Cyclic steps and related supercritical bedforms

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Marine Geology 393 (2017) 4–20
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Marine Geology
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Invited review article
Cyclic steps and related supercritical bedforms: Building blocks of
deep-water depositional systems, western North America
Jacob A. Covault a,⁎, Svetlana Kostic b, Charles K. Paull c, Zoltán Sylvester d, Andrea Fildani e
a Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA
b Computational Science Research Center, San Diego State University, San Diego, CA, USA
c Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA
d Chevron Energy and Technology Company, 1500 Louisiana, Houston, TX, USA
e Statoil, Research Center, Austin, TX, USA
⁎ Corresponding author.
E-mail address: jake.covault@beg.utexas.edu (J.A. Cov
http://dx.doi.org/10.1016/j.margeo.2016.12.009
0025-3227/© 2016 Elsevier B.V. All rights reserved.
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 19 July 2016
Received in revised form 12 December 2016
Accepted 22 December 2016
Available online 28 December 2016
Cyclic steps are long-wave (the ratio of wavelength to height is ≫1), upstream-migrating, upper-flow-regime
bedforms bounded by internal hydraulic jumps (i.e., transition from densimetric Froude supercritical to subcrit-
ical flow) in turbidity currents. They commonly occur in regions with high gradients and slope breaks. Here we
review the morphodynamic evolution and depositional products of cyclic steps and related supercritical
bedforms (e.g., antidunes). We present examples from high-resolution geophysical surveys and monitoring of
continental margins in western North America integratedwith physically based numerical modeling of turbidity
currents and associated bedforms.We compare numericalmodeling results to directmonitoring of turbidity cur-
rents in the Squamish prodelta, British Columbia, Canada. Cyclic steps and antidunes influence phases of canyon-
channel evolution, levee-overbank deposition, and channel-lobe-transition-zone sedimentation, thereby ad-
vancing channels and lobes into the basin. Bedforms range from relatively small cyclic steps and antiduneswithin
active submarine canyons and channels (~101mwavelength; ~100mheight) to large cyclic steps in less confined
levee-overbank environments and the channel-lobe transition zone (~103mwavelength; ~102m height). Cyclic
steps and related supercritical bedforms are important to the morphodynamic evolution of architectural ele-
ments of some deep-water depositional systems, especially those located along tectonically active margins
with high gradients and slope breaks that can promote internal hydraulic jumps in turbidity currents.
© 2016 Elsevier B.V. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Supercritical currents across continental slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Deposits of supercritical currents and hydraulic jumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Controls on the formation of cyclic steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Cyclic steps and related supercritical bedforms in western North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Monterey Fan: Large deep-water depositional system perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. San Mateo canyon-channel system: Small deep-water depositional system perspective . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Squamish prodelta: A natural laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Discussion: Occurrence of cyclic steps and related supercritical bedforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ault).
1. Introduction
Deep-water depositional systems host voluminous archives of Earth
history and natural resources at the terminal sinks of continental-
margin sediment-routing systems (e.g., Clift and Gaedicke, 2002). The
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5J.A. Covault et al. / Marine Geology 393 (2017) 4–20
erosion, transport, and deposition of turbidity currents across deep-
water depositional systems play important roles in the dispersal of sed-
iment and contaminants across continental margins (Paull et al., 2002)
and threaten underwater infrastructure (Cooper et al., 2013; Clare et al.,
2015). These currents also shape deep-water depositional systems into
canyon, channel, levee-overbank, depositional-lobe, and channel-lobe-
transition-zone architectural elements (Mutti and Normark, 1987,
1991; Normark et al., 1993; Piper and Normark, 2001) (Fig. 1). Subma-
rine canyons are erosional V-shaped features indenting the shelf edge
and uppermost slope of the world's continental margins (Normark
and Carlson, 2003; Harris andWhiteway, 2011). Canyons can transition
to U-shaped, lower-relief channels with levee-overbank deposits across
the lower slope and rise (Normark et al., 1993). Canyon-channel sys-
tems transition to depositional lobes across the channel-lobe transition
zone (Normark et al., 1993). The flow dynamics of turbidity currents in-
fluence the evolution of architectural elements of deep-water deposi-
tional systems (Piper and Normark, 2009; Talling et al., 2013, 2015).
Flowdynamics can be characterized by the densimetric Froude number,
Frd, which is a dimensionless ratio of inertial to buoyancy forces in a cur-
rent:
Frd ¼
Uffiffiffiffiffiffiffiffiffiffiffiffiffi
Δρ
ρ
gh
s ð1Þ
where U is depth-averaged current velocity, g is gravitational accelera-
tion, Δρρ is the submerged specific gravity of the current, and h is current
depth. Hereafter, we refer to the densimetric Froude number simply as
the Froude number.
Supercritical turbidity currents (Frd N 1) are thought to be common
in high-gradient submarine canyons and channels of the continental
slope, whereas subcritical turbidity currents (Frd b 1) are common in
lower-gradient channels and depositional lobes of the continental rise
and basin floor (Menard, 1964; Komar, 1971; Hand, 1974; Mutti and
Normark, 1987, 1991; Piper and Normark, 2001) (Fig. 1). The transition
Fig. 1. Architectural elements of a generalized continental mar
The canyon-channel morphology is modified from Nelson et a
from a subaqueous supercritical to subcritical current is not smooth;
rather, it is accomplished via a discontinuity known as an internal hy-
draulic jump (Komar, 1971). Internal refers to a submerged current
flowing under a less dense ambient fluid. A supercritical turbidity cur-
rent might undergo an internal hydraulic jump at a slope break, such
as at the transition from relatively high-gradient and channelized condi-
tions to flatter and locally unchannelized regions of the basin floor
(Komar, 1971; Mutti and Normark, 1987, 1991) (Fig. 1).
Trains of long-wave (the ratio of wavelength to height is NN 1),
upstream-migrating bedforms are common in regions of continental
marginswith high gradientsand slope breaks that can promote internal
hydraulic jumps in turbidity currents (Fildani et al., 2006). These
bedforms have been called sediment waves and scours (e.g., Symons
et al., 2016) (Fig. 1).
What are sedimentwaves? The term sedimentwaves is widely used
to describe large-scale (102–103 m wavelength; 100–102 m wave
height; Symons et al., 2016), symmetrical to asymmetrical wave-like
bedforms that generally migrate upstream (Migeon et al., 2000; Wynn
et al., 2000; Normark et al., 2002; Wynn et al., 2002b; Wynn and
Stow, 2002). Sediment waves are commonly observed in unconfined
submarine environments, including channel levees, continental slopes,
and basin plains (e.g., Damuth, 1979; Normark et al., 1980). Crescentic
sediment waves have also been recognized in active canyons (101–
102 m wavelength; 100–101 m wave height) (e.g., Paull et al., 2010;
Symons et al., 2016). Herein we are concerned with sediment waves
of turbidity-current origin (Kostic, 2011). These sediment waves can
be orthogonal to the submarine-channel trend if they were initiated
by large turbidity currents or they can be subparallel to channel levees
as a result of local spillover (e.g., Normark et al., 2002). Sediment
waves are generally fine-grained, net-depositional bedforms, which
are potentially preserved in the stratigraphic record as retrogradational
(i.e., upstreammigrating) backset beds on their stoss sides truncated by
erosive surfaces on their lee sides (Migeon et al., 2001; Postma et al.,
2014).
What are scours? Scours are crescentic to enclosed depressions that
cut into the seafloor and commonly form linear trains of asymmetrical
gin and the locations of sediment waves and cyclic steps.
l. (1970). Gradient measurements from Komar (1971).
Image of Fig. 1
Fig. 2. Schematic drawing of a series of asymmetrical cyclic steps and densimetric Froude
number (Frd) variability. Modified from Cartigny et al. (2011) and Covault et al. (2014).
6 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
waveforms in levee-overbank environments and the channel-lobe
transition zone (102–104 m wavelength; 101–102 m wave height)
(e.g., Fildani et al., 2006; Symons et al., 2016). Scours are net-erosional
bedforms, which are poorly preserved in the stratigraphic record;
however, they can be prominent features on the modern seafloor
(e.g., Macdonald et al., 2011).
There is growing recognition that many of these bedforms are cyclic
steps (Kostic, 2011). What are cyclic steps? Cyclic steps are long-wave,
upstream-migrating bedforms in regions with high gradients and slope
breaks that can promote internal hydraulic jumps in turbidity currents
(Fig. 2). Bedforms are interpreted to be cyclic steps if internal hydraulic
jumps are documented at lee-to-stoss slope breaks (Fig. 2). The pres-
ence of cyclic steps does not indicate the action of supercritical currents
Fig. 3. Locations of deep-water depositional systems discussed in the text and seafloor slopes of 0
al. (2004). A seafloor slope of 0.0095 (0.5443°) correspondswith Frd=1 based on Eq. (3). Bott
arc-seconds (~90 m). Black lines indicate the extent of National Oceanic and Atmospheric Ad
Centers for Environmental Information, retrieve date November 1, 2015).
traversing long distances along continental slopes, but supercritical-to-
subcritical flow transformations through internal hydraulic jumps. The
internal hydraulic jumps that produce submarine cyclic steps have
been documented in numerical experiments (e.g., Kostic and Parker,
2006), field-scale observations combined with morphodynamic numeri-
calmodeling (e.g., Fildani et al., 2006), physical experiments (e.g., Toniolo
and Cantelli, 2007; Spinewine et al., 2009), and direct monitoring of tur-
bidity currents (e.g., Hughes Clarke, 2016). Fewdatasets exist that direct-
ly monitor turbidity currents in submarine canyon-channel systems
(Talling et al., 2015). Therefore, morphodynamic numerical modeling
can be employed to evaluate whether field-scale trains of sediment
waves and scours are cyclic steps (e.g., Fildani et al., 2006). Purely
morphology- and facies-based recognition of cyclic steps remains a
challenge.
