The concealed coalfield of Canonbie: reply

Abstract

SIRS—Picken (1988) provides new evidence of a major transgressive unconformity within the Scottish Upper Coal Measures with the uplift and erosion of some 200 m of Middle and Upper Coal Measures in the vicinity of the northern margin of the Pennine Basin of Carboniferous sedimentation. This feature invites comparison with the Symon Unconformity situated at the base of the Halesowen Group in the South Staffordshire and Shropshire coal-fields where similar high Upper Coal Measures overlap all horizons of the Carboniferous southwards and eventually rest directly upon the Lower Paleozoic rocks which formed the southern margin of the Pennine Basin. Farther afield the Symon Unconformity has been correlated with the unconformity beneath the Holzer Konglomerat of Germany, which is also taken as the base of the Stephanian sub-stage of the Upper Carboniferous (Wills 1948, 1956; Poole 1976) and it would therefore appear probable that all the measures above the transgressive unconformity described by Picken are of Stephanian age. It is also notable that primary red beds (Etruria Marl facies) are widespread above the horizon of the Charles Marine Band (basal Westphalian C boundary) in South Staffordshire, Warwickshire, Derbyshire and Leicestershire, and mirror the general development of red beds above the Skelton Marine Band in Canonbie and Skipsey's Marine Band elsewhere in Scotland. In the central areas of the Pennine Basin (e.g. Lancashire and North Staffordshire), red beds only form the uppermost 100-150 m of a Westphalian C-D sequence some 775 m thick, which occurs below the Stephanian Ardwick Limestone and Newcastle groups. Four marine have been recorded from the lower part of this sequence and it is possible that the Riddings Marine Band correlates with the uppermost Top Marine Band of the Pennine sequence (taken as the Middle-Upper Coal Measures boundary in England), but it is not clear from Picken's account as to the exact position of the Riddings Marine Band amongst the number of marine bands (Picken 1988, p. 65) recorded from this part of the Canonbie sequence.