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The National Stone Centre encompasses six quarries and has been designated as a Site of Special Scientific Interest (SSSI) due to the geology and presence of mud mounds, reefal structures and lagoonal deposits.
The centre is well signposted locally and there is a car park on site where there is a small parking fee at the honesty box. The site itself is free to walk around. From the car park make your way under the mineral railway bridge down to the main signed areas where the co-ordinates take you to the top of the Geosteps.
Situated in Wirksworth at the southern most part of the Pennines, which is popularly known as the “White Peak”. This is attributed to the pale grey limestone outcrops and walls within the area.
The quarry was last worked in the mid-1960’s to supply crushed stone for the construction of the M1 in the east midlands area, with a peak output at the time of up to 250,000 tons per year.
Palaeoenvironmental setting
The rocks at the site date back to the lower Carboniferous Period (Dinantian) and are between 320 and 330 millon years old. To understand the rock formations on the site you have to imagine that the environment at the time was similar to the warm waters of a Pacific Atoll today. During deposition of the limesone the site would have been located near the equator and over millions of years has slowly moved northwards due to plate tectonics to the position it is found today.
You may think limestone is all the same pale grey rock but if you take a closer look you will see that limestone is made up of numerous fossils including broken shells, crinoid ossicles, corals and bryazoa to name but a few. A simplified overview of the site is as follow. The South East Quarry, found by following the sloping path to the bottom of the site, has rocks of fore reef lithology. Also at a height of approximately 1.5-2.0m of the quarry floor you will see a thin clay band, locally known as a clay wayboard, this was a volcanic ash deposit from the numerous small volcanoes which were around at the time. Coming back up to the Reef Quarry you will see the carbonate mud mound, which is a build up of homogeneous carbonate mud, which is identified by not having any bedding features unlike the surrounding lithology. Behind the carbonate mud mound you can see small thickness beds thinning as they slope up onto the mound. This is part of the Back Reef complex which would have been partly sheltered from strong wave action, and creatures such as corals, crinoids and brachiopods would have resided here. Further back towards to the North Eastern Quarry are the lagoonal deposits, looking towards the quarry face there are deposits of broken shells approximately 2m above the quarry floor, which indicates that the area was also subjected to changes in sea level and beach environments existed at times.
To claim this Earthcache you need to email me the answers to the following questions, together with a photo of either yourself or GPS in front of the carbonate mud mound at Reef Quarry N53°05.586 W001°34.350 (although optional its nice to see when you have been). Most or part of the answers are on the numerous sign boards around the site.
Q1. At co-ordinates N53°05.589 W001°34.299 there is a large flat sloping outcrop of stone which is part of a back reef structure. The outcrop of stone is behind a wire fence to stop people walking over it, also more importantly to stop people removing the fossils. The surface looks dark almost black this is due to a covering of bitumen, which is due to hydrocarbons seeping up fissures and bedding planes from Widmerpool Gulf to the south during subsequent burial of the rocks. If you look closely at the fossils you can see what appears to be tubular segmented branches. (wetting the surface can make them easier to see). They look plant like and have been referred to as ‘sea lilles’. However, this is not true, what is their correct name, what family are they part of and in todays rockpools what are they closely related to. ( A little further research may be required)
Q2. The area in and around the National Stone Centre has been of interest to human activity dating back to the Roman times. They were first selectively quarrying for certain metals and later other minerals were found to be valuable. Name three of these minerals and what are their Specific Gravity. Specific Gravity is a way of defining the density of irregular shaped objects, and you would certainly feel the difference between the minerals when held in the hand. You may find some of these minerals on the surrounding ground or spoil heaps. Not a requirement but may find interesting is by looking closely at the vertical fractures in the rocks they can show mirror images of these minerals as they precipitated out of the mineralised fluids when cooling down, however be aware that the rocks above your head may be loose. So if you go close to rock faces you should always wear a helmet. There may be a hint at co-ordinates N53°05.622 W001°34.400.
Q3. Due to the area being part of a reefal system you can imagine that there would be evidence of shells. Many of the shells found here are from a creature called a Brachiopod. This area has a special Productus Brachiopod, which name defines its size. What is its latin name? (This name is not shown at the site) You may be able to see some on the ground at co-ordinates N53°05.627 W001°34.327. Also some Brachiopods had evolved a way of not being washed away from the sea bed as they lay on there backs filter feeding, what was it?(Pedicle is not the answer)
You may need to do a little research for the answers.
