Tilting of the Australian continent: New evidence from the subsidence and deposition history of the Northern Carnarvon Basin
Patrick Makuluni, Laurent Langhi, Juerg Hauser, Stuart Clark
Figure 1: Free-air gravity anomaly (Sandwell et al., 2014) of the Northern Carnarvon Basin and the distribution of wells used for assessing subsidence, sedimentation, and basin tilt
Studies of global sea-level changes, plate kinematics, marine inundation, and morphology of the continental shelves suggest that the Australian continent has been tilting northeastwards since the Late Cretaceous. Here we investigate the direct impact of this phenomenon and the preceding tectonic events on the evolution and resource potential of the Northern Carnarvon Basin, which sits on the axis of the tilt. We use backstripping and decompaction techniques to develop subsidence, sedimentation, and porosity evolution models for the basin. The goal is to highlight the spatial and temporal variation of subsidence and sedimentation rates and assess their impacts on the porosity of the Early Cretaceous reservoirs within the basin, then give insights into the factors that created accommodation space for sediments.
The results reveal a north-eastward shift of subsidence and sedimentation rates within the region, with the highest subsidence rates (∼90 m/Ma) in the southwest (Exmouth and Barrow sub-basins) from Early Jurassic to Early Cretaceous. In the Middle Cretaceous, subsidence and sedimentation moved northeast towards the Dampier (∼40 m/Ma) and some parts of the Barrow sub-basin (∼35 m/Ma). In the Cenozoic era, the highest subsidence rates moved further northeast towards the Beagle sub-basin (∼40 m/Ma) and the North Rankin platform. The high tectonic subsidence (∼3 km) and sediment supply in the southwestern Exmouth and Barrow sub-basins, which reduced towards the north-east in the Dampier and Beagle Sub-basins (∼1.5 km), were caused by Palaeozoic-Mesozoic rifting events. In contrast, the Cenozoic mantle-driven and subduction-driven tilting of the Australian continent caused the observed local tilting of these sub-basins. Subsidence plots along a NE-SW transect and the porosity evolution model results also demonstrate the tilting occurring in these sub-basins.
Figure 2: Distribution of tectonic subsidence showing the north-eastward shift of subsidence from Jurassic to the present