Palaeochannels in mine workings in the High Hazles Coal (Westphalian B), Nottinghamshire Coalfield, England

Abstract

Palaeochannels have numerous deleterious effects on coal mining including the formation of ‘washouts’, and their detection and delineation in the subsurface is of paramount importance. A palaeochannel system in the roof of the High Hazles Coal (Westphalian B) at Gedling Colliery, Nottinghamshire, is described. The roof strata of this seam are interpreted as the deposits of a lacustrine delta complex formed on an upper delta plain, with the palaeochannels constituting minor deltaic distributaries. The lacustrine delta front deposits consist of a coarsening-upwards sequence of siltstones and sandstones, which form a sheet-like body of coalescing distributary mouth bars that were laid down by friction-dominated effluents. The distributary channels were filled by a variety of processes, giving rise to complex channel deposits. Bedload deposition of sand on bars, collapse and sloughing of channel banks, and deposition of silts and muds from suspension were important mechanisms. The nature of the deposits reflects the mode of channel abandonment, rather than equilibrium channel processes. Overbank flood deposits and prodelta/lacustrine mudstones are also described from the High Hazles roof. Based on this study, criteria are suggested that may enable the successful detection and delineation of palaeochannels in mine workings elsewhere.