The formation and implications of giant blocks and fluid escape structures in submarine lateral spreads

Abstract

Lateral spread (or 'spreading') 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 2D and 3D seismic reflection data to determine the geometry, scale, and origin of an ancient (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 c. 170-300 m thick and covers an area of at least c. 1050 km 2 . The deposit is defined internally by two distinct seismic facies: (i) large, upward-tapering blocks (up to 210-300 m thick, 170-210 m wide, and 800-1200 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 (ii) troughs (160-260 m thick, 190-230 m wide and 800-1200 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 of the MTC. The lack of deformation within the blocks, and their correlation to adjacent in-situ deposits, suggests they underwent very limited transport (c. 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 accounts for the styles and patterns of intra-MTC deformation process. This model invokes evacuation of the lower slope by a pre-cursor MTC that formed the space to trigger the lateral spread event. Our study provides new insights into the genesis and rheology of subaqueous lateral spreads, enabling improved assessments of the threats posed to critical seafloor infrastructure. The genetic links identified between mass wasting and spatially-focused fluid flow indicate that, as well as disturbing the deep seafloor, submarine landslides may also create important deep-sea biodiversity hotspots.

The role of mass‐transport complexes in the initiation and evolution of submarine canyons

“…The scale contrast is interpreted to be due to buried MTCs, which are typically more consolidated than undeformed background slope deposits (i.e. Shipp et al ., 2004; Sawyer, 2007; Wu et al ., 2021). Thus, the incision depth and scale of Canyon‐6 is smaller than other canyons.…”

“…Canyons are often associated with sand‐rich gravity flows which develop into submarine fans, which can act as high quality deepwater hydrocarbon reservoirs (Stow & Mayall, 2000; Weimer & Slatt, 2004; Steventon et al ., 2021). Mass‐transport complexes (MTCs) are gravity‐driven shear failure deposits resulting from creep, spread, slide, slump and debris‐flow processes (Posamentier & Martinsen, 2011; Wu et al ., 2021). MTCs can be extremely erosive, thus containing large volumes of sediments, with single deposits covering areas of >100 km 2 and volumes of >10 000 km 3 (Frey Martinez et al ., 2005; Moscardelli & Wood, 2016; Nugraha et al ., 2019).…”

Long-term slope instability induced by the reactivation of mass transport complexes: An underestimated geohazard on the Norwegian continental margin

“…These slabs can then be softened, fractured and fragmented by high dip-angle fractures, ending up as a series of laterally spread blocks on a gentle submarine slope (Micallef et al, 2007;Baeten et al, 2014;Wu et al, 2021). Due to internal softening, deformation and sediment liquefaction, the size of these blocks often decreases with their transporting distance, before they are completely fragmented and liquefied into debrites and turbidity currents (Bull et al, 2009a;Alves, 2015;Cox et al, 2020).…”

Basin and depositional control on the initiation and development of fluid-escape pipes in the Canterbury Basin, New Zealand.

“…In addition to the physical and internal control on pipe formation, more recent investigations have demonstrated the importance of geobodies and geomorphological structures, such as salt diapirs, masstransport complexes (MTCs), and contourites, in the initiation, modulation, and growth of fluid pipes (Oppo et al, 2021;Browne et al, 2020;Kirkham et al, 2019;Ruge et al, 2021;Wu et al, 2021). Contrary to the traditional notion that fluid pipes form from the structural crests of large anticlines (Cartwright et al, 2021a) or lateral pressure transfer zones (Stump and Flemings 2000;Flemings et al 2003), recent studies have revealed the presence of fluid pipes in several other settings.…”