Middle and Upper Jurassic (Callovian to Kimmeridgian) palynology of the onshore moray firth basin, northeast Scotland

Abstract

The Brora Coal, Brora Argillaceous, Brora Arenaceous, Balintore and Kimmeridge Clay formations of the onshore Moray Firth Basin represent an important Middle to Upper Jurassic (Callovian to Lower Kimmeridgian) reference section close to hydrocarbon‐rich North Sea basins. This composite succession at Brora and Balintore is c. 233 m thick; it is mudstone/siltstone‐dominated and largely rich in zonal and subzonal ammonites. For example, the Callovian succession at Brora is virtually complete, with coverage of all seven ammonite zones. All the five formations examined have yielded abundant palynofloras. The lithostratigraphic units sampled, except the Brora Coal Formation, have yielded rich associations of dinoflagellate cysts. The majority of the Inverbrora Member of the Brora Coal Formation at its type section at Brora is of early Callovian age based on dinoflagellate cysts; this member yielded Meiourogonyaulax caytonensis and Mendicodinium groenlandicum and these species preclude a Bathonian age. This member has been previously attributed to the late Bathonian. Dinoflagellate cysts are diverse and abundant in the overlying Brora Argillaceous to Kimmeridge Clay formations, therefore indicating open marine conditions. The stratigraphic distributions and relative proportions of these Callovian to Lower Kimmeridgian dinoflagellate cyst floras are largely consistent with those reported elsewhere in northern Europe, and the established dinoflagellate cyst biozonations can be readily applied to the Inner Moray Firth Basin. Some taxa, such as Gonyaulacysta dentata, are of distinct Boreal affinity. Furthermore, some minor stratigraphic anomalies were noted, including the range base of Scriniodinium crystallinum being in the early Oxfordian at Balintore. In England and Germany, this bioevent occurs in the late Callovian. Some notable dinoflagellate cyst abundance phenomena were observed. An example of this is the prominence of Korystocysta spp. in the Middle Callovian. This and other quantitative phenomena are of correlative significance. Marine palynomorph diversity increased markedly during the Callovian, stabilizing in the Lower Oxfordian. A suite of characteristic dinoflagellate cysts became extinct in the Middle Oxfordian, and some typically Late Jurassic elements became more prominent at this time. The early Kimmeridgian palynofloras from Ethie are entirely typical of this interval elsewhere in Europe.