Pas de Calais: Middle Jurassic Building Stones (Lead Author WGT)
Middle Jurassic limestones (contemporaneous with the Bath Stone of England) have long been quarried above and below ground in the area around Caen in the department of Calvados in Normandy, NW France. From the 11th century, southern England (Dorset, Hants & West Sussex) was the main importer of stone from Normandy. Similar Building Stone was also imported from the Pas de Calais department (Marquise area) opposite the Kent coast, summarised here.
The Middle Jurassic Limestones of the Pas de Calais (Pays Boulonnais)
For examples of the use of French limestones in Sussex see:
For examples in Hampshire, West Sussex, East Sussex & Kent
see the respective Historic England County Building Stone Atlases https://www.bgs.ac.uk/mineralsuk/buildingStones/StrategicStoneStudy/EH_atlases.html
BATHONIAN Limestones in the Neighbourhood of Marquise
(3) Calcaire des Pichottes: 3.5-3.9m. Marls & fossiliferous limestones (BT.U-CN)
(2) Calcaire de Marquise-Rinxent : Marquise Member : 7-8m. Massive-bedded white-beige or pale blue-grey, fine-coarse oolites with Rhynchonella hopkinsi (BT.M)
(a) Well-rounded “pseudo-oolites” 500-700u. “Millet seed”1. Large pellets or intraclasts (some >10mm) in a finer-grained matrix of ooids or pseudo-ooids 2 (c.200u), sparite cement. “Oncoliths” 3, botryoidal aggregates 4 (2mm), intraclasts. Shell fragments to 5cm (sparite-filled moulds). Bivalves & brachiopods. Bioturbated, “cavernous” weathering.
Low energy environment.
“Not as white as Portland but without yellow tinge of the Cotswolds-Lincs JM biosparites”
(b) Well sorted oolites with no oncoliths. High energy marine environment.
(1) Calcaire de Marquise-Rinxent: Rinxent Member : c.9m. oolites with Clypeus Ploti and Rhynchonella concinna (BT.L). Finer-grained than Marquise, some beds silty.
1 Millet Seed in geology usually refers to near-spherical 1mm quartz sand grains in aeolian sands.
2 Pseudo-ooids: Ooid-size pellets – faecal or micritised ooids, bioclasts &/or intraclasts
3 Oncoliths: Blue-green algal grains 2-20mm, formed in low energy environment
4 Botryoidal aggregates probably includes Grapestones
Compiled by Dr WG Townson CGeolFGS July 2018