The Upper Carboniferous (Westphalian) Coal Measures of the Durham coalfield were deposited on a broad, flat, deltaic plain. In early Westphalian A times, a lower delta plain setting prevailed, evolving through southward deltaic progradation into an upper delta plain by mid-Westphalian A.
Detailed facies analysis of large, opencast exposures, supported by extensive subsurface data, has shown that a hierarchy of depositional controls operated across the Durham area during Westphalian times; (i) on the large scale, depositional geometry was controlled by patterns of major delta progradation and switching; (ii) on the medium scale, by a combination of structurally and compactionally induced subsidence, and (iii) on the small scale, by local sedimentary processes and subsidence patterns.
These observations form the basis of a coal depositional model for the Durham Coal Measures, which predicts that the thickest coals are to be found in upper delta plain domains controlled by compactional subsidence and not underlain by substantial channel sandstones. This model may also be applicable to other coalfields of northern England, and to ancient delta plain sequences elsewhere in the world.