Kinderscoutian and Marsdenian successions in the Bradup and Hag Farm boreholes, near Ilkley, west Yorkshire

Abstract

SUMMARY The Bradup and Hag Farm boreholes were drilled by the British Geological Survey (BGS) into strata of the Upper Carboniferous Millstone Grit Group near Ilkley. They prove (beneath glacial till) a rock succession of Namurian (late Kinderscoutian to earliest Marsdenian) age including five faunal marker bands, two of which are the widespread Reticuloceras coreticulatum (R 1c 4) and Bilinguites gracilis (R 2a 1) marine bands. The other three yielded mainly benthonic assemblages and lacked diagnostic ammonoid taxa, but are tentatively assigned to the R 1c 2, R 1c 3, and Butterly marine bands. Four late Kinderscoutian cycles are identified, and a basal fifth cycle is incomplete. Each comprises a coarsening-upwards sequence from marine mudstones to prodelta-slope siltstones and sandstones, then to fluvial sandstones and other delta top deposits. Three of the fluvial sandstones have conglomeratic bases and overlie erosion surfaces which, in the third and fifth cycles, are immediately underlain by laminites comprising alternating grey sandstone and dark grey clay-rich sandstone laminae, the former varying rhythmically in lamina thickness, and the latter invariably having a thickness of 1–2 mm. Preliminary measurements suggest a possible tidal influence on the deposition of the laminites, an influence previously unrecorded in the Namurian of this part of the Central Pennine Basin.