Birrenswark Volcanic Formation
Birrenswark Volcanic Formation is part of the Inverclyde Group
The Birrenswark Volcanic Formation comprises olivine basalt lavas intercalated with subordinate tuffs and impersistent sedimentary strata including sandstone, mudstone and dolostone (‘cementstone’).
The formation formed during the main initial phase of extensional faulting associated with development of the Northumberland Trough.
Partial type sections occur near Langholm at White Cove (NY 4060 9176) where almost the total sequence about 15.m thick is seen, Warb Law (NY 359 831) where at least five flows about 60 m thick in total occur, and Hartsgarth Fell at the head of the Tarras Water (NY 446 935) where the base of the sequence and upwards through about 29 m is seen (see Lumsden et al., 1967, pp. 73–76).
Lower and upper boundaries
The irregular base of the formation overlies the ‘cornstone’-bearing Kinnesswood Formation in the Solway Basin (Figure 6, Column 7; Figure 10, Columns 2, 3).
The top of the formation is the faulted or irregularly conformable base of the ‘cementstone’-bearing strata of the Ballagan Formation.
Between 15 and 60 m. Best developed between Dinely and Langholm, the lavas thin westwards towards Birrenswark Hill.
Distribution and regional correlation
Solway Basin. From between Dinely and Langholm westward to Kirkbean Glen, southern Kirkcudbrightshire. Correlated with the Kelso Volcanic Formation.
Mid Tournaisian (Courceyan).
- Pallister, J W.1952.The Birrenswark Lavas, Dumfriesshire.Transactions of the Edinburgh Geological Society, Vol. 14, 336–348.
- Lumsden, G I, Tulloch, W, Howells, M F, and Davies, A.1967.The geology of the neighbourhood of Langholm.Memoir of the Geological Survey of Great Britain, Sheet 11 (Scotland)
- Lintern, B C, and Floyd, J D.2000.Geology of the Kirkcudbright–Dalbeattie district.Memoir of the British Geological Survey, Sheets 5W and 5E, part 6W (Scotland)