The Origin and Structure of the Lower Viséan Reef-Knolls of the Clitheroe District, Lancashire

Abstract

Summary The reef-knolls discussed in particular are Crow Hill, Worsaw, Gerna, Sykes and Twiston, all of which lie on the south-eastern limb of the Clitheroe anticline. It is shown that along the eastern side of Worsaw Hill the reef-limestone accumulated at high angles to the horizontal and at depths varying from sea-level down to 400 feet or more below, on a slope running perpendicular to the present strike of the surrounding beds. Shales and thin-bedded limestones were deposited between the reefs and contemporaneously with them on a sinking sea-floor. The larger knolls are considered to be the exposed parts of reefs which were originally ridge-like and ran parallel to the north-west and south-east fault lines and perpendicular to the later main orogenic axes. Some of the reefs may have been several miles in length, but their width rarely exceeded half a mile. Reef sedimentation was followed by uplift which resulted in erosion along the flanks of the reefs and a deepening of the depressions between them. The succeeding Worst on Shales were thus deposited on an uneven surface which resulted primarily from original irregularities of sedimentation but which was modified by subsequent earth-movement. I. Introduction In 1926, in describing the Lower Carboniferous succession of the Clitheroe-Pendle area, I adduced evidence supporting Tiddeman's theory (1900, and Kendall and Wroot 1924, p. 92) of the origin of the reef.knolls. It was argued that the stratigraphy could only be satisfactorily interpreted on the assumption that the limestone hills lying between the villages of

Depositional magnetization of Carboniferous Limestones from the Craven Basin of northern England

“…The geology of the area is wellknown due to the work of Earp et al (1961). Much of the interest in the area has centred on the origin of the reef-knolls within the Clitheroe Limestone Complex (Parkinson, 1944(Parkinson, , 1957Black, 1954) and these have recently been discussed along with a revision of the stratigraphy by Miller & Grayson (1972).…”

The Lower Carboniferous Limestone Knolls of Clitheroe, Lancashire

“…Recent work has strengthened the view (Parkinson, 1926(Parkinson, , 1944) that the compressus Beds rest with at least a non-sequence on the Fenestella Beds, though some former exposures of the latter in Downham Beck in and near the village are no longer at surface.…”

“…They were assigned (Parkinson, 1926(Parkinson, , 1944) to a post-knoll age, but the work of the Geological Survey suggests they are, in part, contemporaneous with the knoll limestone. They contain unnamed goniatites additional to the index form.…”

“…Estimates of original dips of deposition were as high as 50 degrees (Parkinson, 1944). W. W. Black (1954) estimated depositional dips in the Whitewell knolls, west of the area of the Clitheroe Sheet, of up to 50 degrees.…”

“…FOLLOWING the re-survey of the country around Clitheroe and Nelson (Earp et al, 1961) the Geological Survey officers concluded that the Lower Visean knolls of the Clitheroe and Slaidburn Anticlines are lime-banks and not knoll-reefs as argued by Tiddeman (1889), Parkinson (1926Parkinson ( , 1935Parkinson ( , 1936Parkinson ( , 1944Parkinson ( , 1950Parkinson ( , 1957Parkinson ( , 1964, Black (1952Black ( , 1953Black ( , 1954 and Bathurst (1959). They did not consider that the evidence for the presence of reef-builders in the knolls was strong enough to justify the belief that they grew as wave-resistant structures.…”