The Devonian Reef Complexes of the Canning Basin in Context: Subsurface and Adjacent Basins
The field Geology of the Devonian reef complexes along the Lennard Shelf in the Canning Basin, Western Australia, was exhaustively described in GSWA Bulletin 145, which covered the outcropping HST part of the complexes. Outcrops show an intricate interplay between tectonism, long term eustacy, climate, and locally focussed coarse-grained terrigenous influx. Reef complexes became established in the Givetian, with a bank-like margin. Reef scarps developed in the Frasnian. An overall back-stepping pattern reflected the transgressive phase of a long-term Late Devonian depositional cycle. Transgression peaked in the latest Frasnian, after which there was a prograding ‘regressive’ pattern through the Famennian. Conglomerate bodies interfingered with and cut through the reefs in the later Frasnian and Famennian. Reef builders showed remarkable resilience in persisting through and beside clastic influx. Further outboard in the subsurface, localized major clastic wedges correspond partly but not wholly to conglomerates in outcrop, and like them must be tectonically rather than eustatically controlled. A simple LST clastic / HST carbonate model cannot apply. In the Bonaparte Basin to the north, Frasnian tectonism led to siliciclastic deposition, and reefs only developed when tectonism lessened in the Famennian. Even then, a complete transgressive-regressive cycle is preserved, unlike the Famennian of the Canning Basin. Between the Bonaparte and Canning Basins in the Ord Basin, active tectonism led to extensive Frasnian sandy and conglomeratic deposition, with an apparent hiatus in the Famennian. In the Carnarvon Basin to the southwest, the Frasnian is marked by mixed carbonate – clastic deposition, in a ramp setting except for local reefal buildups. Siliciclastic deposition, of coastal sands and then alluvial fan deposits, extended through the Famennian. The differing timing and patterns of carbonate development in each basin indicate a similar climatic setting, but different tectonic regimes and timing across the basins. Famennian clastic pulses in the basins may be far-field effects of the intra-plate Alice Springs Orogeny of central Australia. Frasnian clastic deposition in the Kimberley is attributed to more local transcurrent movement along reactivated Proterozoic sutures of the eastern Halls Creek Orogen. Integrated chronostratigraphic studies may be the best tools for resolving the tectonic and climatic variability in the Devonian of WA.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014