Cyclic steps and related supercritical bedforms (e.g., antidunes) have
emerged as important building blocks of deep-water depositional sys-
tems (Fildani et al., 2006; Kostic, 2011, 2014) (Fig. 1). These bedforms
play roles in canyon-channel evolution, levee-overbank deposition,
and channel-lobe-transition-zone sedimentation (Fildani et al., 2006,
2013; Cartigny et al., 2011; Kostic, 2011, 2014; Covault et al., 2014;
Hamilton et al., 2015; Postma et al., 2016) (Fig. 1). Herewe review inte-
grated studies of recently acquired high-resolution geophysical surveys
and monitoring of continental margins in western North America
(e.g., Paull et al., 2010; Hughes Clarke, 2016) and numerical modeling
of turbidity currents (e.g., Fildani et al., 2006; Kostic, 2011, 2014;
Covault et al., 2014) (Fig. 3). Numerical modeling results are compared
to direct monitoring of turbidity currents in the Squamish prodelta,
British Columbia, Canada. We discuss deep-water depositional systems
.0095 (0.5443°). Outline ofMonterey Fan from Fildani andNormark (2004) andKlaucke et
om slopes N0.0095 (0.5443°) are highlighted in red. Digital Elevation Model resolution is 3
ministration's National Geophysical Data Center US Coastal Relief Model (NOAA National
Image of Fig. 2
Image of Fig. 3
Fig. 4. Stability fields for subaqueous bedforms.
Modified from Stow (2005).
7J.A. Covault et al. / Marine Geology 393 (2017) 4–20
offshore of tectonically active western North America in the context of
other studies of the seafloor, outcrops, and physical experiments to
evaluate the importance of cyclic steps and related bedforms in the
morphodynamic evolution of continental margins.
2. Supercritical currents across continental slopes
Komar (1971, 1975) speculated that many continental slopes are
steep enough to promote supercritical currents (N0.01, or N0.5°) (see
alsoHand, 1974). He reached this conclusion by combining the equation
for the Froude number andMiddleton's (1966) depth-averaged velocity
of a steady, uniform turbidity current:
U ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
8g
Δρ
f 1þ αð Þρ Sh
s
ð2Þ
where f is the Darcy-Weisbach friction factor, α is a term that takes into
account the added fluid drag on the top of the turbidity current, and S is
bed slope. Under steady, uniform conditions, the Froude number be-
comes:
Frd ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
8S
f 1þ αð Þ
s
ð3Þ
which shows that bed and interfacial friction are the primary controls
on the Froude number of a turbidity current. Komar (1975) used f and
α values of 0.04 and 0.9, respectively, based on current velocities of sev-
eralm/s to ~15m/s to calculate a bed slope of ~0.01, or ~0.5°, for critical
flow (i.e., Frd = 1; see also Sequeiros, 2012). This bed-slope value im-
plies that turbidity currents are prone to be Froude supercritical across
continental slopes for discrete length and time scales on a variety of tec-
tonic settings offshore of the United States (Fig. 3). However, we recom-
mend that this calculation of critical bed slope should be used with
caution for natural flows because: 1) Eq. (2) is based on a steady, uni-
form turbidity current, which might be uncommon in natural settings;
and 2) values of bed and interfacial friction are poorly known and esti-
mates can vary over an order of magnitude (Komar, 1971, 1975; Hand,
1974, 1975).
A common bedform that interacts with a supercritical current is the
antidune (Fig. 4), inwhichundulations at the interface between the cur-
rent and the ambient fluid are nearly in phase with those at the bed.
However, antidunes are commonly ephemeral (Alexander et al., 2001;
Kostic et al., 2010; Cartigny et al., 2011), with low preservation poten-
tial. Cyclic steps have greater preservation potential because each
bedform in the series is overriddenby internal hydraulic jumps in a tur-
bidity current (Kostic and Parker, 2006; Kostic, 2011) (Fig. 2). An inter-
nal hydraulic jump is associatedwith a drop in turbulent kinetic energy,
which enhances deposition downstream of the jump (i.e., stoss side of
the bedform; Kostic, 2011). Transitional bedforms between antidunes
and cyclic steps include breaking antidunes, antidunes and cyclic steps
within the same train, and climbing antidunes superimposed on cyclic
steps (Kostic, 2014). Analogywith rivers implies that a characteristic se-
quence of submarine upper-flow-regime bedforms emerges as depth-
averaged flow velocity and Froude number increase: antidunes, transi-
tional bedforms, and cyclic steps (Cartigny et al., 2014; Kostic, 2014)
(Fig. 4).
3. Deposits of supercritical currents and hydraulic jumps
In a comparison of architectural elements of deep-water deposition-
al systems on the modern seafloor and in outcrop, Mutti and Normark
(1987, 1991) interpreted channel-lobe-transition-zone deposits to be
the products of internal hydraulic jumps at the transition in flow regime
from supercritical to subcritical (Fig. 5A and B). Mutti and Normark
(1987) proposed two depositional models of the channel-lobe
transition zone related to the dominant grain size of turbidity currents
(Fig. 5A and B). 1) Turbidity currents that are carrying mostly coarse-
grained sediment can create large-scale scours near the location of the
internal hydraulic jump at the break in slope. Energy loss during the hy-
draulic jump and consequent reduction of competence of the current
produce a sandy wedge just beyond the break in slope at the channel
mouth (Fig. 5A). 2) Turbidity currents that are carrying a mixed load
of sand and mud do not scour the seafloor as intensely and the reduced
settling velocity of the muddy load can promote sediment bypass well
beyond the channel mouth. The resulting deposit includes finer-
grained stratification and is detached from the channel mouth
(Fig. 5B). These early depositional models illustrate the hypothetical
downstream evolution of turbidity currents and their deposits related
to a transition in flow regime from supercritical to subcritical during
an internal hydraulic jump (Fig. 5A and B).
Wynn et al. (2002a) supported these early depositional models of
the channel-lobe transition zone with acoustic imaging of the seafloor
and shallow subsurface comprising a variety of erosional and deposi-
tional features: spoon- and chevron-shaped scours (up to 2.5 km wide
and 20 m deep), large regions of amalgamated scour (up to 9 km
wide), erosional lineations (up to 15 km long), sediment waves (wave-
lengths 1–2 km,wave height up to4m), andmounds of sand and gravel.
These images showedmore of themorphological variability of channel-
lobe-transition-zone features possibly related to internal hydraulic
jumps (Fig. 5C).
Hamilton et al. (2015) and Postma et al. (2016) evaluated the
morphodynamics of turbidity currents in the channel-lobe transition
zone in physical experiments (Fig. 6). The results of an experiment
using saline density currents with crushed plastic to emulate sustained
turbidity currents and bed-load transport are illustrated in Fig. 6
(Hamilton et al., 2015). Supercritical currents incised and extended
the channel, with channel-mouth deposits promoting the development
of an internal hydraulic jump and the deposition of upstreamonlapping
backfill deposits within the channel (Fig. 6). Backfilling eventually re-
sulted in a channel avulsion (Fig. 6).
Image of Fig. 4
Fig. 6. Bathymetric difference maps from a physical experiment simulating the
morphodynamics of turbidity currents in the channel-lobe transition zone. Hamilton
et al. (2015) used saline density currents with crushed plastic to emulate sustained
turbidity currents and bed-load transport. They interpreted a submarine-channel
avulsion cycle: channel extension and deposition at the channel mouth (t = 6 min),
initial hydraulic jump (t = 10 min), upstream retreat of the location of hydraulic jump
(t = 14 min), and channel avulsion (t = 18 min). Dashed lines indicate the region of
the turbidity current, or flow field, at each snapshot in time. Bathymetric difference
maps are based on bathymetry at a time step subtracted from the initial bathymetry.
Densimetric Froude number at time steps 6, 10, and 14 min plotted below. Modified
from Hamilton et al. (2015).
A
B
C
D
Fig. 5. Processes and deposits of supercritical turbidity currents undergoing an internal
hydraulic jump at the channel-lobe transition zone. (A) Relatively small-volume, sand-
rich current. Above: process. Below: resulting deposit. (B) Large-volume, mixed sand
and mud current. Above: process. Below: resulting deposit. The regions of C-C’ and D-D’
are schematically illustrated in parts C and D. Modified from Mutti and Normark (1987).
(C) Map view of channel-lobe transition zone. Modified from Wynn et al. (2002a).
(D) Turbidite facies (Bouma, 1962; Lowe, 1988) produced by deposition on a single
cyclic step. Modified from Postma and Cartigny (2014).
8 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Deposits associated with supercritical currents and hydraulic jumps
are not restricted to the channel-lobe transition zone. Morphodynamic
modeling of cyclic steps has shown that sediment waves and scours
occur in canyon, channel, and levee-overbank architectural elements
of deep-water depositional systems (Cartigny et al., 2011; Kostic,
2011, 2014). Kostic and Parker (2006) developed the first numerical
model that produced submarine cyclic steps; they used an unsteady,
depth-averaged four-equation formulation based on Fukushima et al.
(1985) and Parker et al. (1986), aswell as a novel sediment entrainment
formulation and jump-capturing numerical technique. Following this
breakthrough, Fildani et al. (2006) and Kostic (2011) applied the nu-
merical model to natural examples and suggested that in many cases
the large-scale (up to 10 km wavelength; 100–102 m amplitude), up-
stream migrating sediment waves and scours formed by turbidity cur-
rents are net-depositional or net-erosional cyclic steps, respectively
(Fig. 7). Cartigny et al. (2011) argued that available sediment erosion
models might not be suitable for a wide range of flow conditions.
They characterized an entire train of cyclic steps with an average step
and applied a simplistic steady two-equationmodel together with a hy-
draulic jump equation to generate stability fields for cyclic steps in dif-
ferent settings. This study strengthened previous findings that many
sediment waves can be interpreted as cyclic steps (e.g., Fildani et al.,
2006; Kostic, 2011).
