Controls on axial deep-water channel evolution in compressional basins

Deep-water channels are important agents of sediment, nutrient and pollutant transport; their deposits comprise parts of the largest sedimentary bodies on the earth. However, the initiation and evolution of channels in elongate, compressional basins, remain poorly understood. This shortcoming stems from poor availability of data at the scale required to constrain the development of sedimentary architecture. Here, bathymetry, seismic reflection, and outcrop datasets from two case-studies are used to document the sedimentology and architecture of such channels, constraining models of channel and overbank evolution in different scales of compressional basin.
Analysis of the sedimentology and architecture of the outcropping Arro turbidite system, Ainsa Basin, Spain, revealed that: (1) MTD emplacement into structurally confined basins can both enhance and diminish the ability of subsequent turbidity currents to channelise; (2) the growth of structures with long-axes parallel to flow can encourage channelisation by imposing lateral confinement; (3) nested scales of surfaces that are concave-up in cross-section may have been formed by upstream-migrating bedforms. Two studies of bathymetric, 2D and 3D seismic data imaging a section of the Hikurangi Channel and its overbanks, offshore New Zealand, were used to inform models of large-scale architectural evolution. The first focused on integrating seafloor geomorphology and subsurface architecture, revealing that MTDs derived from channel-wall collapse, together with related upstream migrating knickpoints were responsible for generating channelised stratigraphy. The second focused on the overbanks, revealing that: (1) lateral confinement, here tectonically controlled, may suppress the development of ‘wedge-shaped’ levees; (2) nine controls influence processes of overbank flow and deposition: flow versus conduit size, overbank gradient, flow tuning, Coriolis forcing, contour current activity, flow reflection, centrifugal forcing, interaction with externally derived flows, and interaction of overspill from different locations; (3) the relative influence of these controls changed throughout the depositional period.
This work advances understanding of how deep-water channels in compressional basins evolve and generate channelised stratigraphy. It has implications for the study of seafloor geohazards, modelling hydrocarbon reservoir heterogeneity, and for evaluating the potential of deep-water sediments to sequester pollutants and organic carbon.