Development of cutoff-related knickpoints during early evolution of submarine channels

Abstract

Submarine channels are often thought of as having relatively simple geometries, with significant alongchannel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a kinematic model of channel evolution, we present evidence 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. Waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. The simple processes of meander cutoff followed by knickpoint retreat are intrinsic to submarine channels and result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing. These insights highlight the early evolution of submarine channels, a phase with a record that is commonly fragmented or completely absent as a result of subsequent erosion, and allow a better understanding of the autogenic controls on deep-marine stratigraphy.

Multi‐scale analysis of a migrating submarine channel system in a tectonically‐confined basin: The Miocene Gorgoglione Flysch Formation, southern Italy

“…Commonly, channel architecture records a protracted history of incision and deposition at multiple scales related to different types of sediment‐gravity flows (Hubbard et al ., ). The main features of the sediment‐gravity flows, such as magnitude and both density and type of transported sediment, may vary as a consequence of changes in allogenic (for example, tectonics and sea‐level fluctuations) and autogenic (for example, channel avulsions) factors (Pirmez et al ., ; Kneller, ; Jobe et al ., ; Sylvester & Covault, ).…”

What controls submarine channel development and the morphology of deltas entering deep‐water fjords?

“…Astoria Canyon, Oregon; San Antonia Canyon, Chile; Monterey Canyon, California; Scripts Canyon, California; Mitchell, , ); on open continental slopes (New Jersey continental slope; Mitchell, ); as deep‐water ‘waterfalls’ (Monterey Fan; Masson et al, ); within headless channels (Lake Geneva; Girardclos et al, ); in lakes (Lake Geneva; Lake Wabush; Girardclos et al, ; Turmel et al, ); and in channel meander bed cut‐offs (e.g. offshore Angola; Sylvester and Covault, ).…”

“…Second, system morphology strongly influences the shape and location of valuable oil and gas reservoirs. This affects the shape and distribution of sand layers deposited by submarine channels, or in delta lobes (Weimer and Pettingill, ; Sylvester and Covault, ).…”

Knickpoints and crescentic bedform interactions in submarine channels

“…Firstorder questions remain concerning how submarine knickpoints migrate upstream, and how knickpoint migration interacts with smallerscale associated crescentic bedforms, influencing the longer-term submarine channel evolution and the resulting sedimentary record. Although the morphology and formation mechanisms might differ, knickpoints are observed globally in various settings, and have been reported from erosional submarine canyons (for example, San Antonia Canyon, offshore Chile; Mitchell, 2006), open continental slopes (New Jersey continental slope; Mitchell, 2006), deep-water 'waterfalls' (Monterey Fan; Masson et al, 1995), headless channels (Girardclos et al, 2012) and submarine channel meander bend cut-offs (Cantelli & Muto, 2014;Sylvester & Covault, 2016). In a previous study of Bute Inlet, Heijnen et al (2020) showed that submarine knickpoints can dominate submarine channel and channel-bend evolution, and can migrate upstream very rapidly (hundreds of metres per year).…”