This is a sketch map of north - west England showing the main basement features which controlled Mississippian sedimentation.
Cracoe, Malham and Settle mark the transition between "Block & Basin" and are good localities for seeing Asbian reef limestones. These reefs contrast nicely with the Waulsortian mud mounds around Clitheroe.
Seismic Reflection Data
The concept of 'basinal' and 'block' areas of northern England was derived from work done at outcrop by Phillips 1836; Hudson 1938, 1944; Bott 1967 and Johnson 1967. Recent basin analysis work carried out by Evans, D. J. and Kirby, G. A (Basin Analysis and Stratigraphy Group, British Geological Survey 1999 - 2000) on seismic reflection data, has revealed two distinct seismic facies corresponding to shallow water carbonates and deeper water basinal sediments. These two facies at depth are seen to interdigitate supporting the idea of progressive drowning of the intra-basinal highs. Sea level appears to rise and fall at varying rates adding to an already complex Mississippian history in the Craven Basin.
The main feature of our local geology is the Coal Measures of the Burnley Basin. The higher ground is typically made up of mid-Carboniferous sandstone and shales with Pendle Hill providing the pinnacle of outcrop.
The Ribble Valley is primarily composed of Mississippian limestones. Clitheroe is frequented town for geologists' because of the preserved Waulsortian mud mounds and the extensive assortment of crinoids.
Other areas on the map such as Cowling (European type section for the Mid - Carboniferous Boundary) and Cliviger Valley (Ratten, Paul & Coal Clough) offer splendid sections for study.
The Millstone Grit Group and succeeding rocks of the Pennsylvanian are commonly laid down in cycles of deposition as explained below.
The diagram right represents an ideal course of events in cyclothem evolution. However, cyclothems are seldom seen in entirety as seen in Ratten Clough and Pudsey Clough. These are typical Cliviger valley stream sections exposing rocks of the Millstone Grit Group and Coal Measures. Both series are characterised by a repetitive association of rock types caused by the repeated advance of sandy deltas into a deep water basin.
These cycles of sedimentation are known as cyclothems and ideally consist of sediments that gradually coarsen upwards from shales through siltstones to sandstones being commonly capped by coals in the Coal Measures. The shales frequently contain marine fossils such as bivalves and goniatites. As the goniatites evolved rapidly each marine band usually contains a unique and diagnostic species that therefore facilitates their correlation both locally, regionally and worldwide.