Slides, Slumps, Debris Flows, Turbidity Currents, and ...

Slides, Slumps, Debris Flows, Turbidity Currents, and Bottom Currents: Implications☆ G Shanmugam, University of Texas at Arlington, Arlington, TX, United States © 2018 Elsevier Inc. All rights reserved.

Glossary Abyssal plain The term abyssal plain refers to a flat region of the ocean floor, usually at the base of a continental rise, where slope is less than 1:1000 (Heezen et al., 1959). It represents the deepest and flat part of the ocean floor that occupies between 4000 and 6500 m in the US Atlantic margin. A more general term “basin plain” is commonly used in referring to ancient examples. Agulhas Current The Agulhas Current is the western boundary current that flows down the east coast of Africa from 27 S to 40 S. It retroflects (turns back) due to interactions with the strong Antarctic Circumpolar Current. The Agulhas retroflection has been associated with generating immense “rogue waves.” Ancient The term refers to deep-marine systems that are older than the Quaternary Period, which began approximately 2.58 Ma. Antarctic bottom water (AABW) AABW originates in the northwest corner of the Weddell Sea in the Antarctic region by the formation of ice from surface freezing over the Antarctic continental shelves. Avalanche A large mass of snow, ice, soil, rock, or mixture of these materials moving downslope rapidly under the force of gravity. This term is not useful for interpreting ancient processes because it is difficult to quantify velocity (rapid vs. slow) of processes accurately in the rock record. Back-analysis The method of determining the conditions and developing a suitable model of the slope from a failure (Duncan and Wright, 2005). Basal shear zone The basal part of a rock unit that has been crushed and brecciated by many subparallel fractures due to shear strain. Bathyal Ocean floor that occupies depths between 200 (shelf edge) and 4000 m (656 and 13,120 ft). Note that abyssal plains may occur at bathyal depths. Bathymetry The measurement of seafloor depth and the charting of seafloor topography. Bolide It refers to a bright fireball-like meteor. The term bolide is used synonymously with meteorite. Bottom-current reworking (BCR) It refers to traction (bed load) processes associated with deepwater bottom currents. Bottom currents In deepwater environments, there are four types of bottom currents, namely, (1) thermohaline-induced geostrophic bottom currents, (2) wind-driven bottom currents, (3) deepwater tidal bottom currents, and (4) internal waves and tides (baroclinic currents). These bottom currents should not be confused with turbidity currents. Brecciated clasts Angular mudstone clasts in a rock due to crushing or other deformations. Brecciated zone An interval that contains angular fragments caused by crushing or breakage of the rock. Clastic sediment Solid fragmental material (unconsolidated) that originates from weathering and is transported and deposited by air, water, ice, or other processes (e.g., mass movements). Continental margin The ocean floor that occupies between the shoreline and the abyssal plain. It consists of shelf, slope, and basin (Fig. 2). Continental rise The seafloor that occupies between continental slope (3000 m) and abyssal plain (4000 m, U.S. Atlantic margin). Continental shelf The seafloor that occupies between the shoreline and the shelf-slope break (200 m). Continental slope The seafloor that occupies between the shelf-slope break (200 m) and the slope-rise break (3000 m, U.S. Atlantic margin). Contorted bedding Extremely disorganized, crumpled, convoluted, twisted, or folded bedding. Its synonym is chaotic bedding. Core A cylindrical sample of a rock type extracted from underground or seabed. It is obtained by drilling into the subsurface with a hollow steel tube called a corer. During the downward drilling and coring, the sample is pushed upward into the tube. After coring, the rock-filled tube is brought to the surface. In the laboratory, the core is slabbed perpendicular to bedding. Finally, the slabbed flat surface of the core is examined for geologic bedding contacts, sedimentary structures, grain-size variations, deformation, fossil content, etc. Gravity, box, piston, vibratory, percussion, and conventional cores are commonly used. The Ocean Drilling Program (ODP) uses core with a diameter of 6.8 cm. Deep marine The term deep marine commonly refers to bathyal environments, occurring seaward of the continental shelf break (>200 m water depth), on the continental slope and the basin (Fig. 1). The continental rise, which represents that part of the continental margin between continental slope and abyssal plain, is included here under the broad term basin. ☆

Change History: August 2017. G Shanmugam updated this entire article with an expanded title, keywords with six new entries, and glossary with 12 new entries. The first part is an updated version of the original article with three new sections: (1) “Soft-Sediment Deformation (2) “Submarine fans” with five new figures, and (3) “Hyperpycnal flows” with five new figures. The second part is updated with a new seismic profile of contourites and with two new sections: (1) “Reservoir quality” with two new figures and (2) “Provenance” with one new figure.

Reference Module in Earth Systems and Environmental Sciences

https://doi.org/10.1016/B978-0-12-409548-9.04380-3

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Slides, Slumps, Debris Flows, Turbidity Currents, and Bottom Currents: Implications

Dish structures Concave-up (like a dish) structures caused by upward-escaping water in the sediment. Double mud layers (DMLs) Paired occurrence of mud layers. This is unique to tidal settings. Visser (1980) originally explained the origin of DMLs by alternating ebb and flood tidal currents with extreme time–velocity asymmetry in shallowwater subtidal settings. This feature also occurs in deepwater settings (Shanmugam, 2003). Drained condition A condition under which water is able to flow into or out of soil in the length of time that the soil is subjected to some change in load (Duncan and Wright, 2005). Floating mudstone clasts Occurrence of mudstone clasts at some distance above the basal bedding contact of a rock unit. Flow Continuous, irreversible deformation of sediment–water mixture that occurs in response to applied stress (Fig. 18). Fluid A material that flows. Fluid dynamics A branch of fluid mechanics that deals with the study of fluids (liquids and gases) in motion. Fluid mechanics Study of the properties and behaviors of fluids. Geohazards Natural disasters (hazards), such as earthquakes, landslides, tsunamis, tropical cyclones, rogue (freak) waves, floods, volcanic events, sea-level rise, karst-related subsidence (sinkholes), geomagnetic storms, coastal upwelling, and deepocean currents. Glide plane A slip surface along which major displacement occurs, causing mass-transport deposits (MTDs). Heterolithic facies Thinly interbedded (millimeter- to decimeter-scale) sandstones and mudstones. High-density turbidity currents (HDTCs) HDTC is a euphemism for sandy debris flows (Shanmugam, 1996). Hydrodynamics A branch of fluid dynamics that deals with the study of liquids in motion. Hyperpycnal flows In advocating a rational theory for delta formation, based on the concepts of Forel (1892), Bates (1953) suggested three major flow types: (1) hypopycnal flow for floating river water that has lower density than basin water; (2) homopycnal flow for mixing river water that has equal density as basin water; and (3) hyperpycnal flow for sinking river water that has higher density than basin water. Hyperpycnite Deposits of hyperpycnal flows. The term “hyperpycnite” was first introduced by Mulder et al. (2002) who attributed the origin of inverse grading to deposits of hyperpycnal lows. Shanmugam (2002a) debated the controversial origin of inverse grading. Injectite Injected material (usually sand) into a host rock (usually mudstone). Injections are common in igneous rocks. Internal tides Internal waves that correspond to periods of tides are called internal tides. Internal wave Internal waves are gravity waves that oscillate along the interface between two water layers of different densities (i.e., pycnocline). Gill (1982) illustrated that fluid parcels in the entire water column move together in the same direction and with the same velocity in a barotropic (surface) wave, whereas fluid parcels in shallow and deep layers of the water column move in opposite directions and with different velocities in a baroclinic (internal) wave (Shanmugam, 2013a). Inverse grading Upward increase in average grain size from the basal contact to the upper contact within a single depositional unit. Lithofacies A rock unit that is distinguished from adjacent rock units based on its lithologic (i.e., physical, chemical, and biological) properties (see “Rock”). Liquefaction Allen (1984) used a general process term liquidization to describe mechanisms involving a change of state from solid-like to liquid-like (i.e., “quick”) in cohesionless grain mass. The two mechanisms of liquidization are liquefaction and fluidization. Liquefaction is a phenomenon commonly associated with earthquakes in which water-saturated sands behave like fluids. As seismic waves pass through water-saturated sands, void spaces (pores) between sand particles collapse, causing sediment deformation and ground failure. It occurs as a consequence of increased pore-fluid pressure. Liquefaction involves neither influx of external fluids into the grain mass nor volume change. Lobe A rounded, protruded, wide frontal part of a deposit in map view. Mass transport Mass transport represents the failure, dislodgment, and downslope movement of sediment under the influence of gravity. Continental margins provide an ideal setting for slope failure, which is the collapse of slope sediment from the shelf edge. Following a failure, the failed sediment moves downslope under the pull of gravity when the shear stress exceeds the shear strength. Methodology Four methods are in use for recognizing slides, slumps, debris flows, and turbidity currents and their deposits. Method 1: Direct observations—Deep-sea diving by a diver allows direct observations of submarine mass movements. The technique has limitations in terms of diving depth and diving time. These constraints can be overcome by using a remotely operated deep submergence vehicle, which would allow observations at greater depths and for longer time. Both remotely operated vehicles (ROVs) and manned submersibles are used for underwater photographic and video documentation of submarine processes. Method 2: Indirect velocity calculations—A standard practice has been to calculate velocity of catastrophic submarine events based on the timing of submarine cable breaks. The best example of this method is the 1929 Grand Banks earthquake (Canada) and related cable breaks. This method is not useful for recognizing individual type of mass movement (e.g., slide vs. slump). Method 3: Remote sensing technology—In the 1950s, conventional echo sounding was used to construct seafloor profiles. This was done by emitting sound pulses from a ship and by recording return echoes from the sea bottom. Today, several types of seismic profiling techniques are available depending on the desired degree of resolutions. Although popular in the petroleum industry and academia, seismic profiles cannot resolve subtle sedimentologic features that are required to distinguish turbidites from debrites. In the1970s, the most significant progress in mapping the seafloor was made by adopting multibeam side-scan sonar survey. The Sea MARC 1


(Seafloor Mapping and Remote Characterization) system uses up to 5 km broad swath of the seafloor. The GLORIA (Geological Long-Range Inclined Asdic) system uses up to 45 km broad swath of the seafloor. The advantage of GLORIA is that it can map an area of 27,700 km2 day1. In the 1990s, multibeam mapping systems were adopted to map the seafloor. This system utilizes hull-mounted sonar arrays that collect bathymetric soundings. The ship’s position is determined by Global Positioning System (GPS). Because the transducer arrays are hull-mounted, rather than towed in a vehicle behind the ship, the data are gathered with navigational accuracy of about 1 m and depth resolution of 50 cm. Two of the types of data collected are bathymetry (seafloor depth) and backscatter (data that can provide insight into the geologic makeup of the seafloor). An example is a bathymetric image of the US Pacific margin with mass-transport deposits (Fig. 2). The US National Geophysical Data Center (NGDC) maintains a website of bathymetric images of continental margins. Although morphological features seen on bathymetric images are useful for recognizing mass transport as a general mechanism, these images may not be useful for distinguishing slides from slumps. Such a distinction requires direct examination of the rock in detail. Method 4: Examination of the rock—Direct examination of core and outcrop is the most reliable method for recognizing individual deposits of slide, slump, debris flow, and turbidity current. This method, known as process sedimentology, is the foundation for reconstructing ancient depositional environments and for understanding sandstone petroleum reservoirs. Modern The term refers to present-day deep-marine systems that are still active or that have been active since the Quaternary Period that began approximately 1.8 Ma. Mud offshoot Refers to mud drapes on ripples. Newtonian rheology Fluids with no inherent strength. These fluids, like water, will begin to deform the moment shear stress is applied, and the deformation is linear. Nonuniform flow Spatial changes in velocity at a moment in time. Normal grading Upward decrease in average grain size from the basal contact to the upper contact within a single depositional unit composed of a single rock type. It should not contain any floating mudstone clasts or outsized quartz granules. In turbidity currents, waning flows deposit successively finer and finer sediment, resulting in a normal grading (see “Waning flow”). Outcrop A natural exposure of the bedrock without soil capping (e.g., along river-cut subaerial canyon walls or submarine canyon walls) or an artificial exposure of the bedrock due to excavation for roads, tunnels, or quarries. Planar clast fabric Alignment of long axis of clasts parallel to bedding (i.e., horizontal) (Fig. 19). This fabric implies laminar flow at the time of deposition. Plastic rheology Some naturally occurring materials with strength will not deform until yield stress has been exceeded; once the yield stress is exceeded, the deformation is linear. Such materials with strength are considered to be Bingham-plastic. Johnson (1970) favored a Bingham-plastic rheological model for debris flows. Primary basal glide plane (or décollement) The basal slip surface along which major displacement occurs (Fig. 13). Projected clasts Upward projection of mudstone clasts above the bedding surface of host rock (e.g., sand). This feature implies freezing from a laminar flow at the time of deposition. Rock The term is used for (1) an aggregate of one or more minerals (e.g., sandstone), (2) a body of undifferentiated mineral matter (e.g., obsidian), and (3) solid organic matter (e.g., coal). Scarp A relatively straight, cliff-like face or slope of considerable linear extent, breaking the continuity of the land by failure or faulting. Scarp is an abbreviated form of the term escarpment. Scientific drilling at sea Scientific drilling at sea, which comprise cores recovered from the Deep Sea Drilling Project (DSDP: 1966–83), Ocean Drilling Program (ODP: 1993–2003), Integrated Ocean Drilling Program (IODP: 2003–13), and International Ocean Discovery Program (IODP: 2013–Present). Each ocean drilling program offers a great wealth of core data for studying deep-water sedimentation, among other domains. For example, ODP (2007) reported that during its operation, the drilling program recovered 222,430 m of core from 1797 holes. All DSDP/ODP/OPDP core photographs are available online free and can be downloaded from the ODP web page: http://www-odp.tamu.edu/. Home: Texas A&M University, College Station, Texas. Secondary glide plane Internal slip surface within the rock unit along which minor displacement occurs (Fig. 13). Sediment flows They represent sediment gravity flows. They are classified into four types based on sediment-support mechanisms: (1) turbidity current with turbulence, (2) fluidized sediment flow with upward-moving intergranular flow, (3) grain flow with grain interaction (i.e., dispersive pressure), and (4) debris flow with matrix strength (Middleton and Hampton, 1973). Although all turbidity currents are turbulent in state, not all turbulent flows are turbidity currents. For example, subaerial river currents are turbulent, but they are not turbidity currents. River currents are fluid gravity flows in which fluid is directly driven by gravity. In sediment gravity flows, however, the interstitial fluid is driven by the grains moving downslope under the influence of gravity. Thus, turbidity currents cannot operate without their entrained sediment, whereas river currents can do so. River currents are subaerial flows, whereas turbidity currents are subaqueous flows. Sediment flux (1) A flowing sediment–water mixture. (2) Transfer of sediment. Sediment deformation It refers to a change in the bulk shape of the aggregate of sediment (Maltman, 1994). It is concerned with deformation early in the burial history. Physical processes involved are (Collinson, 1994): (1) partial loss of strength and density inversion (e.g., flame structures); (2) progressive loading of cohesive sediment (e.g., mud diapirs); (3) partial loss of strength and applied shear (e.g., slump folds), (4) liquefaction-induced upward escape of pore water (e.g., dish and pillar

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structures) and sediment–water mixture (e.g., sand boil and sediment injection), (5) synsedimentary faults (e.g., extensional and contractional types), (6) sediment shrinkage (e.g., subaerial desiccation cracks and subaqueous synaeresis cracks), (7) sediment wetting (e.g., buckling on steep slopes of eolian dunes), and (8) compaction (e.g., reduction in the inclination of dipping surfaces. See entry “Soft-sediment deformation structures” (SSDS) and 12 classifications of SSDS (Shanmugam, 2017a). The phrases “sediment deformation” and “soft-sediment deformation” mean one and the same although both phrases are in use. Sedimentology Scientific study of sediments (unconsolidated) and sedimentary rocks (consolidated) in terms of their description, classification, origin, and diagenesis. It is concerned with physical, chemical, and biological processes and products. This article deals with physical sedimentology and its branch, process sedimentology. Seismite Seilacher (1969) introduced the genetic term “seismite” for deformed beds by earthquakes. However, there are no reliable criteria for recognizing paleoseismicity (Shanmugam, 2016b). Shear strength The maximum shear stress that the soil can withstand (Duncan and Wright, 2005). Slope stability analyses A common method for calculating the slope stability is called the “limit equilibrium analyses,” which refer to the principle in which a slope is stable if the resisting forces exceed the driving forces. See Duncan and Wright (2005). Soft-sediment deformation structures (SSDS) Allen (1984, II, p. 343) provided an accurate account of soft-sediment deformation in terms of physics. The two factors that control the origin of SSDS are prelithification deformation and liquidization. Allen (1984) recognized the following structures as SSDS:

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Convolute lamination Load casts Heavy mineral sags Passively deformed beds Dish structures Folds and sand mounds Sheet slumps Imbricate structure Deformed cross bedding However, a recent inventory suggests a plethora of at least 120 different types of SSDS have been recognized in strata ranging in age from Paleoproterozoic to the present time (Shanmugam, 2017d).

