Craigmaddie Muir Sandstone Member

Craigmaddie Muir Sandstone Member (CRMS), Carboniferous, Midland Valley of Scotland

Craigmaddie Muir Sandstone Member is part of the Lawmuir Formation

Name

The member was previously named the Craigmaddie Sandstone Formation by Tait (1973), and the Craigmaddie Sandstones (of the Upper Sedimentary Group, Calciferous Sandstone Series) by Clough et al. (1925).

Lithology

Sandstone, white, cross bedded, with pebbly ‘bands’ (beds) in places. Locally, interbedded with mudstone and rare intercalations of volcanic detritus. Strata within the member were described by Tait (1973) as fine-grained, buff-weathering quartz arenite with conglomerate lenses that consist mainly of mudstone intraclasts.

Genetic interpretation

Tait (1973) interpreted the sandstone member as the deposits of a meandering river system.

Stratotype

Partial type sections were described by Hall et al. (1998), who referred to the prominent outcrops of bedrock on Craigmaddie Muir exposing strata from the base and the middle parts of the member (NS 580 766 to 588 764). The type section of the upper part of the member (about 68 m thick), to its upper boundary placed at the base of the Balmore Marine Band, is recorded from exposures in the subsurface beneath Craigmaddie Muir in the Strathblane–Balmore tunnel (BGS Registration Number NS57NE/30) (NS 5895 7521).

Lower and upper boundaries

The lower boundary of the Craigmaddie Muir Sandstone Member is mapped on Craigmaddie Muir (NS 5820 7652) and Muirhouse Muir (NS 5723 7785) and placed where sandstones without interbeds of conglomerate are observed at outcrop (BGS, 1987b; see also BGS, 1987c). The underlying Douglas Muir Quartz-Conglomerate Member is typically conglomerate with sandstone interbeds and, toward the top of the member, sandstone with pebbles or conglomerate beds (Figure 6, Column.4A). The lower boundary of the Craigmaddie Muir Sandstone Member had previously been mapped slightly lower in the sequence by Tait (1973) who noted it to be gradational containing ‘lenses of conglomerate of similar composition’ to the underlying Douglas Muir Quartz-Conglomerate Member near the base.

The upper boundary of the Craigmaddie Muir Sandstone is placed at the base of the Balmore Marine Band (Hall et al., 1998, fig 9). This is at a higher position than that of Clough et al. (1925, fig. 2) who placed it at the top of the main sequence of sandstones about 45.m below the Craigenglen Beds, but at a lower position than Tait (1973) who placed the boundary beneath the Balgrochan Beds. Tait’s (1973) informal division ‘lower Craigmaddie Muir Sandstone Member’ equates with the Craigmaddie Muir Sandstone Member as presented here.

Thickness

Between 170 and 180 m

Distribution and regional correlation

The member is confined to the fault-bounded block south of the Craigend and Campsie faults and north of the Bankend and Glorat faults, extending from Muirhouse Muir (NS 576 777) eastwards to Craigmaddie Muir (NS 590 765), Craigend Muir (NS 585 776), and the vicinity of Lennoxtown (NS 626 780), north-east of Milngavie, Strathclyde.

Age and biostratigraphical characterisation

Visean (?Asbian–Brigantian). The Balmore Marine Band immediately above the Cragmaddie Muir Sandstone Member has a relatively sparse fauna including brachiopods. Correlatives of this bed contain the bivalve Posidonia becheri, which is thought to be of P1b or P1c age (Hall et al., 1998).