Image of Fig. 6
Image of Fig. 5
Fig. 7. Controls on the evolution of cyclic steps. (A) Base case in which grain size was set equal to 80 μm and the entrainment limiter pwas set equal to 0.04. The entrainment limiter p
ranges from 0 for consolidated bedrock to 1 for unconsolidated, loose sediment. Parts C–H pertain to the same conditions as part A, except for the value of one selected control
parameter. Bed elevation (green lines) change along a hypothetical initial slope (red line) in response to a sequence of overriding turbidity currents. (B) Downstream variation in the
Froude number for the base case in part A. (C) Effect of the initial slope (S0 increased from 1.3% to 2.5%). (D) Effect of bed porosity (λ increased from 0.5 to 0.7). (E) Effect of the inflow
concentration of suspended sediment (C0 increased from 0.01 to 0.03). (F) Effect of the sediment availability (entrainment limiter p increased from 0.04 to 0.06). (G) Effect of the
slope-break location (increased from 6 to 15 km within the model domain). (H) Effect of the inflow Froude number (inflow depth increased from 20 to 100 m). See text for explanation.
Modified from Kostic (2011).
9J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Given the possibility of hydraulic jumps in turbidity currents
flowing over cyclic steps across continental margins, recent studies
have interpretedturbidite facies in outcrop in the context of cyclic
steps (e.g., Postma et al., 2009, 2014; Postma and Cartigny, 2014)
(Fig. 5D). Facies associations across a step comprise massive, rela-
tively coarse-grained sand units (Ta division; Bouma, 1962), possibly
with soft-sediment deformation, just downstream of a scour at the
upstream stoss side of the step, and finer-grained, traction struc-
tured sand and mud downstream to the crest of the step (Migeon
et al., 2001; Normark et al., 2002; Postma and Cartigny, 2014)
(Figs. 5D and 8). The resulting stratigraphic architecture in outcrop
is characterized by flat to lens-shaped units that can be hundreds
of meters across, with backset bedding truncated by erosive surfaces
(Postma et al., 2014; Postma and Cartigny, 2014; Bain and Hubbard,
2016; Pemberton et al., 2016) (Fig. 8).
Facies-based recognition of long-wavelength cyclic steps remains
a challenge because many outcrops are limited in scale. For example,
the number of outcrop examples that unequivocally show the wave-
form geometry of net-depositional sediment waves is limited to
large exposures of overbank deposits (Barton et al., 2007; Campion
Image of Fig. 7
Fig. 8. Block diagram of deposits associatedwith cyclic steps. Only a pair of scourswithin a
series of cyclic steps are shown on the seafloor for simplicity. Note the hypothetical
stratigraphic patterns associated with the evolution of aggrading and upstream-
migrating cyclic steps. Wavelength of individual steps ranges from tens to thousands of
meters. Modified from Postma et al. (2014).
10 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
et al., 2011). As the presence or absence of lamination in turbidites is
primarily driven by the sedimentation rate (Lowe, 1988; Sylvester
and Lowe, 2004; Sumner et al., 2008; Cantero et al., 2012), thick-
bedded and coarse-grained, massive or normally graded turbidites
can be deposited in any location where the bed aggradation rate is
high enough to suppress the development of stratification; and
these locations are not necessarily associated with hydraulic jumps.
Large volumes of deep-water sand are deposited over extensive
basin floors with low gradients (Ricci Lucchi and Valmori, 1980;
Amy and Talling, 2006), yet it is unlikely that supercritical currents
would dominate in these settings. Even turbidity currents in large
submarine channels with low gradients are likely to be subcritical
over most of the continental rise and basin floor (e.g., Amazon Chan-
nel; Pirmez and Imran, 2003).
4. Controls on the formation of cyclic steps
Kostic (2011) performed a dimensionless analysis of the unsteady,
depth-averaged four-equation formulation of Kostic and Parker
(2006) and established the following dimensionless parameters N that
control the variability of the morphodynamics of cyclic steps:
N ¼ f Frd0;Rf ; S0;C0;p;λ;
Lbreak
L
;
vs
U0
;Δτ�; r0; c�f
� �
ð4Þ
where Frd0, C0, and U0 are the inflow values of the Froude number, con-
centration, and velocity, respectively. S0 is the initial bed slope, p is a co-
efficient that characterizes the ability of the bed to resist erosion, λ is
bed porosity, and LbreakL is the ratio of the length of the slope break relative
to the length of the analyzed domain, vsU0 is the ratio of particle fall veloc-
ity to inflow velocity, and Δτ⁎ is the bed Shields number:
Δτ� ¼ Δu�
vs
Rf
� �2
ð5Þ
where Δu⁎ is the drop in shear velocity (u ⁎2=αK, where α is a dimen-
sionless coefficient and K is turbulent kinetic energy) during an internal
hydraulic jump and Rf is the dimensionless particle fall velocity:
Rf ¼
vsffiffiffiffiffiffiffiffiffi
RgD
p ð6Þ
whereD is themean grain size of sediment, r0 is a constant that defines a
ratio of the near-bed to depth-averaged concentration of suspended
sediment and cf⁎ is a coefficient of bed friction. The findings of Kostic
(2011) on controls on migration and stratigraphic architecture of net-
depositional cyclic steps are summarized in Fig. 7, which shows the
effects of initial slope S0, sediment availability p, bed porosity λ, the lo-
cation of a slope break LbreakL , the inflow concentration of suspended sed-
iment C0, and the inflow Froude number (set by inflow depth). Steeper
slopes, higher inflow sediment concentration, and more supercritical
flows characteristic of proximal canyons and channels might promote
shorterwavelength cyclic steps than in less confined and lower gradient
levee-overbank environments and the distal channel-lobe transition
zone (cf. Fig. 14 of Fildani et al., 2006; see also Cartigny et al., 2011;
Kostic, 2011, 2014). The values of D (given by the dimensionless fall ve-
locity Rf) and p are important in determining the degree of erosion ver-
sus deposition of net-depositional cyclic steps (Fig. 7). Moreover, the
key dimensionless parameters that control cyclic-step initiation and de-
position are vsU0 andΔτ
⁎, respectively. The ratio of the sediment fall veloc-
ity to inflow velocity vsU0 defines the cutoff size of sediment that causes
turbidity currents to undergo internal hydraulic jumps (see Kostic,
2011; for the criterion). The drop in the bed Shields number Δτ⁎ across
the jump determines whether a jump is strong enough to leave a depo-
sitional record (Kostic, 2011).
5. Cyclic steps and related supercritical bedforms in western North
America
In light of the increasing number of examples of deposits that have
been linked to supercritical flow and hydraulic jumps, we review the
morphodynamic evolution of deep-water depositional systems in tec-
tonically active western North America: including examples from the
transformmargin of central and southern California and the convergent
margin of British Columbia (Fig. 3). We pair observations and interpre-
tations of the seafloor and shallow subsurface with numerical modeling
of the morphodynamic evolution of sediment-gravity flows over an
erodible bed.
The Monterey submarine fan of Central California offers the oppor-
tunity to investigate the development of architectural elements analo-
gous to large (N104 km2; Bouma et al., 1985) passive-margin fans
(Piper and Normark, 2001; Fildani and Normark, 2004). A submarine
fan is a deep-water depositional system composed of genetically related
deposits of sediment gravity flows, slumps, and slides that form canyon,
channel, levee-overbank, and depositional-lobe architectural elements
that were created in virtual stratigraphic continuity (Nelson et al.,
1978; Bouma et al., 1985; Mutti and Normark, 1987, 1991; Nelson
et al., 1991; Piper and Normark, 2001; Posamentier and Kolla, 2003).
A breadth of sediment waves and scours (101–103 m wavelength;
100–102 m wave height) has been observed on the levee-overbank re-
gions of the fan (Normark et al., 1980; Fildani et al., 2006) and on the
floor of Monterey Canyon (Paull et al., 2010). The linkages of different
architectural elements across an entire continental margin can be stud-
ied in smaller (b103 km2; Bouma et al., 1985) deep-water depositional
systems of the Southern California Borderland (Covault et al., 2014).
We compare insights from deep-water depositional systems offshore
of California to repeat geophysical surveys of fjord prodelta channels
of British Columbia. We also evaluate numerical modeling results in
the context of these surveys (Hughes Clarke et al., 2012a, 2012b,
2014; Hughes Clarke, 2016).
5.1. Monterey Fan: Large deep-water depositional system perspective
Sediment waves of the Central California continental margin have
been studied since the 1970's (Hess and Normark, 1976; Normark
et al., 1980). Multibeam bathymetric data collected by NOAA (Greene
and Hicks, 1990) show sediment waves associated with the Monterey
levee-overbank deposits (Normark et al., 2002) (Fig. 9). The sediment
waves are slightly oblique to the trends of the channels, implying that
they were initiated by flows spilling out from the channels over the le-
vees (Normark et al., 2002). Large-wavelength (of the order of several
km) sedimentwaves are concentric around the highlysinuous planform
Image of Fig. 8
A
C
D
B
Fig. 9. Cyclic steps of the Monterey East channel. (A) Map view of co-rendered bathymetry and slope of the Central California continental margin (NOAA National Centers for
Environmental Information, retrieve date November 1, 2015). (B) Longitudinal profile of the Monterey East channel. (C-D) Results of turbidity-current morphodynamic modeling for
case in which effective grain size was set equal to 70 μm (vs=4.05 mm/s) and the entrainment limiter p was set equal to 0.07. The entrainment limiter p ranges from 0 for
consolidated bedrock to 1 for unconsolidated, loose sediment. (C) Bed elevation (green lines) and turbidity-current interface (blue lines) change along a hypothetical initial slope (red
line) in response to a sequence of overriding turbidity currents. The cyclic steps migrate upstream. Their lengths are of the same order of magnitude as the Monterey East scours.