Soil mechanics Study of the properties and behaviors of soils. Unlike fluid mechanics and solid mechanics that deal with endmembers, soils consist of a heterogeneous mixture of fluids (usually air and water), particles (usually clay, silt, sand, and gravel), organic matter, and gases. Submarine canyon A steep-sided valley that incises into the continental shelf and slope. Canyons serve as major conduits for sediment transport from land and the shelf to the deep-sea environment (Fig. 41). Smaller erosional features on the continental slope are commonly termed gullies; however, there are no standardized criteria to distinguish canyons from gullies. Similarly, the distinction between submarine canyons and submarine erosional channels is not straightforward. Thus, alternative terms, such as gullies, channels, troughs, trenches, fault valleys, and sea valleys, are in use for submarine canyons in the published literature. Submarine fan The term “submarine fans” refers loosely to deposits of variable shapes and sizes in deep-marine environments. The principal elements of submarine fans are canyons, channels, and lobes (see a critical review by Shanmugam, 2016a). The Bouma Sequence Refers to five divisions in a “turbidite” bed, namely Ta, Tb, Tc, Td, and Te (Bouma, 1962). Despite its popularity, this genetic facies model is fundamentally flawed (see Shanmugam, 2016a). Total stress The total stress is the sum of all forces, including those transmitted through particle contacts and those transmitted through water pressures, divided by the total area (Duncan and Wright, 2005). Tropical cyclone It is a meteorologic phenomenon characterized by a closed circulation system around a center of low pressure, driven by heat energy released as moist air drawn in over warm ocean waters rises and condenses. Structurally, it is a large, rotating system of clouds, wind, and thunderstorms (Shanmugam, 2008b). The name underscores their origin in the tropics and their cyclonic nature. Worldwide, formation of tropical cyclones peaks in late summer months when water temperatures are warmest. In the Bay of Bengal, tropical cyclone activity has double peaks, one in April and May before the onset of the monsoon and another in October and November just after. Cyclone is a broader category that includes both storms and hurricanes as members. Cyclones in the Northern Hemisphere represent closed counterclockwise circulation. They are classified based on maximum sustained wind velocity as follows:

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Tropical depression: 37–61 km h1 Tropical storm: 62–119 km h1 Tropical hurricane (Atlantic Ocean): >119 km h1 Tropical typhoon (Pacific or Indian Ocean): >119 km h1 The Saffir–Simpson hurricane scale:


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Category 1: 120–153 km h1 Category 2: 154–177 km h1 Category 3: 178–209 km h1 Category 4: 210–249 km h1 Category 5: >249 km h1

Tsunami Oceanographic phenomena that are characterized by a water wave or series of waves with long wavelengths and long periods. They are caused by an impulsive vertical displacement of the body of water by earthquakes, “landslides,” volcanic explosions, or extraterrestrial (meteorite) impacts. The link between tsunamis and sediment flux in the world’s oceans involves four stages (Shanmugam, 2006b): (1) triggering stage, (2) tsunami stage, (3) transformation stage, and (4) depositional stage (Fig. 34). During the triggering stage, earthquakes, volcanic explosions, undersea “landslides,” and meteorite impacts can trigger displacement of the sea surface, causing tsunami waves. During the tsunami stage, tsunami waves carry energy traveling through the water, but these waves do not move the water. The incoming wave is depleted in entrained sediment. This stage is one of energy transfer, and it does not involve sediment transport. During the transformation stage, the incoming tsunami waves tend to erode and incorporate sediment into waves near the coast. This sediment entrainment process transforms sediment-depleted waves into outgoing mass-transport processes and sediment flows. During the depositional stage, deposition from slides, slumps, debris flows, and turbidity currents would occur. Undrained condition A condition under which there is no flow of water into or out of soil in the length of time that the soil is subjected to some change in load (Duncan and Wright, 2005). Unsteady flow Temporal changes in velocity through a fixed point in space. Waning flow Unsteady flow in which velocity becomes slower and slower at a fixed point through time. As a result, waning flows would deposit successively finer and finer sediment, resulting in a normal grading. Waxing flow Unsteady flow in which velocity becomes faster and faster at a fixed point through time.

Part 1 Slides, Slumps, Debris Flows, and Turbidity Currents Introduction International Projects and Symposiums Mechanics of Sediment Failure and Sliding Soil Strength and Slope Stability The Role of Excess Pore-Water Pressure Nomenclature and Classification Landslide Versus Mass Transport Subaerial processes based on the types of movement and material Subaqueous processes based on mechanical behavior Processes based on transport velocity Recognition of Depositional Facies Slides Slumps Distinguishing between debris flows and turbidity currents Debris Flows Turbidity Currents A Paradigm Shift Triggering Mechanisms Earthquakes Meteorite Impact Tsunami Wave Cyclonic Wave Groundwater Seepage and Other Factors Human Activity Tectonic Oversteepening Sea-Level Lowstand Long-Runout Mechanisms and Problems Basic Concept Subaerial Environments Submarine Environments

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Extraterrestrial Environments Problems Mass Transport in Submarine Canyons Social and Economic Consequences Destructive Aspects Constructive Aspects Reservoir Characterization Soft-Sediment Deformation Structures (SSDS) and Scientific Drilling at Sea Introduction Breccias Lateral Extent Ocean Bottom Currents Mass-Transport Deposits (MTD) Submarine Fans Hyperpycnal Flows Classification Definition of Turbidity Currents River Discharge Grain Size Massive Sandstones Lofting Rhythmites Plant Remains Hyperpycnite Facies Model

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Introduction Since the birth of modern deep-sea exploration by the voyage of HMS Challenger (December 21, 1872 to May 24, 1876), organized by the Royal Society of London and the Royal Navy (Murray and Renard, 1891), oceanographers have made considerable progress in understanding the world’s oceans. Nevertheless, the physical processes that are responsible for transporting sediment downslope into the deep sea are still poorly understood. This is simply because the physics and hydrodynamics of these processes are difficult to observe and measure directly in deep-marine environments. This observational impediment has created an enormous challenge for understanding and communicating the mechanics of gravity-driven downslope processes with clarity. Furthermore, deep-marine environments are known for their complexity of processes and their deposits (Fig. 1), dominated by mass-transport deposits (MTDs) and bottom-current-reworked sands (Shanmugam, 2006a, 2012a). Thus, a plethora of confusing concepts and classifications exist. Second, MTDs constitute major geohazards on subaerial environments (Geertsema et al., 2009; Glade et al., 2005; Jakob and Hungr, 2005; Kirschbaum et al., 2010). They are ubiquitous on submarine slopes (Fig. 2) and destructive (Hampton et al., 1996). Submarine mass movements may bear a tsunamigenic potential and are capable of methane gas release into the seawater and atmosphere (Urgeles et al., 2007). The US Geological Survey (USGS, 2010) has compiled data on worldwide damages caused by large subaerial and submarine MTDs in the twentieth and 21st centuries (Table 1). Annual losses associated with MTDs have been estimated to be about 1–2 billion dollars in the United States (Schuster and Highland, 2001). During a 7-year global survey (2004–10), a total of 2620 MTDs had caused a loss of 32,322 human lives (Petley, 2012). Third, the world’s largest submarine MTD is the Agulhas slump in SE Africa, which is 20,331 km3 in size (Table 2). This submarine MTD is ten times volumetrically larger than the world’s largest subaerial MTD (Markagunt gravity slide, southwest Utah; Fig. 3), which is 2000 km3 in size (Table 2). On Mars, MTDs of immense dimensions (e.g., 3000 km wide) have been studied (Montgomery et al., 2009, their Fig. 9). Large submarine MTDs have important implications for developing deepwater petroleum reservoirs. In fact, many petroleum reservoirs currently produce oil and gas from sandy mass-transport deposit (SMTD) reservoirs worldwide (Shanmugam, 2006a, 2012a). Because the petroleum industry is moving exploration increasingly into the deep-marine realm to meet the growing demand for oil and gas, a clear understanding of deep-marine processes is critical. Therefore, the primary objective of the first part of this article is to bring clarity to the classification of subaerial and submarine downslope processes by combining sound principles of fluid mechanics, soil mechanics, laboratory experiments, study of modern deep-marine systems, and detailed examination of core and outcrop (Table 3; Fig. 3). Specific objectives are (1) to document modern and ancient examples of gravity-induced processes and their deposits worldwide, (2) to review nomenclature and classification of downslope processes, (3) to establish criteria for recognizing depositional facies in the stratigraphic record, (4) to identify the types of triggering mechanisms of sediment failures, (5) to evaluate the potential mechanisms responsible for long-runout MTDs, (6) to address the importance of


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Fig. 1 Schematic diagram showing complex deep-marine sedimentary environments occurring at water depths deeper than 200 m (shelf-slope break). In general, sediment transport in shallow-marine (shelf ) environments is characterized by tides and waves, whereas sediment transport in deep-marine (slope and basin) environments is characterized by gravity-driven downslope processes, such as mass transport (i.e., slides, slumps, and debris flows) and turbidity currents. Bottom currents, composed of thermohaline contour-following currents, wind-driven currents (circular motion), up and down tidal bottom currents in submarine canyons (opposing arrows), and baroclinic currents (not shown) related to internal waves/tides (Shanmugam, 2008c, 2013a), are discussed in Part 2 of this article. Reproduced from Shanmugam, G. (2003). Deep-marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons. Marine and Petroleum Geology 20, 471–491.

mass transport in submarine canyons, (7) to emphasize the social and economic consequences of MTDs, and (8) to evaluate reservoir characterization of MTDs.

International Projects and Symposiums MTDs are ubiquitous in both submarine and subaerial environments (Fig. 3). In understanding submarine mass-transport processes and their deposits, major international projects and symposiums have been organized during the past three decades. Selected examples are as follows: 1. 2. 3. 4. 5.

Arctic Delta Failure Experiment (ADFEX): 1989–92 Geological Long-Range Inclined Asdic (GLORIA), a side-scan survey of the US Exclusive Economic Zone: 1984–91 Sediment Transport on European Atlantic Margins (STEAM): 1993–96 European North Atlantic Margin (ENAM II): 1996–99 STRATA FORmation on the Margins (STRATAFORM): 1995–2001

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Fig. 2 Multibeam bathymetric image of the US Pacific margin, offshore Los Angeles (California), showing well-developed mass-transport deposits (MTDs) on continental slopes. The Palos Verdes MTD (dashed line) covers about 50 km3, and it has been dated to be about 7500 years BP (Normark et al., 2004). Note distinct shelf, slope, and basin settings. The canyon head of the Redondo Canyon is at a water depth of 10 m near the shoreline. MTD, mass-transport deposits. Vertical exaggeration is 6. Modified from USGS (US Geological Survey) (2007). Perspective view of Los Angeles Margin. http://wrgis.wr.usgs.gov/dds/dds-55/pacmaps/la_ pers2.html (Accessed 11.05.08).

6. Seabed Slope Process in Deep Water Continental Margin (Northwest Gulf of Mexico): 1996–2004 7. Continental Slope Stability (COSTA): 2000–04 8. IGCP-511 (IUGS-UNESCO’s International Geoscience Programme 511, which ended in 2009) and IGCP-585 (E-MARSHAL: Earth’s continental MARgins: asSessing the geoHAzard from submarine Landslides) projects (http://www.igcp585.org/; Accessed 08.09.15) include the following: (a) 2002: First International Symposium on “Submarine Mass Movements and Their Consequences”: Nice, France (Locat and Meinert, 2003) (b) 2005: Second International Symposium on “Submarine Mass Movements and Their Consequences”: Oslo, Norway (Solheim, 2006) (c) 2007: Third International Symposium on “Submarine Mass Movements and Their Consequences”: Santorini Is., Greece (Lykousis et al., 2007) (d) 2009: Fourth International Symposium on “Submarine Mass Movements and Their Consequences”: Austin, Texas, the United States (Mosher et al., 2010) (e) 2011: Fifth International Symposium on “Submarine Mass Movements and Their Consequences”: Kyoto, Japan, 2011 (Yamada et al., 2012) (f ) 2013: Sixth International Symposium on “Submarine Mass Movements and Their Consequences”: Kiel, Germany (Krastel et al., 2014) Continental margins provide an ideal setting for slope failure, which is the collapse of slope sediment from the shelf edge. Following a failure, the failed sediment moves downslope under the pull of gravity when the shear stress exceeds the shear strength of the soil. Gravity-driven processes exhibit extreme variability in mechanics of sediment transport, ranging from mobility of kilometer-size solid blocks on the seafloor to transport of millimeter-size particles in suspension of dilute turbulent flows in deepwater


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Table 1 Worldwide large subaerial and submarine mass-transport deposits (MTDs) and their sizes (volume), triggering mechanisms, and damages in the twentieth and 21st centuries. The term “landslide” was originally used to describe these examples Year

Location

Name and type

Triggering mechanism

Size, damage, and loss of human life

1911

Tajikistan

Usoy MTDs

1914

Argentina

1919

Indonesia (Java)

Rio Barrancas and Rio Colorado debris flow Kelut MTDs

Usoy earthquake Magnitude 7.4 Failure of ancient MTD dam Eruption of Kelut volcano

1920 1920

China, Gansu, Haiyuan Mexico

Rio Huitzilapan debris flows

1921

Kazakh Republic

Alma-Ata debris flow

2,000,000,000 m3 54 deaths 2,000,000 m3 Length of flow: 300 km 185 km (length) Lahars caused 5110 deaths and destroyed or damaged 104 villages 50,000 km2 (area) 100,000 þ deaths > 40 km (length) 600–870 deaths 500 deaths

1933

China (Sichuan)

Deixi MTDs

1938

Japan (Hyogo)

Mount Rokko MTDs

1941

Peru

Huaraz debris flow

1945

Peru

Cerro Condor-Sencca MTDs

1949

Khait MTDs

1953

Tajikistan (Tien Shan Mountains) Japan (Wakayama)

Arida River MTDs

1953

Japan (city of Kyoto)

Arida River MTDs

Failure of moraine dam Erosional undercutting Khait earthquake Magnitude 7.4 Rainfall Major typhoon (cyclone) Rainfall

1958

Japan (Shizuoka)

Kanogawa MTDs

Rainfall

1960

Chile

Rupanco region MTDs

1962

Peru (Ancash)

Nevados Huascarán MTDs

Valdivia earthquake Magnitude 7.5 Preceded by heavy rain Not known

1963

Italy (Friuli–Venezia Giulia) The United States (Alaska)

Vaiont Reservoir MTDs

Not known

Alaska earthquake MTDs (also known as “Prince William Sound earthquake”)

Alaska earthquake Magnitude 9.0

1965

China (Yunnan)

MTDs

Not known

1966 1970

Brazil (Rio de Janeiro) Peru (Ancash)

MTDs Nevados Huascarán MTDs

1974

Peru

Mayunmarca MTDs

Rainfall Earthquake Magnitude 7.7 Rainfall

1976

Guatemala

Guatemala earthquake MTDs

1980

China (Yichang, Hubei)

Yanchihe MTDs

1980

The United States (Washington)

Mount St. Helens MTDs

1964

Loess flows, MTDs

Haiyuan earthquake Magnitude 8.5 Earthquake Magnitude 6.5–7.0 Snow melt, subsequent rainfall Deixi earthquake Magnitude 7.5 Rainfall

Guatemala earthquake Magnitude 7.5 Mining activity— occurred on manmade layered slopes Eruption of Mount St. Helens volcano

> 150,000,000 m3 2500 deaths 505 deaths or missing; 130,000 homes were destroyed or badly damaged 10,000,000 m3 4000–6000 deaths 5,500,000 m3 13 bridges were destroyed 245,000,000 m3 7200 deaths 1046 deaths

336 deaths 5122 homes were destroyed 1094 deaths 19,754 homes were destroyed 40,000,000 m3 210 deaths

13,000,000 m3 4000–5000 deaths 250,000 000 m3 2000 deaths 211,000,000 m3 Submarine lMTD at Seward; Turnagain Heights MTD 9,600,000 m3 Loss: $280,000,000 (1964); 122 deaths 450,000 000 m3 444 deaths 1000 deaths 30,000,000–50,000 000 m3 18,000 deaths 1,600,000,000 m3 450 deaths 10,000 MTDs over an area of 16,000 km2 200 deaths 150,000,000 m3 284 deaths This is the world’s largest historical MTD 3,700,000,000 m3 250 homes, 47 bridges, 24 km of rail, and 298 km of highway were destroyed; 57 deaths (Continued )

10

Table 1


(Continued)

Year

Location

Name and type



1983

The United States (Utah)

Thistle MTDs

Snow melt and subsequent rainfall

1983

China (Gansu)

Saleshan MTDs

Rainfall

1983

Ecuador

Chunchi MTDs

1985

Colombia (Tolima)

Nevado del Ruiz debris flows

1985

MTDs

1987

Puerto Rico (Mameyes) Papua, New Guinea (East New Britain) Ecuador (Napo)

