Greenan Castle Pyroclastic Member

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Greenan Castle Pyroclastic Member (GCP), Ayr, Carboniferous, Midland Valley of Scotland[edit]

Greenam Castle Pyroclastic Member is part of the Clyde Plateau Volcanic Formation.


The Greenan Castle Pyroclastic Member was previously known as ‘bedded agglomerate of Greenan Castle’ by Eyles et al. (1949)[1], and Greenan Castle Ash by Whyte (1964)[2]. The present member was defined by Williamson and Monaghan in Stephenson et al. (2002)[3]. See also Sowerbutts (1999)[4]; Whyte (1992)[5].


The member comprises bedded volcaniclastic coarse sandstone, with subsidiary lithic lapilli-tuffs and tuffs.


The type section is on the shore and in the cliff at Greenan Castle, south of Ayr (NS 2311 6195 to NS 2313 6195), where the full thickness of the member is seen (see Eyles et al., 1949[1]; Whyte, 1964[2]; 1992[5]).

Lower and upper boundaries[edit]

Where seen on the shore at Greenan Castle the lower boundary is possibly disconformable on sandstones, mudstones and ‘cementstones’ of the underlying Ballagan Formation (Inverclyde Group).

The upper boundary at the same locality is seen to pass upwards unconformably into mudstones and sandstones of the Lawmuir Formation.


Some 23 m at Greenan Castle in the Ayr district, dying out laterally.

Distribution and regional correlation[edit]

A local unit on the shore and around Greenan Castle south of Ayr, which dies out about 1 km inland. It has been correlated on lithological grounds with the nearby Heads of Ayr Vent.


Chadian to Asbian.


  1. 1.0 1.1 Eyles, V A, Simpson, J B, and Macgregor, A G. 1949. Geology of central Ayrshire. Memoir of the Geological Survey of Great Britain, Sheet 14, parts 8, 13, 15 and 22 (Scotland)
  2. 2.0 2.1 Whyte, F. 1964. The Heads of Ayr vent. Transactions of the Geological Society of Glasgow, Vol. 25, 72–97
  3. Stephenson, M H, Williams, M, Monaghan, A, Arkley, S, and Smith, R A. 2002. Biostratigraphy and palaeoenvironments of the Ballagan Formation (lower Carboniferous) in Ayrshire. Scottish Journal of Geology, Vol. 38, 93–111
  4. Sowerbutts, A A. 1999. Geology of the Dunure, Carrick Hills and Heads of Ayr area. British Geological Survey Technical Report, WA/99/102
  5. 5.0 5.1 Whyte, F. 1992. Heads of Ayr. In Lawson, J D, and Weedon,W S (editors). Geological excursions around Glasgow and Girvan. (Glasgow: the Geological Society of Glasgow.)