A revision of the Jurassic (Bathonian to Oxfordian) lithostratigraphy of the onshore Moray Firth Basin, north-east Scotland

Abstract

Abstract Bathonian to Oxfordian strata occur onshore in two principal locations over 30 km apart on the coast of the Moray Firth, at Brora and Balintore. The existing lithostratigraphy has the same formation names applied to both successions despite profound differences, exemplified in their schemes of local members. Furthermore, three of the formation names include the same place name, and use obsolete lithological terms. We consider that all the Bathonian to Oxfordian members are satisfactory, and propose their retention with original names, with one exception, to provide continuity with the superseded formational scheme. We propose retention of the Brora Coal Formation as currently defined. The Brora Argillaceous, Brora Arenaceous and Balintore formations at Brora are unsatisfactory in a modern context and we propose: i) a new Strathsteven Mudstone Formation, which is mudstone-dominated, and generally coarsens-upwards. ii) a Clynekirkton Sandstone Formation, which is sandstone-dominated and generally coarsens upwards. This formation scheme employs unique geographical names and modern and appropriate lithological terminology. Furthermore, the boundary between the Strathsteven and Clynekirkton formations is placed at a junction that is a change from mud- and silt-dominated lithologies to silt- and fine- and medium-grained sand and is mappable. We consider that the Callovian–Oxfordian succession at Balintore should be assigned to a single formation, viz. the revised Balintore Formation. Apart from the basal Brora Roof Bed, the succession at Balintore does not lithologically resemble that at Brora, and the scheme of the Brora Argillaceous Formation, Brora Arenaceous Formation, and the Balintore Formation as previously defined is unworkable here.