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Site geology

Pleasley Colliery is located in the Nottinghamshire / Derbyshire concealed coalfield which forms part of the eastern limb of the main N-S aligned Pennine uplift.  It lies at a height of 500 ft (152 m) above sea level, about 2 miles (3.2 km) east of the boundary with the exposed coalfield.

The Pit sits directly on a bedrock of  flaggy yellow-brown dolomitic limestone of the Permian Lower Magnesian Limestone (LML) formation which dips gently north-eastwards. There are no significant glacial deposits and rock-head is overlain by a fertile brown soil.  The LML in this area is a major aquifer with high permeability enhanced by substantial fissuring, a factor which led to very high groundwater inflows during the sinking of the shafts. It is generally underlain by the Lower Permian Marl (LPM), a grey limy mudstone which outcrops along the river Meden valley where it is marked by numerous spring lines.

Post Carboniferous geological history

In late Carboniferous times, around 300 million years ago, during the final stages of the  Variscan / Hercynian orogeny (mountain building episode in which the South European  micro-continent assemblage collided with the southern margin of the continental landmass Laurussia where the British Isles region was located), the effects of the collision were felt from the coastal margin in the south as far north as the Scottish Highlands.

In northern England, uplift of the central Pennine spine together with folding and faulting of  the adjacent coal-measure strata took place.  Over the newly elevated Pennine arch, erosion stripped both the  (geologically speaking) recently deposited coal measures and upper parts of the underlying millstone grit formations laid down 20 million years earlier, leaving the coalfields on either side completely separated.

The flanking coalfields were eroded  at a somewhat lesser extent, but still enough to strip away the uppermost layers of the coal measures, leaving a barren undulating landscape which would soon be invaded by the spreading Permian inland Zechstein sea.

 The Magnesion Limestone formations were laid down on this eroded surface which, in eastern England, would appear to still have had significant variations in elevation since the Permian strata thickness increases considerable to the east. The area around Pleasley colliery, however, lay on the very shore of that sea at the time of its maximum extent and the nature of the rock reflect that depositional environment

There is no indication of any significant post-Carboniferous movement other than a slight tilt of a few degrees to the East, although there is some indication that features in the Magnesian Limestone have been influenced by the structural trends in the underlying coal measure.

zechstein -a -m 2

Maximum extent of the Permian inland sea

Local geological details

The base of the Permian strata lies unconformably on folded and eroded Westphalian Middle and Lower Coal Measures (MCM and LCM).   Across the Nottinghamshire concealed coalfield the junction is marked in some places by a thin basal  breccia - the “hard mingled rock” of the shaft sinking record whilst in others there are deposits of wind blown sand. Further north into Yorkshire this is completely replaced by sand which continues throughout the rest of the exposure up to the River Tyne. 

A short distance to the east of the pit, a number of  hard calcareous sandstone ridges are found within the actual limestone strata, running NNE from Mansfield up to Bolsover Moor and beyond. It was through these ridges that,  at the end of the main ice-age, glacial melt-waters  carved the narrow valleys at Pleasley Vale and Mansfield now occupied by the River Meden  and the River Maun.

The type of stone found in the ridges is  quite unique and in the 19th century it was highly prized for its colour, durability and workability. It has been extensively quarried, particularly around Mansfield where it was widely use for building purposes and this is the stone from which the engine house walls were constructed.

The best quality stone was used for the paving of Trafalgar Square, the exterior of the Houses of Parliament and the Natural History Museum in London. Probably the finest example, however, can be found in nearby Southwell Minster where the sunlight streaming through the high windows shows the honey coloured variety to its bes

Geological structure

Pleasley colliery is located on the western slope of a pre-Permian geological structure  known as the Welbeck Trough which forms a shallow saucer-like depression in the strata. It is bound by the Hardstoft - Mansfield  anticline to the west and south, the dipping northern limb of the Eakring anticline to the east and  to the north it is truncated by major faulting.

The coal measures at Pleasley are relatively trouble free, unlike at many of its surrounding collieries. The cleat runs roughly NW-SE, following the trend of the anticline to the west. Two faults running  roughly NW-SE with minor splays and en-echelon displacements lie to the W and E of the pit, and have maximum throws of about 25 ft.

 In the Top Hard seam a large washout trending NNE-SSW lies just to the north east and a considerable quantity of coal is missing as a result. 


Copyright © 2005 - 2020   J.S. Thatcher

Page updated on:

29 Jul, 2020


06:47:33 PM

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