Abstract
AbstractLateral spread and submarine creep are processes that occur near the headwalls of both terrestrial landslides and submarine mass‐transport complexes (MTCs). Both submarine creep and spread deposits may contain giant (km‐scale) coherent blocks, but their transport processes remain poorly constrained. Here we use seismic reflection data to determine the geometry, scale, and origin of a Late Miocene mass‐transport complex (MTC) located in the Kangaroo Syncline, offshore NW Australia. We show that this large remobilised mass of carbonate ooze is ca. 170–300 m thick and covers an area of at least 1,050 km2. The deposit is defined internally by two distinct seismic facies: (a) large, upward‐tapering blocks (210–300 m thick, 170–210 m wide and 800–1,200 m long) with negligible internal deformation, which decrease in height and spacing along the transport direction (identical, but in situ, seismic facies forms undeformed slope material immediately updip of the deposit headwall); and (b) troughs (160–260 m thick, 190–230 m wide and 800–1,200 m long) comprising moderately deformed strata, which contain ‘v’‐shaped, pipe‐like structures that extend upwards from the inferred basal shear surface to the top surface. The lack of deformation within the blocks, and their correlation to adjacent in situ deposits, suggests they underwent limited transport (ca. 50 m–70 m). The relatively high degree of deformation within the intervening troughs is attributed to the vertical expulsion of fluids and sediment during hydraulic failure of the sediment mass. We present a hydraulic failure model that invokes evacuation of the lower slope by a precursor MTC and which formed the space to trigger the lateral spread. Our study also provides new insights into the genesis and rheology of subaqueous lateral spreads. The genetic links identified between mass wasting and spatially focused fluid flow, as well as disturbing the deep seafloor, indicate that submarine landslides may also create important deep‐sea biodiversity hotspots.
Highlights
Mass-transport complex (MTC) is a broad term typically used to describe slope failure deposits resulting from creep, spread, slide, slump and debris flow processes (Figure 1; Nemec, 1990; Varnes, 1978)
The dimensions of the MTC-hosted blocks have been quantitatively analysed based on their morphological characteristics: (a) block height, which is the height between the crest and base of the blocks; (b) block spacing, which is the spacing between the mid-point of the crests of two adjacent blocks (Figure 6b); (c) block tip angle, which is the angle between the block tip and vertical (Figure 6b); and (d) block friction angle, which is the angle between the side of the blocks relative to their base surface (Figure 6b)
We suggest that MTC 3 was triggered due to the removal of material from its distal margin by the emplacement of MTC 2
Summary
Mass-transport complex (MTC) is a broad term typically used to describe slope failure deposits resulting from creep, spread, slide, slump and debris flow processes (Figure 1; Nemec, 1990; Varnes, 1978). Our aim is to evaluate the morphology, internal structure, kinematics, origin and geohazard risk of a large submarine MTC using a high-quality, 3D and 2D seismic reflection dataset from the NW Shelf, offshore Australia Using these data, we can quantify the height and spacing of the contained. Blocks, while a detailed kinematic analysis of intra-MTC structures allows the transport direction to be determined This present study aims to offer a better understanding of spread initiation, translation and deposition, which will help to build a more comprehensive model for submarine mass failures and to help understand, and inform mitigation of the associated geohazard risk. 40%), and by an overall low strength profile (
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