Styles of basal interaction beneath mass transport deposits

Abstract

Erosion of the seafloor is often interpreted to be the result of turbidity currents and reflects their frictional and non-cohesive nature. However, evidence of the interaction between sediment gravity-flows and the substrate forming the sea floor has been increasingly reported in the literature. Based on styles of basal interaction with the substrate, we here propose a broad classification of submarine mass movements labelled free-and no-slip flows. Three mechanisms are proposed for free-slip flows during translation of mass movements that are effectively detached from the substrate; hydroplaning, shear wetting, and substrate liquefaction. In contrast, no-slip flows occur where the mass movement is welded to the substrate, and the strain front lies within the substrate itself. In the latter case, flows can erode by pushing forward and/or ploughing into the substrate, often remobilizing sediments that are later incorporated into the flow, a common characteristic shared by many mass transport deposits (MTDs) containing blocks. Additionally, linear track features (e.g. grooves and striations) are described as a consequence of substrate tooling by rigid blocks. Using outcrops in NW Argentina as a detailed case study, we have recorded evidence for penetration of the strain profile into sediments underlying MTDs and categorised the deformation into no-slip basal deformation that may display continuous and discontinuous profiles. Continuous deformation profiles involve the complete deformation of the uppermost layers of the substrate, while discontinuous deformation profiles preserve a undeformed substrate layer between the MTD and the zone of deformed substrate. These features highlight the erosive and deformational nature of MTDs, and can be used as potential kinematic indicators.

Characterization of the Rapanui mass‐transport deposit and the basal shear zone: Mount Messenger Formation, Taranaki Basin, New Zealand

“…The basal shear zone (bsz) of a submarine MTD is herein defined as a zone of localized strain that forms syndepositionally during mass transport between the base of the overriding mass flow material and the underlying in situ deposits (substratum) and separates less strained or unstrained sediments ( sensu lato Fossen & Cavalcante, ) – the upper and lower contacts of the bsz can be gradational or sharp (Alves & Lourenço, ; Alves, ; Festa et al., ; Sobiesiak et al., ). The bsz can be exclusively composed of remobilized material from the MTD protolith or a mixture between the remobilized material in the mass flow and entrained sediments from the substratum (Fig.…”

“…Common structures in the bsz are small‐scale folds (Clare et al., ; Ogata et al., ; Jablonská et al., ), ‘necking’ or boudinage (Tripsanas et al., ; Ogata et al., ), brecciation/cataclasis (Ineson, ; Farrell & Eaton, ; Callot et al., ), convolute/contorted bedding (Tripsanas et al., ; Butler et al., ) and structures associated with liquidization ( sensu Allen, 1982a). Furthermore, the bsz can be a zone of erosion if the mass flow erodes into the substratum or a bypass zone if there is little or no interaction between the mass flow and the substratum (Sobiesiak et al., ). This spatial complexity in the bsz is the result of changes in a myriad of syndepositional factors during mass flow such as incorporation of water, increase in material velocity, changes in pore fluid pressure, frictional stresses, viscosity, interaction with different underlying lithologies/degrees of lithification, bathymetric obstacles and flow channelization, among others (Mohrig et al., , ; Elverhøi et al., ; Marr et al., ; Lucente & Pini, ; Posamentier & Kolla, ; Ilstad et al., ; De Blasio et al., ; Moscardelli et al., ; Posamentier & Walker, ; Moscardelli & Wood, ; Alves, ; De Blasio & Elverhøi, ; De Blasio, ; Dey et al., ; Otsubo et al., ).…”

“…Consequently, the bsz is believed to accumulate most of the strain/deformation during mass transport and emplacement (Middleton & Hampton et al., ; Ineson, ; Tripsanas et al., ; De Blasio et al., 2004a, 2004b; Dugan, ; Ogata et al., , ; Yamamoto & Sawyer, ; Day‐Stirrat et al., ; Kitamura et al., ; Festa et al., ; Cardona et al., ). The deformation observed in the bsz is not limited to the failed material within the mass flow, but can also progressively extend into the underlying deposits (Ogata et al., ; Valdez Buso et al., ; Sobiesiak et al., ), in a similar manner as a fault damage zone ( sensu Yielding et al., ). In a fault damage zone, deformation is not exclusively confined to the fault plane but nucleates from the fault plane into sediments in the hanging and footwall blocks.…”

“…the basal shear zone). The bsz thickness can increase as the strain boundary migrates downward from the mass flow deforming part of the substratum (Alves & Lourenço, ; Sobiesiak et al., ).…”

“…Recent works have documented the complex nature of the bsz in outcrops of MTDs (Alves & Lourenço, ; Festa et al., ; Ogata et al., , ; Valdez Buso et al., ; Sobiesiak et al., , ; Brooks et al., ; Hodgson et al., ). The bsz thickness can range from a few millimetres to several tens of metres (Alves & Lourenço, ; Sobiesiak et al., ), and its characteristics vary temporally and spatially reflecting likely flow transformations during mass transport episodes (Strachan, ; Fallgatter et al., ).…”