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SeaBeam bathymetry of Monterey Canyon–Fan System offshore of Monterey Bay, California. The axis of Monterey Fan Channel is marked by dashed lines.
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Overbank flow of turbidity currents sweeping through the entrenched Monterey Fan Channel has generated erosional and depositional features along the channel walls and across the adjacent levees. These features, investigated with side-scan sonar, SeaBeam bathymetry, submersibles, and a towed camera sled include fields of sediment waves, overbank cha...
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... fornia Fig. 1 . Acoustic images collected during a Ž . Multi-Spectral Side-looking Sonar MSSS-1 survey were obtained at 30 kHz, at an altitude of 100-300 m, on 6-km wide swaths with 5000 samples per scanline and were co-registered with SeaBeam Ž bathymetry in a UTM map projection Malinverno et . al., 1990 . On the sonar images, light shades indicate ...
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... every 20 m. Left turns were measured counter-clock- wise and are indicated with a negative sign. Right turns were measured clockwise and are noted with a positive sign systems and commonly shaken by earthquakes that have influenced the development of the Monterey Ž and Ascension Canyon systems Atwater, 1989;Mc. Culloch, 1989;Greene et al., 1991; Fig. 1 . Ascen- sion and Monterey Canyons have been the major Ž providers of sediment to Monterey Fan Normark and Gutmacher, 1989;Greene et al., 1989;Gardner . et al., 1996 . The path of Monterey Canyon-Fan system begins at the shoreline in Monterey Bay. The head of Monterey Canyon and its major tributaries: Carmel and Soquel Canyons are ...
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... the major Ž providers of sediment to Monterey Fan Normark and Gutmacher, 1989;Greene et al., 1989;Gardner . et al., 1996 . The path of Monterey Canyon-Fan system begins at the shoreline in Monterey Bay. The head of Monterey Canyon and its major tributaries: Carmel and Soquel Canyons are incised with more Ž . than 1 km of relief into the shelf Fig. 1 . Sediment is supplied to the canyons by rivers that drain the adjacent borderland, and longshore and tidal currents Ž . Wolf, 1969 . Monterey Canyon follows a sinuous path for 75 km through the shelf and slope to a depth of 3000 m where it feeds into the Monterey Fan and becomes a fan channel. The base of the continental slope is ...
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... from the Shepard Meander, the Mon- Ž . terey Fan Channel curves abruptly ; 908 to the left, and its course then follows a straight path for 15 km to its confluence with the Ascension Fan Chan- nel at 3540 m. The channel right-hand wall is ter- Ž . raced and extensively gullied Fig. 11 . Although this is presently a straight segment of the channel, the highest terrace levels have a curved plan view morphology and mark the probable avulsion path of Ž . the Monterey Fan Channel Normark, 1970; Fig. 11 . Here, the levee front is populated by sediment waves with crests that are oblique, but converge towards the Ž . ...
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... to its confluence with the Ascension Fan Chan- nel at 3540 m. The channel right-hand wall is ter- Ž . raced and extensively gullied Fig. 11 . Although this is presently a straight segment of the channel, the highest terrace levels have a curved plan view morphology and mark the probable avulsion path of Ž . the Monterey Fan Channel Normark, 1970; Fig. 11 . Here, the levee front is populated by sediment waves with crests that are oblique, but converge towards the Ž . channel Figs. 9 and 10 . The channel left-hand wall is terraced for 5 km immediately downslope of the Shepard Meander and then it becomes very steep. Neither the right-nor the left-hand levees are well developed along this ...
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... Fig. 11 . Although this is presently a straight segment of the channel, the highest terrace levels have a curved plan view morphology and mark the probable avulsion path of Ž . the Monterey Fan Channel Normark, 1970; Fig. 11 . Here, the levee front is populated by sediment waves with crests that are oblique, but converge towards the Ž . channel Figs. 9 and 10 . The channel left-hand wall is terraced for 5 km immediately downslope of the Shepard Meander and then it becomes very steep. Neither the right-nor the left-hand levees are well developed along this segment of the channel ...
