Lacustrine and palustrine carbonates in a Brigantian (late Dinantian) intrashelf basin in the Derbyshire carbonate platform

Abstract

The Brigantian (late Dinantian) Headstone Laminite provides a record of freshwater carbonate deposition in an intrashelf basin when the surrounding Derbyshire carbonate platform was emergent. The laminated grainstone/carbonate mudstone facies contains calcified plant material, peloids, ostracods and lenses of calcite tufa deposited in a lake margin and sublittoral part of a freshwater lake in a humid palaeoclimate. Precipitation of tufa may have taken place along water courses or resurgences fed by meteoric run‐off and seepage from the karsted carbonate platform. The fenestral carbonate mudstone with calcrete and fenestrae represent deposition in well‐drained parts of the lake margin. A shift to more arid conditions is represented by the laminated dolomudstone facies with an allochem assemblage of calcified plants and micropeloidal dolomicrospar grains and occasional alginite in restricted a lake basin setting. Gypsum crystals and desiccation curls are also present in evaporitic lake margin settings. A return to more humid conditions is indicated by deposition of the laminated grainstone/carbonate mudstone facies with organic‐rich mudstone with thin coal seams and carbonized roots deposited in a poorly drained lake margin setting. This may be a reflection of a gradual transgression after emergence. The eastern margin of the intrashelf basin may have been formed by the Edensor Anticline; however, it is not known if a further complex of lacustrine, palustrine and lagoonal facies was present to the east. Deposition of graded beds containing lithoclasts derived from lacustrine facies were associated with slumping generated by reactivation of structures controlling the intrashelf basin margins.