Burial diagenetic evolution of Lower Carboniferous (Dinantian) of the southern margin of the Askrigg Platform and a comparison with the Derbyshire Platform

In order to predict the style and impact of post-depositional modification of carbon successions, well-studied and accessible outcrop analogues are invaluable. The Lower Carboniferous (Dinantian) carbonate platforms of the Pennine Basin of northern England have a long history of investigation. As such, they offer the potential to evaluate the mechanisms and timing of fluid flux during extensional tectonism, post-rift basinal subsidence and inversion. Carbonate sedimentation took place in the Lower Carboniferous upon footwall-highs bounded by deep-seated, reactivated Caledonian basement faults. This study concentrates upon the diagenetic evolution of the late Dinantian of the southern margin of the Askrigg Platform of North Yorkshire as a comparison with published data from the age-equivalent Derbyshire Platform. A pattern of consistent, predictable, diagenetic modification during early diagenesis is evident, but key differences occur in the burial realm. On both the Askrigg and the Derbyshire Platforms, patterns of dolomitisation, hydrocarbon emplacement and mineralisation can be determined on platform that potentially fingerprint the diagenetic evolution of the adjacent basins. However, within the Craven Basin and Askrigg Platform, there is only local evidence for a fault/fracture control on the migration of Mg-enriched, hydrocarbon-bearing fluids. In contrast, on the Derbyshire Platform, dolomitisation, hydrocarbon emplacement calcite cementation and mineralisation are intimately associated with NW-SE and NE-SW trending faults and fractures. Data suggest that the early influx of coarse grained siliciclastics to the Craven Basin, compared to the basins adjacent to the Derbyshire Platform, offered a strong control on patterns of diagenesis on the adjacent Askrigg Platform. Furthermore, the localisation of structural deformation along the Craven Fault Zone prevented the circulation of fluids onto the southern margin of the Askrigg Platform, due to the absence of open fault/fracture networks. In contrast, the burial diagenetic evolution of the Derbyshire Platform is intimately associated with the fault reactivation and associated fracturing during the Variscan Orogeny.