The bedrock geology of the area is detailed in the table accompanying this article. The topography has been created primarily by quaternary glacial and post glacial Devensian activity.
The environment in the Middle Jurassic consisted of a large river delta flowing into the Cleveland Basin, bound to the north by the Mid-North Sea High, and to the west by the Pennine High (van-Konijnenburg-van Cittert and Morgans, 1999; Powell, 2010) and was comparable to the size of the modern Nile or Mississippi deltas.
The Middle Jurassic deposits of the valley include the Moor Grit Member (Scalby Formation, Ravenscar Group), which might only occur in the area as a post glacial erratic; while the bedded deposits at the base of the valley are made up of the Long Nab Member (Scalby Formation, Ravenscar Group). The Moor Grit rocks contain only fossils of pollen and spores (microfossils), and are therefore sparsely fossiliferous (Fisher and Hancock, 1985; Riding and Wright, 1989).
However, the Long Nab Member contains several faunal trace fossils (Romano and Whyte, 2001; Riding and Wright, 1989), and various floral assemblages from the delta-top, that is, the delta surface as opposed to within and at the base of deltaic channels (van Konijnenburg-van Cittert and Morgans, 1999). The faunal trace fossils are most commonly footprint tracks and trackways, while the plant species are numerous. These consist mainly of Ginkgo huttonii (Fig. 2), Czekanowskia blackii (a czekanowskiale; Fig. 3), Coniopteris hymenophylloides and Coniopteris bella (ferns), and Ptilophyllum hirsutum (a bennettitale).
The Upper Jurassic sequence is predominantly marine, starting with the Fleet Member of the Cornbrash Formation, which contains limestone and calcarenite typical of a shallow marine environment. This suggests a eustatic (worldwide) sea level rise and a large marine transgression into the Cleveland basin (Powell, 2010), probably the result of global warming and the melting of ice caps.
The Fleet Member of the Cornbrash is succeeded by the sandy deposits of the Osgodby Formation, which are also very fossiliferous, commonly containing the bivalves Chlamys fibrosus, Gryphaea dilobata, Trigonia sp. and Melegrinella braamburiensis (Powell, 2010). Subsidence of the marine basin then gives rise to the deep-water deposits of the Oxford Clay. Subsequent shallowing permitted the Lower Calcareous Grit deposits of yellow sandstones with intermittent grey lime-mudstones and large calcareous, calcium carbonate based clasts to be deposited.
The clasts are formed from fragments of the sponge Rhaxella perforata, and Thallassinoides burrows are visible along several bedding planes. The Lower Calcareous Grit Formation is overlain by the Passage Bed Member of the Coralline Oolite Formation, which, in turn, gives way to the oobiosparite deposits of the Hambledon Oolite Member, which are the result of shallow, warm, clear water conditions. (An oobiosparite consists of oolitic or pelitic shelly limestone with sparry calcite.) Corals and algae are common within this formation (Powell, 2010).
The topography of Newtondale is primarily developed by Quaternary glacial processes, giving very distinctive features. A meltwater channel runs through Newtondale and was formed by water flowing sub-aerially into the Vale of Pickering from the Esk Valley area, at the end of the Devensian Ice Age (11.8kya). Broadly, the Devensian ice sheet in the north of Britain progressed in a southerly direction (Fish et al, 2006) and, due to the thickness of the ice sheet, the North York Moors experienced periglacial conditions and were not covered by the ice sheet (Boston et al, 2010). This is illustrated in Fig. 4, which shows the ice margin around the North Yorkshire Moors.
The Devensian glaciation caused a major landscape change over the Levisham Estate, as it formed a large glacial plateau. Spread over this plateau are several boulders made up of Moor Grit, which possibly originated from the north of the area and were transported by meltwater to be deposited as sarsen-like erratics on the Levisham Bottoms plateau (Robinson, 2010). These boulders can be described as post-glacial erratics, as they were transported to their current position after the glaciers had retreated. (Sarsens are boulders that have been formed by erosion at the surface or near the surface during a warm phase in the climate.) Some authorities consider these particular sarsens to be from the Osgodby Formation, the lithology of which mimics closely that of the Moor grit (Robinson 2011).
From Levisham railway station, at the bottom of the valley, the steep sides consist of the Long Nab Member of the Scalby Formation. This is sporadically exposed along the side of the road. At parts of the roadside where the solid bedrock is not exposed, wet acidic soil conditions cause the insectivorous plant, the common butterwort (Pinguicula vulgaris), to flourish. This plant is uncommon in the area, and occurs mainly in soils of the Long Nab Member. The Cornbrash Formation (marked with a bench-like structure) and the Osgodby Formation, which overlays the Cornbrash Formation, are both visible further along the roadside. On the plateau, the marshy ground of the Oxford Clay is overlain by the resistant Lower Calcareous Grit, which dips gently towards the South East (Powell and Ford, 2011; Robinson, 2010).
About the authors
William Rutter is currently studying geology at the University of Glamorgan, Wales (email: firstname.lastname@example.org).
Holly Costigan is currently studying geology at Royal Holloway, University of London (email: email@example.com).
References and further reading
Boston, C.M., Evans, D.J.A., Cofaigh, C.Ó., (2010) Styles of till deposition at the margin of the Last Glacial Maximum North Sea lobe of the British–Irish Ice Sheet: an assessment based on geochemical properties of glacigenic deposits in eastern England. Quaternary Science Reviews 29, 3184–3211.
Fish, P.R., Moore, R., Carey, J.M., (2006) Landslide geomorphology of Cayton Bay, North Yorkshire, UK. Proceedings of the Yorkshire Geological Society 56, 5–14.
Fisher, M.J., Hancock, N.J., (1985) The Scalby Formation (Middle Jurassic, Ravenscar Group) of Yorkshire: reassessment of age and depositional environment. Proceedings of the Yorkshire Geological Society 45, 293–298.
Holmes, A., (1956) Principles of Physical Geology, Second Edition, Thomas Nelson and Sons Publishers.
Kelsall, D., Conduit, C., Kelsall, J., (2009) North York Moors Walks – Pathfinder Guide 28, ISBN 978-1-85458-539-4.
Powell, J.H., (2010) Jurassic sedimentation in the Cleveland Basin: a review. Proceedings of the Yorkshire Geological Society 58, 21–72.
Powell, J., Ford, J., (2011) Geology by Train: Glacial Landscapes and Jurassic Geology of the North Yorkshire Moors Railway (Field Hand-out), Yorkshire Geological Society Field Trip.
Robinson, P.C., (2010) R.G.G. Field Visit to Pickering and Levisham, Field Hand-out.
Robinson, P.C. (2011) pers. com. with Whyte, M. during the Yorkshire Geological Excursion to Newtondale 25th. June 2011.
Van Konijnenburg-van Cittert, J.H.A., Morgans, H.S., (1999) The Jurassic Flora of Yorkshire, Palaeontological Association Field Guide to Fossils: Number 8, ISBN 0-901702-64-1.
Riding, J.B., Wright, J.K., (1989) Palynostratigraphy of the Scalby Formation (Middle Jurassic) of the Cleveland Basin, north-east Yorkshire. Proceedings of the Yorkshire Geological Society 47, 349–354.