Troon Volcanic Member

From Earthwise
Jump to navigation Jump to search

Troon Volcanic Member (TVL), Carboniferous, Midland Valley of Scotland[edit]

Troon Volcanic Member is part of the Passage Formation.


Named after the town of Troon and previously known as the ‘Troon Volcanic Formation’ and ‘Passage Group Lavas’. The present member was defined by Monro (1999)[1]; see also Browne et al. (1999)[2].


The Troon Volcanic Member comprises olivine-microphyric basalt (‘Dalmeny’ type).


Type sections occur in the Lugton Water (NS 332 447) where a full sequence through the lavas is exposed, but the total thickness is only about 10 m and the lavas are highly decomposed. Additionally, the member was encountered in the BGS Gailes Farm Borehole (BGS Registration Number NS33SW/1) (NS 32788 34867) from about 32.84 to 207.68 m depth.

Lower and upper boundaries[edit]

The lower boundary of the member is taken at the lithological change from sandy clastic strata of the underlying parent Passage Formation to basaltic lava.

The upper boundary of the member is taken at the base of the Ayrshire Bauxitic Clay Member and is defined as the lithological change from olivine-microphyric basalt to bauxitic clay. This boundary is described as normally gradational.


Some 10 m thick at Lugton Water and about 175 m in the BGS Gailes Farm Borehole (see above).

Distribution and regional correlation[edit]

North and central Ayrshire.




  1. Monro, S K. 1999. Geology of the Irvine district. Memoir of the British Geological Survey, Sheet 22W, part 21E (Scotland)
  2. Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D, Monro, S K, and Chisholm, J I. 1999. A lithostratigraphical framework for the Carboniferous rocks of the Midland Valley of Scotland.British Geological Survey Research Report, RR/99/07