Clitheroe 'Reef' Belt

© Craven & Pendle Geological Society

Line of Waulsortian Mounds in the Clitheroe area

Origin and Formation

Knoll-reef hypothesis
The Reef Knolls have been subjected to numerous studies. They were first described by Tiddeman (1889) who applied the term "reefs". Subsequent workers (Parkinson 1926; Black 1952 - 1954; Bathhurst (1959) all subscribed to the same name as Tiddeman had instigated. They all believed that the knolls were composed of biogenic material formed on a sinking sea floor with beds on all sides of the knolls showing an original dip away from the central core (quaquaversal dips). Parkinson's main addition to the story was his interpretation of a widespread unconformity whereby the Cephalopod Shales draped over the reef knolls at the end of their growth. Evidence for this was cited as boulder beds in Bellman Quarry.

Carbonate Bank hypothesis
In 1961 Earp et al during the re-survey raised two objections to the reef hypothesis: a) the apparent lack of reef-building faunas such as corals etc. to form the required wave-resistant structures. b) The absence of breccia fans and conglomerates which should be present around such large knolls, especially in the case of Worston and Sykes. They proposed then that the knolls were formed as shoal water lime-banks upon which crinoids would have thrived. Also the high dips and differential compaction seemed to support tectonic tilting. They recognised no unconformity between the reef limestones and the overlying Worston Shales whilst the boulder beds were regarded as superficial features.

It was not until 1972 that the story of the Clitheroe Reefs would take a big step forward with the work of Miller & Grayson.

A Norman Keep

Clitheroe's Norman Keep built on a Waulsortian Mud Mound

The focal point of Clitheroe is the ancient Norman Keep. It is one of the smallest in England and one of the first stone buildings in Lancashire. It was built by Roger de Poitou who was the first Norman Lord of Clitheroe.

The Keep sits proudly on top of one of Craven Basin  Waulsortian Mud Mounds. The mound comprises of light grey, unbedded, micritic limestone, heavily jointed and calcite veined. Crinoid ossicles together with gastropods and brachiopods can be seen.  There is some galena and sphalerite mineralisation in the joints.

The grounds are also the base of the Clitheroe Castle Geological Museum.

Chadian Stratotype
A59 (T) Road Cutting: Grid Reference [SD 774443]

The Chatburn section is the stratotype for the Chadian Stage. The outcrop spans the Four Foot Shale for 170 metres to the Algal bed below which lies in the Bankfield East Beds.

The blue well-bedded, sometimes cherty limestone contains numerous mudstone partings.

Chadian type section

The beds are frequently bioturbated indicating aerobic bottom conditions that would have supporting rich faunal communities. Bioclasts are mainly fragmentary with some bedding planes are crowded with brachiopods. Click here for a closer look!

The Algal Bed and one some 4 metres below it can be found at the north end of the cutting. Beds are composite units, dipping south-east at about 40 degrees and are cut by two mineralised reverse faults.

Peach Quarry Limestone
A59 (T) Road Cutting
Grid Reference [SD 7700 438]

Peach Quarry Limestone

Peach Quarry Limestone is part of the Clitheroe Limestone Formation and lies within the Chadian Stage. At this locality along the A59, the top and base are not exposed.

The outcrop is mainly packstones and grainstones, fine to coarse grained, pale grey, wavy-bedded and cherty with abundant crinoid, algal and pellet grains.

Bedding planes can be crowded with brachiopods and ostracods. The smaller beds frequently contain chaotically arranged crinoid debris indicating that the limestone was storm generated. The shallower nature of Peach Quarry Limestone sedimentation represents an interval of time where Waulsortian-type deposition was interrupted.

Worsaw Hill near Clitheroe

Worsaw Knoll

This Waulsortian mud-mound (along with Crow Hill, Warren Hill and Gerna Hill) is a product of second generation of Waulsortian buildups. All are splendidly developed in the form of a linear belt of knolls running from Twiston and Worsaw Hill near Downham, to Castle Hill in Clitheroe. Over the years they have been called many things: Reef Knolls, Bioherms, Knoll Reefs. Today however, they are termed Waulsortian Mudmounds as first described at the type section which is in Belgium. Salthill is about the centre of the belt of knolls.

Crow Hill, near Clitheroe

Crow Hill

This Waulsortian mud-mound (along with Worsaw Hill, Warren Hill and Gerna Hill) is a product of second generation of Waulsortian buildups. Crow Hill is also noticably smaller than many of the others. All are splendidly developed in the form of a linear belt of knolls running from Twiston and Worsaw Hill near Downham, to Castle Hill in Clitheroe. Over the years they have been called many things: Reef Knolls, Bioherms, Knoll Reefs. Today however, they are termed Waulsortian Mudmounds as first described at the type section which is in Belgium. Salthill is about the centre of the belt of knolls.

Crow Hill
Crow Hill Limestones