The Gronant Formation crops out along the north-east coast of Wales, most conspicuously on the
Great Orme peninsula and the limestone
escarpments south-east of
Prestatyn. It represents the uppermost
Dinantian carbonate package on the North Wales shelf. About 70 m thick, it lies conformably upon the Asbian Great Orme Limestone (part of the Dyserth Limestone Group) and is overlain by the basinal
cherts of the Pentre Chert Formation, a boundary that signals the shift from shelf carbonates to deeper-water
Namurian sedimentation. Warren and colleagues divided the unit into two mappable members: the Bishop's Quarry Limestone (c. 20 m of dark, well-bedded
packstones and
wackestones with thin
mudstone partings) and the Summit Limestone (c. 50 m of paler, locally cherty
grainstones). These beds accumulated during an early
Brigantian rise in relative sea-level in which quiet,
lagoonal muds gave way to better-oxygenated shoal
facies on the shelf margin, producing fining-upwards cycles capped by incipient
palaeokarst surfaces.
Petrographically the limestones show widespread
neomorphism of aragonitic
bioclasts, yet primary features—planar cross-bedding, graded
turbidite sheets and fenestral fabrics—remain visible. The formation yields a rich Brigantian macrofauna dominated by large productid
brachiopods (e.g.
Gigantoproductus,
Linoprotonia), rough-shelled corals such as
Caninia pachyendothecum and
Diphyphyllum lateseptatum, and the
goniatite-associated bivalve
Posidonia becheri at its base, tying the lower boundary to the Plc Zone. These faunal markers make the Gronant beds a valuable datum for correlating late
Viséan shelf carbonates with mixed
clastic–carbonate
successions in the adjoining
Craven Basin. In current
British Geological Survey nomenclature the unit is treated as the uppermost part of the
Clwyd Limestone Group; the earlier usage "Gronant Group" is now considered obsolete, but the historical formation name is retained for continuity with the literature. ==See also==