Large-scale margin collapses along a partly drowned, isolated carbonate platform (Lansdowne Bank, SW Pacific Ocean)

Type Article
Date 2021-06
Language English
Author(s) Etienne Samuel1, 2, Roy Pascal3, Tournadour Elsa2, 4, Roest WalterORCID4, Jorry StephanORCID4, Collot Julien2, Patriat MartinORCID4, Largeau Maria A.2, Roger Jean5, Clerc Camille6, Dechnick Belinda7, Sanborn Kelsey L.7, Lepareur Fanny8, Horowitz Jeremy9, Webster Jody M.7, Gaillot Arnaud4
Affiliation(s) 1 : ADECAL Technopole, ZoNéCo Research Program, 98846 Nouméa, New Caledonia
2 : Geological Survey of New Caledonia, DIMENC, BP M2, 98845 Nouméa, New Caledonia
3 : Laboratoire Géosciences Océan UMR 6538, Université de Bretagne Occidentale, 29280 Plouzané, France
4 : IFREMER, Unité Géosciences Marines, 29280 Plouzané, France
5 : Institut de Recherche pour le Développement (IRD), 98848 Nouméa, New Caledonia
6 : ISEA, Université de la Nouvelle-Calédonie, 98851 Nouméa, New Caledonia
7 : Geocoastal Research Group, School of Geosciences, University of Sydney, NSW 2006, Australia
8 : Museum National d'Histoire Naturelle, 75005 Paris, France
9 : Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, 101 Angus Smith Drive, Townsville, QLD, 4811, Australia
Source Marine Geology (0025-3227) (Elsevier BV), 2021-06 , Vol. 436 , P. 106477 (21p.)
DOI 10.1016/j.margeo.2021.106477
WOS© Times Cited 3
Keyword(s) Isolated carbonate platform, Margin collapse, Slope failure, MTCs

The Lansdowne Bank is a partly drowned, isolated carbonate platform of around 4000 km2 located 300 km west of New Caledonia, in the SW Pacific Ocean, in water depths of 20 to 100 m. New multibeam bathymetric data, high resolution seismic reflection profiles and sediment gravity cores have been acquired on the bank top and adjacent slopes. This dataset reveals an almost continuous 4 km wide outer reef rim located in ca. 50 m water depth, surrounding a gently deepening inner platform, reaching up to 100 m water depth. The bank is bordered by very steep slopes showing numerous erosional morphologies such as canyons, channels and gullies. Along with these bypass features, spectacular bank margin collapses and slope failures are evidenced by up to 20 km-wide bank edge and intraslope failure scars, respectively, resulting in a typical “scalloped” geometry of the bank margin. These failure scars can lead to a complete collapse of the outer reef rim and impact subsequent reef development. Bank margin collapses are evidenced by hectometer to kilometer-scale blocks and debris shed on the slope, likely emplaced by rock fall/avalanching processes originating from the brittle failure of early cemented bank edge and upper slope sediments. In turn, failures triggered on the un-cemented mud-prone middle to lower slopes likely generate more cohesive, submarine debris flows that could be at the origin of erosive morphologies within the debris fields. Estimated individual failure volumes can reach up to 3 km3. Quaternary sea-level lowstands, that would have led to platform exposure, fracturing and karstification, and the development of an erosional sea cliff, as well as subsequent rising sea-level are believed to play a significant role in mass wasting event emplacement, yet “bottom up” submarine processes such as the upslope propagation of bypass morphologies by retrogressive headward erosion cannot be ruled out. In terms of geomorphic and stratigraphic constraints, the documented bank margin collapses affect a terrace located in 70 m water depth around the bank, which, depending on its age and origin, could provide a minimum age for collapse events. Finally, considering the shallow water depth of failure headscarps, the volumes of material involved in the slides as well as their vicinity to the nearby main island of New Caledonia, numerical simulations of the tsunamigenic potential of submarine slides have been performed. They showed that these slides would have been able to produce a meter-scale wave that would reach the northern coast of the island in less than an hour.

Full Text
File Pages Size Access
Author's final draft 68 54 MB Open access
21 30 MB Access on demand
Top of the page

How to cite 

Etienne Samuel, Roy Pascal, Tournadour Elsa, Roest Walter, Jorry Stephan, Collot Julien, Patriat Martin, Largeau Maria A., Roger Jean, Clerc Camille, Dechnick Belinda, Sanborn Kelsey L., Lepareur Fanny, Horowitz Jeremy, Webster Jody M., Gaillot Arnaud (2021). Large-scale margin collapses along a partly drowned, isolated carbonate platform (Lansdowne Bank, SW Pacific Ocean). Marine Geology, 436, 106477 (21p.). Publisher's official version : , Open Access version :