(D) Downstream variation in the Froude number. Modified from Fildani et al. (2006).
11J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Image of Fig. 9
12 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
of Shepard Meander of Monterey Fan (Normark et al., 2002; Fildani
et al., 2006) (Fig. 9). Normark et al. (1980) interpreted sediment
waves on the western levee of Monterey Fan to be a type of antidune
formed by supercritical turbidity currents.
Fildani et al. (2006) applied the numerical model of Kostic and
Parker (2006) to demonstrate that the sediment waves radially depos-
ited around Shepard Meander of Monterey Fan are net-depositional cy-
clic steps (Fig. 9). The sediment waves around Shepard Meander are
dissected by a linear series of large scours (3–5 km in width, 3–6 km
in length, and 80–200 m in depth) (Fig. 9). This geomorphology was
named the Monterey East channel. Fildani et al. (2006) combined
high-resolution seismic-reflection data with numerical modeling to in-
terpret that scours of theMonterey East channel are net-erosional cyclic
steps carved by flow-stripped turbidity currents that incised the older
sediment waves around Shepard Meander (Fig. 9). Fildani et al. (2006,
2013) interpreted the train of net-erosional cyclic steps that define the
Monterey East channel to be an incipient channel and an avulsion in
progress (Fig. 10). These processes might result in channel initiation
on other deep-water depositional systems (e.g., Maier et al., 2011,
2013).
As noted by Mutti and Normark (1987), supercritical flow and hy-
draulic jumps can occur across a significant part of a continentalmargin,
from canyon-channel systems to the channel-lobe transition zone. In
these environments, especially relatively high-gradient, proximal set-
tings, supercritical flows might maintain the canyon or channel by
thalweg reworking into net-depositional cyclic steps (Smith et al.,
2005, 2007; Paull et al., 2010; Cartigny et al., 2011). Smith et al.
(2005) documented sandy, crescentic sediment waves with ~2 m am-
plitude and 35 m wavelength across the active segment of Monterey
Canyon (Fig. 11). Repeat bathymetric surveys showed a complete
reorganization of the sediment waves during a six-month period, with
upstream migration of wave crests observed during a 32-day period
(Smith et al., 2005, 2007). Smith et al. (2005, 2007) attributed
sediment-wavemigration to supercritical turbidity currents transporting
sand and thalweg reworking into sediment waves. Kostic and Smith
(personal communication, 2009–2010) interpreted these sediment
waves to be net-depositional cyclic steps associated with the mainte-
nance of Monterey Canyon.
Paull et al. (2010) studied the sediment waves in Monterey Canyon
with closely spaced (meter-scale) vibracores, and Autonomous Under-
water Vehicle (AUV) repeat bathymetric mapping and Compressed
High-Intensity Radar Pulse (CHIRP) sub-bottom profiling (Fig. 14).
Vibracores contained the deposits of sediment-gravity flows. Similar
to Smith et al. (2007), repeat AUV mapping showed repositioning of
wave crests during a 26-day period (Fig. 11). Paull et al. (2010)
Fig. 10. Submarine-channel evolution from a train of net-erosional cyclic steps to a
relatively sinuous channel with inner-bend deposits and levees. Modified from Fildani
et al. (2013).
hypothesized that the sediment waves could be a result of slumping
and sliding of the floor of Monterey Canyon or they could be cyclic
steps created as a result of alternating supercritical and subcritical
flows. This interpretation was based on the similarity in morphology
of sediment waves in Monterey Canyon with documented net-
depositional cyclic steps and their association with deposits of
sediment-gravity flows. Cartigny et al. (2011) tested the cyclic-step hy-
pothesis with a simplified numerical model of sediment-gravity flows,
which demonstrated that the morphologies of Monterey Canyon sedi-
ment waves are consistent with supercritical flow and hydraulic
jumps leading to the development of cyclic steps. Subsequent work at
theMonterey BayAquariumResearch Institute has revealed similar sed-
iment waves in the active segments of submarine canyons offshore of
California (Tubau et al., 2015), suggesting that they might be a signal
of alternating supercritical and subcritical flows and cyclic steps that
maintain active submarine canyons.
5.2. SanMateo canyon-channel system: Small deep-water depositional sys-
tem perspective
Submarine canyon-channel systems of the Southern California Bor-
derland developed across a tectonically active margin characterized by
steep slopes outboard of narrow shelves (b10 km; Shepard and
Emery, 1941) and nearby hinterlands from which relatively coarse-
grained sediment is shed (Normark et al., 2009) (Fig. 12). Canyon-
channel systems are short (tens of kilometers in length; Covault et al.,
2011, 2012), which allows for more inclusive characterization of their
reaches.
Covault et al. (2014) characterized the geomorphology and shallow
stratigraphy of the SanMateo Canyon-channel systemwith AUV bathy-
metric mapping and CHIRP sub-bottom profiling (Fig. 13). The up-
stream reach of the San Mateo Canyon-channel system is more
continuous, characterized by a V shape and small aspect ratio (b7
width to depth ratio) across a relatively steep regional gradient (~6°).
Downstream, the channel thalweg widens (N18 aspect ratio), and the
regional gradient is lower (~2°) (Fig. 13). This downstream reach com-
prises a series of six crescentic bedforms in close proximity to subsur-
face folds mapped across the tectonically active lower slope (Ryan
et al., 2009) (Fig. 13). High scarps form the upstream lee faces and later-
al margins of the bedforms, whereas gentle, lower relief slopes form the
downstream stoss sides (Fig. 13). The bedforms range in wavelength
from hundreds of meters to a kilometer, with wave heights ~20–50 m.
Subsurface profiles along the thalweg of the downstream reach of the
SanMateo channel show high scarps with truncated seismic reflections
(Fig. 13). Packages of sub-parallel, relatively high-amplitude seismic re-
flections also drape each of the bedforms, with some downstream thin-
ning. Some high-amplitude seismic reflections exhibit slight upstream
accretion on the stoss sides of the bedforms. Packages of bi-
directionally onlapping seismic reflections are present locally in front
of the lee faces of some of the bedforms. An acoustically transparent
layer (N2 m thick) drapes the seafloor beyond the channel (Fig. 13).
This layer was sampled by gravity coring, which predominantly recov-
ered mud and fine-grained sand beds interpreted to be turbidites
(Covault et al., 2014).
The steep, smooth upstream canyon probably promoted supercriti-
cal turbidity currents, which could have undergone hydraulic jumps
downstream across the rugose bathymetry produced as a result of sub-
surface folding (Ryan et al., 2009). Local packages of bi-directionally
onlapping seismic reflections in front of the lee faces of some crescentic
bedforms might be a result of rapid deposition of suspended sedimentassociated with an internal hydraulic jump at abrupt slope breaks
(Mutti and Normark, 1987). The geometry of the bedforms is consistent
with weakly asymmetrical, upstream-migrating to aggradational, net-
depositional cyclic steps (e.g., Migeon et al., 2000; Kostic, 2011).
Morphodynamic numerical modeling results confirm that the bedforms
could be net-depositional cyclic steps that maintain the channel form
Image of Fig. 10
A
B C D
Fig. 11.Multibeam bathymetry (vertical resolution of 0.15m and a horizontal footprint of 0.7 m) differencemaps showing repositioning of sediment waves inMonterey Canyon during a
26 day period. (A) Monterey Canyon. Location of B-D is a dashed black line. (B) Bathymetric data collected July 18, 2007. (C) Bathymetric difference between July 18 and July 19.
(D) Bathymetric difference between July 18 and August 13. Modified from Paull et al. (2010).
13J.A. Covault et al. / Marine Geology 393 (2017) 4–20
and aggrade a relatively consolidated channel floor: each of the six
bedforms is overridden by an internal hydraulic jump of a dilute (b1%
concentration) turbidity current (Fig. 13).
5.3. Squamish prodelta: A natural laboratory
The previous examples offshore of western North America were in-
vestigated by pairing high-resolution observations of the geomorpholo-
gy and shallow subsurface stratigraphy of deep-water depositional
systems with numerical modeling. Direct monitoring of the evolution
of deep-water depositional systems can provide insights into the
morphodynamics of architectural elements similar to physical experi-
ments in small-scale tanks (e.g., Toniolo and Cantelli, 2007; Rowland
et al., 2010; Hamilton et al., 2015; Postma et al., 2016; de Leeuw et al.,
2016) (Fig. 6). Repeat bathymetric mapping of fjord prodeltas of British
Columbia shows the high-resolution morphodynamic evolution of
channels (Hughes Clarke et al., 2012a, 2012b, 2014; Hughes Clarke,
2016).
A geophysicalmonitoringprogramof the active Squamish fjord head
delta in the upper Howe Sound (from the delta front to ~200 m water
depth), British Columbia, was established to investigate the timing
and character of submarine mass wasting (University of New
Brunswick, 2011; Hughes Clarke et al., 2014) (Fig. 14). Squamish River
delivers ~106 m3/year of sediment from a small (of the order of
103 km2) catchment within the tectonically active Coast Mountain
Range of British Columbia to the Howe Sound (Hickin, 1989).
Image of Fig. 11
A
B
Fig. 12. Oblique view of hillshade of the Southern California Borderland highlighting relatively short canyon-channel systems outboard of narrow shelves and common sediment waves
and scours on the slope (Gardner et al., 2002; Covault et al., 2014; NOAA National Centers for Environmental Information, retrieve date November 1, 2015).
14 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Daily (1–3 day period during 4 months) bathymetric surveys (70–
100 kHz; 1 m horizontal and ~30 cm vertical resolution) of the
Squamish prodelta established the style and extent of submarine mass
movements, which included occasional, aperiodic failure of the delta
front at the shelf edge and frequent (daily) upstreammigration of cres-
centic sediment waves within three prodelta channels (Hughes Clarke
et al., 2012a, 2012b, 2014; Hughes Clarke, 2016). During themonitoring
period, 103 mass movements were detected in the channels, with the
majority (49) occurring in the northern channel (Fig. 14). Small sedi-
ment waves (30–70 m wavelength; 2–3 m wave height) dominate the
floor of the northern channel, which exhibits an average gradient of
6°. The mass movements were almost always characterized by up-
stream migration of sediment waves (Hughes Clarke et al., 2012a,
2012b, 2014; Hughes Clarke, 2016). The sediment waves are reminis-
cent of asymmetrical net-depositional cyclic steps.
