This 1988 Enterprise Oil intra-Chatburn marker map comes from UKOGL’s archives. We have sketched a modified fault pattern, to give an interlinked network defining a pile of northwest-moving thrust wedges: which is what the Gisburn-Clitheroe dome is. Each thrust slice (“duplex”) will be heavily fractured, below the imaging resolution of the seismic lines. Seismic resolution is around 40 metres, so we only see the larger faults and fractures.
It’s a very large fold, the grey area is 4-way dip closure over 10 km in length, with three compartments separated by NW to WNW-trending fractures. The fold axes drawn in pale blue are offset by these NW faults, which are oblique sidewalls to the numerous arcuate thrusts which dip south-eastwards. None of the three west-east rollovers has been drilled, to date (Swindon being a stratigraphic borehole).
Red lines are the seismic network, heavily drawn ones are interpreted here by HGL. Faults trending to northwest drawn in black are sidewall, strike-slip faults, notably the Clitheroe and Barnoldswick Faults, these allowed the fold slices to move by variable amounts. The crestal area corresponds to greatest net displacement north-westwards, in the fold core. This structure warrants 3D seismic cover for best definition.
Dashed yellow is the Clitheroe quarry group’s outline, which lies on the SW margin of the culmination closed area. Line -08 across the quarry is shown in the next slide. Blue arrow is a possible trial well location.