The architecture of concealed Dinantian carbonate sequences over the Central Lancashire and Holme highs, northern England

SUMMARY Many of the concepts of early Carboniferous carbonate deposition in ‘block’ and ‘basinal’ areas were developed in northern England, although the subsurface extent and nature of these successions were difficult to define due to limited Dinantian outcrop and borehole data. Detailed interpretation of seismic reflection data from this region, calibrated by borehole and outcrop data, has resulted in the identification of two distinct seismic facies in the subsurface, corresponding to shallow-water carbonates and deeper-water basinal lithologies. The subsurface extent and architecture of these facies have been mapped. Shallow-water carbonates are interpreted from seismically ‘transparent’ units which are broadly lens-like and which are restricted to the Central Lancashire and Holme highs. Surrounding and basinwards of these shallow-water carbonates is a ‘stripy’ seismic facies with a wedge-like form representing basinal-facies rocks. The two seismic facies are interdigitated and attest to a complex history of progressive drowning of the intra-basinal highs. Relative sea-level appears to have risen at varying rates during Dinantian times, with periods of rapid rise resulting in the retreat of shallow-water carbonates and periods of less rapid rise, stillstand or perhaps sea-level fall leading to their outbuilding. No evidence is found of significant footwall erosion of strata associated with fault movements in Chadian to Arundian times as suggested by some published tectonostratigraphic models.