The Carboniferous Period began when what is now Britain had drifted
northwards close to the equator. During Lower Carboniferous (Dinantian) times post-Caledonian crustal extension broke
up the eroded roots of the Caledonian mountains into a series of more
upstanding "blocks" and subsiding "troughs" or basins.
This north-south tensional stretching is believed to be the result of a
subduction event to the south of Britain which led eventually to the Variscan Orogeny. The blocks and troughs are due to
variations in density of the underlying crust.
Disused Millstone from the Millstone Grit.
The Carboniferous "blocks" and "troughs" still
influence the landscape of Northern England today. Furthermore, it is their
general dip or tilt to the east which has resulted in the high ground of the Pennines.The North Pennines consist
of two blocks known as the Alston (to the north) and Askrigg (to the south) Blocks.
During Lower Carboniferous times warm shelf seas encroached on the old land surface. The result in many areas was an unconformity of horizontal marine limestones overlying folded and eroded Lower Palaeozoic rocks, e.g. as seen at Thornton Force and White Scar cave, both near Ingleton, as well as Arcow quarry near Austwick. Lower Carboniferous Limestone of the Great Scar Limestone Group is well displayed around Malham, Horton in Ribblesdale and Ingleton.
However, deposition of marine sediments did not occur evenly over
Northern England. Furthermore, changing sea-levels due to subsidence and/or
worldwide sea-level changes, as well as advancing and receding deltas
resulted in a variety of sediments such as limestones, mudstones, siltstones,
sandstones and coal in a cyclical sequence known as a cyclothem.
These sequences are best displayed in Wensleydale,
e.g. Penhill near Leyburn
and Buckden in Wharfedale
where the hillsides are characterised by a series of stepped features due to limestones and sandstones which are more resistant to
erosion being interbedded with less resistant mudstones and siltstones. They are
known as Yoredale cyclothems,
Yoredale (derived from the River Ure) being the old name for Wensleydale.
During Upper Carboniferous (Namurian) times
sea-level continued to vary but tended to be lower resulting in sediments
from northern deltas spreading in a southerly direction. The advancing deltas
produced an interbedded sequence of shales, coarse sandstones and occasional
limestones. The latter, however are not as predominant as in the Lower
Carboniferous. The coarse sandstones are known
as Millstone Grit since millstones used to be made from them. Because many of
the rocks are poor in nutrients, they give a distinctive bleak landscape,
e.g. the moorlands of the South Pennines, such as Saddleworth Moor along which the M62 passes, and in the
North Pennines, along the A66 over Stainmore.
The effect of Carboniferous geology on past industries is very much in
evidence. Limekilns for fertiliser can be seen e.g. in Hudeshope
Beck, Middleton in Teesdale and building stone,
e.g. black fossiliferous Frosterley
"Marble" from Frosterley near Stanhope as
seen in Durham Cathedral. Evidence of past leadmining,
e.g. hushes and mine entrances, can be seen in the Swaledale
area in Arkengarthdale, Gunnerside Gill and Reeth.
Today, Blue Circle in Weardale use limestone to
Figure above shows position of the continents during Early Carboniferous times. From Cocks, L.R.M. & Torsvik, T.H. 2006. European geography in a global context from the Vendian to the end of the Palaeozoic. In Gee, D. G. & Stephenson, R. A. (eds). European Lithosphere Dynamics. Geological Society, London, Memoirs, 32, 83–95.
The British Isles can be seen just south of the equator.