Submarine channels share morphological similarities with rivers, but observations from modern and ancient systems indicate they are formed under processes and controls unique to submarine settings. Morphologic characteristics of channels-e.g., width, depth, slope, and the relationships among them-can constrain interpretations of channel-forming processes. This work uses morphometric scaling relationships extracted from high-resolution seafloor bathymetry to infer connections between morphology and process in submarine channels. Analysis of 36 modern channels in five geographic regions shows that channel widths vary regionally (from <100 m to >10 km wide) but occupy the same range of aspect ratios (~10:1-100:1). This suggests an autogenic control on aspect ratio, perhaps resulting from feedback processes in levee growth and/or bank erosion, and allogenic (e.g., sediment supply, grain size) controls on channel width. Submarine channel aspect ratios tend to decrease with increasing dimensions, while the opposite relationship has been observed for fluvial channels, likely due to opposing relationships between flow discharge and channel distance. Additionally, observation of an apparent lag between channel thalweg and levee responses to gradient changes suggests that thalweg and levee deposition and erosion may be partially decoupled due to the vertical structure of turbidity currents, with thalweg evolution driven by the basal, higher-shear-stress portion of the flow and levee evolution by the dilute upper portion. The data presented here provide a basis for predicting channel metrics in exploration scenarios, in which data coverage may be sparse. This documentation of a diverse suite of channels also captures the range of scales and variability exhibited globally by submarine channel systems, providing context for local studies.

This study describes the character of submarine mass movement and associated deformation as revealed by an exceptionally well-exposed portion of a seismic-scale masstransport deposit (MTD) within the upper Miocene Mohakatino Formation (Taranaki Basin, New Zealand). The North Awakino MTD is at least 55 m thick and crops out along the northern Taranaki coastline for ~11 km in wave-cut platforms and in cliffs as much as 100 m high. Spectacular softsediment deformation features are developed in remobilized sediment gravity fl ow deposits that initially accumulated within a lowgradient intraslope basin. Sedimentary facies within the North Awakino MTD comprise laterally extensive, thick-to thin-bedded volcaniclastic sandstone and mudstone. Distinct postdepositional deformation styles are associated with bedding type: folds developed in thick-bedded sandstone are larger (fold heights to tens of meters) and more laterally continuous (to 1 km) than those developed in thinner bedded facies.Regional geologic relationships suggest that nearly the full width of the North Awakino MTD is exposed in outcrop, providing a rare opportunity to observe lateral relationships between the marginal and central portions of the MTD. We conducted a rigorous paleoslope analysis of slump fold, fault, and bedding orientations using both existing and newly proposed methodologies. Separate analysis of seven subregions within the North Awakino MTD reveals that the predicted MTD transport direction varies widely along the outcrop extent. Most notably, slump folds and faults within the inferred margins have mean orientations that are suborthogonal to those within the central portions of the MTD. This relationship is hypothesized to be a consequence of edge effects that may be related to lateral compression along the margins of the MTD. Our analysis demonstrates the importance of accounting for spatial hetero geneity in slump structure orientations when determining the paleoslope orientation through kinematic analysis. Our inference of west-directed translation suggests that the North Awakino MTD formed in response to a local change in the bathymetric slope orientation that was likely the result of tectonically induced basin deformation.

Morphometric analysis of submarine fan systems, the largest sedimentary deposits on Earth, demonstrates scaling relationships between genetically related channels and lobeshaped bodies (LBs) deposited beyond the channel terminus, providing insight into the architectural development of these systems. Compiling dimensional data from depositional systems that cover a range of sediment supply characteristics, tectonic settings, and geographic locations enables investigation into global trends in depositional morphology. LBs have a consistent, scale-independent length-to-width ratio of ~2:1. The thickness-to-area ratios for LBs show multiple morphologic trends, likely driven by topographic confinement, with LBs getting proportionally thicker in relation to increasing confinement. Morphometric analysis of genetically related channel dimensions (width, relief, cross-section area) and LB dimensions (length, width, thickness, area, volume) reveals robust scaling relationships; most notably, channel width and cross-sectional area can be used to predict the volume and depositional area of related LBs. These relationships demonstrate that LBs proportionally scale to their concomitant channels, and thus to the volume of sediment supplied prior to an avulsion. While the dimensions of submarine fans scale to associated terrestrial catchments, the building blocks of submarine fans (i.e., channels and LBs) do not, suggesting a down-system decoupling (or lack of scaling) at LB deposition time scales. Applying these morphometric trends and scaling relationships as input parameters for source-to-sink and reservoir models can improve predictions of stratigraphic architecture, sediment partitioning, and sediment/ carbon flux in modern and ancient submarine fan systems.

Constraining the avulsion dynamics of rivers and submarine channels is essential for predicting the distribution of sediment, organic matter, and pollutants in alluvial, deltaic, and submarine settings. We create a geometric channel-belt framework relating channel, levee, and floodplain stratigraphy that allows comparative analysis of avulsion dynamics for rivers and submarine channels. We utilize 52 channel-overbank crosssections within this framework to provide avulsion criteria for submarine channels, and how they differ from rivers. Superelevation and a new channel-floodplain coupling metric are two key parameters that control channel-belt thickness in both rivers and submarine channels. While rivers only superelevate 1 channel depth above the floodplain prior to avulsion, submarine channels are more stable during aggradation, with superelevation values commonly > 3 channel depths. Additionally, channel-floodplain coupling in rivers is often weak, with floodplain aggradation negligible compared to channel aggradation, making rivers avulsion-prone. However, floodplain aggradation is more significant for submarine channels, resulting in stronger channel-floodplain coupling and thus a decreased potential for avulsion. The combination of enhanced superelevation and strong channel-floodplain coupling results in submarine channel-belts that can be as thick as ∼10 channel depths, while fluvial channel belts are limited to 2 channel depths. Submarine channels are more stable because turbidity currents have ∼50x lower density contrast between flow and ambient fluid as compared to rivers. This density contrast creates far less potential energy for avulsion, despite the much greater relief of submarine levees compared to fluvial levees. The modern Amazon submarine channel showcases this stability, with a channel belt that is ∼5 channel-depths thick for more than 400 streamwise km, which is more than twice the superelevation that a river is capable of. We interpret that enhanced floodplain aggradation and levee aggradation (and thus superelevation) in submarine channel belts are promoted by unique submarine flow characteristics, including turbidity current overspill, flow-stripping, and hemipelagic processes. We emphasize that rivers and submarine channels display very different avulsion dynamics and frequencies, profoundly affecting the stratigraphic architecture of channel-belt and downstream distributary deposits.

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