The BGS Lexicon of Named Rock Units — Result Details

Saltwick Formation

Computer Code: SWK Preferred Map Code: SwK
Status Code: Full
Age range: Aalenian Age (JA) — Aalenian Age (JA)
Lithological Description: Grey mudstone, yellow-grey siltstone and yellow, fine- to coarse-grained sandstone (fluvial, fluvio-deltaic and paralic lithofacies). Sandstones commonly display sharply erosional bases, and channel-fill bedforms. Locally, thin coal seams, seatearth mudstone and nodular sideritic ironstone beds may be present. Plant remains and plant rootlets are common in some beds.
Definition of Lower Boundary: The lower boundary is taken at the unconformable or disconformable boundary between the underlying heterolithic, marine Dogger Formation (ferruginous sandstone; ironstone; limestone; or calcareous mudstone) and the sandstone, siltstone or mudstone (with plant fragments) of the Saltwick Formation. Where the Dogger Formation is absent due to penecontemporaneous erosion, the Saltwick Formation rests unconformably on grey, calcareous mudstone or siltstone (commonly shelly) of the marine Lias Group, generally the Whitby Mudstone Formation, or on lower stratigraphical units, such as the Redcar Mudstone Formation, near the Market Weighton High.
Definition of Upper Boundary: The upper boundary is taken at the conformable, abrupt upward transition from the plant debris-rich, cross-stratified sandstones, siltstones and mudstones of the Saltwick Formation to the calcareous mudstone, ooidal ironstone or ferruginous sandstone, commonly with shelly fossils, at the base of the Eller Beck Formation.
Thickness: About 50m on the North Yorkshire Coast, between Whitby and Scarborough, and inland in the North Yorks Moors and Cleveland Hills; 20 to 25m in the Hambleton Hills on the western escarpment (Powell, et al., 1992; Frost, 1998), thinning southwards to about 5 to 10m in the Howardian Hills.
Geographical Limits: North Yorks Moors, Cleveland Hills and Howardian Hills; well exposed in several coastal cliff sections between Whitby [NZ 890 115] and Saltwick Bay [NZ 917 108] and south from Blea Wyke Point [NZ 995 010] to Hayburn Wyke [TA 010 971]. Offshore, the formation is equivalent, in part, to the Wroot Formation of the West Sole Group (Lott and Knox, 1994).
Parent Unit: Ravenscar Group (RAG)
Previous Name(s): Lower Estuarine "Series" [Obsolete Name And Code: See CLH, GRF, SWK And EBB] (LET)
Hayburn Formation (-5069)
Hayburn Beds (-4356)
Lower Deltaic Series (-1213)
Alternative Name(s): none recorded or not applicable
Type Section  Cliff section on the North Yorkshire coast at Saltwick Bay [NZ 917 108] southeast of Whitby (Hemingway and Knox, 1973). Grey mudstone and siltstone with plant debris and rootlets (Saltwick Formation) overlie yellow-brown, ferruginous sandstone (Dogger Formation). Also present within the Saltwick Formation are yellow-weathering, cross-bedded, laterally impersistent, channel sandstones and grey mudstones (the latter in abandoned channels). The upper boundary with ferruginous sandstone of the Eller Beck Formation is present in the cliff, but is better exposed farther south near Hayburn Wyke [TA 010 971]. 
Cope, J C W, Duff, K L, Parsons, C F, Torrens, H S, Wimbledon, W A and Wright, J K. 1980. A correlation of Jurassic rocks in the British Isles. Part 2: Middle and Upper Jurassic. Geological Society of London Special Report, 15, 73pp. 
Sylvester-Bradley, P C. 1949. Revised nomenclature for Yorkshire Estuarine Series. Geological Magazine, Vol.86, 263. 
Frost, D V. 1998. Geology of the country around Northallerton. Memoir of the British Geological Survey, Sheet 42 (England and Wales). 
Hemingway, J E. 1949. A revised terminology and subdivision of the Middle Jurassic rocks of Yorkshire. Geological Magazine, Vol.86, 67-71. 
Rawson, P F and Wright, J K. 2000. The Yorkshire Coast. Geologists' Association Guide No.34. (London: The Geologists' Association.) 130pp. 3rd Edition. 
Hemingway, J E. 1974. Jurassic. 161-233 in Rayner, D H and Hemingway, J E (eds), The geology and mineral resources of Yorkshire. (Leeds: Yorkshire Geological Society.) 
Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
Knox, R W O'B, Howard, A S, Powell, J H and van Buchem, F S P. 1991. Lower and Middle Jurassic sediments of the Cleveland Basin N.E. England: Shallow marine and paralic facies seen in their sequence stratigraphic context. Field Excursion Guide, No.5; 13th International Sedimentological Congress, Nottingham, UK. 1990. 66pp. 
Powell, J H, Cooper, A H C and Benfield, A C. 1992. Geology of the country around Thirsk. Memoir of the British Geological Survey, Sheet 52 (England and Wales). 
Hemingway, J E and Knox, R W O'B. 1973. Lithostratigraphical nomenclature of the Middle Jurassic strata of the Yorkshire Basin of north-east England. Proceedings of the Yorkshire Geological Society, Vol.39, 527-535. 
Fox-Strangways, C. 1892. The Jurassic Rocks of Britain, Vol.1. Yorkshire. Memoir of the Geological Survey of the United Kingdom. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E033 E034 E035 E042 E043 E044 E052 E053 E054 E063