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... higher than the left-hand levee. The left-hand levee merges with the back of the outside levee of the Shepard Meander and is not prominent along this Ž . segment of the channel Figs. 2, 8, 10 and 13 . The right-hand levee extends laterally for 15 km and its relief decreases downslope to 60 m above the chan- Ž . nel wall at axial depths of 3620 m Figs. 2 and 13 . The relief of the left-hand levee also decreases Ž . downslope Figs. 2 and 13; Table 1 . The right-hand levee front is crossed by sediment waves oriented oblique to the channel. The wave crests are continu- ous for several kilometers, but they are reduced in Ž . amplitude from those upstream. Gardner et al. 1996 identified a similar ...
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... outside levee of the Shepard Meander and is not prominent along this Ž . segment of the channel Figs. 2, 8, 10 and 13 . The right-hand levee extends laterally for 15 km and its relief decreases downslope to 60 m above the chan- Ž . nel wall at axial depths of 3620 m Figs. 2 and 13 . The relief of the left-hand levee also decreases Ž . downslope Figs. 2 and 13; Table 1 . The right-hand levee front is crossed by sediment waves oriented oblique to the channel. The wave crests are continu- ous for several kilometers, but they are reduced in Ž . amplitude from those upstream. Gardner et al. 1996 identified a similar wave field to that described by Ž . Normark et al. 1980 along this segment of ...
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... . 5 As found by many other authors, right-hand levees are preferentially higher than left-hand levees where the channel is straight, but along channel bends outside levees are much higher than inside Ž . levees Fig. 11 . Levee heights and the thalweg gradient decrease downstream. Fig. 13. Shaded relief image constructed from SeaBeam bathymetry of the upper Monterey Fan. Along straight channel segments of both the Monterey and Ascension Fan Channels sediment waves trend oblique to the channel. Linear expansion of the overflow is suggested by the wave ...
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... . 5 As found by many other authors, right-hand levees are preferentially higher than left-hand levees where the channel is straight, but along channel bends outside levees are much higher than inside Ž . levees Fig. 11 . Levee heights and the thalweg gradient decrease downstream. Fig. 13. Shaded relief image constructed from SeaBeam bathymetry of the upper Monterey Fan. Along straight channel segments of both the Monterey and Ascension Fan Channels sediment waves trend oblique to the channel. Linear expansion of the overflow is suggested by the wave morphology. Wave fields that are oriented transverse and radial to the ...
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... part of the channelized turbidity current overflows the channel it becomes overbank flow. The overbank flow continues to move towards the local downslope direction. Where the channel is straight, overbank flow travels away from the chan- Ž nel with a linear wavefront. Dispersal analogous to . Ž diffusion is one dimensional proportional to 1rr; . Fig. 14 . Where the channel bends, overbank flow has a radial wavefront and dispersal is two dimen- Ž 2 . sional proportional to 1rr . The radial overbank flow is dispersed laterally outward from the channel and over the levees. The linear wavefront produces parallel waves whose height and wavelength does not change significantly with distance ...
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... with distance from the Ž . channel Figs. 5-10 . Where the path of the channel is straight but there is some curvature in the channel walls, there appears to be both radial and linear expansion of the overflow because the sediment waves tend to converge towards the channel, yet their morphology does not change with distance Ž . from the channel Fig. 11 ...
Citations
... O¡shore marine gravel and sandwave deposits have been documented in a number of turbidite fan systems (e.g. McHugh & Ryan, 2000), but these deposits typically exhibit very low-angle cross-strati¢cation. High-angle gravel and sandwave deposits are known from a range of water depths (100^1000 m) in the Messina Strait and its approaches (e.g. ...
... CLTZs settings (Bonnel, Dennielou, Droz, Mulder, & Berné, 2005;Damuth, 1979;Heiniӧ & Davies, 2009;Hofstra, 2016;Hofstra et al., 2018;Howe, 1996;Kidd, Lucchi, Gee, & Woodside, 1998;Lonsdale & Hollister, 1979;Malinverno, Ryan, Au!ret, & Pautot, 1988;Masson, Kenyon, Gardner, & Field, 1995;McHugh & Ryan, 2000;Migeon et al., 2001;S. A. Morris et al., 1998;Nelson, Goldfinger, Johnson, & Dunhill, 2000;Normark & Dickson, 1976;Normark, Hess, Stow, & Bowen, 1980;Normark & Piper, 1991;Normark, Piper, Posamentier, Pirmez, & Migeon, 2002;Palanques et al., 1995;Piper, Shor, & Clarke, 1988;Piper, Shor, Farre, O'Connell, & Jacobi, 1985;Shor, Piper, Clarke, & Mayer, 1990;Wynn, Kenyon, et al., 2002;Wynn, Piper, & Gee, 2002;. ...
