Midland Valley of Scotland

Carboniferous rocks occupy much of the Midland Valley of Scotland, but are commonly obscured at surface by Quaternary deposits. The succession occupies an ENE-trending graben bounded by the complexes of the Highland Boundary Fault to the northwest and the Southern Upland Fault to the southeast. Onshore, the graben is about 90 km wide and extends some 150 km from the Ayrshire coast and Glasgow in the west to the east Fife and East Lothian coasts in the east (Fig. 14.1). The basins within the graben are associated with Carboniferous rocks more than 6 km thick. The Highland Boundary and Southern Upland faults were active and helped control sedimentation, initially during the Tournaisian as sinistral strike/oblique slip faults and subsequently in the Visean to Westphalian a regime of dextral strike/oblique-slip deformation (Browne & Monro 1989; Ritchie et al. 2003; Underhill et al. 2008). Isolated exposures also occur on the Island of Arran and at Machrihanish in Kintyre. The Midland Valley of Scotland was separated from basins to the south (Tweed and Solway Firth basins and the Northumberland Trough- see Chapter 13) by the Lower Palaeozoic rocks of the Southern Uplands block, which formed a positive, mainly emergent area throughout the Carboniferous. However, this was breached during the Carboniferous by narrow NW–SE trending basins, for example Stranraer and Sanquhar to Thornhill. The Scottish Highlands to the north, of Lower Palaeozoic and Precambrian rocks, were similarly a positive, mainly emergent area with outcrops of Carboniferous (Johnstone 1966) limited to the west coast around Inninmore (Sound of Mull), Bridge of Awe (Pass of Brander) and Glas Eilean (Sound of Islay).