Salthill Quarry

© Craven & Pendle Geological Society

Waulsortion Mudmound

Waulsortian Mudmound development

Locality 1

The photograph (right) shows the core of the exposed Waulsortian mudmound; Bellman Limestone Member, Clitheroe Limestone Formation. (check out the Carboniferous link for details on geologicla time and formations).

All "reefs" in the Clitheroe region were initially thought to be typical coral or algal-coral build-ups. Today they are considered lithologically similar to "Waulsortian" mudmounds and compare favourably to the type area in Belgium.

The photograph above shows dark crinoidal limestone draping over a mudmound. There is an erosion surface (unconformity?) at the top of the mudmound. This is where the Bank facies (light grey micritic limestone) meets the Inter-bank facies. If you look closely there is eveidence for a boulder bed which formed when the mound was subject to subaerial erosion. The darker shaley crinoidal Inter-bank facies buried the mud-mound and smoothed out an irregular seafloor. This facies is richly crinoidal.

Waulsortian mudmound development in Salthill Quarry has been looked at by Lees et al (1985). Initially they defined four phases (A, B, C, and D). Each of these phases contain features linked to water depth of formation, with phase D being in the shallower water. Regarding Salthill Quarry, the Waulsortian facies is more representative of phases C to D thus indicating water depths of 250 metres to less than 220 metres. The presence of fossil algae on the tops of the mudmounds confirm some mound development took place in the photic zone.

These limestone facies associations in the Clitheroe Quarries were identified by Miller, J & Grayson, R.F. (1972) in "Origin and structure of the Lower Viséan "reef" limestones near Clitheroe, Lancashire" PYGS Vol. 38 , 607. Other Reference: Riley, N.J. 1995 "Stratigraphy of the Worston Shale Group, Dinantian, Craven Basin, north-west England" PYGS Vol. 48 , 163