In 2012, hourly multibeam water column imaging and a rapidly
dipping towed optical backscatter probe recorded turbidity currents
during the upstream migration of sediment waves (Hughes Clarke,
2016). Water column imaging shows turbidity currents interacting
with sediment waves on the seafloor: accelerating currents down
the steep (b40°) lee face of sediment waves expand and undergo ap-
parent internal hydraulic jumps close to the slope break, followed by
stoss side deposition and reworking by the bypassing current
(Hughes Clarke, 2016). Moreover, the water column imaging poten-
tially shows the development of flow stratification with a basal,
high-density layer and an upper, low-density layer (Postma et al.,
2009; Cartigny et al., 2014; Postma and Cartigny, 2014; Talling
et al., 2015; Hughes Clarke, 2016). These processes are similar to
those of a turbidity current over cyclic steps (Kostic and Parker,
2006).
We applied the morphodynamic model of Kostic (2011) to demon-
strate that the crescentic sediment waves within the northern channel
of the Squamish prodelta could be transitional upper-flow-regime
bedforms between cyclic steps and antidunes (Figs. 14 and 15). The
modeling input parameters are provided in the Fig. 14 caption. The re-
sults in Fig. 14 show the morphodynamics of channel maintenance by
thalweg reworking into cyclic steps and antidunes by dilute turbidity
currents. The three most upstream sediment waves are slowly
upstream-migrating cyclic steps characterized by internal hydraulic
jumps of a turbidity current. The downstream sediment waves interact
with turbidity currents as antidunes (i.e., undulations of the bed and
turbidity current interface are in phase and the flow is supercritical).
This is consistent with observations from physical experiments and nu-
merical modeling, which showed that antidunes can be found together
with or superimposed on cyclic steps (Spinewine et al., 2009; Kostic,
2014).
The results in Fig. 15 show themorphodynamics of channel mainte-
nance across a single step during six days to compare to bathymetric dif-
ference maps of Hughes Clarke et al. (2012b). The step is significantly
reworked as the location of an internal hydraulic jump migrates up-
stream. The lee side of the step is eroded and the stoss side retrogrades
(i.e., migrates upstream) as sediment is deposited. Direct monitoring
paired with morphodynamic numerical modeling sheds new light on
the potential for significant submarine-channel reworking, even during
relatively short-duration monitoring of turbidity-current events
(i.e., several to 12 days on the Squamish prodelta; Hughes Clarke, 2016).
Image of Fig. 12
A
B
C
D
Fig. 13. Cyclic steps of the San Mateo Canyon-channel system. (A) Map view of co-rendered bathymetry and slope (Covault et al., 2014). (B) CHIRP seismic-reflection profile. Lee sides of
cyclic steps are labeled 1 to 6. Inset: line-drawing trace of seismic stratigraphy. (C–D)Results of turbidity-currentmorphodynamicmodeling for case to investigate channelmaintenanceby
dilute (b1% concentration) turbidity currents. Grain size was set equal to 30 μm and the entrainment limiter p was set equal to 0.01. The entrainment limiter p ranges from 0 for
consolidated bedrock to 1 for unconsolidated, loose sediment. (C) Bed elevation (green lines) and turbidity-current interface (blue lines) change along the San Mateo channel
longitudinal profile (red line) in response to a sequence of overriding turbidity currents. The cyclic steps appear to slowly aggrade and migrate upstream, consistent with seismic
stratigraphy. (D) Downstream variation in the Froude number. Modified from Covault et al. (2014).
15J.A. Covault et al. / Marine Geology 393 (2017) 4–20
6. Discussion: Occurrence of cyclic steps and related supercritical
bedforms
In western North America, high gradients and slope breaks can pro-
mote supercritical turbidity currents and, under the right conditions
(Kostic, 2014), internal hydraulic jumps (Kostic and Parker, 2006;
Kostic, 2011). These flows can generate cyclic steps and other upper-
flow-regime bedforms, which range from relatively small (~101 m
wavelength; ~100 m height)cyclic steps and antidunes within active
submarine canyons and channels (Figs. 11 and 14), to large (~103 m
Image of Fig. 13
B
D
C
A
Fig. 14. Cyclic steps of the Squamish prodelta. (A)Map viewof co-rendered bathymetry and hillshade (Talling et al., 2015). (B)Map viewof hillshade of the northern channel (Talling et al.,
2015). (C-D) Results of turbidity-current morphodynamic modeling. Core data of grain size were not available. Grain size was set equal to 20 μm and the entrainment limiter p was set
equal to 0.06 based on best fit between field data and numerical prediction. Initial inflow velocity of 25 cm/s is of the same order of magnitude as Hughes Clarke et al. (2012b). Initial
inflow depth was set to 1.0 m to be consistent with the thin supercritical basal layer recorded on the Squamish prodelta (Hughes Clarke, 2016). Initial inflow concentration of
suspended sediment was set to 0.003 to ensure supercritical flow. (C) Bed elevation (green lines) and turbidity-current interface (blue lines) change along the interpreted paleoslope
profile (red line; Talling et al., 2015) in response to a sequence of overriding turbidity currents. (D) Downstream variation in the Froude number. See text for explanation.
16 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Image of Fig. 14
A B
C
Fig. 15. Cyclic steps of the Squamish prodelta. (A) Bathymetric difference profiles across a single crescentic bedform (Hughes Clarke et al., 2012b). Initial profile is the red line. Subsequent
bed elevations are the green lines. (B–C) Results of turbidity-currentmorphodynamicmodeling. Input parameters are the same as described in Fig. 14. (B) Bed elevation (green lines) and
turbidity-current interface (blue lines) change along the interpreted paleoslope profile (red line) in response to a sequence of overriding turbidity currents. (C) Downstream variation in
the Froude number. See text for explanation.
17J.A. Covault et al. / Marine Geology 393 (2017) 4–20
wavelength; ~102 m height) cyclic steps in less confined levee-
overbank environments (Fig. 9) and the channel-lobe transition zone
(Fig. 13). The governing equations describing the morphodynamics of
cyclic steps indicate that steeper slopes and higher concentration,
coarser-grained flows characteristic of proximal, confined canyons and
channels promote shorter wavelengths of cyclic steps compared to un-
confined levee-overbank environments and the channel-lobe transition
zone (Kostic, 2011). Symons et al. (2016) documented a similar range of
bedforms in a compilation of published examples of sediment waves
and scours. However, the different scales of bedforms might be more a
result of sampling bias than depositional environment (see discussion
in Section 4.2 p. 139–140 of Symons et al., 2016). The achievable hori-
zontal and vertical resolutions of multibeam bathymetric data are
b20% and b1% of water depth, respectively (Hughes Clarke, 1998).
Therefore, relatively small (~101 m wavelength; ~100 m height) cyclic
steps and antidunes might not be imaged in deeper water.
Cyclic steps might be fundamentally important to the
morphodynamic evolution of architectural elements of some deep-
water depositional systems. Fig. 1 shows the distribution of architectur-
al elements of a generalized continentalmargin and the locations of sed-
iment waves and scours inspired by the examples presented above.
Monterey Fan comprises a range of cyclic steps that might also be
found in association with architectural elements of large passive-
margin fans (Piper and Normark, 2001; Fildani and Normark, 2004).
Sedimentwaves inMonterey Canyon are likely to be cyclic steps (Kostic
and Smith, personal communication, 2009–2010; Cartigny et al., 2011),
which are important for submarine-canyon maintenance (Paull et al.,
2010). Sediment waves radially deposited around Shepard Meander of
Monterey Fan are net-depositional cyclic steps important for levee-
overbank evolution (Fildani et al., 2006). The incipient Monterey East
channel is composed of a train of net-erosional cyclic steps, which can
form a template for channel formation by flow stripping (Fildani et al.,
2006, 2013). The San Mateo Canyon-channel system is characterized
by net-depositional cyclic steps during channel maintenance (Covault
et al., 2014). Processes of channel maintenance by intense thalweg
reworking into a train of cyclic steps and antidunes by dilute turbidity
currents are captured in repeat monitoring surveys of the Squamish
prodelta (Hughes Clarke, 2016) and further supported by our numerical
simulations. Together, these studies reveal a breadth of evolutionary
patterns of deep-water depositional systems as a result of the
morphodynamic interaction between locally supercritical turbidity cur-
rents and the seafloor.
Cyclic steps and related upper-flow-regime bedforms are more
common than previously reported across other deep-water basin
margins, including passive-margin slopes subjected to gravity-
driven tectonic deformation that produces diapirism, growth
faults, folds and toe thrusts (e.g., the intraslope basin province of
the western Gulf of Mexico and offshore of Nigeria; Heiniö and
Davies, 2009; Armitage et al., 2012), tectonically active convergent
margins subjected to basin-localized subsidence, fault-supported
inner and outer margin uplift, and construction of a frontal prism
of accreted sediment (e.g., Lamb et al., 2008; Zhong et al., 2015),
as well as transform margins (e.g., Tubau et al., 2015). These set-
tings have rugose bathymetry, which offers the initial perturba-
tions that can promote the spontaneous development of cyclic
steps (Kostic, 2011). Fig. 16 shows a compilation of canyon-
channel longitudinal profiles and gradients from a range of conti-
nental margins: from the tectonically active margins of western
North America to the Atlantic passive margin offshore of the
Americas and West Africa (Covault et al., 2011, 2012). Water
Image of Fig. 15
A B
Fig. 16. Seafloor canyon-channel longitudinal profiles and gradients across normalized lengths. (A) Short, steep systems of tectonically activemarginswith relativelymeager, sand-rich or
mixed-caliber sediment supply. The San Mateo Canyon-channel system is highlighted in red. (B) Long systems with smooth, slightly concave profiles of relatively mature continental
margins associated with some of the largest submarine fans in the world. The Monterey Canyon-channel system is highlighted in red. Modified from Covault et al. (2011, 2012).
