Palynology of samples from the Ballagan Formation of the Glenrothes borehole, Fife

This report records palynological analysis of 32 samples from the Glenrothes Borehole, Fife [NO 2561 0314] and includes data from a further 12 samples reported on by Turner (1995). The borehole was sampled in detail to investigate the potential for high precision correlation within the Ballagan Formation in the Midland Valley of Scotland, following detailed work at the Heads of Ayr section, Ayrshire (Stephenson et al. 2002; Stephenson, 2001).
Due to rather patchy recovery and poor preservation, correlations of the Ballagan Formation in the Glenrothes Borehole are necessarily tentative; however it seems likely that lower parts of the Ballagan Formation are present in the Glenrothes Borehole than in the section at the Heads of Ayr. The presence of Pustulatisporites dolbii (recorded only from the LL-PC Biozones, Higgs et al. 1988) and the absence of Schopfites claviger suggests that the sequence below 316.95 m depth may be assignable to the PC Biozone (Tn2b/c to Tn3a age, Higgs et al., 1988).
The age of the upper part of the Ballagan in Glenrothes is latest Tournaisian (CM Biozone Tn3c) since Schopfites claviger and Auroraspora macra are present and Lycospora pusilla is absent. The part of the Ballagan above 246.0 m depth may correspond to the upper parts of the Ballagan at the Heads of Ayr because Acanthotriletes cf. macrogaleatus is present (but very rare) at this level and at 223.8 m depth, but other taxa characteristic of the upper parts of the Ballagan at the Heads of Ayr are not present. The age of the succeeding Pathead Beds is also uncertain due to very poor palynomorph preservation, but may be at least TC Biozone in age (late Holkerian – early Asbian) based on the presence of L. pusilla and possible specimens of Schulzospora sp.
Samples analysed in parallel for palynology and ostracods indicate that aquatic algal spores of the zygnemataceae indicate low salinity conditions. Correlation of autochthonous algal spore assemblages and ostracod faunas will be of further use in palaeoenvironmental determinations.
In previous work on the Ballagan Formation at the Heads of Ayr (Stephenson et al., 2002; Stephenson, 2001), it was suggested that assemblages dominated by algal forms may be indicative of impersistent low salinity lakes on low gradient coastal plains, and that the inverse relationship between terrestrially derived and autochthonous algal palynomorphs in these assemblages may be explained by local lacustrine drowning of terrestrial plant communities.
New lithofacies information presented here appears, however, to favour relatively shallow water conditions for algal spore assemblages since the latter are associated mainly with dessication cracked sediments It is now thought likely that they contain few terrestrially derived spores because of contemporaneous weathering, repeated wetting and drying and or alkaline dissolution in subaerial or near subaerial conditions. Algal spores may have been produced in small stagnant pools on the ground surface.
The lower part of Ballagan Formation in the Glenrothes Borehole, including the Mains of Errol Member, was deposited in shallow water and frequently sub aerial conditions while above about 280 m depth there is evidence of more persistent aquatic conditions because fish appear to be more common in this section, and facies indicative of sub aerial exposure or shallow water are fewer. At present it is not possible to be sure whether these more stable aquatic conditions were marine or freshwater since fish can occupy both, but the occurrence, at a number of horizons, of conchostracans and fresh-brackish water ostracods indicate that much of this section may have been deposited in low salinity conditions.
A summary of the biostratigraphy and palaeoenvironments of the Ballagan Formation in the Glenrothes Borehole is given in Fig. 1.