Channel‐lobe transition zones (CLTZs) are identified in many modern deep‐water systems, but few exhumed examples have been identified. Exposures of the Oligocene‐Miocene Tajau Sandstone Member (TSM), Kudat Formation, northern Sabah, Malaysia, provides the opportunity to document a CLTZ from an active basin margin. This work provides the first detailed field‐based sedimentological logging to produce a quantitative database on facies, sedimentary structures, bed type, and statistical analysis. This is particularly important to produce a robust stratigraphic framework of the TSM. Sedimentary facies support interpretation of subaqueous sediment density flows, and key features, including scour‐fills, antidunes, and dune‐scale bedforms, suggest changes in gradient and/or flow confinement and the development of hydraulic jumps. Eight bed types are recognized including: (a) tripartite beds with a debrite (BT1), interpreted as hybrid event beds recording downslope flow transformation between turbulent and laminar states; (b) beds with a mixture of depositional, erosional, and bypass features (BT2, BT4, BT5), interpreted as recording the transitions between supercritical and subcritical flow conditions triggered by hydraulic jumps; (c) bipartite beds with a basal massive sandstone overlain by fine‐grained facies (BT3), interpreted as hyperconcentrated flow deposits with evidence of downcurrent flow transformation; (d) bipartite beds with a basal high‐density turbidite sharply overlain by a low‐density turbidite (BT6), interpreted as turbidites with evidence of sediment bypass; (e) basal tractive structures capped by fine‐grained facies as the product of reworking of very coarse‐ to coarse‐grained sediments caused by lateral spreading of turbulent flows; and (f) Bouma Tbcde sequences (BT8) interpreted as high‐to‐low‐density turbidites. Our depositional model for the TSM comprises: (a) an aggradational channel‐lobe transition zone (CLTZs/BTA 1 and BTA 2) which was dominated by hydraulic jumps and sediment bypass; and (b) stacked lobe (i.e., lobe‐axis/BTA 3a, lobe‐off axis/BTA 3b, frontal lobe fringe/BTA 3c, and distal lobe fringe/BTA 3d) located in the northern and southern parts of the study area, which is dominated by tabular, sheet‐like elements bioturbated with the Nereites ichnofacies. The aggradational stacking of CLTZs deposits observed in the TSM may be explained by high subsidence rates combined with high sediment supply rates associated with a tectonically active margin setting. The Oligocene‐Miocene(?) submarine fan deposits of the Kudat Formation in the Kudat Peninsula are thought to be equivalent and potentially analogous to hydrocarbon‐bearing turbidites of offshore Stage II of Sabah Basin.
... According to Wynn and Stow (2002), sediment waves can be classified into three types: turbidity current sediment waves, bottom current sediment waves, and soft sediment deformation sediment waves. Among these three types of bedforms, the sediment waves associated with turbidity currents have been revealed and reported in deep-water systems all around the world, distributed either in channels (Piper et al., 1985(Piper et al., , 1988Hughes Clarke et al., 1990;Normandeau et al., 2018), levees (Normark et al., 1980(Normark et al., , 2002Nakajima et al., 1998;McHugh and Ryan, 2000;Migeon et al., 2000Migeon et al., , 2001Nakajima and Satoh, 2001;Lewis and Pantin, 2002), or channel-lobe transition zones (Morris et al., 1998;Wynn et al., 2002aWynn et al., , 2002bCarvajal et al., 2017). For turbidity current sediment waves, fine-grained sediment waves usually develop in unconfined systems such as channel-levees or lobes, while coarse-grained waves typically occur in channel thalwegs and channel-lobe transition zones Wynn and Stow, 2002;Normark et al., 1980Normark et al., , 2002Wynn et al., 2000aWynn et al., , 2000bWynn et al., , 2000cMcHugh and Ryan, 2000;Migeon et al., 2000Migeon et al., , 2001Ercilla et al., 2002aErcilla et al., , 2002bGonthier et al., 2002;Lee et al., 2002;Maselli and Kneller, 2018). ...