Reventador MTDs

1987

Venezuela

Rio Limon, debris flow

Rain and/or snow (wettest year of century) Eruption of Nevado del Ruiz volcano Rainfall from tropical storm Bairaman earthquake Magnitude 7.1 Reventador earthquakes Magnitudes 6.1 and 6.9 and rainfall Rainfall

21,000,000 m3 This is the most expensive disaster to fix in US history with a loss of $600,000,000 (1983) 35,000,000 m3 237 deaths 1,000,000 m3 150 deaths

1987

Colombia

Villa Tina MTDs

Pond leakage

1988

Brazil

Rainfall

1989

Rainfall

221 deaths

Touzhai MTDs

Rainfall

1991

China (Huaying, Sichuan) China (Zhaotong, Yunnan) Chile

Rio de Janeiro and Petropolis MTDs Xikou MTDs

2,000,000 m3 210 deaths 20,000,000 m3 217 deaths Approximately 300 deaths

Antofagasta debris flows

Rainfall

1993

Ecuador

La Josefina MTDs

1994

Colombia (Cauca)

Paez MTDs

1998

Large MTDs MTDs MTDs

Rainfall Rainfall

More than 100 individual slope failures Hurricane Mitch caused torrential rainfall. Approximately 10,000 deaths

MTDs

Rainfall

1999

Northern India (Malpa Himalayan region) Italy (Campania) Honduras, Guatemala, Nicaragua, El Salvador Venezuela (Vargas, northern coastal area) Taiwan

Mine excavation and heavy rainfall Paez Earthquake Magnitude 6.0 Rainfall

18,000,000 m3 216 deaths 500,000,000–700,000,000 m3 “Hundreds” of deaths were reported 20,000,000–25,000,000 m3 13 bridges destroyed 250 km2 (area) 272 deaths 221 deaths

MTDs

2000

Tibet

Yigong MTD

2001

El Salvador

MTDs, lateral spreading, liquefaction

2002

Russia (North Ossetia)

Kolka Glacier debris flows

Chi-Chi earthquake Magnitude 7.3 Meltwater from snow and glacier Two earthquakes January 13, 2001: Magnitude 7.7 February 13, 2001: Magnitude 6.6 Detachment of large glacier, causing a debris flow

Nearly 1 m of heavy rain fell in a 3-day period. There were as many as 30,000 deaths Loss: $1,900,000,000 in 2001 11,000 km2 (area) 158 deaths 100,000 000 m3 109 deaths The January earthquake caused MTDs over a 25,000 km2 area (including parts of Guatemala). The February earthquake caused MTDs over a 2500 km2 area 585 deaths

2003

Sri Lanka (Ratnapura and Hambantota) The United States (San Bernardino County, California)

MTDs

Rainfall

Debris flows

Rainfall

1986

1991

1998 1998

1999

2003

Bairaman MTDs

23,000 deaths 129 deaths 200,000,000 m3 75,000,000–110,000,000 m3 1000 deaths

Travel distance: 19.5 km 110,000,000 m3 volume of glacial ice deposited 2,000,000–5,000,000 m3 of ice debris at end of runout 125 deaths 24,000 homes and schools destroyed 260 deaths > 1,000,000 m3 (total volume) 16 deaths


Table 1

11

(Continued)

Year

Location

Name and type



2005

Pakistan and India

MTDs

2006

MTDs

2008

The Philippines (Leyte) China (Sichuan)

Kashmir earthquake Magnitude 7.6 Rainfall

MTDs

Wenchuan earthquake Magnitude 8.0

2008

Egypt (East Cairo)

Al-Duwayqa MTD

2010

Uganda (Bududa)

Debris flows

Destabilization due to man-made construction Heavy rainfall

2010

Brazil (Rio de Janeiro)

Debris flows

Heavy rainfall

Thousands of MTDs 25,500 deaths 15,000,000 m3 1100 deaths 15,000 MTDs 20,000 deaths Still being assessed Affected area was 6500 m3 volume and rocks weighed about 18,000 tons 107 deaths 400 þ deaths Still being assessed 350 deaths Still being assessed

Source: USGS (US Geological Survey) (2010). Worldwide overview of large landslides of the 20th and 21st centuries. http://landslides.usgs.gov/learning/majorls.php (Accessed 01.02.13).

environments (Shanmugam, 2009). In communicating this variability without confusion, a review of soil mechanics, nomenclature, and classification of downslope processes is necessary.

Mechanics of Sediment Failure and Sliding Sediment failures on continental margins are controlled by the pull of gravity, the source of the material (bedrock vs. regolith), the strength of the soil (grain size, mineralogy, compaction, cementation, etc.), the weight of the material, the slope angle, the porewater pressure, and the planes of weaknesses. In order to evaluate sediment failures in general, one needs to conduct a slope stability analysis for describing the sediment behavior and sediment strength during loading or deformation.

Soil Strength and Slope Stability The most fundamental requirement of slope stability is that the shear strength of the soil must be greater than the shear stress required for equilibrium (Duncan and Wright, 2005; Shanmugam, 2014a). The two conditions that result in slope instability are (1) a decrease in the shear strength of the soil and (2) an increase in the shear stress required for equilibrium. The decrease in the shear strength of the soil is caused by various in situ processes, such as an increase in pore-water pressure, cracking of the soil, swelling of clays, and leaching of salt. The increase in shear stress is induced by loads at the top of the slope and an increase in soil weight due to increased water content, seismic shaking, etc. A common method for calculating the slope stability is the “limit equilibrium analyses” in soil mechanics. A stable slope can be maintained only when the factor of safety for slope stability (F) is larger than or equal to 1 (Duncan and Wright, 2005, Eq. 6.1 and 13.2): F¼

S Shear strength of the soil ¼ 1 t Shear stress required for equilibrium

where S ¼ available shear strength, which depends on the soil weight, cohesion, friction angle, and pore-water pressure, and t ¼ equilibrium shear stress, which is the shear stress required to maintain a just-stable slope. It depends on the soil weight, porewater pressure, and slope angle. The shear strength is equal to the maximum shear stress that can be absorbed by the slope without failure and can be defined by the Mohr–Coulomb failure criterion: S ¼ c þ s tan f where S ¼ available shear strength (Fig. 4A), c ¼ cohesion (nonfrictional) component of the soil strength, s ¼ total normal stress acting on the failure surface, and ’ ¼ angle of internal friction of the soil. By combining the equations of shear strength and Mohr–Coulomb failure criterion, the factor of safety (F) can be expressed as

12


Table 2 Comparison of large-volume (>100 km3) mass-transport deposits (MTDs) in submarine environments with four of the largest MTD in subaerial environments Volume (km3)

Environment (age)

Comments

1. Agulhas Slump, SE African margin (Dingle, 1977)

20,331

Submarine (postPliocene)

2. Chamais Slump, SE African margin (Dingle, 1980) 3. Nuuanu Debris Avalanche, NE Oahu, Hawaii (Moore et al., 1994; Normark et al., 1993)

17,433 5000

Submarine (Neogene) Submarine (2.7 Ma, Ward, 2001)

4. Storegga Slide, offshore Norway (Bugge et al., 1987; Haflidason et al., 2005) 5. WMTD, Amazon Fan, equatorial Atlantic (Piper et al., 1997)

2400–3200

Submarine (8100 years BP)

The world’s largest submarine MTD triggered by earthquakes Triggered by earthquakes Triggered by volcanic activity; debris avalanche is a velocity-based term (see text) Triggered by earthquakes

2000

Submarine (Late Pleistocene)

6. Insular Slope Slide, Puerto Rico (Schwab et al., 1993) 7. Brunei Slide, NW Borneo (Gee et al., 2007)

1500 1200

Submarine (Quaternary?) Submarine (Quaternary?)

8. Saharan debris flow, NW African margin (Embley, 1976; Embley and Jacobi, 1977; Gee et al., 1999)

600–1100

Submarine (60,000 years BP)

1000

Submarine (Pleistocene)

1000 900 200–800

MTD (reference)

9. Orotava–Icod–Tino debris avalanche, NW African slope (Wynn et al., 2000) 10. Slump Complex, Israel (Frey-Martinez et al., 2005) 11. Bassein slide, Sunda Arc, NE Indian Ocean (Moore et al., 1976) 12. Alika 1 and 2 debris avalanches, NE Oahu, Hawaii (Normark et al., 1993) 13. Nile MTC, offshore Egypt (Newton et al., 2004)

670

Submarine (Plio-Quaternary) Submarine (Late Quaternary) Submarine (300000–105,000 years BP) Submarine (Quaternary)

14. Copper River slide, Kayak trough, northern Gulf of Alaska (Carlson and Molnia, 1977) 15. MTC 1, Trinidad (Moscardelli et al., 2006)

590

Submarine (Holocene)

242

Submarine (Plio-Pleistocene)

200

Submarine (Pleistocene)

185–200

Submarine (1929)

165

Submarine (24–50 ka)

160

Submarine (15–20 ka)

152

Submarine (Holocene)

60

Submarine (Pliocene and Pleistocene) Submarine (Holocene) Subaerial (21–22 Ma)

16. Cape Fear MTD, The Carolina trough, the US Atlantic margin (Lee, 2009; Popenoe et al., 1993) 17. The 1929 Grand Banks MTD, off the US Atlantic coast and Canada (Bornhold et al., 2003; Driscoll et al., 2000; Heezen and Ewing, 1952; Piper and Aksu, 1987) 18. Currituck Slide, the US Atlantic margin (Locat et al., 2009) 19. East Breaks Slide (western lobe), NW Gulf of Mexico (McGregor et al., 1993) 20. MTD, Mississippi Canyon area, Gulf of Mexico (McAdoo et al., 2000) 21. Jan Mayen Ridge, Norwegian–Greenland Sea (Laberg et al., 2014) 22. Owen Ridge, Oman coast, Arabian Sea (Rodriguez et al., 2013) 23. Markagunt gravity slide, southwest Utah (the United States) (Hacker et al., 2014) 24. Saidmarreh slide, Kabir Kuh anticline, SW Iran (Harrison and Falcon, 1938)

40 1700–2000

25. Mount St. Helens, the United States (Schuster, 1983; Tilling et al., 1990)

2.8

Subaerial (10,370 120 years BP; Shoaei and Ghayoumian, 1998) Subaerial (May 18, 1980)

26. Usoy, Tadzhik Republic (formerly the USSR) (Bolt et al., 1975)

2.0

Subaerial (1911)

20

WMTDs: western mass-transport deposits. Possibly triggered during falling sea level (Damuth et al., 1988) Triggered by earthquakes Triggered by sediment loading, gas hydrates, and earthquakes Long-runout volcaniclastic debris flows of over 400 km on gentle slopes that decrease to as little as 0.05 Debris avalanche is a velocity-based term (see text) Triggered by earthquakes Triggered by earthquakes Triggered by volcanic activity; debris avalanche is a velocity-based term (see text) MTC, mass-transport complex; triggered by rapid sedimentation Possibly triggered by earthquakes and rapid sedimentation MTC 1, mass-transport complex 1; triggered by tectonic activity and rapid sedimentation Triggered by salt tectonism and gashydrate decomposition Triggered by earthquakes M ¼ 7.2 Triggered by earthquakes and high pore pressure Possibly triggered by salt tectonism Triggered by salt tectonism and rapid sedimentation Retrogressive movement Retrogressive slumps The world’s largest prehistoric subaerial volcanic MTD The world’s second largest prehistoric subaerial MTD triggered by earthquakes The world’s largest historic subaerial MTD triggered by volcanic eruption (USGS, 2004) The world’s second largest historic subaerial MTD triggered by earthquakes M ¼ 7.4 (USGS, 2010)

Note that the world’s largest submarine MTD (20,331 km3) is ten times volumetrically larger than the world’s largest subaerial MTD (2000 km3). The term “landslide” was used to describe many of these examples by the original authors. The locations of selected examples are shown in Fig. 3. Compiled from several sources.


13

Fig. 3 Map showing 50 examples (locations) of submarine (black triangle) and subaerial (white triangle) mass-transport deposits (MTDs) that are often erroneously called “landslides.” Submarine and subaerial classification of each MTD denotes its depositional setting. Note locations of core studies (numbered yellow circles) and outcrop studies (numbered red circles) of deepwater successions carried out by the present author worldwide on MTDs and SMTDs (see Table 3 for details). Blank world map credit: http://upload.wikimedia.org/wikipedia/commons/8/83/Equirectangular_projection_SW.jpg (Accessed 05.09.15). Reproduced from Shanmugam, G. (2015). The landslide problem. Journal of Palaeogeography 4, 109–166.

F¼

c þ s tan f t

A sediment failure is initiated when the factor of safety for slope stability (F) is 800 km. It has a scar area of 27,000 km2 and a headwall length of 300 km (Solheim et al., 2005a). The Storegga Slide on the southern flank of the plateau exhibits mounded seismic patterns in sparker profiles. Although it is called a slide in publications, the sediment core of this deposit is composed primarily of slumps and debrites. Unlike kilometer-wide modern slides that can be mapped using multibeam mapping systems and seismic reflection profiles, huge ancient slides are difficult to recognize in outcrops


27

Fig. 12 Outcrop photograph showing sheetlike geometry of an ancient sandy submarine slide (1000 m long and 50 m thick) encased in deepwater mudstone facies. Note the large sandstone sheet with rotated/slumped edge (left). Person (arrow): 1.8 m tall. Ablation Point Formation, Kimmeridgian (Jurassic), Alexander Island, Antarctica. Photo courtesy of D.J.M. Macdonald. Reproduced from Macdonald, D. I. M., Moncrieff, A. C. M. and Butterworth, P. J. (1993). Giant slide deposits from a Mesozoic fore-arc basin, Alexander island, Antarctica. Geology 21, 1047–1050.

because of limited sizes of outcrops on land (Woodcock, 1979). A summary of width-to-thickness ratio of modern and ancient slides is given in Table 6.

Slumps A slump is a coherent mass of sediment that moves on a concave-up glide plane and undergoes rotational movements causing internal deformation (Fig. 7A). Slumps represent rotational shear-surface movements. In multibeam bathymetric data, distinguishing slides from slumps may be difficult because internal deformation cannot always be resolved. In seismic profiles, nonetheless, slumps may be recognized because of their chaotic reflections. Therefore, a general term mass transport is preferred when interpreting bathymetric images. Slumps are capable of transporting gravel and coarse-grained sand because of their inherent strength. The general characteristics of slumps are as follows:

• • • • • • • • • •

Gravel to mud lithofacies Basal zone of shearing (core and outcrop) Upslope areas with tensional faults (Fig. 14) Downslope edges with compressional folding or thrusting (i.e., toe thrusts) (Fig. 14) Slump folds (Helwig, 1970) interbedded with undeformed layers (core and outcrop) (Figs. 15 and 16) Irregular upper contact (core and outcrop) Chaotic bedding in heterolithic facies (core and outcrop) Rotated elongate grains (Maltman, 1987) (microscopic) Grain fractures (Maltman, 1994) (microscopic) Steeply dipping and truncated layers (core and outcrop) (Fig. 17)

28


Fig. 13 (A) Sketch of a cored interval showing blocky wireline log motif of a sandy slide/slump unit. (B) Sedimentologic log showing details. VF, very fine sand; F, fine sand; injected sand, natural injection of sand into host mudstone; primary glide plane (décollement), the basal primary slip surface along which major displacement occurs; shear zone, interval of a rock unit that has been crushed and brecciated by many subparallel fractures due to shear strain; secondary glide plane, internal slip surface along which minor displacement occurs; floating mud clasts, occurrence of mud clasts at some distance above the basal contact. (C) Core photograph showing an upper sand interval (light color) and a lower mudstone interval (dark color). The basal contact (arrow) is interpreted as a primary glide plane (a décollement) of a sandy slide/slump. Note a sand dike (i.e., injectite) at the base of shear zone. Eocene, North Sea. Compare this small-scale slide (15 m thick) with a large-scale slide (50 m thick) in Fig. 12. Reproduced from Shanmugam, G. (2006). Deep-water processes and facies models: implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier.

