The Carboniferous-Permian Grant Group of the Canning Basin, Western Australia, was deposited during the Late Palaeozoic Ice Age. This study utilises extensive seismic and well data to improve understanding of the controls on depositional style and architecture of the Grant Group. The study is based on 12 2D seismic surveys acquired between 1981 and 1990 on the Crossland Platform, Barbwire Terrace and Fitzroy Trough, and a newly acquired 3D seismic data on the Lennard Shelf, integrated with data from 66 exploration/appraisal wells. Particular focus has been on the structural evolution of the Canning Basin and its influence on Grant group deposition, the complex morphology of the Base Grant unconformity, and recognition of evidence for glacial environments from seismic and well data. Previous workers subdivided the Grant Group into the lower Reeves Formation and upper Grant Group. In this study the Reeves Formation is interpreted to be clearly a separate stratigraphic unit, defined as a syn-rift sequence restricted to the Fitzroy Trough. It records a growth of more than 1870 m toward the Fenton Fault. Movement along the Devonian-Carboniferous extensional faults is interpreted to have ceased prior to the deposition of the Grant Group. An angular unconformity observed at the base of the Reeves Formation is interpreted to be evidence for the middle Carboniferous Meda Transpressional Movement. Two large compressional anticlines underlying the Reeves Formation can be associated with a left-lateral bend in the Fenton Fault. The transpressional movement is interpreted to be characterised by a dominant dextral strike-slip movement. The event separates two major extensional phases of the Devonian-Carboniferous faults, the Devonian-Lower Carboniferous Pillara Extension and the Upper Carboniferous Point Moody Extension. The overlying Grant Group was deposited during a post-rift sag phase. Minor displacement of the Grant Group, associated with some faults, is the result of the later reactivation caused by the Triassic-Jurassic Transpressional Movement. The cessation of faulting prior to the Grant Group deposition supports the interpretation that the extensive diamictites observed throughout the Canning Basin are most-likely glacial in origin and not related to faulting. The base Grant Group Unconformity is observed to be a complex surface that develops as a result of a variety of processes, including faulting, salt dissolution and glacial erosion. Localised thickening of the older Worral Formation produces discrete topographic highs that dominate the Broome-Crossland Platform. They are interpreted to have formed initially as local depressions associated with subsurface dissolution of underlying Mallowa Salt. This resulted in deposition of a thickened Worral at these locations. Later partial dissolution of salt at the margins of these structures occurred prior to the Grant Group deposition, evident from reflector onlap onto these so called “Worral Sombreros” within the lower most part of the Grant Group. Later complete removal of salt, resulted in post depositional deformation of the Grant. The Grant Group can be divided into a number of formations, that have been correlated and mapped throughout the study area and their seismic facies interpreted to improve understanding of the depositional environments and evolution. The basal Betty Formation (≈80-500 m) consists predominantly of sandstone with thick intervals of diamictite and conglomerate and minor mudstone. Seismic interpretation in this study, together with integrated well analysis, supports previous studies that suggest it was deposited during repeated cycles of glacial advance and retreat. At least four cycles can be defined from this study, based on recognition of major erosional surfaces on the Lennard Shelf. The Winifred Formation (≈25-110 m) is mudstone dominated interval with minor sandstones, deposited during a major deglaciation. The Carolyn Formation (≈60-450 m) consists of massive and cross-bedded sandstones with thin intervals of mudstone. This study has recognised for the first time two probable glacial intervals restricted to the Lennard Shelf and Fitzroy Trough during deposition of Carolyn Formation. Detailed mapping has identified NW-SE to N-S oriented channels and palaeo-valleys systems, interpreted based on their character, to be formed sub-glacially by melt water. This extends the glacial influence in the basin to the end of the Grant group and these results provide valuable data on the influence of structural evolution and ice sheet dynamic and distribution within the Canning Basin. New information on the depositional architecture of the Grant Group also improves understanding of the potential for reservoir development with a section that has proven hydrocarbon potential.

Carbonate facies patterns and stratal architecture are the product of the complex interaction of internal (e.g., reef-building biota, sediment production) and external drivers (e.g., tectonics, climate, and relative sea level). In the Canning Basin of Western Australia, many of these drivers are in flux across the Late Devonian Frasnian--Famennian (F--F) boundary and significant variations in reefbuilding biota and long-term accommodation are observed. This study documents the evolution of the Canning Basin's Devonian reef complexes across the F--F boundary and proposes a new interpretation of the stratal architecture and paleobathymetric profile of the Famennian. Data presented here demonstrate the evolutionof a shelf-crest system in the Famennian, with beds expanding basinward and the reef growing in water depths of approximately 5-15 m. The paleobathymetric profile of the Famennian described by this study represents a departure from the well-documented barrier-reef system of the Frasnian. Digital outcrop models help capture the heterogeneity of the Famennian system and allow for characterization of the Devonian reef complexes across the F--F boundary. Syndepositional fractures are a ubiquitous feature of high-relief, reefrimmed carbonate systems and these features exert a profound influence on many facets of platform evolution. This study documents strong variability in syndepositional fracture patterns as a function of lithofacies and depositional setting and evidence for the temporal evolution of the mechanical properties of the Devonian reef complexes is presented. A statistically significant relationship is documented between syndepositional fracture development and variations in stratigraphic architecture, approximated here by platform-margin trajectory. This relationship implies a significant stratigraphic control on syndepositional deformation in carbonate platforms and suggests that external drivers are not required to generate early fractures in high-relief carbonate platforms.

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