Joanne C., Collot Jean-Yves, Lamarche G., Migeon S. (2010). Continental slope reconstruction after a giant mass failure, the example of the Matakaoa Margin, New Zealand. Marine Geology, 268 (1-4), p. 67-84. ISSN 0025-3227.
Titre du document
Continental slope reconstruction after a giant mass failure, the example of the Matakaoa Margin, New Zealand
Joanne C., Collot Jean-Yves, Lamarche G., Migeon S.
Source
Marine Geology, 2010,
268 (1-4), p. 67-84 ISSN 0025-3227
During the Pleistocene, the Matakaoa Debris Avalanche (MDA) removed similar to 430 km(3) of material and formed a 50 km-long re-entrant in the Matakaoa margin, offshore East Cape, New Zealand. In this study, we examine the post-avalanche processes of continental slope reconstruction via the analysis of bathymetry, seismic-reflection data and one sediment core. The study reconstructs the post-MDA history of the Matakaoa margin and reveals how the giant mass-transport event laid the foundation for present variations in the margin's morphology. After the MDA, 600 +/- 150 ka, the high terrigenous discharge of the Raukumara Peninsula rivers (>38 Mt/yr at present) contributed to the construction of two depositional systems that each are up to 800 m thick: 1) the Pleistocene Sediment Wedge (PSW), resulting from detritic-rich hemipelagic sedimentation, partly reconstructed the slope and healed the western section of the MDA scarp; and 2) the Matakaoa Turbidite System (MTS) developed at the outlet of the Matakaoa Canyon that is fed by the Waiapu River, and nestled against the eastern section of the MDA scarp. In the eastern half of the re-entrant, the topography resulting from the avalanche included a 25 km-wide confined depocentre where the aggradational MTS started to construct through the development of a sediment fan and a turbidite plain. The construction of these two architectural elements at the base of the continental slope lowered the slope angle which restrained further destabilization in the eastern half of the re-entrant. In contrast, in the re-entrant's western half, slope reconstruction (deposition of PSW) has been counteracted by destabilization processes including: localized erosion associated with the headward development of slope canyons, and broad-scale failures resulting from differential compaction and gravity tectonics. Such instability may have contributed to produce the similar to 1000 km(3) Matakaoa Debris Flow (38-100 ka). Our analysis points out that a collapsed margin subject to high sedimentation rates is likely to undergo further mass-failures on the long-term (>300 ka).
