Palaeolimnology and organic geochemistry of the Middle Devonian in the Orcadian Basin

Summary An interdisciplinary study of the Middle Devonian lacustrine laminites from the Orcadian Basin of NE Scotland has enabled the construction of a predictive source-rock model which we have applied to the Moray Firth area. Parameters characterizing areal source-rock extent, primary organic input, and the depths, salinity levels and redox potential of the depositional water column are discussed, together with the quantity and maturity of the preserved sedimentary organic matter. On the basis of this model, we suggest that a Middle Devonian component is present in the Beatrice crude (an atypical North Sea oil) in the Moray Firth Basin. This proposal is largely supported by molecular geochemical evidence.