Waulsortian mudmound

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A Waulsortian mudmound is a geographical feature formed in warm tropical waters in the Viséan geological age, now transposed to the temperate regions in Europe. It is a type of bioconstruction, rich in fossils. The rock comprises light grey, unbedded, micritic limestone, heavily jointed with calcite veining. There is some galena and sphalerite mineralisation in the joints. The fossils are mainly Crinoid ossicles together with gastropods and brachiopods.

The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 346.7 to 330.9 Ma. It follows the Tournaisian age/stage and is followed by the Serpukhovian age/stage.

Calcite carbonate mineral

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".

Galena Rocksalt group, sulfide mineral

Galena, also called lead glance, is the natural mineral form of lead(II) sulfide. It is the most important ore of lead and an important source of silver.


The term Waulsortian was first used in 1863 to describe an area of limestone near Waulsort in Namur, Belgium. Similar mudstone was recognised in the Clitheroe area of Lancashire England by Arthur Vaughan in 1916. [1]

Waulsort Place in Wallonia, Belgium

Waulsort is a settlement in the Belgian Walloon municipality of Hastière, province of Namur.

Clitheroe a town in Lancashire, England

Clitheroe is a town and civil parish in the Borough of Ribble Valley in Lancashire, England, approximately 34 miles (55 km) northwest of Manchester. It is near the Forest of Bowland, and is often used as a base for tourists visiting the area. In 2016, Clitheroe Built Up Area had an estimated population of 15,517.


On a firm bed of limestone, under the deep waters of the tropical sea, crinoids fixed themselves to the rock. The oceans gentle currents eroded the base rock creating a lime-rich mud which was propelled by the current. Where the water was too rapid, the crinoids were displaced, but where it was slower they formed a barrier which arrested the mud forming a micritic deposit. Further crinoids attached themselves, and the deposit thickened to an eventual depth of 200m. In the mudmound one finds fossils of the crinoids bone structure and the angle of deposit shows the direction and speed of mudflow. [2]

Clitheroe reef belt

There has been much debate on how the low micritic limestone hills in the Craven Basin were formed, one theory led to them being called reef knolls, knoll reefs,or bioherms but work in 1972 by Miller & Grayson [3] identified them as mud mounds with the same fossil content as those near Waulsort. They include accessible geological sites at Clitheroe Castle, Salthill and Bellman quarries, Crow Hill and Worsaw, Gerna and Sykes. [4]

Clitheroe Castle Grade I listed historic house museum in the United Kingdom

Clitheroe Castle is a ruined early medieval castle in Clitheroe in Lancashire, England. It was the caput of the Honour of Clitheroe, a vast estate stretching along the western side of the Pennines.

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  1. Kabrna 2011, p. 20.
  2. Kabrna 2011, pp. 19-24.
  3. Miller, J.; Grayson, R.F. (1972). "Origin and structure of Lower Viséan "reef"limestones near Clitheroe, Lancashire". proceedings of the Yorkshire Geological Society. 38: 607–638.
  4. Kabrna, Paul. "Clitheroe Reef Belt". Craven Basin:Waulsortian Mudmounds. Craven & Pendle Geological Society. Retrieved 8 October 2015.