18 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
depths and downstream lengths were resampled every 10 km for
systems N100 km long and every 1 km for systems b100 km long.
In settings characterized by steep slopes, such as offshore of the
tectonically active transform margin of California and passive-
margin slopes subjected to gravity-driven tectonic deformation in
the western Gulf of Mexico and offshore of Nigeria, canyon-
channel gradients are potentially large enough to promote super-
critical flow, which is a necessary condition for the formation of cy-
clic steps (Kostic, 2011). Considering that passive-margin slopes
subjected to gravity-driven tectonic deformation are targets of pe-
troleum exploration and production, the processes and deposition-
al products of cyclic steps might be important considerations in the
exploration and modeling of some hydrocarbon reservoirs (Hoyal
et al., 2011, 2014). That said, the majority of reaches of long,
passive-margin canyon-channel systems are characterized by low
gradients, which might promote subcritical flow conditions within
the channel (e.g., Amazon and Zaire channels; Pirmez and Imran,
2003) (Fig. 16). Further work is needed to better understand the
nature of more depositional turbidity currents traveling over
lower slopes like the ones in low-gradient channels and on the
basin floor, and the role that supercritical flow and hydraulic
jumps might play in these settings. Even in passive-margin
canyon-channel systems, higher gradients and slope breaksacross
levee-overbank environments or at the channel-lobe transition
zone can promote supercritical turbidity currents and, under the
right conditions, hydraulic jumps forming cyclic steps and/or relat-
ed supercritical bedforms (e.g., antidunes; Kostic, 2011, 2014)
(e.g., Fig. 1).
7. Summary
The Froude number has been used to characterize the dynamics
of turbidity currents and its influence on the evolution of deep-
water depositional systems since the 1960's (Menard, 1964;
Komar, 1971; Mutti and Normark, 1987, 1991). Early models
stressed the importance of flow-regime change in the channel-lobe
transition zone (Komar, 1971; Mutti and Normark, 1987, 1991). Sub-
sequent advances in the acquisition of high-resolution geophysical
surveys of continental margins, combined with monitoring data
and numerical modeling, show that cyclic steps are common signals
of hydraulic jumps in turbidity currents in submarine canyon, chan-
nel, levee-overbank, and channel-lobe-transition-zone architectural
elements (Fildani et al., 2006; Cartigny et al., 2011; Kostic, 2011,
2014). Examples offshore of western North America show upper-
flow-regime cyclic steps and supercritical antidunes as important
features of channel initiation and maintenance: they drive the ad-
vance of channels and depositional lobes into the basin, and they
are formed as a result of bed reworking by turbidity currents in prox-
imal canyon heads and laterally spreading sheets in levee-overbank
and channel-lobe-transition-zone architectural elements. Further-
more, hydraulic jumps that produce cyclic steps interpreted in the
field and combined with morphodynamic numerical modeling of
turbidity currents are confirmed by direct monitoring. Cyclic steps
and related supercritical bedforms are increasingly recognized as
fundamentally important building blocks of the morphodynamic
evolution of deep-water depositional systems in a variety of tectonic
settings and continental slopes. These upper-flow-regime bedforms
are particularly common in relatively high-gradient slope canyon-
channel systems and the channel-lobe transition zone characterized
by a slope break and/or diminished lateral confinement. Future re-
search opportunities include facies-based recognition of long-
wavelength cyclic steps, the importance of transitional upper-flow-
regime bedforms between cyclic steps and antidunes in the
evolution of deep-water depositional systems, and the role of super-
critical flow and hydraulic jumps in lower slopes on the basin floor.
In this review, we presented examples of stratigraphic products
Image of Fig. 16
19J.A. Covault et al. / Marine Geology 393 (2017) 4–20
integrated with short-term observations from direct monitoring,
morphodynamic numerical modeling, and physical experiments.
This integrated approach can further constrain the fundamental pro-
cesses that operate in deep-water depositional systems; integration
is critical because observing natural, large-scale turbidity currents
in the deep sea has proven challenging.
Acknowledgments
JAC acknowledges support of the sponsors of the Quantitative Clas-
tics Laboratory (http://www.beg.utexas.edu/qcl). The authors thank
John Hughes Clarke for stimulating conversations during the early de-
velopment of this manuscript. The authors thank William R. Normark
for his guidance and anticipation of the importance of cyclic steps in
the evolution of submarine fans and related turbidite systems. Bill un-
selfishly shared many of his early observations and hypotheses with
us.We thank KatherineMaier, Christopher Stevenson, and Guest Editor
David Piper for reviews that improved the focus of the manuscript.
References
Alexander, J., Bridge, J.S., Cheel, R.J., Leclair, S.F., 2001. Bedforms and associated
sedimentary structures formed under supercritical water flows over aggrading
sand beds. Sedimentology 48 (1), 133–152.
Amy, L.A., Talling, P.J., 2006. Anatomy of turbidites and linked debrites based on
long distance (120 × 30 km) bed correlation, Marnoso Arenacea Formation,
Northern Apennines, Italy. Sedimentology 53 (1), 161–212.
Armitage, D.A., McHargue, T., Fildani, A., Graham, S.A., 2012. Postavulsion channel evolu-
tion: Niger Delta continental slope. AAPG Bull. 96 (5), 823–843.
Bain, H.A., Hubbard, S.M., 2016. Stratigraphic evolution of a long-lived submarine channel
system in the Late Cretaceous Nanaimo Group, British Columbia, Canada. Sediment.
Geol. 337, 113–132.
Barton, M.D., Craig, P., Prather, B., Copus, J., 2007. 41 facies architecture of channel-levee
deposits, Lago Nordenskjold and Laguna Mellizas Sur, Cerro Toro Formation, Chile.
AAPG Stud. Geol. 56, 157–161.
Bouma, A.H., 1962. Sedimentology of some Flysch Deposits: A Graphic Approach to Facies
Interpretation. Elsevier Pub, Co.
Bouma, A.H., Normark, W.R., Barnes, N.E. (Eds.), 1985. Submarine Fans and Related Turbi-
dite Systems. Springer Science & Business Media.
Campion, K.M., Dixon, B.T., Scott, E.D., 2011. Sediment waves and depositional im-
plications for fine-grained rocks in the Cerro Toro Formation (Upper Creta-
ceous), Silla Syncline, Chile. Mar. Pet. Geol. 28 (3), 761–784.
Cantero, M.I., Cantelli, A., Pirmez, C., Balachandar, S., Mohrig, D., Hickson, T.A., Yeh, T.H.,
Naruse, H., Parker, G., 2012. Emplacement of massive turbidites linked to extinction
of turbulence in turbidity currents. Nat. Geosci. 5 (1), 42–45.
Cartigny, M.J., Postma, G., van den Berg, J.H., Mastbergen, D.R., 2011. A comparative study
of sediment waves and cyclic steps based on geometries, internal structures and nu-
merical modeling. Mar. Geol. 280 (1), 40–56.
Cartigny, M.J., Ventra, D., Postma, G., Den Berg, J.H., 2014. Morphodynamics and sedimen-
tary structures of bedforms under supercritical-flow conditions: new insights from
flume experiments. Sedimentology 61 (3), 712–748.
Clare, M.A., Cartigny, M.J.B., North, L.J., Talling, P.J., Vardy, M.E., Hizzett, J.L.,
Sumner, E.J., Hughes Clarke, J.E., Spinewine, B., 2015, May. Quantification of
near-Bed Dense Layers and Implications for Seafloor Structures: New Insights
into the most Hazardous Aspects of Turbidity Currents. In Offshore Technology
Conference. Offshore Technology Conference.
Clift, P., Gaedicke, C., 2002. Accelerated mass flux to the Arabian Sea during the middle to
late Miocene. Geology 30 (3), 207–210.
Cooper, C., Wood, J., Andrieux, O., 2013, May. Turbidity Current Measurements in the
Congo Canyon. Proceedings of the Annual Offshore Technology Conference (OTC
23992).
Covault, J.A., Fildani, A., Romans, B.W., McHargue, T., 2011. The natural range of
submarine canyon-and-channel longitudinal profiles. Geosphere 7 (2),
313–332.
Covault, J.A., Shelef, E., Traer, M., Hubbard, S.M., Romans, B.W., Fildani, A., 2012. Deep-
water channel run-out length: insights from seafloor geomorphology. J. Sediment.
Res. 82 (1), 25–40.
Covault, J.A., Kostic, S., Paull, C.K., Ryan, H.F., Fildani, A., 2014. Submarine channel initia-
tion, filling and maintenance from sea-floor geomorphology and morphodynamic
modelling of cyclic steps. Sedimentology 61 (4), 1031–1054.
Damuth, J.E., 1979. Migrating sediment waves created by turbidity currents in the north-
ern South China Basin. Geology 7 (11), 520–523.
de Leeuw, J., Eggenhuisen, J.T., Cartigny, M.J., 2016. Morphodynamics of submarine chan-
nel inception revealed by new experimental approach. Nat. Commun. 7.
Fildani, A., Normark, W.R., 2004. Late Quaternary evolution of channel and lobe com-
plexes of Monterey Fan. Mar. Geol. 206 (1), 199–223.
Fildani, A., Normark, W.R., Kostic, S., Parker, G., 2006. Channel formation by flow strip-
ping: large-scale scour features along the Monterey East Channel and their relation
to sediment waves. Sedimentology 53 (6), 1265–1287.
