Probable Landslide Detachment Surfaces And Post-slide Deposits Sampled In The Yamba Slide Complex, New South Wales, Australia.
Presented by Dr. Thomas HUBBLE on 24 Sep 2013 from 13:30 to 14:00
Type: Oral presentation, full-paper
Session: 07: Australia, Latin America
Track: Oral presentations
The Yamba Slide Complex is located on eastern Australia's upper continental slope offshore from the town of Yamba in northern New South Wales. It is a composite submarine landslide feature in which near-surface, slab slides up to sixty meters thick have been detached and removed from the upper portion of a larger rotational slump block approximately 2 km wide, 4 km long and some hundreds of metres thick. Four cores have been recovered from three sites within the slide complex and one core from the continental slope adjacent to the complex. All four cores present sharp and distinct boundary surfaces separating upper layers of soft, unconsolidated hemipelagic mud from lower layers of denser, moderately consolidated to stiff hemipelagic mud. Sedimentologic descriptions and mini-shear vane data are presented for the four cores and this data is interpreted in the context of the available bathymetric and seismic reflection data as well as the regional geology. The shortest of the four cores collected from the Yamba Slide Complex presents an interesting transition between the lower stiff hemipelagic muds and the upper unconsolidated mud units. This core was recovered from a site that apparently shed the thickest, translational slab slide removed from the Yamba complex (approximately 60 m). Its transition zone is a ten centimeter thick, upper-fining mud-flake paraconglomerate which presents rounded to sub-rounded, mud-pebble intraclasts imbedded in a mud matrix. This paraconglomerate overlies significantly stiffer material which is presently located at a depth of 1.4 below the seafloor. Mini-shear vane results for these stiff muds are consistent with burial of these lower layer materials at depths of more than forty metres and it is probable that the stiff, hemipelagic mud layers represent in-situ, below-slide-plane materials. The upward-fining paraconglomerate is interpreted to be a post-slide deposit, which was possibly deposited immediately after, and as a consequence of the removal of a translational slab-slide block. The contact between the base of this mud-flake paraconglomerate and the stiff muds is interpreted to be either a surface eroded down through the slab-slide’s detachment surface; or the slab-slide’s actual detachment surface upon the removed upper block slid donwslope. All four of the boundary surfaces presented in the three within slide cores and the one slide-adjacent core site taken from the Yamba Slide Complex are suggested to represent submarine landslide detachment surfaces and/or actual slide plane surfaces.