Submarine channel initiation, filling and maintenance from sea‐floor geomorphology and morphodynamic modelling of cyclic steps

Abstract

Advances in acoustic imaging of submarine canyons and channels have provided accurate renderings of sea-floor geomorphology. Still, a fundamental understanding of channel inception, evolution, sediment transport and the nature of the currents traversing these channels remains elusive. Herein, Autonomous Underwater Vehicle technology developed by the Monterey Bay Aquarium Research Institute provides high-resolution perspectives of the geomorphology and shallow stratigraphy of the San Mateo canyon-channel system, which is located on a tectonically active slope offshore of southern California. The channel comprises a series of crescent-shaped bedforms in its thalweg. Numerical modelling is combined with interpretations of sea-floor and shallow subsurface stratigraphic imagery to demonstrate that these bedforms are likely to be cyclic steps. Submarine cyclic steps compose a morphodynamic feature characterized by a cyclic series of long-wave, upstream-migrating bedforms. The bedforms are cyclic steps if each bedform in the series is bounded by a hydraulic jump in an overriding turbidity current, which is Froude-supercritical over the lee side of the bedform and Froude-subcritical over the stoss side. Numerical modelling and seismic-reflection imagery support an interpretation of weakly asymmetrical to near-symmetrical aggradation of predominantly fine-grained net-depositional cyclic steps. The dominant mode of San Mateo channel maintenance during the Holocene is interpreted to be thalweg reworking into aggrading cyclic steps by dilute turbidity currents. Numerical modelling also suggests that an incipient, protoSan Mateo channel comprises a series of relatively coarse-grained net-erosional cyclic steps, which nucleated out of sea-floor perturbations across the tectonically active lower slope. Thus, the interaction between turbiditycurrent processes and sea-floor perturbations appears to be fundamentally important to channel initiation, particularly in high-gradient systems. Offshore of southern California, and in analogous deep-water basins, channel inception, filling and maintenance are hypothesized to be strongly linked to the development of morphodynamic instability manifested as cyclic steps.

The Stratigraphic Record of Submarine-Channel Evolution

“…However, recent monitoring data record the hourly to annual interaction between submarine channels and sediment-gravity flows (e.g., Zeng et al, 1991;Xu et al, 2004;Paull et al, 2010;Conway et al, 2012;Cooper et al, 2013;Sumner and Paull, 2014;Talling et al, 2015;Hughes Clarke, 2016). These data underscore the short-term transience of seafloor geomorphology and multi-phase bed reworking, local deposition, and bypass of sediment-gravity flows active during channel initiation, maintenance, and filling (e.g., Covault et al, 2014). Furthermore, insights from monitoring have inspired reinterpretation of outcropping sedimentary rocks (e.g., Fildani et al, 2013;Hubbard et al, 2014;Bain and Hubbard, 2016;Pemberton et al, 2016).…”

“…Cyclic steps are long-wave (the ratio of wavelength to height is >>1), upstreammigrating bedforms, commonly with asymmetrical waveforms in cross section, which develop in regions with high gradients and slope breaks that promote repeated internal hydraulic jumps in an overriding turbidity current (Kostic, 2011). These bedforms have been documented in fieldscale observations combined with morphodynamic modeling (e.g., Fildani et al, 2006;Kostic, 2011;Covault et al, 2014), physical experiments (e.g., Spinewine et al, 2009), direct monitoring of turbidity currents (e.g., Hughes Clarke, 2016), and recently in outcrops . These features might play a significant role in the development of stratigraphic architecture and facies distribution within relatively high-gradient channels.…”

Hatteras Transverse Canyon, Hatteras Outer Ridge and environs of the U.S. Atlantic margin: A view from multibeam bathymetry and backscatter

“…Upper Hatteras Fan has a zone composed of what appears to be cyclic steps (Parker, 1996;Kostic and Parker, 2006;Fildani et al, 2006;Cartigny et al, 2011;Konstic, 2011;Covault et al, 2014) that rises as much as 50 m above the main channel floor (Figs. 6 and 7) immediately downslope from the large depositional feature (Fig.…”

Integrating outcrop and subsurface data to assess the temporal evolution of a submarine channel–levee system

“…Triggers for avulsion events include allocyclic controls such as changes in climate, sea level, or tectonics (Kolla, 2007;Maier et al, 2012). Autocyclic controls may include increasing channel sinuosity (Kolla, 2007), limited downstream accommodation, and backfilling of individual channel thalwegs caused by lobe deposition (Prélat et al, 2010) or breaching of a levee and response to a changed base level (Fildani et al, 2006;Brunt et al, 2013a;Covault et al, 2014;Ortiz-Karpf et al, 2015). However, the lack of longitudinal migration of the C2 avulsion node points to an underlying control, such as a break-in-slope, although this is too subtle to resolve at outcrop.…”

“…The architecture and evolution of deep-water channel systems has been of particular interest in both the hydrocarbon industry and academic study in recent years with detailed investigations using highresolution reflection seismic data sets (e.g., McHargue and Webb, 1986;Badalini et al, 2000;Babonneau et al, 2002Babonneau et al, , 2004Abreu et al, 2003;Deptuck et al, 2003Deptuck et al, , 2007Posamentier, 2003;Posamentier and Kolla, 2003;Schwenk et al, 2005;Mayall et al, 2006;Kolla, 2007;Cross et al, 2009;Catterall et al, 2010;Armitage et al, 2012;Jobe et al, 2015;Ortiz-Karpf et al, 2015) and seabed imaging techniques (e.g., Torres et al, 1997;Maier et al, 2011Maier et al, , 2013Covault et al, 2014), although these provide limited detailed information on subseismic-scale elements and the range and distribution of sedimentary facies. This gap has been addressed through the use of analogous systems at outcrops (Badescu et al, 2000;Blikeng and Fugelli, 2000;Campion et al, 2000;Clark and Gardiner, 2000;Gardner et al, 2003;Beaubouef, 2004;Pickering and Corregidor, 2005;Hodgson et al, 2011;Brunt et al, 2013b;Hubbard et al, 2014;Masalimova et al, 2016).…”