Deep-water and fluvial sinuous channels—Characteristics, similarities and dissimilarities, and modes of formation

Abstract

High-resolution 3D seismic data of several subsurface examples reveal significant differences in internal architecture and evolution of fluvial and deep-water sinuous channel systems, although there are many similarities in external morphologies of both systems. Channel migrations or shifts in fluvial systems, with point-bar scrolls, are relatively continuous laterally and show a downstream component; they are commonly a single seismic phase thick, with flat tops. In deep-water systems, channel migrations or shifts, with or without point-bar scroll-like features, may be lateral, either continuous or discrete, and laterally to vertically aggrading, again either continuous or discrete; they are single to multiple seismic phases thick, with or without a downstream component. Even the most laterally migrated channel complex commonly aggrades, to varying degrees, from the inside to the outside of sinuous loops. Similarities between fluvial and deep-water sinuous channel systems discussed here imply that sinuosity enhancements in both cases are the result of gradual processes, involving interaction of flows, sediments and alluvial plain or seafloor in attempts to build equilibrium profiles. Flat gradients, high width to depth ratios of valleys/channel belts, fine sediment grain sizes, a certain degree of bank cohesiveness, and presence of secondary circulations in flows were pre-requisites in both systems. However, a number of factors appear to have caused major differences in the internal architecture and modes of evolution of fluvial and deep-water channels. These include differences in (1) density contrasts of flows relative to ambient fluids, (2) entrainments of ambient fluids into flows, (3) effects of centrifugal and Coriolis forces on flows, (4) frequency, volume and duration of steady vs. catastrophic flows, (5) modes of sediment transport, and (6) effects of sea level changes on deposition. Furthermore, within deep-water systems, changes in flow parameters and sediment grain size can cause erosion, bypassing or deposition in space and time and result, through cuts and fills, in sinuous channels with lateral migrations, vertical aggradations and combinations thereof.