Cringate Volcaniclastic Member

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Cringate Volcaniclastic Member (CRNV), Fintry-Touch Block, Carboniferous, Midland Valley of Scotland[edit]

Cringate Volcaniclastic Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

Previously named the Cringate Interbasaltic Beds (Francis et al., 1970)[1].

Lithology[edit]

The Cringate Volcaniclastic Member consists of variably stratified volcaniclastic sedimentary rocks and/or tuffs. An exposure in the north-east bank of the Endrick Water at (NS 6800 8750) shows poorly stratified dull red tuff or volcaniclastic sedimentary rock with persistent beds of red mudstone, interspersed with lenticular masses, up to 1.5 m thick, of unsorted lava fragments set in a matrix of greenish clay. The fragments include decomposed basalt up to 20 cm across, commonly rounded but with irregular margins that seem to interlock. Some are scoriaceous with small irregular amygdales filled with chlorite or carbonate minerals. The matrix includes carbonate minerals but also contains some grains of quartz and feldspar.

Stratotype[edit]

The type section is in the Endrick Water, between the Fintry Hills and the south-western Gargunnock Hills, north-east of Glasgow (NS 678 879 to NS 682 873) (Francis et al., 1970)[1]. A reference section is in a left-bank tributary of the Endrick Water near Cringate (NS 683 874 to NS 6858 8756).

Lower and upper boundaries[edit]

In the Endrick Water at (NS 6807 8742), the Cringate Volcaniclastic Member overlies highly decomposed microporphyritic basalt, thought to be roughly equivalent to middle parts of the Spout of Ballochleam Lava Member (Francis et al., 1970)[1]. In a left-bank tributary of the Endrick Water at (NS 6858 8756), about 40 m of tuff or volcaniclastic sedimentary rock is overlain by 6 m of microporphyritic basalt that forms a waterfall (Francis et al., 1970)[1]. The basalt is probably one of the highest lavas of the Spout of Ballochleam Lava Member.

Thickness[edit]

At least 45 m.

Distribution and regional correlation[edit]

The member is restricted to the Fintry-Touch Block (Francis et al., 1970)[1] and specifically to the valley of the Endrick Water around Cringate (NS 685 873), between the Fintry Hills and the south-western Gargunnock Hills, north-east of Glasgow.

Age[edit]

Mid Visean (Arundian to Asbian).

References[edit]

  1. 1.0 1.1 1.2 1.3 1.4 Francis, E H, Forsyth, I H, Read, W A, and Armstrong, M. 1970. The geology of the Stirling district. Memoir of the Geological Survey of Great Britain, Sheet 39 (Scotland)