Abstract The Chandeleur Submarine Landslide Complex occurs on the upper Mississippi Fan of the Gulf of Mexico in approximately 1100 m of water, 200 km SE of New Orleans, Louisiana. This part of the Mississippi Fan received high sedimentation throughout the Pleistocene, causing high pore fluid pressure and abundant slope failures, though few as large as the Chandeleur. Given its large size, proximity to major coastal cities and seafloor infrastructures, we examine the Chandeleur Slide to understand what led to the initial slope failure and decipher its post-failure transport behaviour using 2D and 3D multichannel seismic surveys, high-resolution bathymetric data, and well logs. We find a large sediment mass with a translational-rotational behaviour that was displaced to the south/SE up to 40 km from the source area. The Chandeleur Slide includes extensional faulting in the headscarp area and compressional structures in the toe where confined by a natural ramp-like structure. Beneath the Chandeleur Slide, we identify a regional sand-rich unit (called the Blue Unit) that is known to be overpressured. Beneath the Blue Unit we observe an upward-migrating salt diapir. We suggest one possible scenario for the origin of the Chandeleur Slide is the combined effects of an upward-migrating salt diapir impinging on an already overpressured Blue Unit, leading to the initial failure. The initial failure was followed by retrogressive headwall retreat northward, which created the prominent scarp on the seafloor. In total, the Chandeleur Slide complex covers an area of about 1000 km 2 and contains about 300 km 3 of sediment.

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.