Fildani, A., Hubbard, S.M., Covault, J.A., Maier, K.L., Romans, B.W., Traer, M., Rowland, J.C.,
2013. Erosion at inception of deep-sea channels. Mar. Pet. Geol. 41, 48–61.
Fukushima, Y., Parker, G., Pantin, H.M., 1985. Prediction of ignitive turbidity currents in
Scripps Submarine Canyon.Mar. Geol. 67 (1–2), 55–81.
Gardner, J.V., Dartnell, P., Stone, J.C., Mayer, L.A., Clark, J.E.H., 2002. Bathymetry and select-
ed perspective views offshore greater Los Angeles, California (No. 2002-4126).
Greene, H.G., Hicks, K.R., 1990. Ascension–Monterey canyon system: history and develop-
ment. Geology and Tectonics of the Central California Coast Region - San Francisco to
Monterey. American Association of Petroleum Geologists Pacific Section,
pp. 229–249.
Hamilton, P.B., Strom, K.B., Hoyal, D.C., 2015. Hydraulic and sediment transport properties
of autogenic avulsion cycles on submarine fans with supercritical distributaries.
J. Geophys. Res. Earth Surf. 120 (7), 1369–1389.
Hand, B.M., 1974. Supercritical flow in density currents. J. Sediment. Res. 44 (3).
Hand, B.M., 1975. Supercritical flow in density currents: reply. J. Sediment. Res. 45 (3).
Harris, P.T., Whiteway, T., 2011. Global distribution of large submarine canyons: geomor-
phic differences between active and passive continental margins. Mar. Geol. 285 (1),
69–86.
Heiniö, P., Davies, R.J., 2009. Trails of depressions and sediment waves along submarine
channels on the continental margin of Espirito Santo Basin, Brazil. Geol. Soc. Am.
Bull. 121 (5–6), 698–711.
Hess, G.R., Normark, W.R., 1976. Holocene sedimentation history of the major fan valleys
of Monterey Fan. Mar. Geol. 22 (4), 233–251.
Hickin, E.J., 1989. Contemporary Squamish River sediment flux to Howe Sound, British
Columbia. Can. J. Earth Sci. 26 (10), 1953–1963.
Hoyal, D., Sheets, B., Wellner, R., Box, D., Sprague, A., Bloch, R., 2011, April. Architecture of
Froude Critical-Supercritical Submarine Fans: Tank Experiments Versus Field Obser-
vations. American Association of Petroleum Geologists Annual Convention and
Exhibition.
Hoyal, D.C.H., Demko, T., Postma, G., Wellner, R.W., Pederson, K., Abreu, V., Fedele, J.J., Box,
D., Sprague, A., Ghayour, K., Strom, K., 2014, April. Evolution, Architecture and Stratig-
raphy of Froude Supercritical Submarine Fans. American Association of Petroleum
Geologists Annual Convention and Exhibition.
Hughes Clarke, J., 1998, March. The Effect of Fine Scale Seabed Morphology and Texture
on Fidelity of Swath Bathymetric Sounding Data. Proc Canadian Hydrographic Conf
98 pp. 10–12.
Hughes Clarke, J., 2016. First wide-angle view of channelized turbidity currents links mi-
grating cyclic steps to flow characteristics. Nat. Commun. 7, 11896.
Hughes Clarke, J., Brucker, S., Muggah, J., Church, I., Cartwright, D., Kuus, P.,
Hamilton, T., Pratomo, D., Eisan, B., 2012a. The Squamish ProDelta: Monitoring
Active Landslides and Turbidity Currents. Canadian Hydrographic Conference
2012, Proceedings p. 15.
Hughes Clarke, J., Brucker, S., Muggah, J., Hamilton, T., Cartwright, D., Church, I.,
Kuus, P., 2012b. Temporal Progression and Spatial Extent of Mass Wasting
Events on the Squamish Prodelta Slope. Landslides and Engineered Slopes:
Protecting Society Through Improved Understanding. pp. 1091–1096.
Hughes Clarke, J., Marques, C.R.V., Pratomo, D., 2014. Imaging active mass-wasting and
sediment flows on a fjord delta, Squamish, British Columbia. Submarine Mass Move-
ments and Their Consequences. Springer International Publishing, pp. 249–260.
Klaucke, I., Masson, D.G., Kenyon, N.H., Gardner, J.V., 2004. Sedimentary processes of the
lower Monterey Fan channel and channel-mouth lobe. Mar. Geol. 206 (1), 181–198.
Komar, P.D., 1971. Hydraulic jumps in turbidity currents. Geol. Soc. Am. Bull. 82 (6),
1477–1488.
Komar, P.D., 1975. Supercritical flow in density currents: a discussion. J. Sediment. Res. 45
(3).
Kostic, S., 2011. Modeling of submarine cyclic steps: controls on their formation, migra-
tion, and architecture. Geosphere 7 (2), 294–304.
Kostic, S., 2014. Upper flow regime bedforms on levees and continental slopes: turbidity
current flow dynamics in response to fine-grained sediment waves. Geosphere 10
(6), 1094–1103.
Kostic, S., Parker, G., 2006. The response of turbidity currents to a canyon–fan transition: in-
ternal hydraulic jumps and depositional signatures. J. Hydraul. Res. 44 (5), 631–653.
Kostic, S., Sequeiros, O., Spinewine, B., Parker, G., 2010. Cyclic steps: a phenomenon of su-
percritical shallow flow from the highmountains to the bottom of the ocean. J. Hydro
Environ. Res. 3 (4), 167–172.
Lamb, M.P., Parsons, J.D., Mullenbach, B.L., Finlayson, D.P., Orange, D.L., Nittrouer, C.A.,
2008. Evidence for superelevation, channel incision, and formation of cyclic steps
by turbidity currents in Eel Canyon, California. Geol. Soc. Am. Bull. 120 (3–4),
463–475.
Lowe, D.R., 1988. Suspended-load fallout rate as an independent variable in the analysis of
current structures. Sedimentology 35 (5), 765–776.
Macdonald, H.A., Wynn, R.B., Huvenne, V.A., Peakall, J., Masson, D.G., Weaver, P.P.,
McPhail, S.D., 2011. New insights into the morphology, fill, and remarkable longevity
(N0.2 my) of modern deep-water erosional scours along the northeast Atlantic mar-
gin. Geosphere 7 (4), 845–867.
Maier, K.L., Fildani, A., Paull, C.K., Graham, S.A., McHargue, T.R., Caress, D.W., McGann, M.,
2011. The elusive character of discontinuous deep-water channels: new insights from
Lucia Chica channel system, offshore California. Geology 39 (4), 327–330.
Maier, K.L., Fildani, A., Paull, C.K., McHargue, T.R., Graham, S.A., Caress, D.W., 2013. Deep-
sea channel evolution and stratigraphic architecture from inception to abandonment
from high-resolution autonomous underwater vehicle surveys offshore central
California. Sedimentology 60 (4), 935–960.
Menard, H.W., 1964. Marine Geology of the Pacific. (Chapter 9). McGraw-Hill, New York,
pp. 191–222.
Middleton, G.V., 1966. Experiments on density and turbidity currents: II. Uniform flow of
density currents. Can. J. Earth Sci. 3 (5), 627–637.
http://www.beg.utexas.edu/qcl
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0005
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0080
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0085
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0115
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0140
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0140
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0145
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0145
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0150
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0155
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0155
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0160
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0160
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0165
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0165
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0165
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0170
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0170
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0170
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0175
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0175
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0180
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0180
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0180
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0185
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0185
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0190
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0190
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0220
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0220
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0225
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0225
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0225
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0235
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0235
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0240
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0240
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0240
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0240
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0240
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0245
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0245
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0250
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0250
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0250
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0250
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0255
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0255
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0260
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0260
20 J.A. Covault et al. / Marine Geology 393 (2017) 4–20
Migeon, S., Savoye, B., Faugeres, J.C., 2000. Quaternary development of migrating sedi-
ment waves in the Var deep-sea fan: distribution, growth pattern, and implication
for levee evolution. Sediment. Geol. 133 (3), 265–293.
Migeon, S., Savoye, B., Zanella, E., Mulder, T., Faugères, J.C., Weber, O., 2001. Detailed
seismic-reflection and sedimentary study of turbidite sediment waves on the Var
Sedimentary Ridge (SE France): significance for sediment transport and deposition
and for the mechanisms of sediment-wave construction. Mar. Pet. Geol. 18 (2),
179–208.
Mutti, E., Normark, W.R., 1987. Comparing examples of modern and ancient turbidite sys-
tems: problems and concepts. Marine Clastic Sedimentology. Springer, Netherlands,
pp. 1–38.
Mutti, E., Normark, W.R., 1991. An integrated approach to the study of turbidite systems.
Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems.
Springer, New York, pp. 75–106.
Nelson, C.H., Carlson, P.R., Byrne, J.V., Alpha, T.R., 1970. Development of the Astoria can-
yon-fan physiography and comparison with similar systems. Mar. Geol. 8 (3),
259–291.
Nelson, C.H., Normark, W.R., Bouma, A.H., Carlson, P.R., 1978. Thin-bedded Turbidites in
Modern Submarine Canyons and Fans. Sedimentation in Submarine Canyons, Fans,
and Trenches. pp. 177–189.
Nelson, C.H., Maldonado, A., Barber Jr., J.H., Alonso, B., 1991. Modern sand-rich and mud-
rich siliciclastic aprons: alternative base-of-slope turbidite systems to submarine
fans. Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Sys-
tems. Springer, New York, pp. 171–190.
NOAA National Centers for Environmental Information, 2015. U.S. coastal relief model.
(retrieve date November 1). http://www.ngdc.noaa.gov/mgg/coastal/crm.html.
