Fell Sandstone Formation
Fell Sandstone Formation is part of the Border Group.
The name is derived from the Larriston Fells (Peach and Horne, 1903).
The Fell Sandstone Formation in the north-east Northumberland Trough comprises fine- to medium-grained, mica-poor, subarkosic sandstone with sparse interbeds of red mudstone (Smith, 1967). This passes towards the central part of the trough into a continuation of the cyclical successions of fine-grained subarkosic sandstone, siltstone, mudstone and thin limestone present in the underlying Lyne Formation, although in the Fell Sandstone the sandstones are thicker and the limestones thinner (Day, 1970). Seatearths are common in the formation, but only in the upper part. Thin olivine basalt lavas occur as the Kershopefoot basalts (Williamson in Stephenson et al., 2003). At Southerness, members of the formation include the Gillfoot Sandstone and Powillimount Sandstone members. In the Colvend and Rerrick outliers the formation includes the Rascarrel Member.
The sandstone is interpreted as having been deposited from both low-gradient meandering rivers and high-gradient braided perennial rivers, which occupied channel belts several kilometres wide along the axial part of the Northumberland Trough (Hodgson, 1978). The Fell Sandstone succession in the central part of the trough represents deposition in a mixed fluviodeltaic and shallow marine environment.
The Fell Sandstone Formation reaches its most characteristic development in the Simonside Hills in the Rothbury area of Northumberland (B. Young, written communication, 24 June 2004). Type sections occur at Murton High Crags, south-west of Berwick-upon-Tweed (NT 9620 4950), on the foreshore at Burnmouth (NT 9580 6110), and on the River White Lyne (NY 5110 7320). Further sections occur south-west of Berwick-upon-Tweed (NT 9300 4500). In Annandale, the Hoddom No.2 Borehole (BGS Registration Number NY17SE/3) (NY 1641 7285) included the Fell Sandstone Formation from 41.60 to 102.62 m depth. The type section of the Kershopefoot basalts is at Kershopefoot Quarry (NY 5005 8339), but neither the top nor bottom of the sequence is seen.
Lower and upper boundaries
The base of the Fell Sandstone Formation is locally unconformable and diachronous on a range of Lower Carboniferous strata, including the Lyne Formation in the central parts of the Northumberland Trough (Figure 8, Column 11). Locally, it is defined as the base of the Whitberry Band (WBB) (Figure 11, Column 2). At Brampton, the base of the Fell Sandstone Formation rests conformably on the Ballagan Formation, Inverclyde Group (Figure 11, Column 1), but in the north-east part of the Northumberland Trough the same boundary is unconformable (Figure 8, Column 12).
The top of the formation is locally unconformable and diachronous at the base of the Clattering Band (CTB) of north-west Northumberland (Figure 8, Column 11), its correlative the Kingsbridge Limestone (KBL), or in the Langholm area, the Glencartholm Volcanic Beds (GV), of the Tyne Limestone Formation (Yoredale Group) (Figure 10, Column 3).
The formation ranges from 130–300 m thick in the north-east of the Northumberland Trough. It is 350–450 m thick in the central part of the trough measured between the bases of the Whitberry and Clattering bands. At Annandale, in the Hoddom No. 2 Borehole (see above) the Fell Sandstone Formation is about 61 m thick. The Kershopefoot basalts attain a maximum thickness of about 36.5 m (Williamson in Stephenson et al., 2003).
Distribution and regional correlation
Tweed Basin and the northern and central parts of the Northumberland Trough–Solway Basin, from Burnmouth, Berwickshire in the north-east to Southerness, Kirkcudbrightshire in the south-west. The Kershopefoot basalts occur in scattered outcrops south-east of Langholm between (NY 40 83 and 50 83).
Deposition of the formation occurred earliest in the north-east of the Northumberland Trough (Chadian to Holkerian). In the central part of the trough, the equivalent strata are of Arundian to Holkerian age.
- Peach, B N, and Horne, J.1903.The Canonbie Coalfield: its geological structure and relations to the Carboniferous rocks of the North of England and Central Scotland.Transactions of the Royal Society of Edinburgh, Vol. 40, 835–877.
- Smith, T E.1967.A preliminary study of sandstone sediment-ation in the Lower Carboniferous of the Tweed basin.Scottish Journal of Geology, Vol. 3, 282–305
- Day, J B W.1970.Geology of the country around Bewcastle.Memoir of the Geological Survey of Great Britain, Sheet 12 (England and Wales)
- Stephenson, D, Loughlin, S C, Millward, D, Waters, C N, and Williamson, I T.2003.Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front.Geological Conservation Review Series, No. 27. (Peterborough: Joint Nature Conservation Committee.)
- Hodgson, A V.1978.Braided river bedforms and related sedimentary structures in the Fell Sandstone Group (Lower Carboniferous) of North Northumberland.Proceedings of the Yorkshire Geological Society, Vol. 41, 509–532