Palynology of the Ballagan Formation in the Birnieknowes and Splimersford boreholes of the Midland Valley of Scotland

This report records the results of palynological analysis of 54 samples from the Spilmersford and Birnieknowes boreholes, National Grid Reference NGR [NT 4570 6902] and [NT 7373 7546]. respectively
Overall the palynological yield from the Spilmersford Borehole is very poor; many of the samples were barren, and those that yielded palynomorphs, contained mainly leiospheres or rare spores. Very few palynomorphs of biostratigraphic significance were recorded and no specimens of Lycospora pusilla, the zonal index of the Viséan Pu Biozone were recorded, which is surprising since the studied section in Spilmersford includes the CM–Pu transition as determined by Neves and Ioannides (1974) and Neves et al. (1973).
Although no specimens of Lycospora pusilla were recorded in the present study of the Spilmersford Borehole, the occurrence of an ‘upper Ballagan’ assemblage (see Stephenson et al. 2002) at a depth of 2732.5 feet, and a probable ‘upper Ballagan’ assemblage at a depth of 2794.5 feet, is consistent with the placing of the CM-Pu biozonal boundary at a depth of 2628.5 feet as determined by Neves and Ioannides (1974) and Neves et al. (1973).
In comparison to the assemblages of the Spilmersford Borehole, those of the Birnieknowes Borehole are diverse and well preserved, and contain the zonal indices of the CM and Pu biozones. On the basis of the presence of Lycospora pusilla, the upper part of the borehole section (at a depth of 938.33 feet), can be assigned to the earliest Viséan Pu Biozone of Clayton et al. (1977).
The evidence of this study, of Lycospora pusilla first appearing at a depth of 938.33 feet, supports the view given in the text of Neves et al. (1973), which places the CM/Pu biozonal boundary at that depth. However the common occurrence of Schopfites claviger in the highest samples (such as MPA 51099, depth 898.25 feet) and the absence of Perotrilites tesselatus and Schulzospora campyloptera in those samples suggests that the age of the highest part of the studied section does not extend into the younger TC biozone, as suggested in the text of Neves et al. (1973).
This study has highlighted problems in the stratigraphic placement of the CM/Pu biozonal boundary. According to the present analysis, the Birnieknowes Borehole contains only one sample from which specimens of L. pusilla were recovered. The 11 samples above (within the range 934.91–892.5 feet depth) contained no specimens of L. pusilla, and several of these assemblages are indistinguishable from typical CM Biozone assemblages in that they contain S. claviger and A. macra. If the horizon at a depth of 938.33 feet had not been sampled, it is probable, in the absence of other evidence, that the whole studied section would have been assigned to the CM Biozone. This difficulty highlights the importance of continued joint ostracod/palynology biostratigraphic studies and the need to investigate other essentially nonbiostratigraphic methods such as δ13Corg stratigraphic studies of sedimentary kerogen (see Stephenson, Leng et al., 2002).