Controls on Deep-Water Cutoff Styles and Their Impact on Stratigraphic Architecture

Abstract

Deep-water channels can form highly aggradational channel belts relative to their fluvial counterparts. Initial work has suggested that deep-water channels develop their sinuosity early on, reach a planform equilibrium, and then undergo near vertical aggradation during which channel migration is limited and cutoffs are rare. However, observations from seismic data increasingly suggest that continued meander expansion and translation of some submarine channels can occur during aggradation and lead to a range of cutoff styles and/or avulsions. We characterize a spectrum of cutoffs with neck lengths ranging from narrow (less than a channel width in length) to wider. Some deep-water sinuous channels undergo aggradation without any significant valley confinement, e.g. the Amazon Channel. In this setting, cutoffs during aggradation are possible - but primarily of relatively short neck length styles. Wider neck length cutoffs are unlikely to form in such systems due to the steep gradient of the levee-overbank region. Once the flow goes overbank, it cannot reoccupy the channel; instead it initiates a channel avulsion. In environments with valley confinement, e.g. the Benin-Major canyon, reduced gradients within the valley can enable a greater range of cutoff neck lengths. We use a forward stratigraphic model to assess the timing and conditions of cutoff formation in systems with and without valley confinement. Furthermore, the model is used to quantify the impact these cutoff styles might have on the stratigraphic architecture and connectivity of these systems. The nature of cutoffs and channel migration is fundamental to the creation of channel-belt stratigraphy and has important implications on the nature of sandbody stacking patterns in submarine channel systems.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019