Clarehill
Also within
Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Cretaceous · Rock Type: Chalk, Flint, Limestone, Mudstone
Description
Clarehill Cretaceous Stratigraphy Clarehill is of importance because of its geology. Specifically the site is representative of the attenuated Ulster White Limestone Formation in the Lagan Valley. The site also contains well preserved cylindrical or barrel-form flints known as Paramoudras from the Ballymagarry Chalk Member. The term paramoudra was first introduced from this district in the early 19th century by the eminent geologist William Buckland. The term is probably a corruption of an Irish name, probably padhramoudras 'ugly Paddies' or peura muireach 'sea pears'. Clarehill exposes all members of the Ulster White Limestone Formation from the Garron Chalk Member to the Tanderagee Chalk Member. The Garron Chalk Member, 0.9 m thick, consists of highly glauconitic chalk with a few phosphatised quartz pebbles and glauconite stained and unaltered fragments of Mercia Mudstone. The Portrush Chalk Member is 2.7 m thick. The lower part of the member is characterised by glauconite stained intraformational erosion surfaces with associated bioturbation, tenned the South Antrim Hardgrounds, and is flint free. Above these, the chalk is bedded with flint nodules. The top of the member is drawn at a poorly developed bedding plane immediately below the lowest paramoudra. The Ballymagarry Chalk Member, previously described as the Paramoudra Beds is 13 m thick and is characterised by a large increase in the amount of flint with massive nodules and nodular zones and with numerous paramoudras. The top of the member is marked by a prominent and laterally continuous bedding plane, below which debris from the fossil shell Inoceramus is very abundant. The Tanderagee Chalk Member, 3.4 m thick, is very fossiliferous and is characterised by slabby rather than massive chalk with courses of tabulate flints. The hardgrounds demonstrate that sedimentation of the Portrush Chalk Member was in comparatively shallow-water conditions with reduced, and at times, arrested sedimentation. This member contains hexactinellid sponges and a rich fauna of aragonite-shelled molluscs preserved as moulds and steinkerns coated with a green skin of glauconite. The paramoudras were originally thought to be sponges Poterion cretaceum but they are now regarded to be of inorganic origin. The sequence exposed in Clarehill Quarry demonstrates the importance of the Lagan Valley positive area during chalk sedimentation. The sequence is much condensed and the lowest 8 members of the Ulster White Limestone Formation are not developed here. Clarehill provides excellent outcrop of the upper part of the Ulster White Limestone Formation and is representative of the sequences developed over the Lagan Valley positive area. In particular, the paramoudras are well developed in this quarry in the area from where they were first described. https://www.daera-ni.gov.uk/publications/clarehill-assi