Abstract Understanding and predicting architecture and facies distribution of syn-rift carbonates is challenging owing to complex control by climatic, tectonic, biological and sedimentological factors. CarboCAT is a three-dimensional stratigraphic forward model of carbonate and mixed carbonate–siliciclastic systems that has recently been developed to include processes controlling carbonate platform development in extensional settings. CarboCAT has been used here to perform numerical experiment investigations of the various processes and factors hypothesized to control syn-rift carbonates sedimentation. Models representing three tectonic scenarios have been calculated and investigated, to characterize facies distribution and architecture of carbonate platforms developed on half-grabens, horsts and transfer zones. For each forward stratigraphic model, forward seismic models have also been calculated, so that modelled stratal geometries presented as synthetic seismic images can be directly compared with seismic images of subsurface carbonate strata. The CarboCAT models and synthetic seismic images corroborate many elements of the existing syn-rift and early-post-rift conceptual model, but also expand these models by describing how platform architecture and spatial facies distributions vary along-strike between hanging-wall, footwall and transfer zone settings. Synthetic seismic images show how platform margins may appear in seismic data, showing significant differences in overall seismic character between prograding and backstepping stacking patterns.

Abstract: The initiation, growth and interaction of faults within an extensional rift is an inherently four-dimensional process where connectivity with time and depth are difficult to constrain. A 3D discrete element model is employed that represents the crust as a two-layered brittle–ductile system in which faults nucleate, propagate and interact in response to local heterogeneities and resulting stresses. Faults nucleate in conjugate sets throughout the model brittle crust; they grow through a combination of tip propagation and interaction of co-linear segments to form larger normal faults. Segment linkage occurs by merging of adjacent fault segments located along strike, downdip or oblique to one another. Finally, deformation localizes onto the largest faults. Displacement distribution on faults is highly variable with marked along-strike and temporal variations in displacement rates. Displacement maxima continuously migrate as smaller fault segments interact and link to form the final fault plane. As a result, displacement maxima associated with fault nucleation sites are not coincident with the location of the maximum finite displacement on a fault where segment linkage overprints the record. The observed style of fault growth is consistent with the isolated growth model in the earliest stages which then gives way to a coherent (constant-length) fault growth model at greater strains.

Abstract Deformation above mobile salt along continental margins results in a complex array of structures that have a profound effect on sea-floor geomorphology and create a slope characterised by a 3D array of salt-cored highs and intervening sub-basins. We present examples of the various ways the growth of salt-related fold and fault arrays controls submarine channel complexes at local to regional scales using standard attributes, spectral decomposition and RGB blending of 3D seismic datasets from Tertiary passive margins. Sediment transport pathways commonly divert around salt-cored highs and become fixed by early-formed structures high on the slope resulting in long-lived, major sediment (channel complex) fairways that are ‘pinned.’ During early stages of fold growth channels tend to be simple and isolated and are orientated perpendicular to the regional slope. However, as folds grow and interact, the channel belts increase in sinuosity and their cross-sectional and long-profile geometry becomes progressively more variable and complex as slope roughness increases. As a result, channel orientations become increasingly variable with local deviations parallel to fold axes and channel complex sinuosity mimicking the spacing of the main salt-cored structures. Avulsion nodes, channel complex depth and width, levee development, and the internal architecture of component depositional elements within channel complexes all show systematic variation with respect to structural location. Amplification of salt-cored folds and growth of diapirs also leads to local oversteepening and slope failure resulting in development of mass transport complexes that may dam entry or exit points between mini-basin depocentres.