The BGS Lexicon of Named Rock Units — Result Details

Donald's Hill Ignimbrite Formation

Computer Code: DHI Preferred Map Code: notEntered
Status Code: Full
Age range: Paleocene Epoch (GP) — Paleocene Epoch (GP)
Lithological Description: Tuff, creamy white, grey to pinkish grey, formerly ignimbritic, silicic welded ash-flow, with streaky poorly banded matrix, quartz phenocrysts and vlvanogenic lithic and crystal fragments now completely replaced by cryptocrystalline silica; clasts, exclusively of flint nodules reworked by erosion from Cretaceous chalk.
Definition of Lower Boundary: Welded tuff (as described under Lithology) disconformably overlies the karstified chalk surface of the Late Cretaceous Ulster White Limestone Formation. The upper few centimetres of the chalk are faintly stained yellow in some areas. Locally the base of the tuff oversteps onto Triassic, Carboniferous and Dalradian "basement" rocks.
Definition of Upper Boundary: The welded tuff of the Donald's Hill Ignimbrite Formation is overlain by basalt lave flows of the Antrim Lave Group.
Thickness: 0.6 to 1.1m
Geographical Limits: On the western margin of the Antrim Plateau (Northern Ireland) for a distance of about 30km from the west flank of Donald's Hill to Sounding Hill quarry, southsoutheast of Magherafelt, County Londonderry.
Parent Unit: Antrim Lava Group (ALR)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  Low cliff exposure on west side of Donald's Hill, County Londonderry. 
Mitchell, W I, Cooper, M R, Hards, V L and Meighan, I G. 1999. An occurrence of silicic volcanic rocks in the early Palaeogene Antrim Lava Group of Northern Ireland. Scottish Journal of Geology, Vol.35(2), 179-185. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable