Abstract Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700–800 m of the section captured in detail not available with industry seismic data. We present nine new high-resolution seismic lines from three separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300 m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.

Abstract The North East Atlantic Margin and Australian North West Shelf share similar tectonic evolutions. Both are passive margins of similar age and size, both experienced significant periods of reactivation, inversion and volcanism, and both host significant oil and gas resources. The main differences between these two margins lie in their modern tectonic settings and hydrocarbon resources. The North West Shelf occurs at a present-day collisional plate boundary, the dynamics of which strongly control the location of oil and gas reserves, whereas the North East Atlantic has not yet entered a collisional phase. The North West Shelf tends to be gas prone, in contrast to its European counterpart. Recent mapping of Neogene to Recent modification across the North West Shelf highlights the influence of inherited basement architecture, long-wavelength strain partitioning and continuous flexural deformation. Similarities in the structural evolution of these two margins, especially in terms of the role of the basement structure, episodic modification, the location and extent of Cenozoic inversions and the role of inversion in controlling hydrocarbon distribution, illustrate the importance of these issues in passive margin development. Lessons learned from the Australian example include that structural inheritance has an overwhelming control on later reactivation, and that even small amounts of shortening strain (1–2%) can lead to significant modifications of structural traps and petroleum habitats.

Sumba Island, Indonesia, occupies a forearc position within the Australian-Indonesian convergent margin. It represents a sliver of arc crust that has moved into its current position from elsewhere. Tectonically it lies at a junction between different lithospheric types. To the west, an intraoceanic volcanic arc system occurs at which Australian oceanic lithosphere converges on Indonesian arc lithosphere. To the east, a volcanic arc – continental collision zone involves Australian continental lithosphere in collision with the Indonesia arc. Sumba lies at the transition between these different regimes and represents the focus of a number of structural and tectonic features. We suggest that collision of a promontory of Australian continental lithosphere with Sumba at ca 8 Ma created many of the structural features on the Australian side of the plate boundary, partitioned the lithosphere into structural domains that reflect different deformation histories since the Neogene (22 Ma), and contributed to the uplift of Sumba at ca 8 Ma. The shape of the collided promontory controls the shape of the uplifted Sumba Block. The proposed 8 Ma age for collision correlates well with deformation events in Sumba, the Timor Sea and the Browse Basin. Structures created or reactivated by the collision form the boundaries of deformational provinces within the North West Shelf of Australia.