Normark, W.R., Carlson, P.R., 2003. Giant Submarine Canyons: Is Size Any Clue to Their
Importance in the Rock Record? Special Papers-Geological Society of America,
pp. 175–190
Normark, W.R., Hess, G.R., Stow, D.A.V., Bowen, A.J., 1980. Sediment waves on the Monte-
rey Fan levee: a preliminary physical interpretation. Mar. Geol. 37 (1), 1–18.
Normark, W.R., Posamentier, H., Mutti, E., 1993. Turbidite systems: state of the art and fu-
ture directions. Rev. Geophys. 31 (2), 91–116.
Normark, W.R., Piper, D.J., Posamentier, H., Pirmez, C., Migeon, S., 2002. Variability in form
and growth of sediment waves on turbidite channel levees. Mar. Geol. 192 (1),
23–58.
Normark, W.R., Piper, D.J., Romans, B.W., Covault, J.A., Dartnell, P., Sliter, R.W., 2009. Sub-
marine canyon and fan systems of the California continental borderland.Geol. Soc.
Am. Spec. Pap. 454, 141–168.
Parker, G., Fukushima, Y., Pantin, H.M., 1986. Self-accelerating turbidity currents. J. Fluid
Mech. 171, 145–181.
Paull, C., Greene, H., Ussler, W., Mitts, P., 2002. Pesticides as tracers of sediment transport
through Monterey Canyon. Geo-Mar. Lett. 22 (3), 121–126.
Paull, C.K., Ussler III, W., Caress, D.W., Lundsten, E., Covault, J.A., Maier, K.L., Xu, J.,
Augenstein, S., 2010. Origins of large crescent-shaped bedforms within the axial
channel of Monterey Canyon, offshore California. Geosphere 6 (6), 755–774.
Pemberton, E.A., Hubbard, S.M., Fildani, A., Romans, B., Stright, L., 2016. The stratigraphic
expression of decreasing confinement along a deep-water sediment routing system:
outcrop example from southern Chile. Geosphere 12 (1), 114–134.
Piper, D.J., Normark, W.R., 2001. Sandy fans–from Amazon to Hueneme and beyond.
AAPG Bull. 85 (8), 1407–1438.
Piper, D.J., Normark, W.R., 2009. Processes that initiate turbidity currents and their influ-
ence on turbidites: a marine geology perspective. J. Sediment. Res. 79 (6), 347–362.
Pirmez, C., Imran, J., 2003. Reconstruction of turbidity currents in Amazon Channel. Mar.
Pet. Geol. 20 (6), 823–849.
Posamentier, H.W., Kolla, V., 2003. Seismic geomorphology and stratigraphy of deposi-
tional elements in deep-water settings. J. Sediment. Res. 73 (3), 367–388.
Postma, G., Cartigny, M.J., 2014. Supercritical and subcritical turbidity currents and their
deposits—a synthesis. Geology 42 (11), 987–990.
Postma, G., Cartigny, M., Kleverlaan, K., 2009. Structureless, coarse-tail graded Bouma Ta
formed by internal hydraulic jump of the turbidity current? Sediment. Geol. 219
(1), 1–6.
Postma, G., Kleverlaan, K., Cartigny, M.J., 2014. Recognition of cyclic steps in sandy and
gravelly turbidite sequences, and consequences for the Bouma facies model. Sedi-
mentology 61 (7), 2268–2290.
Postma, G., Hoyal, D.C., Abreu, V., Cartigny, M.J., Demko, T., Fedele, J.J., Kleverlaan, K.,
Pederson, K.H., 2016. Morphodynamics of supercritical turbidity currents in the
channel-lobe transition zone. Submarine Mass Movements and their Consequences.
Springer International Publishing, pp. 469–478.
Ricci Lucchi, F., Valmori, E., 1980. Basin-wide turbidites in a Miocene, over-supplied deep-
sea plain: a geometrical analysis. Sedimentology 27 (3), 241–270.
Rowland, J.C., Hilley, G.E., Fildani, A., 2010. A test of initiation of submarine leveed chan-
nels by deposition alone. J. Sediment. Res. 80 (8), 710–727.
Ryan, H.F., Legg, M.R., Conrad, J.E., Sliter, R.W., 2009. Recent faulting in the Gulf of Santa
Catalina: San Diego to Dana Point. Geol. Soc. Am. Spec. Pap. 454, 291–315.
Sequeiros, O.E., 2012. Estimating turbidity current conditions from channel morphology:
a Froude number approach. J. Geophys. Res. Oceans 117 (C4).
Shepard, F.P., Emery, K.O., 1941. Submarine Topography off the California Coast. 31. Can-
yons and Tectonic Interpretation: Geological Society of America Special Paper, p. 171.
Smith, D.P., Ruiz, G., Kvitek, R., Iampietro, P.J., 2005. Semiannual patterns of erosion and
deposition in upper Monterey Canyon from serial multibeam bathymetry. Geol.
Soc. Am. Bull. 117 (9–10), 1123–1133.
Smith, D.P., Kvitek, R., Iampietro, P.J., Wong, K., 2007. Twenty-ninemonths of geomorphic
change in upper Monterey Canyon (2002–2005). Mar. Geol. 236 (1), 79–94.
Spinewine, B., Sequeiros, O.E., Garcia, M.H., Beaubouef, R.T., Sun, T., Savoye, B., Parker, G.,
2009. Experiments on wedge-shaped deep sea sedimentary deposits in minibasins
and/or on channel levees emplaced by turbidity currents. Part II. Morphodynamic
evolution of the wedge and of the associated bedforms. J. Sediment. Res. 79 (8),
608–628.
Stow, D.A., 2005. Sedimentary Rocks in the Field: A Color Guide. Gulf Professional
Publishing.
Sumner, E.J., Amy, L.A., Talling, P.J., 2008. Deposit structure and processes of sand deposi-
tion from decelerating sediment suspensions. J. Sediment. Res. 78 (8), 529–547.
Sylvester, Z., Lowe, D.R., 2004. Textural trends in turbidites and slurry beds from the Oli-
gocene flysch of the East Carpathians, Romania. Sedimentology 51 (5), 945–972.
Symons, W.O., Sumner, E.J., Talling, P.J., Cartigny, M.J., Clare, M.A., 2016. Large-scale sedi-
ment waves and scours on the modern seafloor and their implications for the preva-
lence of supercritical flows. Mar. Geol. 371, 130–148.
Talling, P.J., Paull, C.K., Piper, D.J., 2013. How are subaqueous sediment density flows trig-
gered, what is their internal structure and how does it evolve? Direct observations
from monitoring of active flows. Earth Sci. Rev. 125, 244–287.
Talling, P.J., Allin, J., Armitage, D.A., Arnott, R.W., Cartigny, M.J., Clare, M.A., Felletti, F.,
Covault, J.A., Girardclos, S., Hansen, E., Hill, P.R., et al., 2015. Key future directions
for research on turbidity currents and their deposits. J. Sediment. Res. 85 (2),
153–169.
Toniolo, H., Cantelli, A., 2007. Experiments on upstream-migrating submarine
knickpoints. J. Sediment. Res. 77 (9), 772–783.
Tubau, X., Paull, C.K., Lastras, G., Caress, D.W., Canals, M., Lundsten, E., Anderson, K.,
Gwiazda, R., Amblas, D., 2015. Submarine canyons of Santa Monica Bay, Southern
California: variability in morphology and sedimentary processes. Mar. Geol. 365, 61–79.
University of New Brunswick, 2011. Squamish prodelta experiment 2011. http://www.
omg.unb.ca/Projects/SQ_2011_html/.
Wynn, R.B., Stow, D.A., 2002. Classification and characterisation of deep-water sediment
waves. Mar. Geol. 192 (1), 7–22.
Wynn, R.B.,Weaver, P.P., Ercilla, G., Stow, D.A., Masson, D.G., 2000. Sedimentary processes
in the selvage sediment-wave field, NE Atlantic: new insights into the formation of
sediment waves by turbidity currents. Sedimentology 47 (6), 1181–1197.
Wynn, R.B., Kenyon, N.H., Masson, D.G., Stow, D.A., Weaver, P.P., 2002a. Characterization
and recognition of deep-water channel-lobe transition zones. AAPG Bull. 86 (8).
Wynn, R.B., Piper, D.J., Gee, M.J., 2002b. Generation and migration of coarse-grained sed-
iment waves in turbidity current channels and channel–lobe transition zones. Mar.
Geol. 192 (1), 59–78.
Zhong, G., Cartigny, M.J., Kuang, Z., Wang, L., 2015. Cyclic steps along the South Taiwan
Shoal and West Penghu submarine canyons on the northeastern continental slope
of the South China Sea. Geol. Soc. Am. Bull. 127 (5–6), 804–824.
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0265
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0265
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0265
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0270
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0270
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0270
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0270
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0275
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0280
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0280
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0280
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf9555
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf9555
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0285
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0290
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0290
http://www.ngdc.noaa.gov/mgg/coastal/crm.html
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0300
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0300
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0305http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0310
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0310
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0335
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0340
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0340
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0340
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0345
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0345
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0350
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0350
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0355
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0385
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0385
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0390
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0390
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0395
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0430
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0430
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0435
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0435
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http://www.omg.unb.ca/Projects/SQ_2011_html/
http://www.omg.unb.ca/Projects/SQ_2011_html/
http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0470
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http://refhub.elsevier.com/S0025-3227(16)30390-5/rf0490
	Cyclic steps and related supercritical bedforms: Building blocks of deep-�water depositional systems, western North America
	1. Introduction
	2. Supercritical currents across continental slopes
	3. Deposits of supercritical currents and hydraulic jumps
	4. Controls on the formation of cyclic steps
	5. Cyclic steps and related supercritical bedforms in western North America
	5.1. Monterey Fan: Large deep-water depositional system perspective
	5.2. San Mateo canyon-channel system: Small deep-water depositional system perspective
	5.3. Squamish prodelta: A natural laboratory
	6. Discussion: Occurrence of cyclic steps and related supercritical bedforms
	7. Summary
	Acknowledgments
	References