Excerpt

Lower Old Red Sandstone (ORS) sediments have been recorded from a number of localities onshore around the margins of the Orcadian Basin (Westoll 1977; Mykura 1983; Mykura and Owens 1983). Similar sediments have not previously been reported from offshore but Mykura (1983) suggested that a number of isolated basins of this age might exist in the Moray Firth. One of these predicted basins has recently been penetrated by a borehole drilled by Burmah Oil Exploration Ltd.

The Burmah well 12/27–1 lies about 45 km northeast of Lossiemouth, and is located to the south of the Great Glen Fault (Fig. 1). Approximately 3200 feet (976 m) of Lower Devonian sediments are recorded in the well. The miospore populations recovered are extremely sparse, and include carbonised examples of Emphanisporites annulatus, E. robustus, Calamospora spp. and Retusotriletes spp. These limited assemblages together with the total absence of all characteristic Middle or late Devonian taxa suggests an early Devonian age for the sediments (B. Owens, pers. com.). The carbonisation recorded is commonly found in Devonian spores from onshore sequences (J. Marshall, J. Brown and S. Hindmarsh, verbal communication to Orcadian Basin conference, Cambridge, September 1984).

Downhole logs and well cuttings indicate that the lithology is fine grained throughout the 3200 feet. Three short cores have been cut and these are composed predominantly of mid to dark grey coloured, slightly micaceous claystones with interbedded dark grey siltstones up to about 4 feet (1.2 m) thick. Variable amounts of dolomite are found throughout, sometimes comprising . . .