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Kirkwood Formation (KRW), Carboniferous, Midland Valley of Scotland

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==Kirkwood Formation [http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=KRW (KRW)], Carboniferous, Midland Valley of Scotland ==
Kirkwood Formation is part of the [[Strathclyde Group]].
=== Name ===
Taken from Kirkwood Farm, Strathclyde Region. The name was introduced by Monro (1982)<ref name="Monro82">Monro, S K. 1982. Stratigraphy, sedimentation and tectonics in the Dalry Basin, Ayrshire. Unpublished PhD Thesis, University of Edinburgh</ref>.

=== Lithology ===
The Kirkwood Formation consists of tuffaceous mudstones and tuffs, locally intercalated with non-tuffaceous sedimentary rocks, with some marine horizons developed. The tuffaceous mudstones and tuffs vary in colour from dark reddish brown to greenish grey. Non-tuffaceous sedimentary rocks, sandstones, siltstones and limestones, generally grey in colour, also occur within a restricted area intercalated with volcaniclastic rocks.

=== Genetic interpretation ===
The strata were largely formed by the reworking of materials derived from the underlying volcanic rocks but some primary ash-fall tuffs may be present. The formation shows extensive lateritisation, the product of a period of intense subaerial tropical weathering. There are some marine incursions.

=== Stratotype ===
The type section of the Kirkwood Formation occurs between 38.9 and 75.45 m depth in the Kirkwood Borehole (BGS Registration Number NS34NE/11) (NS 3885 4716), near Kilmarnock (Monro, 1999)<ref name="Monro99">Monro, S K. 1999. Geology of the Irvine district. ''Memoir of the British Geological Survey'', Sheet 22W, part 21E (Scotland)</ref>. This is the complete thickness of the formation at this locality.

=== Lower and upper boundaries ===
The base of the formation is taken at the lithological change from the underlying lavas of the [[Clyde Plateau Volcanic Formation]] into volcaniclastic sedimentary rocks (Figure 6, Column 4A).

The top is generally taken at the base of the overlying mudstones, siltstones and sandstones of the [[Lawmuir Formation]] or the cyclical limestones and clastic lithologies of the [[Lower Limestone Formation]] ([[Clackmannan Group]]). This boundary is commonly irregular and transitional with an interdigitation of lithologies.

=== Thickness ===
The Kirkwood Formation varies in thickness, from about 6 to more than 41 m (Monro, 1999, fig. 9)<ref name="Monro99"></ref> with thinning generally taking place towards the areas where the [[Clyde Plateau Volcanic Formation]] is thick. In the Irvine district, Monro (1999, p. 35, fig. 11)<ref name="Monro99"></ref> recorded a thickness of 41.39 m encountered in the Coalhill No. 2 Borehole (BGS Registration Number NS24NW/20) (NS 2432 4653) (a minimum thickness since the borehole did not reach the [[Clyde Plateau Volcanic Formation]]), and referred to localised thinning in boreholes close to the Dusk Water Fault. In the Kilmarnock district MacPherson et al. (2000, p.9)<ref>MacPherson, K A T, Smith, R A, and Akhurst, M C. 2000. Geology of the Kilmarnock district. ''Sheet description of the British Geological Survey'', Sheet 22E (Scotland)</ref> stated that the thickness of the formation averages around 15 m. BGS (1996)<ref>British Geological Survey. 1996. Campbeltown. Scotland Sheet 12, Provisional Series. Solid and Drift 1:50.000. (Keyworth, Nottingham: British Geological Survey.)</ref> gave a generalised thickness of 18.75 m for the formation in the main coalfield area at Machrihanish.

=== Distribution and regional correlation ===
Western Midland Valley and Machrihanish.

=== Age ===
Visean (Asbian to early Brigantian) (Monro, 1999<ref name="Monro99"></ref>; Browne et al., 1999<ref>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</ref>)

== References ==
<references/>
[[Category:Carboniferous lithostratigraphical nomenclature]]

Kirkwood Formation - Revision history

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Geosource>Volunteer 01: /* Kirkwood Formation (KRW), Carboniferous, Midland Valley of Scotland */