The Stratigraphy and Structure of Part of the South-East Durham Coalfield

Abstract

Summary During the last few years, a geologically little known area of south-east Durham, lying between the worked area of the Durham coalfield and the West Hartlepool Fault, has been explored by a gravity survey and a series of boreholes, with a view to the possible siting of a new coal mine. This work has proved an extension of the Durham coalfield, lying in a downfolded area beneath Permian rocks and fairly thick glacial deposits in the neighbourhood of Dalton Piercy. Some thirty million tons of coal are probably present in seams in the communis Zone of the Durham Coal Measures, but these are unlikely to be economically workable at the present time. The six new bore-holes have been correlated with earlier boreholes in the Fishburn area to the west and with shafts and boreholes, including two of the recent offshore bore-holes, to the north and east. Additional data obtained from the cores of the Permian rocks have augmented earlier work and led to a clearer understanding of some outstanding problems, in particular the position within the sequence of the thick Hartlepool Anhydrite and its probable relationship to the Middle Magnesian Limestone reef of Durham. Two alternative interpretations of the structure are offered in the paper; one assumes the likely easterly continuation of the Butterknowle disturbance, and the other the termination of this fault by an extension of the north-south trending Castle Eden disturbance.

Marine Permian of England

“…Lee and Harwood (1989) deduced that the brecciated rock had undergone a complex diagenetic history and that the brecciation occurred at about the time when abundant replacive anhydrite in the rock was being dissolved; they speculated that this dissolution might have been effected by fluids introduced during Tertiary re-activation of the nearby Butterknowle Fault. Farther east, away from known faults, apparently secondarily brecciated dolomite was reported by Magraw et al (1963) at a comparable stratigraphic level in Elwick No.1 Borehole (NZ 45313117) and Dalton Nook Plantation Borehole (NZ 4811 3144).…”

“…The brecciation and associated mineralogical changes are greatest in the lowest 10-30 m ofthe formation and diminish unevenly upwards, but there are places where large blocks of strata have foundered with relatively little brecciation or alteration, and other places where severe brecciation and diagenetic changes extend well up into the formation and even into the overlying Roker Dolomite Formation. Early suggestions that the more extensive brecciation of rock in the coastal cliffs might have accompanied or followed the dissolution of interbedded evaporites were strongly supported by Trechmann (1913) in view of the known presence of thick anhydrite beneath the Roker Dolomite at Hartlepool, but the confirmation of the precise stratigraphical position of the anhydrite awaited the drilling of cored coal-exploration bores offshore (Magraw et al, 1963). Early suggestions that the more extensive brecciation of rock in the coastal cliffs might have accompanied or followed the dissolution of interbedded evaporites were strongly supported by Trechmann (1913) in view of the known presence of thick anhydrite beneath the Roker Dolomite at Hartlepool, but the confirmation of the precise stratigraphical position of the anhydrite awaited the drilling of cored coal-exploration bores offshore (Magraw et al, 1963).…”

“…Though previously described as 'a sort of mylonite' by Woolacott (1909), who regarded it as part of his evidence for regional thrusting, the thin mixed layer between the Trow Point Bed and the Cycle EZ2 breccias is now accepted as the dissolution residue of the Hartlepool Anhydrite; in coal exploration boreholes offshore, the same stratigraphical interval is occupied by up to 150 m of massive anhydrite, which is directly underlain by the Trow Point Bed (Magraw et al, 1963;Smith and Francis, 1967, plate 13A;Smith, 1986, fig. 10).…”

Emplacement and diagenesis of gypsum and anhydrite in the late Permian Raisby Formation, north-east England

“…The regional dip of the Raisby Formation is an average of 1.3° east and so the change in fill of cavities correlates broadly with increasing depth below the present land surface. Compiled from data collected during this study, Woolacott (1919), Raymond (1962), Magraw et al (1963) and Smith & Francis (1967).…”

“…Woolacott (1912) first interpreted them originally to have contained gypsum and/or anhydrite. Since then, many other authors have noted the presence, and inferred the former presence, of calcium sulphates in the Raisby Formation (Magraw et al 1963;Smith & Francis 1967;Jones 1969;Jones & Hirst 1972;Mills & Hull 1976), but these occurrences have not been studied in detail. This paper describes the evidence for the former presence of calcium sulphate minerals in the Raisby Formation at outcrop, and investigates their origin and later diagenetic history.…”