Development of Cutoff-Related Knickpoints in Submarine Channels: Insights From Kinematic Modeling and Implications for Reservoir Architecture

Abstract

Submarine channels are often thought of as having relatively simple geometries, with significant along-channel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a simple kinematic model of channel evolution, we explore the along-channel slope variability, its evolution through time, and the implications for reservoir architecture and connectivity. Both the field data and modeling suggest that channels on the seafloor can develop slope variability as a result of meander cutoff events. When cutoffs develop, the shortened flow paths produce locally steep gradients, thus initiating knickpoints. In an incising channel system, waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. Cutoffs and steep channel segments also form in aggrading channels and contribute to the architectural complexity, but these aggradational cutoff deposits tend to be connected to the sand-rich axial part of the system. In general, knickpoint gradient is proportional with overall slope, local along-cutoff slope, and local sinuosity; and is inversely related to mean along-channel slope and mean sinuosity. Because continental slope gradients are significantly larger than those characteristic of lowland rivers, cutoff-related knickpoints are larger and steeper in submarine channels than in meandering rivers. In sinuous slope channel systems, the process of meander cutoff followed by knickpoint retreat result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017