Submarine Landslides Along the Mixed Siliciclastic‐Carbonate Margin of the Great Barrier Reef (Offshore Australia)

Submarine landslides on modern mixed siliciclastic-carbonate margins are poorly understood compared to their counterparts in other settings. We present a synthesis of four representative submarine landslides types along the Great Barrier Reef margin, the largest extant mixed siliciclastic-carbonate province in the world. The investigated examples are 5–31 km in length, extend over 18–528 km2, and have remobilized an estimated 0.025–32 km3 of sediments. They display morphological features corresponding to debris avalanches and slides. The estimated timing of two dated landslides is coincident with deglaciations corresponding to the transitions MIS 12–11 and MIS 2–1. Large seismic events were the most likely triggering mechanism for the landslides, where high pore water pressure in examples close to paleo-deltaic systems could also have preconditioned the eventual failure. A potential preconditioning factor, yet to be confirmed, is the geologic control associated with alternating mixed siliciclastic and carbonate sediments in the failed lithologies. The Gloria Knolls Slide is large enough to have significant tsunamigenic potential. Tsunami simulations show that this landslide would produce a sizable tsunami under present-day sea level conditions, with coastal run-up heights of 0.5–2 m. We highlight a reef buffering effect due to broader-scale shelf bathymetry and the complex structure of coral reefs.