Devonian palynology of samples from Caithness

The palynology of samples from the Dounreay-2 Borehole and from outcrop in the Dounreay area, is described. The palynological assemblages recovered are sparse or barren, and the organic residue of the rocks is dominated by brown amorphous organic material (AOM) of possible lacustrine algal origin, though material of probable land plant origin is also present at certain levels in Dounreay-2. Spores are poorly preserved and many show the effects of pyrite growth. A few assemblages contain Rhabdosporites langii and one (from Quarry on Bannerman’s Farm; MPA 50686, PY735, 0407 6656,) contains Grandispora velata; these taxa allow a date to be suggested using standard Devonian biozonations. This and other evidence suggests that the Dounreay-2 sequence and the palyniferous outcrop samples are Eifelian in age.
On the basis of palynostratigraphical trends and other lithological evidence Bolt & Cole (1992) suggested a position for the Achanarras horizon in Dounreay–1 and simple lithostratigraphic correlation based on this implies a position for the Achanarras horizon at approximately 275m in Dounreay-2 (see Fig. 3). Such a position appears to be broadly consistent with admittedly sparse palynostratigraphic data.
Most of the surface samples contain Rhabdosporites spp. and Ancyrospora spp. but all lack G. lemurata, in these characteristics they are similar to those recorded within the studied parts of Dounreay-1 and –2 and can therefore be considered to be broadly correlative. Two of the surface samples contain assemblages that can be related more precisely to palynostratigraphic trends within the Dounreay boreholes, these are MPA 50689 [0433 6504] and MPA 50686 [0407 6656]. Both of these samples probably correlate with a level above 260.25m in Dounreay-1 and MPA 50686 probably correlates to a level not more than 60m stratigraphically above the Achanarras horizon.
Unpublished palynostratigraphical information on the Caithness Middle Devonian has been documented and this, combined with information from this and further studies, should help in the development of a local biozonation scheme to support mapping activities in Caithness.