... Among these three types of bedforms, the sediment waves associated with turbidity currents have been revealed and reported in deep-water systems all around the world, distributed either in channels (Piper et al., 1985(Piper et al., , 1988Hughes Clarke et al., 1990;Normandeau et al., 2018), levees (Normark et al., 1980(Normark et al., , 2002Nakajima et al., 1998;McHugh and Ryan, 2000;Migeon et al., 2000Migeon et al., , 2001Nakajima and Satoh, 2001;Lewis and Pantin, 2002), or channel-lobe transition zones (Morris et al., 1998;Wynn et al., 2002aWynn et al., , 2002bCarvajal et al., 2017). For turbidity current sediment waves, fine-grained sediment waves usually develop in unconfined systems such as channel-levees or lobes, while coarse-grained waves typically occur in channel thalwegs and channel-lobe transition zones Wynn and Stow, 2002;Normark et al., 1980Normark et al., , 2002Wynn et al., 2000aWynn et al., , 2000bWynn et al., , 2000cMcHugh and Ryan, 2000;Migeon et al., 2000Migeon et al., , 2001Ercilla et al., 2002aErcilla et al., , 2002bGonthier et al., 2002;Lee et al., 2002;Maselli and Kneller, 2018). Fine-grained sediment waves normally present lengths up to 7 km and heights up to 80 m, and form on slope gradients of 0.1-0.7 • (Carter et al., 1990;Migeon et al., 2000;Normark et al., 2002;Wynn and Stow, 2002). ...
This study uses 3D reflection seismic data to investigate how sediment gravity flows contribute to the evolution of the lower continental slope of the Myanmar margin that is part of the Bengal Fan, the largest deep-water fan system in the world. Seafloor and subseafloor data show large sediment wave fields that developed on both flanks of an extensive submarine canyon. The sediment waves exhibit asymmetric stoss and lee sides, wave lengths and heights of 850–3000 m and 25–70 m, respectively, and an upslope direction of migration. Seismic data reveals the presence of multiple fields of vertically stacked sediment waves, interbedded with units characterised by a chaotic seismic facies that accumulate mainly in the troughs of the sediment waves and can be tracked laterally to the adjacent canyons. According to their seismic facies, geometry, and internal architecture these chaotic units are interpreted as debrites. Seismic attributes extracted from different horizons indicate that the sediment waves are dominated by fine-grained sediment, while the debrites are probably associated with coarser-grained deposits. The debrites fill the troughs of the sediment waves, as well as the downstream portions of canyon thalweg, thus flattening the paleo-seafloor. The sediment waves are interpreted as cyclic steps formed by low-density turbidity currents flowing across the slope down to the basin floor, where the change in gradient favours the formation of hydraulic jumps and the transition from supercritical to subcritical flow conditions. A conceptual model for the sediment wave evolution was proposed for the study area, in the transitional environment on the lower slope, with low-density gravity flow deposits and high-density debris flow deposits alternatively accumulating on the major gravity flow conduits.
... Several different models are proposed for gully origins, such as sea-level oscillations (Chiocci and Normark 1992), mass wasting and sediment erosion on the steep continental slopes (Field et al. 1999;Dowdeswell et al. 2004), and turbidity currents (Garcia et al. 2006). McHugh and Ryan (2000) suggested that gullies occur by overbank turbidity current activity in the Monterey Fan, whereas Greene et al. (2002) proposed an erosive nature for the same area. Depending on their geometry, sizes, distribution and erosive character, we interpret that the gullies are originated by mass wasting along the canyon walls and overbank turbidity currents as suggested by Dondurur et al. (2013) for offshore Amasra further east of the SC. ...
... In the proximal part immediately beyond the shelf break, the gullies are possibly formed by gravitational mass wasting on the oversteepened upper slope. In the distal part to the north, however, the cause of the gully formation is possibly overbank spillover of the turbidity currents as suggested by McHugh and Ryan (2000). The intensive erosional truncation at both sides of the gully walls indicates the erosive nature of overbank turbidity current activity in these areas ( Fig. 6(b)). ...
