The stratigraphic record of submarine-channel evolution

Abstract

Submarine-channel systems record basin-margin sediment dispersal and can host signi cant natural resources.We review the facies architecture (i.e., facies heterogeneity and stacking patterns) of outcropping submarine-channel systems, focusing on the Cretaceous Tres Pasos Formation, Magallanes basin, southern Chile.The fundamental building block of submarine-channel systems is the channel- ll architectural element.A channel ll comprises thick-bedded turbidite sandstone deposited in the deepest segment of the bounding channel surface (i.e., the thalweg), which transitions laterally to thin-bedded heterolithic deposits in the margins. Submarine-channel lls stack to form composite channel systems, which commonly exhibit an evolution from early channel incision and lateral migration to late-stage aggradation.The incising-to-aggrading trajectory of a submarine-channel system is likely in uenced by adjustments toward an equilibrium gradient that is established and maintained by feedbacks between the slope and overriding sediment-gravity ows.A steep slope will promote swift ows that are erosive; a more gradual gradient will promote sluggish ows that aggrade sediment.A combination of these two processes brings the channel oor closer to an equilibrium gradient. Changes in sediment-gravity- ow properties driven by allogenic controls, such as eustatic sea-level change, have also been linked to the incising-to-aggrading trajectory of channel systems.We illustrate the evolution of channel systems with a surface-based stratigraphic forward model.The model allows us to visualize the three-dimensional (3D) stacking patterns of channel systems, which control heterogeneity and sand body connectivity in channelized hydrocarbon reservoirs. Future research opportunities include the interpretation of stratigraphic products integrated with direct monitoring of turbidity currents, physical experiments, and numerical modeling to understand the 3D facies architecture and stratigraphic evolution of channel systems.