Geological setting
The Carbonierous limestone massif lies on a Pre-Carboniferous basement block of Ordivician slates and a possible Pre-Cambrian belt of volcanic rock extending south eastwards from Wirksworth. These are only known through boreholes and geophysics. The sequences of Dinantian limestones are characterised by basin, shelf and marginal facies. The basin facies in Widmerpool Gulf is defined by the Widmerpool Formation a thick sequence of calcareous mudstones, siltstones and sandstones with interbedded darker fissile mudstones. The grading within these units is thought to be caused by turbidity currents, with an absence of shallow water faunas they are inferred as deeper marine environment. Duffield borehole has revealed they extend to 3,453 feet in depth and are round 1,600 feet in thickness.[1]
The lowest of the shelf and marginal facies is the Bee Low Limestone, which consists of upto 280 feet of pale grey off-white, fine grained to porcellanous, massively bedded limestones partly oolitic in areas. Present are limited corals and brachiopod faunas. Interbedded lavas and clay wayboards are also associated with these limestones.[1]
The Monsal Dale Limestones consits of upto 150 feet of variable dark and grey limestones with fossiliferous bands and areas of chert nodules, these overly the Matlock Lower Lava of which there is an Upper Lava within the sequence, both vary in thickness with lateral extent. Carbonate mud build-ups and more varied faunas are also seen.[1]
The Eyam Limestone consists of up to 60 feet of fossiliferous, thinly bedded, cherty limestones with shale partings, containing corals and brachiopods. Overlying unconformably are the Longstone mudstones of some 20 feet thick.[1] Subsidence in the Namurian led to the deposition of shales and sandstones up to 1.5km thick (Millstone Grit Series), followed by the Westphalian Coal Measures in the late Carboniferous, with continuation of subsidence effecting the basins. Therefore, the top of the Derbyshire Platform was buried by 2-3km of Carboniferous sediments.[2]
Structural inversion occured at the end of the Carboniferous to the early Permian as a result of the compressional forces of the Variscan Orogeny. The inversion caused much of the Upper Carboniferous to be eroded, successive magnesium limestone was deposited in the are during the Permo-Triassic, followed by Jurassic and Cretaceous sediments, the latter Mesozoic cover subsequently being eroded away after renewed up-warping in the Tertiary.[2]
The area around Wirksworth is also extensively mineralised by Galena, Fluorspar, Baryte and Calcite with less common Sphalerite and Chalcopyrite. The mineralisations veins appear to have re-activated both compressional and relaxation faults, which are associated with folding of the Derbyshire ‘Dome’ and folding developed during sedimentation in the lower Carboniferous limestones, these trending mainly E-W and NE-SE. [3]
[1] Frost,D.V. & SmartJ.G.O. (1979) Geology of the country north of Derby. Mem. Geol. Surv.G.B. sheet 125. [2] Ford,T.D. & Quirk,D.G. (1985) Mineralisation of the South Pennines Geology Today 11 (5) pp177-182. [3] Mostaghel,M.A. & Ford,T. (1986) A Sedimentary Basin Evolution for Ore genesis in the South Pennine Orefield. Mercian Geologist. Vol.10, no3, pp209-224.
This site has a very complex but interesting geology, if you want to find out more the following people have written numerous papers on the site and Derbyshire geology in general: Ford,T.D., Gutteridge,P., Walkden,G.M., Frost & Smart to name but a few. The British Geological Survey also publish geological maps and a book covering the area, British Regional Geology: the Pennines and adjacent areas.
Also more information can be found about the site at www.nationalstonecentre.org.uk . There is a discovery centre, shop and cafe on the site. So you can have a nice cuppa while the geokids can go panning for gold and gems. You may also see stone carving or traditional stone walling taking place on some weekends.
This Earthcache has been allowed with the kind permission of the National Stone Centre, please respect all areas of the site.
There is disabled parking and certain areas are attainable for wheelchairs, however, most of the site is uneven and steep. Hope you have a fun time at the site.
Congratulations to BalooCrew and Plasmawave on **FTF**
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