Multi-channel seismic, 3.5-kHz Chirp seismic, and multibeam bathymetric data were collected along the western Black Sea margin, offshore Sakarya River, to investigate the morphology and to evaluate the potential geologic hazards. The multibeam bathymetric data show that the morphology of the margin is controlled by the Sakarya Canyon consisting of three distinct canyon heads, all incising the southern continental shelf. Deep-water sediment erosion along the canyon walls and scour marks along the distal canyon floors indicate that both Sakarya and Kefken Canyons may be active in terms of sediment erosion and turbidity currents. We identify the depositional and erosional features in the area by means of echo-character mapping. The distribution of different echo-types is mainly controlled by the morphology of the margin, as well as the shape, location, and structure of the major canyon systems. Erosional features, constituting 47% of the total surficial area, are classified as slides, erosional truncations, gravitational mass wasting, gullies, and outcropping seafloor while depositional features, constituting 53% of the total surficial area, comprise shelf sediments, turbidites, pelagic/hemi-pelagic sediments, and sediment waves. Different types of geohazards coexist along the Sakarya Canyon, which are classified as hazards linked to (1) local and/or regional tectonism, (2) morphology of the continental margin (turbidity currents, slope overstepeening), and (3) prevailing sedimentary processes (mass transports, submarine fluid flow, loss of support due to the truncation scarps and bedforms).
... Sediment waves are a type of long wavelength (tens of metres to kilometres) depositional bedform that vary in grain size from mud to gravel-dominated, linked to their depositional setting ( Fig. 1; Wynn & Stow, 2002). They have been identified in numerous modern channel-lobe transition zones (CLTZs; Normark & Dickson, 1976;Damuth, 1979;Lonsdale & Hollister, 1979;Normark et al., 1980Normark et al., , 2002Piper et al., 1985;Malinverno et al., 1988;Praeg & Schafer, 1989;Howe, 1996;Kidd et al., 1998;Morris et al., 1998;McHugh & Ryan, 2000;Migeon et al., 2001;Wynn & Stow, 2002;Wynn et al., 2002a,b;Heini€ o & Davies, 2009), where they form part of a distinctive assemblage of depositional and erosional bedforms (Mutti & Normark, 1987, 1991Normark & Piper, 1991;Palanques et al., 1995;Morris et al., 1998;Wynn et al., 2002a,b;Macdonald et al., 2011). However, the detailed sedimentological and stratigraphic record of sediment waves from CLTZs and channel-mouth settings is not widely documented. ...
In modern systems, submarine channel–lobe transition zones show a well‐documented assemblage of depositional and erosional bedforms. In contrast, the stratigraphic record of channel–lobe transition zones is poorly constrained, because preservation potential is low and criteria have not been established to identify depositional bedforms in these settings. Several locations from an exhumed fine‐grained base of slope system (Unit B, Laingsburg depocentre, Karoo Basin) show exceptional preservation of sandstone beds with distinctive morphologies and internal facies distributions. The regional stratigraphy, lack of a basal confining surface, wave‐like morphology in dip section, size and facies characteristics support an interpretation of subcritical sediment waves within a channel–lobe transition zone setting. Some sediment waves show steep (10 to 25°) unevenly spaced (10 to 100 m) internal truncation surfaces that are dominantly upstream‐facing, which suggests significant spatio‐temporal fluctuations in flow character. Their architecture indicates that individual sediment wave beds accrete upstream, in which each swell initiates individually. Lateral switching of the flow core is invoked to explain the sporadic upstream‐facing truncation surfaces, and complex facies distributions vertically within each sediment wave. Variations in bedform character are related to the axial to marginal positions within a channel–lobe transition zone. The depositional processes documented do not correspond with known bedform development under supercritical conditions. The proposed process model departs from established mechanisms of sediment wave formation by emphasising the evidence for subcritical rather than supercritical conditions, and highlights the significance of lateral and temporal variability in flow dynamics and resulting depositional architecture.
