Shale mobility: From salt-like shale flow to fluid mobilization in gravity-driven deformation, the late Albian-Turonian White Pointer Delta (Ceduna Subbasin, Great Bight, Australia)

Large offshore depocenters above a weak detachment level (either salt or shale) can undergo gravity spreading and/or gliding. The gravitational systems (e.g., gliding deltas) are classically composed of an updip domain affected by extensional listric normal faults and a downdip domain affected by toe thrusts. While the role of salt in such systems is a classic tectonic process, the role and mechanical behavior of mobile shale levels in shale-prone gravity-driven systems are increasingly questioned. A three-dimensional seismic data set in the Ceduna Subbasin (Australia) displays the late Albian-Turonian White Pointer Delta (WPD) as having an unusual diversity of shale-cored structures. The early flow of shale resulted in depocenters showing wedges, internal unconformities, and shale diapirs and ridges, while fluidization of shales underneath a significant burial resulted in mud volcanism, secondary radial fault sets, and collapse features beneath the Campanian-Maastrichtian Hammerhead Delta, which lies above the WPD. Massive shale mobilization, together with downdip shortening and distal margin uplift, localized a major thrust in the core of the basin, ending the downward-propagating failure of the WPD. Mobilization of thick shale intervals, either as salt-like flow or mud volcanism, appears to have been a key process in the deformation, which should be considered at large scale for worldwide gravity-driven deformation systems.

Automated summary

Large offshore depocenters above a weak detachment level can undergo gravity spreading and/or gliding. The mechanical behavior of mobile shale levels in shale-prone gravity-driven systems is increasingly questioned. Seismic data from the Ceduna Subbasin in Australia reveals the importance of shale mobilization in worldwide gravity-driven deformation systems.