Gloria Knolls Slide: A prominent submarine landslide complex on the Great Barrier Reef margin of north-eastern Australia

Abstract

We investigate the Gloria Knolls Slide (GKS) complex on the Great Barrier Reef margin of northeastern Australia, the largest extant mixed carbonate-siliciclastic province in the world. Based on the most complete bathymetric and sub-bottom profile datasets available for the region, we describe the main surface and subsurface geomorphologic characteristics of this landslide complex. The GKS forms a 20 km along-slope and 8 km across-slope indentation in the margin, extending from 250 to 1350 m depth, and involves a volume of 32 km 3 of sediment remobilized during three events. Three main seafloor terrains can be distinguished based on seafloor morphology: a source area, a proximal depositional area and a distal depositional area. The source area includes a main headwall scarp with a maximum height of 830 m and a secondary scarp at 670 m depth. The proximal depositional area is flat and smooth, and lacks debris exposed on the seafloor. The distal depositional area has a hummocky surface showing a distinctive cluster of eight knolls and over 70 small debris blocks. A dredge sample from the top of the largest knoll at a depth of 1170 m reveals the presence of a cold-water coral community. In the sub-bottom profiles, the mass-transport deposits in the GKS are identified below the background sediment drape as partially confined, wedge-shaped bodies of mostly weak amplitude, transparent reflectors in the proximal *Manuscript Click here to download Manuscript: The Gloria Knolls Slide_APB et al_CLEAN.docx Click here to view linked References 2 depositional area; and more discontinuous and chaotic in the distal depositional area. The failed sediment slabs of the GKS were evacuated, transported and disintegrated downslope in three events following a sequential failure process spreading successively from the lower slope to the upper slope. The first event initiated at the lower slope at the depth of the secondary scarp, moved downslope and disintegrated over the basin floor leaving coherent blocks. The subsequent second and third events were responsible for the formation upslope of the main scarp in the GKS. The timing of emplacement of the first GKS event, constrained by radiometric age of fossil biota from the surface of the largest slide block, was at least before 302±19 ka. The presence of alternating mixed carbonate and siliciclastic lithologies that build the slope might have played an important role as a preconditioning factor in this region. Preliminary estimations suggest that unusually large seismic events were the most likely triggering mechanism for the GKS. This work contributes to the understanding of large massmovement deposits in mixed carbonate-siliciclastic margins and provides a useful morphologic characterization and evolutionary model for assessing its tsunamigenic potential with further numerical simulations. In addition, the discovery of a cold-water coral community on top of the largest knoll has implications for identifying similar landslide-origin cold-water coral communities on the GBR margin.

Examining the impact of the Great Barrier Reef on tsunami propagation using numerical simulations

“…For both landslide cases, these dimensions were determined in previous work (Puga-Bernabéu et al 2013a, and were thus adopted here (see Table 1). For the Gloria Knolls Slide, slide dimensions were determined using bathymetry data containing the slide scar (Puga-Bernabéu et al 2016.…”

“…Despite Australia's proximity to the seismically active sourceregions (Dominey-Howes 2007;Davies and Griffin 2018), the manner in which tsunami behaviour is regulated by the GBR, which partitions Australia's coastline from these convergent margins, is not well understood (Webster et al 2016). Additionally, the discovery of large (volume > 30 km 3 ) landslide scars and slumps on the nearby continental slope (Puga-Bernabéu et al 2016 warrants an investigation into the GBR's ability to protect against landslide-generated tsunamis. Though believed to occur less frequently than their coseismic counterparts, landslide-generated tsunamis such as the 1998 Sissano, Papua New Guinea event (Synolakis et al 2002) can occur suddenly within close proximity to the shoreline, causing significant localized damage and limiting opportunities for warning and swift response.…”

“…Puga-Bernabéu et al 2016), when reef platforms are covered by coral, offshore amplitudes markedly decline from over ~4 m to under ~2 m landward of the platforms…”

“…The present study focuses on two notable features on the central GBR margin. The first is the Gloria Knolls landslide complex(Puga-Bernabéu et al 2016), which is the largest among the documented submarine landslide cases on the northeastern Australian margin (total estimated…”

Carbonate slope re‐sedimentation in a tectonically‐active setting (Western Sicily Cretaceous Escarpment, Italy)

“…Slope architecture also depends on the controlling factors of sediment shedding occurring on platform tops and/or their adjacent slopes (Spence & Tucker, ; Playton et al ., ; Reijmer et al ., 2015a). Controlling factors of slope architecture include: (i) sea‐level fluctuations (for example, Bahamas: Hine et al ., ; Schlager & Ginsburg, ; Eberli & Ginsburg, ; Reijmer et al ., , , 2015a; Wunsch et al ., ; Mulder et al ., ; Great Barrier Reef: Webster et al ., , ; Puga‐Bernabéu et al ., , ; Maldives: Betzler et al ., ); (ii) tectonics (for example, Southern Provence: Floquet & Hennuy, ; Hennuy, ; Floquet et al ., ; Reijmer et al ., 2015b; Pyrenees: Drzewiecki & Simo, ; general reviews: Payros & Pujalte, , and references therein; Playton et al ., , and references therein); and (iii) the system growth itself (Canning Basin: Playton & Kerans, ,b; Delaware Basin: Playton & Kerans, ). In addition, the downslope movement of sediment‐laden flows covers a variety of processes that may coexist within a single gravity flow event.…”