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... Widespread morphological features associated to overbanking https://doi.org/10. 1016/j.pocean.2018.02.020 processes, such as levees, crevasse splays, sediment waves, megaflutes, cyclic scours scars, gullies and erosive channels have been described in canyon systems (i.e., Piper, 1991, Nakajima et al., 1998;McHugh and Ryan, 2000;Migeon et al., 2001;Wynn et al., 2002;Migeon et al., 2004;Maier et al., 2011;Gong et al., 2012;Casalbore et al., 2014). The study of these overbanking features may provide insights about the hydrodynamics, thickness, and erosive capabilities of the turbidity currents (e.g., Normark et al., 1980;Piper and Normark, 1983). ...
... Northern levee The most evident feature associated to overbanking flows from the lower reach of the GMS is the well-developed levee recognized along its northern (right) flank, whereas it is morphologically less evident along the opposite (left) flank. This asymmetry of the GMS levees is similar to what was observed for several submarine canyons in the Northern Hemisphere (e.g., Babonneau et al., 2012;Klaucke et al., 1998;Komar, 1973;McHugh and Ryan, 2000) and it has been tentatively explained by the Coriolis force due to the Earth's rotation. In the northern hemisphere, this force should push turbidity currents to the right, leading to the preferential overflow processes on the right flank (Wells, 2009;Peakall et al., 2012). ...
The collection of high-resolution multibeam bathymetry, single-channel seismic profiles, TOBI side scan sonar data, and gravity cores allowed the characterization of the main morpho-sedimentary processes acting along the lower reach of the shelf-indenting Gioia-Mesima canyon-channel system (GMS) and the surrounding continental slope (southern Tyrrhenian Sea). This last area, developing across a depth range of 1000–1700 m, shows a complex morphology due to the interaction between downslope gravitative processes (mainly turbidite sheet flows) and abrupt changes in slope gradients related to tectonically-controlled scarps. Particularly, several erosive-depositional features (levee deposits, sediment undulations, channels) have been related to overflow processes from the northern flank of the GMS, although the lower reach of the GMS is characterized by strong entrenchment (canyon height ranging from 120 to 270 m) and low sinuosity. Morphological and seismic stratigraphy data indicate that the distribution and dimension of these features vary in response both to the proximity to the external levee of the GMS and to the topographic gradient of the lower continental slope. Particularly, we were able to discriminate between a gently sloping sector (on average 1.5°) dominated by sedimentary bypass of the turbidity currents and a steeper sector (about 3°), where the erosional capability of these currents seems to increase. Indeed, three channels, 4,3–6,5 km long and up to 20 m deep, incise this steeper sector, running parallel to each other at a distance of 1250–1500 m. To support the capability of overbanking flow in producing these channels, we used a physical model for the ignition of turbidity currents that provides realistic values for the ignitive state of the overbanking turbidity flows. More generally, the methodological approach used in this study may be useful to provide constraints on the genesis and evolution of erosive-depositional features in other tectonically-controlled margins, where sedimentary gravity flows interact with an uneven morphology.
... Accentuated levee geometry is also evident on the outer levee on channel bends due to higher volumes of inertial overspill here (e.g. McHugh & Ryan 2000;Posamentier 2003). ...
... The outer regions of the master bounding levee within submarine channel systems commonly show distinct sediment waves in both ancient, seismically-imaged systems (e.g. Nakajima et al. 1998;McHugh & Ryan 2000;Normark et al. 2002;Migeon et al. 2004) and in modern examples (Lewis & Pantin 2002;Normark et al. 2002;Posamentier 2003;Posamentier & Kolla 2003;Bøe et al. 2004;Migeon et al. 2004). Sediment waves are believed to be created either by flowstripping and over-spilling of channelised turbidity currents (Migeon et al. 2004;Posamentier 2003) or where a pre-existing rugose topography may act as a template for sediment wave initiation (Bøe et al. 2004;Migeon et al. 2004 2000) and show greater relief on the outside of meander bends, which is attributed to increased flow stripping at the channel bends. ...
The Upper Cretaceous Cerro Toro Formation, southern Chile, is characterised by thin-bedded turbidites that envelope a series of coarse-grained, confined slope complex systems, interpreted as part of the Lago Sofia Member. This deep-water slope system overlies basin floor sheets of the Punta Barrosa Formation, and is overlain by the sand-filled slope channels of the Tres Pasos Formation.
Particularly distinctive beds, known as TEDs (transitional event deposits), are up to 40 m thick, laterally extensive, have prominent fluted bases, and have a vertical fabric starting with (1) a thin, inversely-graded, clast-supported base; then (2) a normally-graded and clast-supported interval; (3) an increasingly sand and clay matrix-supported conglomerate, with (4) a progressive upwards increase in matrix and normally grading, both in the floating gravel clast and matrix grain sizes, towards the top; and (5) a co-genetic sandstone on top. In the Cerro Toro formation, these TEDs tend to occur as multiple beds in the initial phases of deposition of each channel complex system. The TEDs are highly aggradational, slightly more amalgamated in the channel-axis, and more layered towards the margins. The fabric of these spectacular event beds is described in some detail from measured sections, combined with petrographic analysis and high-resolution field mapping.
The 4 km x 200 m channel systems are contained within topographically irregular bathymetric lows that formed sediment pathways, interpreted to be either the result of slope deformation, or contained by poorly preserved, tectonically disrupted or slumped external levee. Syn-sedimentary tectonism is interpreted to be responsible for sharp changes in the system’s architecture from channels to ponds, marked by a sharp change in lithofacies from dominantly conglomerates to dominantly sandstones. A refined architectural analysis is proposed, focusing on the recurrent pattern of at least 5 cycles of conglomerate-filled channel systems – ponded sheet sandstones.
... The western levee of JDF Channel at this point is on the outside of a southerly bend and shows evidence of crevasse-splay and radial sediment waves characteristic of overbank morphology and flow from JDF into this channel (e.g. McHugh and Ryan, 2000;Normark et al., 2002;Keevil, 2005). At its northern end, the JDF West Channel is a broad open channel, narrowing to the SW, with lower levees. ...
The Washington continental margin presents both a classic test of submarine paleoseismology, and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system.New and archive core, bathymetric, backscatter and seismic reflection data from the Washington Cascadia margin show that during high-stand conditions, the northernmost canyons, Barkley, Nitinat, JDF, and to some extent Quillayute are relict systems, with little Holocene recharge. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to a varying degrees by northward transport of Columbia River derived sediment.All systems are nonetheless active conduits for turbidity currents during the Holocene, which are weaker and more restricted than Pleistocene counterparts.Sedimentologic and CT analysis, supported by radiocarbon ages, micropaleontology, and the Mazama ash datum show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment.However, the Pleistocene Astoria and Nitinat fans, are largely inactive in the Holocene, with turbidity current activity limited to the proximal parts of the main channels.Within active systems, the turbidite record is modulated by local landsliding and growth of active folds and faults.
... A range of depositional styles within these confined systems and details of their facies architecture have been explored in shallow seismic, outcrop and modern morphological studies. Studies of modern submarine sand-rich systems (MALDONADO et alii, 1985;PICKERING et alii, 1986a;MASSON, 1994;MCHUGH & RYAN, 2000;TALLING et alii, 2015) and the use of high-resolution seismic data (MAYALL et alii, 2006) provide important information about depositional processes and geometries, but supply little information on the vertical stacking patterns and internal facies architecture of these deposits. ...
Submarine sand-rich slope fans within confined basins have long been recognized as components of deepwater depositional systems and, in some areas, they host important hydrocarbon accumulations. The Bric la Croce-Castelnuovo turbidite system (BCTS) of northern Italy offers an opportunity to study an exposed sand-rich slope fan system, allowing reconstruction of the main architectural elements of a fan, from slope to basin floor. The system belongs to the Langhe Basin, the major depocentre of the TPB (Tertiary Piedmont Basin), an episutural basin set upon a complex of Alpine nappes of the Liguria-Piemonte Western Alps. The system consists of three main erosional and depositional zones from up- to down-stream (from SE to NW): i) a base of slope zone; ii) a channel-lobe transition zone; iii) a lobe zone. Downslope and upslope migration of these sectors determines, through time, their superimposition and gives rise to a generation of depositional units of different hierarchical order ranging from metre-thick simple facies sequences to decametres composite facies sequence, expression of single and composite architectural elements as channel and lobe complexes. The vertical organisation of the BCTS reflects its overall forestepping. Thin-bedded turbidites interpreted as distal lobes are overlain by stacked sandsheets and aggradational channels attributed to the mid-fan setting. At the top of the series, coarse-grained sandy channels correspond to the maximum of forestepping. The logged sections and the geological mapping provide a valuable data set that can be used to study the spatial-temporal relationships between facies of channelized and nonchannelized strata (lobe deposits) along a depositional profile, cut roughly parallel to the main palaeocurrent flow. The sands were derived from south and flowed toward the north. The portion of the BCTS which crops out is approximately 160 m thick and extends for about 10-12 km in a SW-NE direction. Research involved a detailed analysis of facies (genetic facies related to depositional processes), physical stratigraphy of stacking and correlation patterns. The detailed correlation panels allowed evaluating how facies changed along the depositional profile and this was considered as the expression of the flow transformation during its movement. Based on these considerations, it has been possible to reconstruct different facies tracts, which are related to flows with different volume and efficiency recording a coeval phase of sedimentation in the channel, channel-transition and lobe zones
... Their height, defined as relief above the channel floor, depends on the rate of sediment supply, the period of time over which they have been growing, and the amount of erosion or deposition within the adjacent channel; heights typically range from a few tens of metres to as much as four hundred metres (Migeon et al., 2012). The heights of conjugate external levees may be asymmetric, caused either by centrifugal forces acting on overspilling currents at outer bends (in which case the asymmetry reverses from right hand to left hand bends), or by the Coriolis effect due to the Earth's rotation, which causes the average height of the levee on one side of the channel (the right in the northern hemisphere and the left in the southern hemisphere) to be consistently higher than the other (Babonneau et al., 2012;Klaucke et al., 1998;Komar, 1969;Komar, 1973;McHugh and Ryan, 2000). Levee width can vary between a few hundred metres to tens of kilometres ( Fig. 4), and appears to scale with the width of the channel (Nakajima and Kneller, 2013;Posamentier and Walker, 2006;Skene et al., 2002), and with the grain-size ( Fig. 5) which, along with height, aspect ratio and shape, is partly related to the gradient of the slope on which the levee is constructed (Nakajima and Kneller, 2013). ...
... Some external levees are characterized by other sedimentary features such as sediment waves and cyclic steps. Sediment wave fields can spread up to several square kilometres (Babonneau et al., 2012;McHugh and Ryan, 2000;Migeon et al., 2000;Nakajima et al., 1998;Normark et al., 2002;Savoye et al., 2009), and are produced either by regional bottom currents (Wynn and Masson, 2008;Faugeres and Mulder, 2011 and references therein) or overspilling turbidity currents (e.g. Migeon et al., 2001;Mulder, 2011;Normark et al., 2002). ...
... The term terrace has previously been used in deep-water environments to describe areas adjacent to a channel that are topographically flat or subdued in cross-section, without implying any specific process or origin (Babonneau et al., 2004). Terraces have been identified mostly from bathymetric and side-scan sonar data from modern deep-water systems such as the Indus canyon (Von Rad and Tahir, 1997), Bengal fan (Hübscher et al., 1997), Hueneme fan (O'Connell et al., 1995;Piper and Hiscott, 1999;Torres et al., 1997), Rhone fan (O'Connell et al., 1995;Torres et al., 1997), Amazon fan (Damuth et al., 1988), La Jolla canyon , the Villafranca channel in the Tyrrhenian Sea (Gamberi and Rovere, 2011), Toyama channel (Nakajima et al., 1998), the Congo canyon (Babonneau et al., 2010(Babonneau et al., , 2004, and the Monterey fan channel (McHugh and Ryan, 2000). Interpretations of terraces include what have been described as slumped levee blocks (Hackbarth and Shew, 1994) and rotated slumps, depositional terraces (Von Rad and Tahir, 1997), "confined" or "underfit" internal levees (Hübscher et al., 1997;Piper and Hiscott, 1999), inner levees (Deptuck et al., 2003), flat lying features resulting from channel entrenchment (Babonneau et al., 2010;Deptuck et al., 2003), over-bank, channel margin, and inner external levee (Morris et al., 2014). ...
