Seafloor geomorphology and submarine landslide hazards along the continental slope in the Carnarvon Basin, Exmouth Plateau, North West Shelf, Australia

Abstract

3D exploration seismic data were interpreted to investigate the locations and characteristics of submarine slope failures along the continental slope in the offshore Carnarvon Basin on Australia’s North West Shelf. Seisnetics™, a patented genetic algorithm was used to process the 3D seismic data to extract virtually all trough and peak surfaces in an unbiased and automated manner. The extracted surfaces were combined in the 3D visual database to develop a seafloor digital terrain model that extends from the continental slope to the Exmouth Plateau. The 3D data were used to map the subsurface extent and geometry of landslide failure planes, as well as to estimate the thickness and volumes of slide deposits. This paper describes the geomorphic characteristics of five of the survey areas. Geomorphic mapping shows the presence of slope failures ranging from small (20 km across) mass transport complexes (MTC). The features are associated with debris flow chutes, turbidity flow channels, and debris fields. Analysis of failure planes show prominent grooves or striations related to the mobilisation of slide material down both the continental slope and Exmouth Plateau and into the Kangaroo Syncline. Submarine slope failures can occur at the continental shelf break in about 200–300 m of water and run out to the Exmouth Plateau surface in about 1,100–1,400 m water depths. The largest individual slides in the survey areas have widths of 30 km and minimum run-out lengths of 75 km, though associated turbidity flow deposits likely extend much further. The subsurface expression of the large MTCs illustrates a history of sediment accumulation along the mid-slope followed by repeated slope failure and debris run-out. Sediment accumulation and slope failure processes are actively occurring along the continental slope and submarine landslides thus are a major driver of hazard to subsea infrastructure development. Smaller more frequent slides may pose a greater hazard than large infrequent MTCs.

The formation and implications of giant blocks and fluid escape structures in submarine lateral spreads

“…Cores from Ocean Drilling Program (ODP) wells 762 and 763 have established that the dominant lithology in this interval is nannofossil-rich carbonate ooze (Exon et al, 1992;Boyd et al, 1993). These deposits are characterised by high porosities (c. 70%) and high water saturations (c. 40%), and by an overall low strength profile (<20kPa) ; see Figure 5 from Hengesh et al, 2012). These physical properties increase the slope instability and related geohazard risk of the Exmouth Plateau area.…”

“…Prolonged slope instability is recorded in the presence of large (e.g. c. 500km 3 gorgon slide; Hengesh et al, 2012), stacked, slope-to-basin floor MTCs in the upper part (i.e. post-Oligocene) of the passive margin mega-sequence (Hengesh et al, 2012;Scarselli et al, 2013;Nugraha et al, 2018;Nugraha et al, 2019).…”

“…c. 500km 3 gorgon slide; Hengesh et al, 2012), stacked, slope-to-basin floor MTCs in the upper part (i.e. post-Oligocene) of the passive margin mega-sequence (Hengesh et al, 2012;Scarselli et al, 2013;Nugraha et al, 2018;Nugraha et al, 2019). The study area is located in the axis of the Kangaroo Syncline, between the Exmouth Plateau to the west and the NW Shelf to the east (Figure 2a, 2d).…”

“…We divide the studied stratigraphic interval into three seismic units (SU-1-3). SU-1 is c. 500 m thick near the axis of the Kangaroo syncline, thinning westward and eastward to c. 200 m. SU-1 contains packages of chaotic, medium-to high-amplitude seismic reflections interpreted as stacked MTCs (Figure 3b-c) (Hengesh et al, 2012;Nugraha et al, 2018). SU-2 is thinner than SU-1, but also varies in thickness, being slightly thicker near the centre of the Kangaroo Syncline (c. 60 m) and thinning gradually westward and eastward to c. 30 m (Figure 3b).…”

Physical sedimentary controls on subtropical coastal and shelf sedimentary systems: Initial application in conceptual models and computer visualizations to support archaeology

“…Of course, coastal and marine environments are influenced by a mixture of all these drivers, and our purpose here is certainly not to argue that these individual drivers are the definitive drivers for those cases described below, but rather to show that they are clearly useful to help illustrate some key aspects relevant to archaeology. There are of course a range of other factors that may influence shelf and coastal sedimentation, such as (i) the effects of very rare but known events such as tsunamis (Scheffers, Scheffers, Kelletat, & Bryant, ), (ii) large‐scale failures of submerged sedimentary bodies (Hengesh, Dirtsein, & Stanley, ) or exposed reef edges, and (iii) changes of coastal “state,” whereby relatively small changes in coastal configuration, such as closure of a narrow lagoon entrance, can lead to major changes in sedimentary environments. Over long timescales, sea‐level change per se can influence the location of the primary process drivers as part of the geological history, and, among other things, can affect shelf sediment availability through playing a part in modulating biogenic sediment production, and cyclones through changing water depths.…”