Kilbirnie Mudstone Member
Kilbrinie Mudstone Member is part of the Limestone Coal Formation
The Kilbirnie Mudstone Member comprises mostly dark grey mudstone with ironstone, sporadic shelly marine bands and siltstone, medium-grained rooted grey sandstone and coal. The strata occur in upward-coarsening cycles, some capped by thin coal beds. The member includes the Dalry Clayband Ironstone, a grey argillaceous ironstone, and the Johnstone Shell Bed mudstone, with a marine fauna.
The cyclical nature of the member indicates periodic delta progradation, with the mudstone of the Johnstone Shell Bed being the result of a marine transgression.
The type section is in Paduff Burn, starting 200 m north of Place (NS 3028 5483) to the centre of Kilbirnie (NS 3148 5450) (Monro, 1999). Here can be seen some 30 m of mudstones overlying the Top Hosie Limestone. They include the Dalry Clayband Ironstone (0.5.m thick) and the Johnstone Shell Bed (at least 2.2.m thick) with a marine fauna of brachiopods and bivalves. Above this bed are upward coarsening sedimentary cycles including sandstones (commonly over 4 m thick) and thin coals. The sequence is partly intruded by dolerite dykes (Monro, 1999, pp. 50–51).
Lower and upper boundaries
The base of the member is taken at the top of the Top Hosie Limestone (TOHO), the highest of a number of thin limestones at the top of the Lower Limestone Formation (Figure 6, Column 4).
The top of the member is taken at the lithological change from mudstone of the Kilbirnie Mudstone Member, to the overlying dominantly sandstone-bearing cyclical sequences of the parent Limestone Coal Formation. The upper boundary is diachronous.
Between 0 and 45 m.
Distribution and regional correlation
North Ayrshire. Not present south of the Inchgotrick Fault.
- Monro, S K.1999.Geology of the Irvine district.Memoir of the British Geological Survey, Sheet 22W, part 21E (Scotland)
- 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
- Paterson, I B, Hall, I H S, and Stephenson, D.1990.Geology of the Greenock district.Memoir of the British Geological Survey, Sheet 30W part 29E (Scotland)