Table 6

Dimensions of modern and ancient mass-transport deposits (MTDs) and turbidites

Example

Width-to-thickness ratio (observed dimensions)

Slide, Lower Carboniferous, England (Gawthorpe and Clemmey, 1985) Slide, Cambrian–Ordovician, Nevada (Cook, 1979) Slide, Jurassic, Antarctica (Macdonald et al., 1993) Slide, Modern, US Atlantic margin (Booth et al., 1993) Slide, Modern, Gulf of Alaska (Carlson and Molnia, 1977) Slide, middle Pliocene, Gulf of Mexico (Morton, 1993) Slide/slump/debrite/turbidite, 5000–8000 BP, Norwegian continental margin (Jansen et al., 1987) Slump, Cambrian–Ordovician, Nevada (Cook, 1979) Slump, Aptian–Albian, Antarctica (Macdonald et al., 1993) Slump/slide/debrite, lower Eocene, Gryphon Field, the United Kingdom (Shanmugam et al., 1995) Slump/slide/debris flow, Paleocene, Faeroe Basin, north of Shetland Islands (Shanmugam et al., 1995) Slump, Modern, SE Africa (Dingle, 1977) Slump, Carboniferous, England (Martinsen, 1989) Slump, lower Eocene, Spain (Mutti, 1992) Debrite, Modern, British Columbia (Prior et al., 1984) Debrite, Cambrian–Ordovician, Nevada (Cook, 1979) Debrite, Modern, US Atlantic margin (Embley, 1980) Debrite, Quaternary, Baffin Bay (Hiscott and Aksu, 1994) Debrite, Modern, NW African margin (Masson et al., 1997) Turbidite (depositional lobe), Cretaceous, California (Weagant, 1972) Turbidite (depositional lobe), lower Pliocene, Italy (Casnedi, 1983) Turbidite (basin plain), Miocene, Italy (Ricci Lucchi and Valmori, 1980) Turbidite (basin plain), 16,000 BP, Hatteras Abyssal Plain (Pilkey, 1988)

7:1 (100 m wide/long, 15 m thick) 30:1 (30 m wide/long, 1 m thick) 45:1 (20 km wide/long, 440 m thick) 40–80:1 (2–4 km wide/long, 50 m thick) 130:1 (15 km wide/long, 115 m thick) 250:1 (150 km wide/long, 600 m thick) 675:1 (290 km wide/long, 430 m thick) 10:1 (100 m wide/long, 10 m thick) 10:1 (3.5 km wide/long, 350 m thick) 21:1 (2.6 km wide/long, 120 m thick) 28:1 (7 km wide/long, 245 m thick) 171:1 (64 km wide/long, 374 m thick) 500:1 (5 km wide/long, 10 m thick) 900–3600:1 (18 km wide/long, 5–20 m thick) 12:1 (50 m wide/long, 4 m thick) 30:1 (300 m wide/long, 10 m thick) 500–5000:1 (10–100 km wide/long, 20 m thick) 1250:1 (75 km wide/long, 60 m thick) 3000–5000:1 (60–100 km wide, up to 20 m thick) 167:1 (10 km wide/long, 60 m thick) 1200:1 (30 km wide/long, 25 m thick) 11,400:1 (57 km wide/long, 5 m thick) 125,000:1 (500 km wide/long, 4 m thick)


29

Fig. 14 Sketch of a submarine slump sheet showing tensional glide plane in the updip detachment area and compressional folding and thrusting in the downdip frontal zone. Reproduced from Lewis, K. B. (1971). Slumping on a continental slope inclined at 1 –4 . Sedimentology 16, 97–110.

Fig. 15 Core photograph showing alternation of contorted and uncontorted siltstone (light color) and clay stone (dark color) layers of slump origin. This feature is called slump folding. Paleocene, North Sea. Reproduced from Shanmugam, G. (2006). Deep-water processes and facies models: Implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier.

30


Fig. 16 Outcrop photograph showing slump-folded heterolithic facies (arrow) overlain by undeformed deepwater sandstone. Eocene, La Jolla, California.

• • • • • •

Duplex-like structures (Shanmugam et al., 1988b) Associated slides (core and outcrop) (Fig. 12) Associated sand injections (core and outcrop) (Fig. 17) Lenticular to sheetlike geometry with irregular thickness (seismic and outcrop) Contorted bedding has been recognized in Formation MicroImager (FMI) (Hansen and Fett, 2000, their Fig. 11) Chaotic facies in high-resolution seismic profiles

Distinguishing between debris flows and turbidity currents Sediment flows (i.e., sediment-gravity flows) are composed of four types: (1) debris flow, (2) turbidity current, (3) fluidized sediment, and (4) grain flow (Middleton and Hampton, 1973). In this article, the focus is on debris flows and turbidity currents because of their importance. These two processes are distinguished from one another on the basis of fluid rheology and flow state. The rheology of fluids can be expressed as a relationship between applied shear stress and rate of shear strain (Fig. 18). Newtonian fluids (i.e., fluids with no inherent strength), like water, will begin to deform the moment shear stress is applied and the deformation is linear. In contrast, some naturally occurring materials (i.e., fluids with strength) will not deform until their yield stress has been exceeded (Fig. 18); once their yield stress is exceeded, deformation is linear. Such materials (e.g., wet concrete) with strength are considered to be Bingham plastics (Fig. 18). For flows that exhibit plastic rheology, the term plastic flow is appropriate. Using rheology as the basis, deepwater sediment flows are divided into two broad groups, namely, (1) Newtonian flows that represent turbidity currents and (2) plastic flows that represent debris flows. In addition to fluid rheology, flow state is used in distinguishing laminar debris flows from turbulent turbidity currents. The difference between laminar and turbulent flows was demonstrated in 1883 by Osborne Reynolds, an Irish engineer, by injecting a thin stream of dye into the flow of water through a glass tube. At low rates of flow, the dye stream traveled in a straight path. This regular motion of fluid in parallel layers, without macroscopic mixing across the layers, is called a laminar flow. At higher flow rates, the dye stream broke up into chaotic eddies. Such an irregular fluid motion, with macroscopic mixing across the layers, is called a


31

Fig. 17 Summary of features associated with slump deposits observed in core and outcrop. Slump fold, an intraformational fold produced by deformation of soft sediment; contorted layer, deformed sediment layer; basal shear zone, the basal part of a rock unit that has been crushed and brecciated by many subparallel fractures due to shear strain; glide plane, slip surface along which major displacement occurs; brecciated zone, an interval that contains angular fragments caused by crushing of the rock; dish structures, concave-up (like a dish) structures caused by upward-escaping fluids in the sediment; clastic injections, natural injection of clastic (transported) sedimentary material (usually sand) into a host rock (usually mud). Reproduced from Shanmugam, G., Bloch, R. B., Mitchell, S. M., Beamish, G. W. J., Hodgkinson, R. J., Damuth, J. E., Straume, T., Syvertsen, S. E. and Shields, K. E. (1995) Basin-floor fans in the north Sea: Sequence stratigraphic models vs. Sedimentary facies. AAPG Bulletin 79. 477–512, with permission from AAPG.

turbulent flow. The change from laminar to turbulent flow occurs at a critical Reynolds number (the ratio between inertia and viscous forces) of about 2000 (Fig. 18).

Debris Flows A debris flow is a sediment flow with plastic rheology and laminar state from which deposition occurs through freezing en masse. The terms debris flow and mass flow are used interchangeably because each exhibits plastic flow behavior with shear stress distributed throughout the mass (Nardin et al., 1979). In debris flows, intergranular movements predominate over shear-surface movements. Although most debris flows move as incoherent mass, some plastic flows may be transitional in behavior between coherent mass movements and incoherent sediment flows (Marr et al., 2001). Debris flows may be mud-rich (i.e., muddy debris flows), sand-rich (i.e., sandy debris flows), or mixed types. In multibeam bathymetric data, recognition of debrites is possible. Debris flows are capable of transporting gravel and coarse-grained sand because of their inherent strength. The general characteristics of muddy and sandy debrites are as follows:

• • • • •

Gravel to mud lithofacies Floating or rafted mudstone clasts near the tops of sandy beds (core and outcrop) (Fig. 19) Floating armored mudstone balls in sandy matrix (core and outcrop) Planar clast fabric (core and outcrop) (Fig. 19) Projected clasts (core and outcrop) (Fig. 20)

Fig. 18 Graph showing rheology (stress–strain relationships) of Newtonian fluids and Bingham plastics. Note that the fundamental rheological difference between debris flows (Bingham plastics) and turbidity currents (Newtonian fluids) is that debris flows exhibit strength, whereas turbidity currents do not. Reynolds number is used for determining whether a flow is turbulent (turbidity current) or laminar (debris flow) in state. Compiled from several sources (Dott, 1963; Enos, 1977; Middleton and Wilcock, 1994; Phillips and Davies, 1991; Pierson and Costa, 1987). Reproduced from Shanmugam, G. (1997a). The Bouma Sequence and the turbidite mind set. Earth-Science Reviews 42, 201–229.

Fig. 19 Core photograph of massive fine-grained sandstone showing floating mudstone clasts (above the scale) of different sizes. Note planar clast fabric (i.e., long axis of clast is aligned parallel to bedding surface), revealed by the projected part of the clast, suggesting deposition from a laminar sandy debris flow. Note sharp and irregular upper bedding contact (top of photo). Paleocene, North Sea. Modified from Shanmugam, G. (2006). Deep-water processes and facies models: Implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier.


33

Fig. 20 Underwater photograph showing a pocket of rounded cobbles up to 15 cm in diameter in massive sandy matrix at a depth of 130 m (427 ft) in Los Frailes Canyon, Baja California. Note projected nature of clasts from the upper sediment surface. Photo by R.F. Dill. After Shepard and Dill (1966), Rand McNally & Company. Published in Shanmugam, G. (2012a). New perspectives on deep-water sandstones: Origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier..

Fig. 21 Photograph showing larger pumice blocks near the front of a volcanic debris flow associated with the eruption of the Mount St. Helens on May 18, 1980. This type of depositional mechanism would result in inverse grading in the rock record. Photo by Leighley, T. A., USGS, 17 October 1980. Credit: http://libraryphoto. cr.usgs.gov/cgi-bin/show_picture.cgi?ID¼ID.CVO-F.73ct&SIZE¼large (Accessed 27.02.11).

34


Fig. 22 Outcrop photograph showing inverse grading with floating boulder-size clasts near the top of sandstone unit (arrow). Note random fabric of clasts. Middle Miocene, San Onofre Breccia, Dana Point, California. This lithofacies has been interpreted to be sandy debrite associated with alluvial fan and fan delta. Reproduced from Shanmugam, G. (2012a). New perspectives on deep-water sandstones: origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier.

Fig. 23 Side view of flume tank showing strong debris flows with well-developed snout. Note the absence of turbulent suspension on top. Also note irregular upper surface caused by sudden freezing of the flow. Deformation in the front suggests strongly coherent character of flow, which may be called a slump. Reproduced from Shanmugam, G. (2006). Deep-water processes and facies models: Implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier.

• • •

Imbricate clasts (experiment) (Major, 1998) Brecciated mudstone clasts in sandy matrix (core and outcrop) Concentration of larger clasts (pumice blocks) near the front of volcanic debris flows or lahars (Fig. 21), which would result in inverse grading of clasts in the rock record

•

Inverse grading of clasts and rock fragments with random fabric (core and outcrop) (Fig. 22)


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Fig. 24 (A) Outcrop photograph showing sheetlike geometry of a sandy debrite unit (arrow). See Bouma and Coleman (1985, their Fig. 3) for a similar view of this unit. (B) Close-up view of a floating mudstone clast in the middle of the sandstone unit. Annot sandstone (Eocene–Oligocene), Peïra Cava area, French Maritime Alps. Reproduced from Shanmugam, G. (2002b). Ten turbidite myths. Earth-Science Reviews 58, 311–341.

• • • • • • • • • • •

Inverse grading of quartz granules in sandy matrix (core and outcrop) Inverse grading, normal grading, inverse to normal grading, and absence of any grading of matrix (core and outcrop) Floating quartz granules in sandy matrix (core and outcrop) Pockets of gravels in sandy matrix (core and outcrop) Preservation of delicate mud fragments with planar fabric in sandy matrix (core and outcrop) Irregular snout (experiment) (Fig. 23) Irregular, sharp upper contacts (core and outcrop) Side-by-side occurrence of garnet granules (density: 3.5–4.3) and quartz granules (density: 2.65) (core and outcrop) Lenticular to sheet in geometry (Fig. 24) Lobe-like geometry (map view) in the Gulf of Mexico (Fig. 25) Tonguelike geometry (map view) in the North Atlantic (Fig. 26)

The modern Amazon submarine channel has two major debrite deposits (east and west) (Damuth and Embley, 1981; Piper et al., 1997). The western debrite unit is about 250 km long, 100 km wide, and 125 m thick. In the US Atlantic margin, debrite units are about 500 km long, 10–100 km wide, and 20 m thick (Fig. 26). On the NW African continental margin, the Canary debrite is 60–100 km wide and 5–20 m thick and traveled about 600 km (Masson et al., 1997). A summary of width-to-thickness ratio of modern and ancient debrites is given in Table 6. Based on experimental sandy debris flows showing detached blocks (Shanmugam, 2000), on documented long-runout natural sandy debris flows in modern oceans (Gee et al., 1999), and in the ancient record (Teale and Young, 1987), long-runout sandy debrite blocks are viable candidates for developing thick, isolated, sandstone petroleum reservoirs in deepwater environments (Fig. 27). Because of clay-poor nature (Marr et al., 2001), isolated outrunner sandy debrites have great potential for serving as sandstone petroleum reservoirs. So, the petroleum industry needs to be mindful of these new perspectives in developing future petroleum plays.

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Fig. 25 Schematic diagram showing lobe-like distribution of submarine debris flows in front of the Mississippi River Delta, Gulf of Mexico. This shelf-edge deltaic setting, associated with high sedimentation rate, is prone to develop ubiquitous debris flows, mud diapers, and contemporary faults due to depositional loading. Mud diaper, intrusion of mud into overlying sediment causing dome-shaped structure; chute, channel. This region is subjected to frequent and intense cyclonic waves (e.g., Hurricane Katrina in 2005; Shanmugam, 2008b) that also generate mass movements resulting in the destruction of petroleum platforms and pipelines. Reproduced from Coleman, J. M. and Prior, D. B. (1982). Deltaic environments. In: Scholle, P. A. and Spearing, D. (eds.) Sandstone depositional environments, pp. 139–178. Tulsa, OK: American Association of Petroleum Geologists Memoir.

Turbidity Currents A turbidity current is a sediment flow with Newtonian rheology and turbulent state (Fig. 28) in which sediment is supported by turbulence and from which deposition occurs through suspension settling (Dott, 1963; Middleton and Hampton, 1973; Sanders, 1965; Shanmugam, 1996, 2006a). Turbidity currents exhibit unsteady and nonuniform flow behavior (Fig. 29), and they are surgetype waning flows. As they flow downslope, turbidity currents invariably entrain ambient fluid (seawater) in their frontal head portion due to turbulent mixing (Allen, 1985a,b). With increasing fluid content, plastic debris flows may tend to become Newtonian turbidity currents (Fig. 7A). However, not all turbidity currents evolve from debris flows. Some turbidity currents may evolve directly from sediment failures. Although turbidity currents may constitute a distal end-member in basinal areas, they can occur in any part of the system (i.e., shelf edge, slope, and basin). In seismic profiles and multibeam bathymetric images, it is impossible to recognize turbidites as a depositional facies. Turbidity currents cannot transport gravel and coarse-grained sand in suspension because they do not possess the strength like debris flows. The general characteristics of turbidites are as follows:

• • • • • • •

Fine-grained sand to mud Normal grading (core and outcrop) (Fig. 30) Sharp or erosional basal contact (core and outcrop) (Fig. 30) Gradational upper contact (core and outcrop) (Fig. 30) Thin layers, commonly centimeters in thickness (core and outcrop) (Fig. 31) Sheetlike geometry in basinal settings (outcrop) (Fig. 31) Lenticular geometry that may develop in channel-fill settings

In the Hatteras Abyssal Plain (North Atlantic), turbidites have been estimated to be 500 km wide and 4 m thick (Pilkey, 1988). A summary of width-to-thickness ratio of modern and ancient turbidites is given in Table 6.

Fig. 26 Tonguelike distribution of mass flows (i.e., debris flows) in the North Atlantic. Debrite units are about 500 km long, 10–100 km wide, and 20 m thick. Note a debrite tongue has traveled to a depth of about 5250 m water depth. CI, contour intervals. Reproduced from Embley, R. W. (1980). The role of mass transport in the distribution and character of deep-ocean sediments with special reference to the north Atlantic. Marine Geology 38, 23–50. See Fig. 59 for core photographs showing soft-sediment deformation Structures (SSDS) from ODP 150, Site 905.

Fig. 27 Conceptual model showing long-runout sandy debrite blocks away from the shelf edge. Based on studies of sandy debris flows and their deposits in flume experiments (Marr et al., 2001; Shanmugam, 2000), documentation of long-runout sandy debris flows in modern oceans (Gee et al., 1999) and interpretation of long-runout ancient “olistolith” (Teale and Young, 1987). Reproduced from Shanmugam, G. (2012a). New perspectives on deep-water sandstones: origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier.

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Fig. 28 Photograph of front view of experimental turbidity current showing flow turbulence. Photo from experiments conducted by M. L. Natland and courtesy of G. C. Brown. Published in Shanmugam, G. (2012a). New perspectives on deep-water sandstones: origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier.

Fig. 29 Schematic illustration showing the leading head portion of an unsteady, nonuniform, and turbulent turbidity current. Due to turbulent mixing, turbidity currents invariably entrain ambient fluid (seawater) at their head regions. Modified from Allen, J. R. L. (1985). Loose-boundary hydraulics and fluid mechanics: Selected advances since 1961. In: Brenchley, P. J. and Williams, P. J. (eds.) Sedimentology: Recent developments and applied aspects, pp. 7–28. Oxford: Published for the Geological Society by Blackwell Scientific Publications.


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Fig. 30 Core photograph showing turbidite units with sharp basal contact, normal grading, and gradational upper contact. Arrow marks a normally graded unit with fine-grained sand at bottom (light gray) grading into clay (dark gray) near top. Note that these thin-bedded units cannot be resolved on seismic data. Zafiro Field, Pliocene, Equatorial Guinea.

Fig. 31 Outcrop photograph showing tilted thin-bedded turbidite sandstone beds with sheetlike geometry, lower Eocene, Zumaya, northern Spain. Reproduced from Shanmugam, G. (2006). Deep-water processes and facies models: Implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier.

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A Paradigm Shift The turbidite exuberance that dominated the deepwater domain for nearly a century is waning as a consequence of emerging new concepts of SMTDs. In fact, numerous authors have interpreted or reinterpreted sandy and gravelly deepwater deposits as SMTDs in the ancient stratigraphic record (Shanmugam, 2012a, Table 1.2). The turbidite paradigm is fundamentally defective because it is built on facies models, such as the “Bouma sequence” for classic turbidites deposited by low-density turbidity currents (Bouma, 1962) and the “Lowe sequence” for coarse-grained turbidites deposited by HDTCs (Lowe, 1982). These vertical facies models were derived solely from the study of ancient rock record using outcrops, without any empirical data of “sandy turbidity currents” from modern oceans. The primary attraction to the vertical facies model of HDTCs and their deposits, composed of R1, R2, R3, S1, S2, and S3 divisions in ascending order (Lowe, 1982), is that it allows one to interpret ancient deepwater coarse sandstone and conglomerate deposits as turbidites (Mulder, 2011; Mutti, 1992). But turbidite facies models are fatally flawed for the following key reasons: 1. Turbidity currents are inherently low in sediment concentration or low in flow density (Fig. 7B), and hence, true HDTC cannot exist in nature (Shanmugam, 1996, 2000, 2012a).

Fig. 32 (A) Schematic diagram showing an ideal turbidite bed with nine turbidite divisions by combining the five divisions of the “Bouma sequence” (Bouma, 1962) and the five divisions of the “Lowe sequence” of high-density turbidites (Lowe, 1982). According to Lowe (1982), S3 ¼ Ta. On the right-hand column, I have included my interpretation of these divisions. (B) Summary diagram revealing the total lack of empirical data for high-density turbidity currents (see Shanmugam (2012a) for details. (A) Reproduced from Shanmugam, G. (2012a). New perspectives on deep-water sandstones: Origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier.


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2. No one has ever documented empirical data on active “gravelly or sandy turbidity currents” in modern oceans using vertical sediment concentration profiles and grain-size measurements. All claims of modern sandy turbidity currents are dubious (Shanmugam, 2012a). 3. No one has ever documented the vertical facies model showing the R1, R2, R3, S1, S2, and S3 divisions of the Lowe (1982) sequence and the Ta, Tb, Tc, Td, and Te divisions of the Bouma (1962) sequence in ascending order (Fig. 32A) in modern deepsea sediments (Shanmugam, 2000, 2012a). 4. No one has ever replicated turbulent turbidity currents that could carry coarse sand and gravel in suspension in laboratory flume experiments that could produce the R1, R2, R3, S1, S2, and S3 divisions in ascending order (Shanmugam, 2012a). 5. The complete “Bouma sequence” (with Ta, Tb, Tc, Td, and Te divisions) has never been documented in modern deep-sea sediments. Nor has it been reproduced in flume experiments. Furthermore, this model suffers from a lack of sound theoretical basis (Hsü, 2004; Leclair and Arnott, 2005; Sanders, 1965; Shanmugam, 1997a). Leclair and Arnott (2005, p. 4) state that “. . . the debate on the upward change from massive (Ta) to parallel laminated (Tb) sand in a Bouma-type turbidite remains unresolved.” The ultimate objective of facies models is to interpret ancient strata (i.e., the unknown). However, the turbidite facies models, developed exclusively from the ancient strata without validation from the modern environment (i.e., the known), promote circular reasoning (Fig. 32B). Despite the lack of vital validation from modern sediments and the absence of experimental corroboration, the turbidite paradigm grew in popularity due to ten popular myths (Shanmugam, 2002b, 2016a). In stark contrast to elusive HDTC in modern oceans, SMTDs have been documented extensively by direct observations, underwater photographs, and remote-sensing techniques in modern submarine canyons (Shepard and Dill, 1966), on modern submarine fan lobes (Gardner et al., 1996), and on modern continental rise (USGS, 1994). In the total absence of evidence for uniformitarianism (i.e., the modern-ancient link), the original turbidite facies models (Bouma, 1962; Lowe, 1982) and their subsequent derivatives with an alternative nomenclature (Talling et al., 2012), or other explanations (Postma et al., 2014), are inconsequential. Thus, a paradigm shift is in progress.

Triggering Mechanisms A triggering mechanism is defined in this article as “the primary process that causes the necessary changes in the physical, chemical, and geotechnical properties of the soil, which results in the loss of shear strength that initiates the sediment failure and movement.” Commonly, triggering processes are considered “external” with respect to the site of failure. In continental margins, several triggering mechanisms may work concurrently or in tandem (e.g., earthquake-triggered tsunamis). Sowers (1979) articulated the challenge of identifying the single mechanism that is responsible for the failure as follows: “In most cases, several ‘causes’ exist simultaneously; therefore, attempting to decide which one finally produced failure is not only difficult but also technically incorrect. Often the final factor is nothing more than a trigger that sets a body of earth in motion that was already on the verge of failure. Calling the final factor the cause is like calling the match that lit the fuse that detonated the dynamite that destroyed the building the cause of the disaster.” Although more than one triggering mechanism can cause a single process (e.g., debris flows) at a given site, there are no objective criteria to distinguish either the triggering mechanism or the transport process from the depositional record yet (Mulder et al., 2011; Shanmugam, 2006b, 2012b). Nevertheless, an understanding of the multitude of triggering mechanisms is imperative in evaluating sediment failures and related MTDs (Feeley, 2007; Locat and Lee, 2005; Masson et al., 2006). There are at least 21 triggering mechanisms that can initiate sediment failures in subaerial and submarine environments (Table 7). I have classified these mechanisms into three major groups based on their duration of activity (Table 7): (1) shortterm events that last for only a few minutes to several hours, days, or months; (2) intermediate-term events that last for hundreds to thousands of years; and (3) long-term events that last for thousands to millions of years (Shanmugam, 2012a,b). Conceivably, some intermediate-term events may last for a longer duration. The importance here is that short-term events and long-term events are markedly different in their duration. I have discussed each triggering mechanism in some detail elsewhere (Shanmugam, 2012a). Of the 21 mechanisms, the following are selected for discussion.

Earthquakes Tectonic activity is the primary cause of earthquakes. Earthquakes affect the stability of slopes in two ways. First, the acceleration during the seismic ground motion affects the soil in a cyclic manner. Second, the cyclic strains induced by the earthquake loads may reduce the shear strengths of the soil (Duncan and Wright, 2005). Earthquakes are considered to be the single most common triggering mechanism for known historic submarine mass movements (Mosher et al., 2010). Based on the spatial distribution of MTDs on the US Atlantic margin, Twichell et al. (2009) suggested that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were the primary triggering mechanism of sediment failures. Seismic energy released during earthquakes not only can trigger sediment failures but also can promote long-runout MTDs.

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Table 7


Types and duration of triggering mechanisms of sediment failures

Types of triggering 1. Earthquake (Heezen and Ewing, 1952; Henstock et al., 2006) 2. Meteorite impact (Barton et al., 2009/2010; Claeys et al., 2002) 3. Volcanic activity (Tilling et al., 1990) 4. Tsunami waves (Shanmugam, 2006b) 5. Rogue waves (Dysthe et al., 2008) 6. Cyclonic waves (Bea et al., 1983; Prior et al., 1989; Shanmugam, 2008b) 7. Internal waves and tides (Shanmugam, 2013b,c,d, 2014b) 8. Ebb tidal current (Boyd et al., 2008) 9. Monsoonal rainfall (Petley, 2012) 10. Groundwater seepage (Brönnimann, 2011) 11. Wildfire (Cannon et al., 2001) 12. Human activitya (Dan et al., 2007) 13. Tectonic eventsb: (a) tectonic oversteepening (Greene et al., 2006), (b) tensional stresses on the rift zones (Urgeles et al., 1997), (c) oblique seamount subduction (Collot et al., 2001), among others 14. Glacial maxima, loading (Elverhøi et al., 1997, 2002); glacial meltwater (Piper et al., 2012b) 15. Salt movement (Prior and Hooper, 1999) 16. Depositional loading (Behrmann et al., 2006; Coleman and Prior, 1982) 17. Hydrostatic loading (Trincardi et al., 2003) 18. Ocean-bottom currents (Locat and Lee, 2002) 19. Biological erosion in submarine canyons (Dillon and Zimmerman, 1970; Warme et al., 1978) 20. Gas hydrate decomposition (Maslin et al., 2004; Popenoe et al., 1993; Sultan et al., 2004) 21. Sea-level lowstand (Damuth and Fairbridge, 1970; Shanmugam and Moiola, 1982; Shanmugam and Moiola, 1988; Vail et al., 1991)

Environment of sediment emplacement Subaerial and submarine Subaerial and submarine Subaerial and submarine Subaerial and submarine Submarine Subaerial and submarine Submarine Submarine Subaerial Subaerial and submarine Subaerial Subaerial and submarine Subaerial and submarine

Duration Short-term events: a few minutes to several hours, days, or months

Intermediate-term events: hundreds to thousands of years

Submarine Submarine Submarine Submarine Submarine Submarine Submarine Submarine

Long-term events: thousands to millions of years

Compiled from several sources. The change in numbering is to reflect the change in duration of triggering events. Note: Schuster and Wieczorek (2002) reviewed landslide triggers and types. Talling (2014) provided a review of triggers of subaqueous sediment density flows in various settings. Updated after Shanmugam (2012a,b, 2013a). a Although human activity is considered to be the second most common triggering mechanism (next to earthquakes) for known historic submarine mass movements (Mosher et al., 2010), it is irrelevant for interpreting ancient rock record. b Some tectonic events may extend over millions of years.

Meteorite Impact The role of meteorite impact on deepwater sedimentation has not received sufficient attention so far. The Chicxulub asteroid impact at the K–T boundary in northern Yucatán, Mexico, is of interest (Fig. 33). This K–T event had generated major mass movements directly not only by the impact-induced seismic shocks but also by the impact-triggered tsunamis (Claeys et al., 2002; Smit et al., 1996). The Chicxulub event-triggered MTDs and other deposits have been documented at the K–T boundary all around the Gulf of Mexico (Bourgeois et al., 1988; Claeys et al., 2002; Grajales-Nishimura et al., 2000; Lawton et al., 2005; Smit et al., 1996). Seismic energy released during meteorite impacts not only can trigger sediment failures but also can promote long-runout MTDs.

Tsunami Wave Tsunamis are oceanographic phenomena that represent a water wave or series of waves, with long wavelengths and long periods, caused by an impulsive vertical displacement of the body of water by earthquakes, MTDs, volcanic explosions, or extraterrestrial (meteorite) impacts. The transport of tsunami-induced sediment into the deep sea includes mass transport (Shanmugam, 2006b, 2012b). Tsunami wave-related deposition in deepwater environments may be explained in four progressive steps (Fig. 34): (1) triggering stage, (2) tsunami stage, (3) transformation stage, and (4) depositional stage. Tappin et al. (2001) had proposed that


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Fig. 33 Map showing the site of Chicxulub meteorite impact at the K–T boundary in Yucatán, Mexico. Stars represent approximate locations of mass-transport deposits and tsunami-related deposits associated with the Chicxulub impact at the K–T boundary (Bourgeois et al., 1988; Claeys et al., 2002; Grajales-Nishimura et al., 2000; Lawton et al., 2005; Smit et al., 1996; Takayama et al., 2000). Generalized outline of Lower Tertiary Wilcox trend: from several sources (e.g., Lewis et al., 2007; Meyer et al., 2007). Reproduced from Shanmugam, G. (2012a). New perspectives on deep-water sandstones: Origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier.

Fig. 34 Depositional model showing the link between tsunamis and deepwater deposition. (A) (1) Triggering stage in which earthquakes trigger tsunami waves. (2) Tsunami stage in which an incoming (up-run) tsunami wave increases in wave height as it approaches the coast. (3) Transformation stage in which an incoming tsunami wave erodes and incorporates sediment and transforms into sediment flows. (B) (4) Depositional stage in which outgoing (backwash) sediment flows (i.e., debris flows and turbidity currents) deposit sediment in deepwater environments. Suspended mud created by tsunami-related events would be deposited via hemipelagic settling. Reproduced from Shanmugam, G. (2006). The tsunamite problem. Journal of Sedimentary Research 76, 718–730.

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Fig. 35 (A) Highstand sedimentologic model showing calm shelf waters and limited extent of sediment transport in the shoreface zone (short green arrow) during fair-weather periods. Shoreface bottom-current velocities during fair weather are in the range of 10–20 cm s1 (Snedden et al., 1988). The shelf edge at 200 m water depth separates shallow-water (shelf ) from deepwater (slope) environments. (B) Highstand sedimentologic model showing sediment transport on the open shelf, over the shelf edge, and in submarine canyons during periods of tropical cyclones (storm weather) into deepwater (long red arrow). Mass-transport processes are commonly induced by intense hurricanes (e.g., Hurricane Katrina, 2005). Modified from Shanmugam, G. (2008). The constructive functions of tropical cyclones and tsunamis on deepwater sand deposition during sea level highstand: Implications for petroleum exploration. American Association of Petroleum Geologists Bulletin 92, 443–471.

submarine MTDs may have triggered local tsunamis in Papua New Guinea. The significance of this relationship is that tsunamis can trigger submarine MTDs, which in turn can trigger tsunamis. Such mutual-triggering mechanisms can result in frequent sediment failures in deep-marine environments.

Cyclonic Wave Tropical cyclones are meteorologic phenomena. Structurally, tropical cyclones are large, rotating systems of clouds, winds, and thunderstorms. In the Northern Hemisphere, the rotation is counterclockwise, but in the Southern Hemisphere, the rotation is clockwise due to the Coriolis force. Other details are discussed by Shanmugam (2008b). On the US Pacific margin, a large slump mass of about 100,000 m3 in size was triggered by the May 1975 cyclone in the Scripps Canyon, California (Marshall, 1978). Based on empirical data on sediment transport, a sedimentologic model for demonstrating cyclonic-wave-induced transport of gravel, sand, and mud into the deep sea during sea-level highstand has been proposed (Fig. 35).

Groundwater Seepage and Other Factors Brönnimann (2011) had recognized seven triggering mechanisms associated with hydrogeology: (1) suction, (2) rising pore-water pressure, (3) seepage forces, (4) inner erosion, (5) liquefaction, (6) overpressure, and (7) mechanisms related to high plasticity. Although these processes are important in affecting slope stability, they are not considered here as principal triggering mechanisms, with the exception of groundwater seepage (Table 7). The reason is that the excess pore-water pressure, for example, is a piezometric response in situ to external forces, such as rainfall, glacial loading, and human activity. Furthermore, the in situ lithologic properties are closely tied to controlling pore-water pressures and related sediment failures. These complications are evident in the 1979


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Fig. 36 Please substitute a better version of this igure (PPT attached). Illustration of the 1979 sediment failure that occurred at the Nice International Airport in southern France. The Nice sediment failure has been attributed to a combination of both external and internal factors (Dan et al., 2007). (A) Internal (in situ) lithologic factor composed of clay and sand layers. (B) Human factor involving the building of airport embankment. (C) External meteorologic and internal geotechnical factors. See text for details. Diagram is based on the concept of Dan et al. (2007, their Fig. 20). Reproduced from Shanmugam, G. (2015). The landslide problem. Journal of Palaeogeography 4, 109–166.

sediment failure that occurred at the Nice International Airport in southern France. The 1979 Nice incident has been attributed to a combination of both external and internal factors (Dan et al., 2007, their Fig. 20). These complications are illustrated in Fig. 36: 1. Internal lithologic factor (Fig. 36A): The presence of a high-permeability sand layer, which served as a freshwater conduit, was significant in increasing the sensitivity of the surrounding clay by leaching. 2. External human factor (Fig. 36B): The international airport was constructed on a platform enlarged by land-filling material. The 1979 expansion of the airport apparently resulted in local loading beneath the embankment, which was responsible for softening of the mechanical properties of the sensitive clay layer and for its “creeping” movement. 3. External meteorologic factor (Fig. 36C): Intense rainfall over the entire Var drainage basin and the Nice coast in southern France 2 weeks before the 1979 event was vital in preconditioning the site for a potential slope failure. 4. Internal geotechnical factor (Fig. 36C): After a period of rainfall, seepage of fresh ground water through the high-permeability sand layer into the surrounding clay had caused an increase in the pore-water pressure, which led to the reduction of the effective shear strength that resulted in the Nice sediment failure on October 16, 1979. As a result, a part of the airport extension, which was built to be a harbor, collapsed into the Mediterranean Sea. Although the pore-water pressure was the last factor involved in a long line of processes that caused the sediment failure, it was not the sole triggering mechanism.

Human Activity The second most common triggering mechanism (next to earthquakes) for known historic submarine mass movements has been human activity (Mosher et al., 2010). Three modern examples are as follows: 1. The 1979 extension of the international airport at Nice, France (Dan et al., 2007) (see section “The Role of Excess Pore-Water Pressure” for details) 2. The 1980 underground mining in Húbei, China (Huang and Chan, 2004) 3. The 1983 construction of the submarine Nerlerk berm in the Beaufort Sea, Canada (Lade, 1993; Sladen et al., 1985)

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Although human activity is included here for completeness (Table 7), it is of no consequence for interpreting ancient stratigraphic record in earth sciences.

Tectonic Oversteepening Tectonic compression has elevated the northern flank of the Santa Barbara Basin and overturned the slope in southern California along the US Pacific margin (Greene et al., 2006). Several thrust faults exist beneath the shelf, at the shelf break, and along the middle to upper slope. Uplift (thrusting) along these slopes has led to oversteepening and sediment failure. This sediment failure, known as the Goleta slide, is composed of slumps and mudflows (Fig. 10). Samples from this failure contain gravel, sand, and mud lithofacies. This 300-year-old sediment failure occurred during the present highstand.

Sea-Level Lowstand In the petroleum industry, the sea-level lowstand model is the perceived norm for explaining deepwater sands (Fig. 37A). An example is the attribution of reservoir sands in the Kutei basin in the Makassar Strait (Indonesian seas) to a lowstand of sea level (Saller et al., 2006). Nonetheless, the Kutei basin’s location is frequently affected by earthquakes, volcanoes, tsunamis, tropical cyclones, monsoon floods, the Indonesian throughflow, and M2 baroclinic tides (Shanmugam, 2008a). These daily activities of the solar system (e.g., earthquakes, meteorite impacts, tsunamis, and cyclonic waves) do not come to a halt during sea-level lowstands. These short-term events are the primary triggering mechanisms of deepwater sediment failures. A deepwater Paleocene sand (B100 m or 328 ft. thick) of the Lower Tertiary Wilcox trend, which occurs above the K–T boundary in the BAHA #2 wildcat test well, has been interpreted as “lowstand” turbidite fan in the northern Gulf of Mexico (Meyer et al., 2007, their Fig. 3). Alternatively, because of the opportune location of the Lower Tertiary Wilcox trend and its stratigraphic position and age, the drilled Paleocene sand could be attributed to the Chicxulub impact and related seismic shocks and tsunamis (Fig. 33). Such alternative real-world possibilities are often overlooked because of the prevailing mindset of the sea-level lowstand model (Allin et al., 2016). Contrary to the lowstand model, empirical data suggest that tropical cyclones and tsunamis are the two most underrated phenomena when it comes to understanding sediment transport into the deep sea during periods of sea-level highstands (Shanmugam, 2008b). Given the high frequency of cyclones and tsunamis during the present highstand, deposition of deepwater

Fig. 37 (A) Conventional sea-level model showing the popular belief that deepwater deposition of sand occurs during periods of lowstand and deposition of mud occurs during periods of highstand (Shanmugam and Moiola, 1988; Vail et al., 1991). The present highstand is estimated to represent a period of 20,000 years. BP, before present. (B) 200,000 cyclones are estimated to occur during the present highstand in the Indian Ocean (Bay of Bengal) and the Atlantic Ocean. (C) 140,000 tsunamis are estimated to occur during the present highstand in the Pacific Ocean. The implication is that sands can be deposited during periods of sea-level highstands, thus making the conventional model obsolete. Reproduced from Shanmugam, G. (2008). The constructive functions of tropical cyclones and tsunamis on deepwater sand deposition during sea level highstand: Implications for petroleum exploration. American Association of Petroleum Geologists Bulletin 92, 443–471.


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Fig. 38 Conceptual models showing sliding movement of a rigid body in subaerial environments. (A) Ideal model in which the predicted runout length (L) is equal to vertical fall height (H) (e.g., Collins and Melosh, 2003). (B) Long-runout model in which the runout length (L) exceeds the vertical fall height (e.g., Hampton et al., 1996). (C) Basic equations derived from the work of Heim (1932) on the “Elm slide” in the Swiss Alps. A rigid-body sliding motion, inferred for the Elm slide by Iverson et al. (1997), is illustrated in (A) and (B).

sand is not unique to periods of lowstands (Fig. 37). Thus, the lowstand model is inappropriate for explaining the timing of deepwater sands.

Long-Runout Mechanisms and Problems Basic Concept The basic premise of long-runout MTDs is that they travel further than the distance predicted by simple frictional models. Heim’s (1932) study of the subaerial “Elm slide” in the Swiss Alps has been the source of the following basic equations for understanding the mobility of MTDs (Fig. 38): 1. H/L ¼ tan ’, where H represents the vertical fall height, L represents the runout distance, and ’ is the Coulomb angle of sliding friction (Griswold and Iverson, 2008). 2. H/La 1/V, where V is the initial volume of the moving mass (McEwen, 1989). 3. H/L ¼ 1, where L is the normal-runout distance (Fig. 38A) (Collins and Melosh, 2003). 4. H/L 1, where L is the long-runout distance (Fig. 38B) (Hampton et al., 1996). Although there are many documented cases of long-runout MTDs in both subaerial (Table 5) and submarine (e.g., submarine slides in Hawaii with >200 km of runout distances; Moore et al., 1989) environments with runout distances measuring up to 100 times their vertical fall height and high speeds of up to 500 km h 1 (Martinsen, 1994), the geologic community was reluctant to accept mechanisms that attempted to explain MTDs that travel farther and faster than expected. The classic case has been the interpretation of blocky features as giant submarine “landslides” with long-runout distances on the north flanks of Molokai and Oahu by Moore (1964). But Macdonald and Abbott (1970, p. 365) questioned the abnormal size of these features, compared with previously known “landslides,” and proposed an alternative interpretation that the large features were in situ volcanoes. Langford and Brill (1972) also rejected a “landslide” interpretation. But subsequent measurements of the magnetic stratigraphy of East Molokai volcano by Holcomb (1985) confirmed Moore’s “landslide” interpretation. A major turning point on the skepticism over longrunout MTDs occurred on May 18, 1980 when the eruption of Mount St. Helens in the United States generated impressive longrunout subaerial MTDs that were captured on videotapes (see The Learning Channel, 1997).

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Subaerial Environments There are at least 20 potential mechanisms that could explain the mechanical paradox of long-runout MTDs (Brunsden, 1979; Hungr, 1990; Schaller, 1991; Terzaghi, 1950; among others). Selected examples of subaerial mechanisms are as follows: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Lubrication by liquefied saturated soil entrained during transport (Heim, 1882; Hungr and Evans, 2004) Dispersive pressure in grain flows (Bagnold, 1954) Fluidization by entrapped air (Kent, 1966) Cushion of compressed air beneath the slide (Shreve, 1968) Fluidization by dust dispersions (Hsü, 1975), akin to grain flows (Bagnold, 1954) Spontaneous reduction of friction angle at high rates of shearing (Campbell, 1989; Scheidegger, 1975) Vaporization of water at the base and related excess pore-water pressure (Goguel, 1978) Frictional heating along a basal fluid-saturated shear zone and related rise in pore-water pressure (Goren and Aharonov, 2007; Voight and Faust, 1982) Self-lubrication by frictionally generated basal melt layers (De Blasio and Elverhøi, 2008; Erismann, 1979; Weidinger and Korup, 2009) Acoustic fluidization (Melosh, 1979) Mechanical fluidization or inertial grain flow (Davies, 1982) Fluidization by volcanic gases (Voight et al., 1983) Excess pore-water pressure (Cruden and Hungr, 1986; Iverson, 1997) Self-lubrication by granular flows acting as basal shear zone (Cleary and Campbell, 1993) Seismic energy released during meteorite impacts, proposed for Mars (Akers et al., 2012), that is also applicable to Earth

Submarine Environments Submarine environments with long-runout MTDs have been broadly grouped into five types by Hampton et al. (1996): (1) fjords, (2) active river deltas on the continental margin, (3) submarine canyon-fan systems, (4) open continental slopes, and (5) oceanic volcanic islands and ridges. To this list, a sixth type of “glacially influenced continental margins” (Elverhøi et al., 1997) needs to be added. In general, submarine MTDs not only are larger than subaerial MTDs in size but also have longer-runout distances than subaerial MTDs (Table 5). Along the Norwegian–Barents Sea margin, for instance, individual debrite bodies are tonguelike in geometry, 50 km3 in sediment volume, 2–10 km in width, and 10–50 m in height and have runout distances of up to 200 km (Elverhøi et al., 1997, their Fig. 1b). Submarine MTDs with long-runout distances of over 100 km commonly occur on slopes of 100 m deep), offshore St. Croix, a current meter measured net downcanyon currents reaching velocities of 2 m s1 and oscillatory flows up to 4 m s1. Hugo had caused erosion of 2 m of sand in the Salt River Canyon at a depth of about 30 m. A minimum of 2 million kg of sediment was flushed down the Salt River Canyon into deepwater (Hubbard, 1992). The transport rate associated with Hurricane Hugo was 11 orders of magnitude greater than that measured during fair-weather period. In the Salt River Canyon, much of the soft reef cover (e.g., sponges) had been eroded away by the power of the hurricane. Debris composed of palm fronds, trash, and pieces of boats found in the canyon were the evidence for storm-generated debris flows. Storminduced sediment flows have also been reported in a submarine canyon off Bangladesh (Kudrass et al., 1998), in the Capbreton Canyon, Bay of Biscay in SW France (Mulder et al., 2001), in the Cap de Creus Canyon in the Gulf of Lions (Palanques et al., 2006), and in the Eel Canyon, California (Puig et al., 2003), among others. Evidently, sediment transport in submarine canyons is accelerated by tropical cyclones and tsunamis in the world’s oceans. A characteristic attribute of modern and ancient submarine canyons is that they contain both MTDs and tidalites in close association (Shanmugam, 2003, discussed in Part 2). This facies association, which is unique to canyon environments, can be used as a criterion for recognizing submarine canyon settings in the rock record where direct evidence for canyon filling is lacking.

Social and Economic Consequences Destructive Aspects MTDs triggered by catastrophic events, such as earthquakes, tropical cyclones, and tsunamis, destroy offshore oil-drilling platforms and other infrastructures (Bea, 1971; Hampton et al., 1996; Jiang and LeBlond, 1992; Shanmugam, 2008b). Velocities of subaerial pyroclastic flows reached up to 1078 km h1 in association with the lateral blast of the Mount St. Helens in 1980 (Tilling et al., 1990). This event destroyed 250 homes, 47 bridges, and 24 km of rail in Washington, the United States (Table 1). The 1983 Thistle MTD in Utah was the most expensive disaster of this type in US history with a loss of US$600 million (1983). In west central British Columbia, Canada, numerous destructive MTDs (prehistoric to present) have impacted pipelines, hydro transmission lines, roads, and railways, disrupting service to communities (Geertsema et al., 2009, their Table 1). Submarine mudflows, triggered by the 1969 Category 5 Hurricane Camille, destroyed the offshore South Pass Block 70B platform in the Mississippi River Delta area, Gulf of Mexico (Sterling and Strohbeck, 1975). The seafloor in this area, at a depth of about 90 m, moved downslope >1000 m (Hooper and Suhayda, 2005). Mudflows and mudslides, triggered by the 2004 Category 5 Hurricane Ivan (Nodine et al., 2006), toppled the Mississippi Canyon 20 platform at a depth of 146 m near the shelf edge (Hooper and Suhayda, 2005) and damaged up to 17 pipelines (MMS, 2005). On the OCS of the Gulf of Mexico, the 2005 Category 5 Hurricane Katrina destroyed 46 petroleum platforms and damaged 20 others (MMS, 2006). Of the 4000 platforms in the


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Gulf of Mexico, 113 were destroyed by Hurricanes Katrina and Rita (NOIA, 2005). Hurricane Katrina-induced mudflows also damaged at least six pipelines. Hurricane Katrina alone had caused nearly 50 oil spills (Pine, 2006). Mass-transport events not only result in oil spills offshore but also cost severe loss of human lives on land. The 1985 eruption of the Nevado del Ruiz volcano in Colombia and related debris flows caused 23,000 deaths (Table 1). In December 1999, torrential rains fell in the Vargas State, Venezuela, which resulted in widespread mudslides and 30,000 deaths (Table 1).

Constructive Aspects The economic importance of SMTDs in deepwater petroleum exploration and production is becoming increasingly evident worldwide. Examples are (1) the Ormen Lange gas field located inside the Storegga Slide scar, offshore Norway (Solheim et al., 2005b); (2) petroleum-producing reservoirs composed of SMTDs and associated sand injections in the North Sea (Duranti and Hurst, 2004; Purvis et al., 2002; Shanmugam et al., 1995), Norwegian Sea (Shanmugam et al., 1994), Gulf of Mexico (Meckel, 2010; Shanmugam, 2006a, 2012a), Mexico (Grajales-Nishimura et al., 2000), Brazil (Shanmugam, 2006a, 2012a), West Africa (Shanmugam, 2006a), Australia (Meckel, 2010), Russia (Meckel, 2010), China (Zou et al., 2012), and the Bay of Bengal, India

Fig. 43 (A) Index map showing locations of the Krishna–Godavari (KG) Basin and the KG-D6 block (offshore, state of Andhra Pradesh) on the eastern continental margin of India. (B) Map showing location of our study area in the KG-D6 block. (C) Root-mean-square (RMS) seismic amplitude map of our study area showing locations of cored wells 1, 2, and 3. RMS map represents the entire reservoir (400 ms time window). Amplitude color code: bright red, high amplitude (gas-charged sandy lithologies); yellow, intermediate amplitude (mixed lithologies); blue to dull green, low amplitude (nonsandy or muddy lithologies). Sinuous and lobate planform geometries are present. Note position of well 2 in a sinuous form. Reproduced from Shanmugam, G., Shrivastava, S. K. and Das, B. (2009). Sandy debrites and tidalites of Pliocene reservoir sands in upper-slope canyon environments, offshore Krishna-Godavari basin (India): Implications. Journal of Sedimentary Research 79, 736–756.

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(Shanmugam et al., 2009); (3) reservoir characterization of SMTD (Meckel, 2011); and (4) hydrocarbon traps associated with MTDs (Alves and Cartwright, 2010; Beaubouef and Abreu, 2010). Importantly, MTDs form a significant component of deepwater stratigraphy. An example is the Espḭrito Santo Basin in SE Brazil where MTDs constitute >50% of Eocene–Oligocene strata (Gamboa et al., 2010). In the KG Basin, Bay of Bengal (India), for example, Pliocene canyons are sinuous, at least 22 km long, relatively narrow (500–1000 m wide), deeply incised (250 m), and asymmetrically walled (Shanmugam et al., 2009). Submarine canyon geometry has been readily recognized on seismic profiles and on RMS amplitude images (Fig. 43). Examination of conventional cores shows that sandy debrites and sandy tidalites occur as sinuous canyon-fill sands. Reservoir sands, composed mostly of amalgamated units of sandy debrites, are thick (up to 32 m), low in mud matrix (12 km) distribution of MTD (mass-transport deposits) in the three cored sites. (C) Core photograph and related sketch showing fault and deformed clay layers in MTD. Red arrow points to location of site. (D) Core photograph and related sketch showing steeply-dipping clay layers in MTD. Figures from Expedition 308 Scientists (2006). Site U1322. In: Flemings, P. B., Behrmann, J. H., John, C. M. and the Expedition 308 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 308. College Station, TX: Texas A&M University. https://doi.org/10.2204/iodp.proc.308.106.2006, with additional labels by G. Shanmugam.

Breccias Earthquakes certainly do generate SSDS, as they have been documented from the currently active Nankai Trough in Southwest Japan. IODP Expedition 316 cores from this trough contain brecciated mud clasts (Fig. 47). Also, volcanic activities commonly generate breccias in the deep sea, such as in the Arabian Sea (Pandey et al., 2016a,b) and the Rio Grande Rise, South Atlantic (Thiede, 1977). However, earthquake-induced breccias cannot be distinguished from volcanic breccias. The reason is that in regions like Iceland, where both earthquakes and volcanic eruptions occur concurrently due to their plate-tectonic setting (Shanmugam, 2017b, his Fig. 6). In the case of the Arabian Sea, both mass movements and volcanic activities played a joint role in developing brecciated mud clasts. Furthermore, there are no objective criteria to distinguish tectonic breccias from depositional breccias (e.g., debrites). This is because brecciated mud clasts look similar irrespective of their origin.

Lateral Extent IODP Expedition 308 of the Ursa Basin in the Gulf of Mexico has shown that Pleistocene mass-transport deposits (MTD) contain not only common SSDS, such as deformed layers and steeply dipping layers (Fig. 48), but also can be correlated over a 12-km distance (Fig. 48B). This laterally extensive unit with SSDS is strictly a product of depositional MTD, and earthquakes have nothing to do with their lateral distribution. I also described DSDP Leg 96 cores (Mississippi Fan, Gulf of Mexico) at Lamont-Doherty Earth Observatory, New York, which contain intervals of depositional slumps that are unrelated to earthquakes (Shanmugam et al., 1988a). Furthermore, tsunamis, cyclones, and meteorite impacts are known to have generated widespread distribution of SSDS (Shanmugam, 2016a). Therefore, the popular criterion that seismicity-induced strata with SSDS are uniquely extensive (Owen and Moretti, 2011; Simms, 2003) is untenable.


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Fig. 49 (A) Image showing location of ODP Leg 175, Site 1085, Mid-Cape Basin, off South Africa, South Atlantic. Note north flowing Benguela Current. (B) A seismic profile with ODP Site 1085, Mid-Cape Basin. (C) Core photograph showing convolute layers. Red arrow points to position of photograph. (B) and (C) are both from Shipboard Scientific Party (1998), with additional labels by G. Shanmugam.

Ocean Bottom Currents Types of bottom currents are discussed below in Part 2 of this chapter. Convolute bedding is a common type of SSDS. They have been reported from the ODP Leg 175, off South Africa in the Mid-Cape Basin, South Atlantic (Fig. 49). The significance of this occurrence in association with a depositional slump is that it is likely be related to the Benguela Current (Table 2, Case study 21), not earthquakes. The Benguela Current is an ocean current that flows northward along the west coast of Africa from Cape Point in the south to 16 S. These nutrient-rich waters cause the Benguela Upwelling. These robust and critical datasets have commonly been overlooked by most researchers of SSDS.

Mass-Transport Deposits (MTD) (1) DSDP Site 180 is located on the Aleutian Trench slope (Fig. 50). Piper (1975), who emphasized sediment deformation in DSDP cores, reported bowed laminae (Fig. 50C) and suggested that these SSDS are natural in origin and associated with mass transport. (2) IODP Expedition Site U1418 is also located in the vicinity of the Aleutian Trench in the Gulf of Alaska (Fig. 51). Cores show mud clasts (Fig. 51), breccias, and contorted laminae in clay. Jaeger et al. (2014a,b) suggested that these SSDS are related to mass-transport deposits (MTD). (3) ODP Site 884 is located near the western tip of the Aleutian Islands in the North Pacific (Fig. 52). Cores show slump folds and normal faults (Fig. 52). Again, these SSDS are associated with mass-transport deposits (Shipboard Scientific Party, 1993).

Fig. 50 (A) Image showing the location of DSDP Site 180 (filled red circle) in the Gulf of Alaska. (B) A NWSE cross section showing the location of Site 180 in the Aleutian Trench. Note Giacomni Seamount. (C) Core photograph and related sketch showing bowed laminae. Red arrow points to site location. (A) Image credit: NOAA. (B) From Shipboard Scientific Party (1973). 1. Introduction. In: Initial reports of the deep sea drilling project, vol. 18, pp. 58. Washington: United States Government Printing Office. doi:10.2973/dsdp.proc.18.101.1973. (C) Photograph from Piper, D. J. W. (1975). Appendix II. Deformation of stiff and semilithified cores from legs 18 and 28. In: Deep sea drilling project, vol. 28, pp. 977 979. doi:10.2973/dsdp.proc.28.app2.1975.

Fig. 51 (A) Image showing the location of IOPD Expedition 341 Site U1418 (filled red circle) in the Gulf of Alaska. GS ¼ Giacomni Seamount (see Fig. 9B for cross section). (B) Seismic profile showing the position of Site U1418. (C–E) Core photographs showing mud clasts in clayey matrix. Red arrow points to position of core photograph near the bottom of core. Core photographs from Jaeger et al. (2014b). Additional labels by G. Shanmugam.


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Fig. 52 (A) Image showing location of ODP Site 884 (filled red circle) in the North Pacific. Note the site position near the western tip of Aleutian Islands. (B) Core photograph showing normal fault (white arrow). (C) Core photograph showing slump fold in mud. (A) Image credit: NOAA. (C) Core photographs from Shipboard Scientific Party (1993). Site 884. In: Rea, D. K., Basov, I. A., Janecek, T. R., Palmer-Julson, A., et al. Proceedings of ocean drilling program, initial reports, vol. 134, pp. 209–302. College Station, TX. doi:10.2973/odp.proc.ir.145.108.1993. Additional labels by G. Shanmugam.

In other words, SSDS are associated with MTDs not only in tectonically active subduction zones, but also in other basins, such as the Gulf of Mexico (Fig. 48). The implication is that SSDS are not unique to seismically active regions. The widespread distribution of MTD along the U.S. Atlantic margin has been well documented (Embley, 1980; Shipboard Scientific Party, 1994; Twichell et al., 2009). Geophysical and sedimentological studies of widespread MTD were also carried out on the Amazon Fan, Equatorial Atlantic (Damuth and Embley, 1981; Piper et al., 1997; Shanmugam, 2006a). However, sedimentological features like slump folds, steeply-dipping layers, and breccias are not only classified as SSDS but also as depositional features of MTD in numerous case studies (Table 9). Some obvious observations and their implications are: (1) Slump fold is associated with MTD not only in a seismically active environment near the Aleutian Islands (Fig. 52) and in the NanTroSEIZE Complex, Philippine Sea Plate (Fig.53), but also with MTD, unrelated to earthquakes, in a submarine canyon environment in the Edop Field, offshore Nigeria (Fig. 54). (2) Steeply-dipping layers, possibly caused by slumping, are associated not only with seismically active environment in the Amami Sankaku Basin, Philippine Sea (Fig. 55), but also with MTD in a passive depositional setting in the Gulf of Mexico (Fig. 48). (3) Load casts are not unique to a particular triggering mechanism because they are commonly associated with turbidites and MTD of different triggering mechanisms (Table 9; Fig. 56). (4) Similarly, faults (Fig. 57), sand injections (Fig. 58), brecciated mud clasts and folds (Fig. 59) are present in both MTD and SSDS. The problem is how to distinguish MTD from SSDS. After all, slump structures are not only classified as SSDS but are also considered a type of MTD. Attempting to separate SSDS from MTD is a distinction without a difference—a logical fallacy.

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Fig. 53 (A) Image showing location of IODP Expedition 333, Site C0018 (filled red circle) in the NanTroSEIZE complex. White barbed line ¼ position of deformation front of accretionary prism. Yellow arrow ¼ estimated far-field vectors between Philippine Sea Plate and Japan. The Shikoku Basin was previously drilled during DSDP Leg 58 (Klein et al., 1980). (B) A NWSE seismic profile showing position of Site C0018. Note the accretionary prism above the subducting Philippine Sea Plate. Also note location of Site C0012 near the SE end of seismic profile on a Knoll (see Fig. 58 for details). (C) Core photograph showing slump fold in mudstone. Red arrow points to Site C0018 location. (D) CT-Scan image of slump fold in core. (A) Figure from Expedition 333 Scientists (2011). Integrated ocean drilling program expedition 333 preliminary report NanTroSEIZE Stage 2: Subduction inputs 2 and heat flow. College Station, TX: Texas A&M University. doi:10.2204/iodp. pr.333.2011, with additional labels by G. Shanmugam. (B) Figure from Expedition 333 Scientists (2011). Integrated ocean drilling program expedition 333 preliminary report NanTroSEIZE Stage 2: Subduction inputs 2 and heat flow. College Station, TX: Texas A&M University. https://doi.org/10.2204/iodp.pr.333.2011. (D) Figure from Expedition 333 Scientists (2012b). Site C0018. In: Henry, P., Kanamatsu, T., Moe, K. and the Expedition 333 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 333. College Station, TX: Texas A&M University. https://doi.org/10.2204/iodp.proc.333.103.2012, with additional labels by G. Shanmugam.

The other problem is the interrelationship between earthquakes and MTD. For example, an earthquake can trigger MTD and in turn MTD can trigger earthquakes, with both generating SSDS. In the real world, all these triggering mechanisms can and do occur simultaneously (Fig. 60). There are no objective criteria to resolve this problem yet. However, the wealth of available core data from scientific drilling at sea offers hope that the trigger and MTD problems may be resolved by undertaking a global research initiative. (A) Image credit: http://oceancurrents.rsmas.miami.edu/atlantic/img_topo2/benguela2.jpg. Labels added by G. Shanmugam. (B) and (C) are both from Shipboard Scientific Party (1998). Site 1085. In: Wefer, G., Berger, W. H., Richter, C., et al. Proceedings of ocean drilling program, initial reports, vol. 134. College Station, TX, pp. 385–428, doi:10.2973/odp.proc.ir.175.113.1998, with additional labels by G. Shanmugam. (A) From Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 Scientists (2014a). Expedition 341 summary. In: Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 341, pp. 1 130. College Station, TX: Texas A&M University. (B) From Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 Scientists (2014b). Site U1418. In: Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 (eds.) Proceedings of the integrated ocean drilling program, vol. 341. doi:10.2204/iodp.proc.341.104.2014. (C–E) Core photographs from Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 Scientists (2014b). Site U1418. In: Jaeger, J. M., Gulick, S. P. S., LeVay, L. J. and the Expedition 341 (eds.) Proceedings of the integrated ocean drilling program, vol. 341. doi:10.2204/iodp.proc.341.104.2014. Additional labels by G. Shanmugam.

Fig. 54 (A) Map showing location of the Edop Field (filled red circle), offshore Nigeria. (B) A submarine canyon-fill model dominated by MTD in the Edop Field (Pliocene), offshore Nigeria. (C) Core photograph showing primary glide plane between overlying sand and underlying slump-folded mudstone, Pliocene, offshore Nigeria. Red arrow points to Well 25C from which the core was recovered. (A) Base image credit: NOAA. (B) and (C) are from Shanmugam, G. (2012a). New perspectives on deep-water sandstones, origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier, with permission from Elsevier.

Fig. 55 (A) Image showing location of IODP Expedition 351, Site U1438 (filled red circle) in the Philippine Sea Region. (B) Core photograph showing steeply-dipping layers (yellow arrow) in tuffaceous mudstone, possibly aused by slumping. Red arrow points to site location. Figure from Expedition 351 Scientists (2015). Site U1438. In: Arculus, R. J., Ishizuka, O., Bogus, K. and the Expedition 351 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 351. College Station, TX: Texas A&M University. doi:10.14379/iodp.proc.351.103.2015 with additional labels by G. Shanmugam.

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Fig. 56 (A) Image showing location of IODP Expedition 349, Site U1431 (filled red circle) in the East Subbasin of the South China Sea. (B) Lower part of the lithologic log of Site U1431 showing Miocene units. (C) Core photograph showing volcanic breccia. (D) Core photograph showing load cast. (E) Core photograph showing steeply-dipping layers. (F) Core photograph showing inverse grading. Red arrows point to positions of photographs. All images are from Expedition 349 Scientists (2015). Site U1431. In: Li, C.-F., Lin, J., Kulhanek, D. K. and the Expedition 349 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 349. College Station, TX: Texas A&M University. https://doi.org/10.14379/iodp.proc.349.103.2015, with additional labels by G. Shanmugam.

Submarine Fans The term “submarine fans” refers loosely to deposits of variable shapes and sizes in deep-marine environments (Shanmugam, 2016a). The principal elements of submarine fans are canyons, channels, and lobes. Submarine fans constitute important sites of sediment accumulation in the world’s oceans (Fig. 61). Barnes and Normark (1985) compiled dimensions of 21 modern fans and 10 ancient systems. Fans have impressive dimensions (Fig. 62). The world’s largest submarine fan, known as the Bengal Fan, has a length of 3000 km, a width of 1430 km, and a sediment thickness of 16.5 km (Curray et al., 2003). The Bengal Fan virtually occupies the entire length of the Bay of Bengal, and covers an area of 2800–3000 (103 km2) (Curray et al., 2003). In his seminal publication on turbidite fans, Bouma (1962, p. 98) used the term “cone” for describing submarine fans. Bouma (1962) proposed the most convincing link between the turbidite facies model with five divisions, namely Ta, Tb, Tc, Td, and Te (Fig. 63A), and their areal distribution on a submarine fan (Fig. 63B). The classical models of both modern and ancient submarine fans have clearly implied a fan-shaped morphology with channels and lobes (Fig. 64) composed of turbidites (Bouma et al., 1985). However, a distinction was made to reserve the term “submarine fans” for modern systems, and the term “turbidite systems” for ancient systems (Bouma et al., 1985; Normark, 1987). Despite the constant promotion of the turbidite-fan link, no one has ever documented the existence of sandy turbidity currents in modern deep-water environments. Incongruously, Grotzinger et al. (2007) used an underwater photograph of sandfalls (Fig. 64C) in speculating sandy turbidity currents that could develop submarine fans, but offered no direct photographic documentation of sandy turbidity currents in the deep sea (See Section “A paradigm shift” above). Contrary to the popular belief that submarine fans are mostly composed of tubidites (Mutti, 1992), core data show that mass-transport deposits (MTD) are the dominant facies (Fig. 65). Shanmugam (2016a) summarized 29 different types of submarine-fan models and related problems. One of them deals with development of submarine fans by hyperpycnal flows. I expand on that important issue with additional details below.


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Fig. 57 (A) Regional bathymetric map showing seismic reflection profiles (red line, NDS3) and location of Site U1434 (filled red circle). (B) Seismic profile Line NDS3, with location of Site U1434. (C) and (D) Core photographs showing faults. (E) Line-scan image of a fault observed in the claystone. (F) White brush strokes are drawn on the image tracing the claystone laminations, whose orientation change slightly between hanging and foot walls. From Expedition 349 Scientists (2015). Site U1434. In: Li, C.-F., Lin, J., Kulhanek, D. K. and the Expedition 349 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 349. College Station, TX: Texas A&M University. https://doi.org/10.14379/iodp.proc.349.106.2015.

Hyperpycnal Flows In advocating a rational theory for delta formation, Bates (1953) suggested three major flow types: (1) hypopycnal flow for floating river water that has lower density than basin water (Fig. 66A); (2) homopycnal flow for mixing river water that has equal density as basin water (Fig. 66B); and (3) hyperpycnal flow for sinking river water that has higher density than basin water (Fig. 66C). Mulder et al. (2003) expanded the applicability of the concept of hyperpycnal flows from shallow water (deltaic) to deep-water (continental slope and abyssal plain) environments. A recent development in explaining the origin of submarine fans is by hyperpycnal flows (Warrick et al., 2013; Gamberi et al., 2015; Zavala and Arcuri, 2016). In this new development, hyperpycnal flows are considered analogous to turbidity currents in many respects (Mulder et al., 2003; Steel et al., 2016). This is confusing because turbidity currents and their behavior have been well understood from theoretical (Bagnold, 1962; Sanders, 1965; Middleton and Hampton, 1973; Kneller, 1995), experimental (Middleton, 1967), and outcrop (Mutti, 1992) studies. However, our understanding of hyperpycnal flows in deep-water (i.e., seaward of the shelf-slope break at about 200 m water depth) is strictly speculative. Therefore, I attempt to provide some clarity on this matter (Shanmugam, 2018a,b,c).

Classification Zavala and Arcuri (2016) proposed two types of hyperpycnal flows, namely, sandy and muddy types (Fig. 67). Importantly, they proposed two types of turbidites, namely “intrabasinal turbidites” and “extrabasinal turbidites” (Fig. 68). Intrabasinal turbidites are those with sediments derived locally from adjacent shelf and got transported into the basin by “classic” turbidity currents. In contrast, extrabasinal turbidites are those with sediments derived from distant land and delta and got transported into the basin during river-discharged floods by “flood-triggered” turbidity currents or hyperpycnal flows. Other words, large river-delta fed submarine fans on passive continental margins, such as the Mississippi Fan and the Amazon Fan, would be classified as extrabasinal

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Fig. 58 (A) Detailed bathymetric map of Kashinosaki Knoll and Nankai Trough showing location of Site C0012 (filled red circle). See Fig. 53 for details of Site C0018, located northwest of this site. (B) Sand injection (dike) in silty claystone. Yellow triangles show the trend of dike. Red arrow points to site location on the Knoll. From Expedition 349 Scientists (2015). Site U1431. In: Li, C.-F., Lin, J., Kulhanek, D. K. and the Expedition 349 Scientists (eds.) Proceedings of the integrated ocean drilling program, vol. 349. College Station, TX: Texas A&M University. https://doi.org/10.14379/iodp.proc.349.103.2015, with additional labels by G. Shanmugam.

turbidite fans. Because deposits of hyperpycnal flows are called “hyperpycnites” (Mulder et al., 2003), related submarine fans could be termed hyperpycnite fans (Fig. 68). There are fundamental problems with the concept of hyperpycnal flows and related deposits in the deep sea, beyond the shelf-slope break (Fig. 68).

Definition of Turbidity Currents The problem with Zavala and Arcuri’s (2016) classification of turbidity currents based on provenance (internal source vs. external source) is in conflict with the conventional definition of turbidity currents based on the principles of physics. For example, a turbidity current is a sediment flow with Newtonian rheology (Fig. 18) and turbulent state in which sediment is supported by fluid turbulence and from which deposition occurs through suspension settling (Dott, 1963; Sanders, 1965; Middleton and Hampton, 1973; Allen, 1985; Shanmugam, 1996, 2006a,b, 2012a,b,c). Furthermore, typical turbidity currents can function as truly turbulent suspensions only when their sediment concentration by volume is below 9% or C < 9% (Bagnold, 1962). Without acknowledging the well-established basics of turbidity currents that have been the norm for over 75 years, redefining turbidity currents as “hyperpycnal flows” (Fig. 68) is a sedimentological fallacy.

River Discharge The popular notion that river discharges are directly control hypepycnal flows (Zavala and Arcuri, 2016) is a myth. For example, from a detailed monitoring of a fjord-head delta in British Columbia, Canada, Clare et al. (2016) reported that the largest river discharges did not create hyperpycnal flows. Furthermore, Lamb and Mohrig (2009) tested the leading hypothesis by Mulder et al. (2003) in which hyperpycnal-flow velocity scales directly with river discharge, such that individual turbidites record the rising and


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Fig. 59 (A) Map showing the distribution of MTD on the U.S. Atlantic Continental Margin. Copyright Clearance Center’s RightsLink: Licensee: G. Shanmugam. License Number: 4131030357402. License Date: June 16, 2017. Note position of ODP Leg 150, Site 905 (filled red circle) added in this study. (B) Core photograph showing brecciated chalk clast. (C) Core photograph showing brecciated chalk clast (Eocene) in sandy clay matrix. Note that the upper sharp edge of the chalk clast was originally interpreted as fault boundary by the Shipboard Scientific Party (1994). (D) Core photograph showing folds and flow structures in sandy clay matrix. Color photograph courtesy of J.E. Damuth. Core features from Site 905 are typical of MTD. Red arrow points to site location. (A) Embley, R. W. (1980). The role of mass transport in the distribution and character of deep-ocean sediments with special reference to the north Atlantic Marine. Geology 38, 23–50; with permission from Elsevier. (B) From Shipboard Scientific Party (1994). Site 905. In: Mountain, G. S., Miller, K. G., Blum, P., et al., Proceedings of ocean drilling program, initial reports, vol. 134, pp. 255–308. College Station, TX. doi:10.2973/odp.proc.ir.150.109.1994, with additional labels by G. Shanmugam. (C) Color photograph courtesy of J.E. Damuth. (D) From Shipboard Scientific Party (1994). Site 905. In: Mountain, G. S., Miller, K. G., Blum, P., et al., Proceedings of ocean drilling program, initial reports, vol. 134, pp. 255–308. College Station, TX, https://doi.org/10.2973/odp.proc.ir.150.109.1994, with additional labels by G. Shanmugam.

Fig. 60 Diagram illustrating complex interrelationships among the order of triggers, sediment transport, state of liquefaction, and deposition of SSDS. There are 21 triggers and they are all directly or indirectly responsible for transport processes, depositional mechanisms, and related liquefaction. Note that an earthquake can trigger tsunami waves that in turn can trigger mass movements. Thin red arrows: Triggering of other triggers. Thin blue arrows: One or more sediment transport processes with or without flow transformations. Thick grey arrow: Final deposition. Note that mass movement can function both as a trigger and as a transport process. Figure from Shanmugam, G. (2016a). Submarine fans: A critical retrospective (1950–2015). Journal of Palaeogeography 5 (2), 110–184.

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Fig. 61 Map showing locations of modern and ancient deep-water systems, commonly known as submarine fans, discussed during the COMFAN Meeting in 1982 (Bouma et al., 1985). Publication: Springer eBook, Submarine fans and related turbidite systems. With permission from Springer. Figure from Shanmugam, G. (2016a). Submarine fans: A critical retrospective (1950–2015). Journal of Palaeogeography 5 (2), 110–184.

falling discharge of a flooding river. Lamb and Mohrig (2009, p. 1070) concluded that “Where hyperpycnal rivers enter oceans or lakes of sufficient depth, the flow moves through a backwater zone, a depth-limited plume, and a plunging plume, and this significantly affects the transfer of momentum from river to turbidity current. Importantly, the boundaries of these zones shift during the course of a river flood, resulting in a potentially large regime, in space and time, where local hyperpycnal plume velocities are anticorrelated with river discharge. The result is a complex depositional signature including multiple stacked inverse and normally graded units, in some cases, even from a simple single-peaked hydrograph.” Clearly, the application of the hyperpycnal concept to deep-water deposits is untenable.

Grain Size Modern and ancient submarine fans contain a complex blend of gravel, sand, and mud (Shanmugam and Moiola, 1988). However, hyperpycnal flows cannot be responsible for transporting gravel and sand from the land, carrying them across the shelf, and delivering them into the deep sea. The reason for this assertion is that no one has ever documented by direct measurement or observation of transport of gravel and sand by hyperpycnal flows in suspension from the shoreline to the deep sea. Plunging

Fig. 62 (A) Dimensions of modern and ancient deep-water systems, commonly known as submarine fans, discussed during the COMFAN Meeting in 1982 (Bouma et al., 1985). Numbers correspond to those used in Fig. 61. Note that Curray et al. (2003) estimated a maximum thickness of 16.5 km for the Bengal Fan. Note that the Surveyor (Submarine) Fan, with 700-km-long channel (Reece et al., 2011), in the Gulf of Alaska (not shown) was drilled in 2013 during Expedition 341 of the JOIDES Resolution (Jaeger et al., 2014a,b); (B) Map showing variability in size and areal distribution pattern of modern and ancient deep-water systems. Note that the term “fan” may not be applicable to each and every one of these examples. Figures are from Barnes, N. E., Normark, W. R. (1985). Diagnostic parameters for comparing modern submarine fans and ancient turbidite systems. In: Bouma, A. H., Normark, W. R., Barnes, N. E. (eds.) Submarine fans and related turbidite systems, pp. 13–14. New York: Springer-Verlag, with permission from Springer. Figure from Shanmugam, G. (2016a). Submarine fans: A critical retrospective (1950–2015). Journal of Palaeogeography 5 (2), 110–184.

Fig. 63 The first turbidite-fan link proposed by Bouma (1962). (A) The turbidite facies model with five internal divisions (Ta, Tb, Tc, Td, and Te). This vertical facies model is commonly known as “the Bouma Sequence”; (B) Areal distribution of turbidite facies in a submarine fan. After Bouma (1962). Figure from Shanmugam, G. (2016a). Submarine fans: A critical retrospective (1950–2015). Journal of Palaeogeography 5 (2), 110–184.

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Fig. 64 (A) Conceptual diagram of a modern fan showing suprafan lobe by Normark (1970), with permission from AAPG. Redrawn by Mutti (1992); (B) conceptual diagram of the classic ancient fan showing inner-, middle-, and outer-fan segments by Mutti and Ricci Lucchi (1972). Simplified after Mutti (1992); (C) Underwater photograph showing cascading sandfall at a depth of 40 m (130 ft) in a gully leading down into San Lucas Canyon, Baja California. Such pure sandfalls would develop massive sand intervals in the rock record and would be interpreted as sandy debrites. However, Grotzinger et al. (2007) used this photograph as evidence for initiating sandy turbidity currents that could develop submarine fans, with no empirical data. Photo by R.F. Dill. After Shepard and Dill (1966), Rand McNally & Company. Figure from Shanmugam, G. (2016a). Submarine fans: A critical retrospective (1950–2015). Journal of Palaeogeography 5 (2), 110–184.

hyperpycnal flows, at best, may be characterized as a trigger, not as a major transport mechanism of sand and gravel across the shelf. Plunging phenomenon occurs when a sediment-laden, commonly muddy, river enters a standing body of water of relatively lower density (Fig. 66C). During plunging of rivers, any gravel and sand transported by the river got dropped immediately at the entry point forming a delta. Only the remaining muddy flow travels further downslope. But these muddy flows, no matter what we call them (hyperpycnal flow or turbidity current), are weak and they do not carry gravel and sand into the deep sea for developing submarine fans. Without acknowledging this fundamental factor, Warrick et al. (2013) suggested formation of submarine fans by hyperpycnal plume-derived sediments in the Santa Barbara Channel, California. Shallow-water muddy hyperpycnal flows should not be confused with deep-water sandy turbidity currents (Shanmugam, 2012a). In a comprehensive review of hyperpycnal flows, Talling (2014, p. 179) concluded that “Weak and dilute flows generated by plunging hyperpycnal flood discharges most likely deposits thin (mm to 30 30 30 30 26.5 26 25 21.5 21 20 20 19 17 17 17a 12 10

403–468 900 1000–2000 2100 slope 4000–4600 3000–5000 4300–5200 1500–4000 10–3200 5300–5800 3300–3500 >4800 2000–3000 5200 3008 2000–3000 4000–8000

a

One-year vector averaged speed.

Wind-Driven Bottom Currents The Gulf Stream is a powerful, warm, and swift Atlantic Ocean current that originates at the tip of Florida and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. The Gulf Stream proper is a westernintensified current, largely driven by wind stress (Wunsch, 2002). The Loop Current in the eastern Gulf of Mexico is a winddriven surface current (Fig. 74A), and it is genetically linked to the Gulf Stream in the Atlantic Ocean. The Loop Current enters the Gulf of Mexico through the Yucatán Strait as the Yucatán Current; it then flows in a clockwise loop in the eastern gulf as the Loop Current and exits via the Florida Strait as the Florida Current (Nowlin, 1972; Mullins et al., 1987). Finally, this current merges with the Antilles Current to form the Gulf Stream (Fig. 74A). The Loop Current also propagates eddies into the north-central Gulf of Mexico, where the Ewing Bank area is located, a case study used in this article (Fig. 74B). Velocities in eddies that have detached from the Loop Current have been recorded as high as 200 cm s1 at a depth of 100 m (Cooper et al., 1990). Current-velocity measurements, bottom photographs, high-resolution seismic records, and GLORIA side-scan sonar records indicate that the Loop Current influences the seafloor at least periodically in the Gulf of Mexico (Pequegnat, 1972). Computed flow velocities of the Loop Current vary from nearly 100 cm s1 at the sea surface to more than 25 cm s1 at 500 m water depth (Nowlin and Hubert, 1972). This high surface velocity suggests a wind-driven origin for these currents. Flow velocities measured using a current meter reach up to 19 cm s1 at a depth of 3286 m (Pequegnat, 1972). Kenyon et al. (2002b) reported 25 cm s1 current velocity measured 25 m above the seafloor. Such currents are capable of reworking fine-grained sand on the seafloor. Current ripples, composed of sand at a depth of 3091 m on the seafloor (Fig. 75), are the clear evidence of deep bottomcurrent activity in the Gulf of Mexico today (Pequegnat, 1972). These current ripples are draped by thin layers of mud. If these mud drapes on sand ripples were preserved in the rock record, they would be termed “mud offshoots” (Fig. 72). Deposits of the Loop Current have been interpreted in the cores from the Ewing Bank 826 Field, Plio-Pleistocene, Gulf of Mexico. The Ewing Bank Block 826 Field is located nearly 100 km off the Louisiana coast in the northern Gulf of Mexico (Fig. 74B). It contains hydrocarbon-producing clastic reservoir sands that have been interpreted as bottom-current-reworked sands (Shanmugam et al., 1993a,b). Cores from the Gulf of Mexico show a variety of traction structures that include horizontal layers


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Fig. 72 Summary of traction features interpreted as indicative of deepwater bottom-current reworking by all types of bottom currents. Each feature occurs randomly and should not be considered as part of a vertical facies model. Reproduced from Shanmugam, G., Spalding, T. D. and Rofheart, D. H. (1993). Process sedimentology and reservoir quality of deep-marine bottom-current reworked sands (sandy contourites): An example from the Gulf of Mexico. AAPG Bulletin 77, 1241–1259, with permission from AAPG.

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Fig. 73 (A) Core photograph showing well-sorted fine-grained sand and silt layers (light gray) with interbedded mud layers (dark gray). Note sand layers with sharp upper contacts, internal ripple cross laminae, and mud offshoots. Also note lenticular nature of some sand layers. Pleistocene, continental rise off Georges Bank, Vema 18–374, 710 cm, water depth 4756 m. (B) Core photograph showing rhythmic layers of sand and mud, inverse grading, and sharp upper contacts of sand layers (arrow), interpreted as bottom-current reworked sands. Paleocene, North Sea. (A) Adapted from Hollister, C. D. (1967). Sediment distribution and deep circulation in the western North Atlantic (Ph.D. dissertation), p. 467 (Fig. VI-1, p. 208). New York: Columbia University; Bouma, A. H. and Hollister, C. D. (1973). Deep ocean basin sedimentation. In: Middleton, G. V. and Bouma, A. H. (eds.) Turbidites and deep-water sedimentation, pp. 79–118. SEPM Pacific section Short Course. Anaheim, CA: SEPM, with permission from SEPM. (B) Reproduced from Shanmugam, G. (2012). New perspectives on deep-water sandstones: Origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier, with permission from Elsevier.

(Fig. 76A), low-angle cross laminae (Fig. 76B), ripple cross laminae, flaser bedding, mud offshoots in ripples, eroded and preserved ripples, and inverse grading (Shanmugam et al., 1993a,b). Most of the features are interpreted as the products of deposition by traction or combined traction and suspension (Fig. 72). As with deposits of contour-following thermohaline currents, it is impossible to establish that a given sedimentary structure in the rock record was originated by wind-driven bottom currents, without establishing the paleo-water circulation pattern independently. Again, the general term “bottom-current-reworked sands” is appropriate in many cases. Sand layers with traction structures occur in discrete units, but not as part of a vertical sequence of structures. Because traction structures are also observed in deposits of thermohaline-induced bottom currents, caution must be exercised in classifying a deposit as a “contourite” based solely on traction structures without independent evidence for contour-following bottom currents in the area.

Tidal Bottom Currents in Submarine Canyons Deep-marine tidal bottom currents in submarine canyons and in their vicinity are one of the best studied and most extensively documented modern geologic processes (e.g., Beaulieu and Baldwin, 1998; Petruncio et al., 1998; Shepard, 1976; Shepard et al., 1969, 1979; Xu et al., 2002). During the past four decades, an understanding of deep-marine tidal bottom currents has been achieved by synthesizing a great wealth of information that includes direct observations from deep-diving vehicles, dredging from


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Fig. 74 (A) Sea-surface temperature (SST) image showing the Loop Current in the Gulf of Mexico and the axis of the Gulf Stream in the Atlantic Ocean along the US continental margin on March 12, 2011. Darker orange to red color enhancement represents temperatures in the upper 70 s F. (B) Location map of the Ewing Bank and adjacent areas in the northern Gulf of Mexico. Solid dots show locations of cores. (A) Image credit: NOAA’s Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin–Madison, the United States, http://cimss.ssec.wisc.edu/goes/blog/wpcontent/uploads/2011/03/MODIS_SST_20110312_ 1615_largescale.png (Accessed 05.09.15). Reproduced from Shanmugam, G. (2012). New perspectives on deep-water sandstones: Origin, recognition, initiation, and reservoir quality. In: Handbook of petroleum exploration and production, vol. 9, 524 p. Amsterdam: Elsevier, with permission from Elsevier. (B) Reprinted from Shanmugam, G., Spalding, T. D. and Rofheart, D. H. (1993). Process sedimentology and reservoir quality of deep-marine bottom-current reworked sands (sandy contourites): An example from the Gulf of Mexico. AAPG Bulletin 77, 1241–1259, with permission from American Association of Petroleum Geologists.

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Fig. 75 Undersea photograph showing possible mud-draped (arrow) current ripples at 3091 m water depth in the Gulf of Mexico. Similar mud drapes may explain the origin of mud offshoots observed in the core (see Fig. 72). A current measuring nearly 18 cm s1 was recorded on the day this photograph was taken. Current flow was from upper left to lower right. Bar scale is 50 cm. Alaminos Cruise 69-A-13, St.35. From Pequegnat, W. E. (1972). A deep bottom-current on the Mississippi Cone. In: Capurro, L. R. A., Reid, J. L. (eds.) Contribution on the physical oceanography of the Gulf of Mexico Texas A&M University Oceanographic Studies, vol. 2, pp. 65–87. Houston, TX: Gulf Publishing. Reproduced from Shanmugam, G. (2006). Deep-water processes and facies models: Implications for sandstone petroleum reservoirs. In: Handbook of petroleum exploration and production, vol. 5, 476 p. