Controls on syndepositional fracture patterns, Devonian reef complexes, Canning Basin, Western Australia

Syndepositional fractures are an important feature of high-relief carbonate systems and exert a profound control on many facets of platform evolution and reservoir development. Based on data collected from the Canning Basinʹs Devonian reef complexes this study characterizes syndepositional fracture patterns as a function of variations in: lithofacies, depositional position, stratigraphic architecture, and mechanical stratigraphy. Fracture parameters, such as extension and fracture intensity, are documented to vary strongly as a function of lithofacies. The highest syndepositional extension values occurring in the microbial facies of the Famennian platform margin, with extension values three times higher than observed in equivalent Frasnian strata. Position along the depositional profile exerts a strong control on fracture patterns, with an approximate two-fold increase in syndepositional extension and fracture intensity typically observed from the platform interior to the platform margin. Syndepositional fracture intensity is shown to vary systematically with changes in platform-margin trajectory, with high fracture intensities observed in strongly progradational platforms and decreased fracture development in aggradational and retrogradational platforms. Evidence for the temporal evolution of the mechanical stratigraphy of the Devonian reef complexes is presented, with early-lithified strata effectively behaving as a single, large-scale (50–150 m) mechanical unit during syndepositional fracture development, while secondary fractures become increasingly affected by bed-scale (0.25–5 m) mechanical heterogeneity introduced by progressive diagenesis. The results presented here potentially provide a tool for predicting fracture characteristics (e.g., intensity, orientation, location, and vertical extent) from limited subsurface data and provide a method for characterizing syndepositional deformation in other systems.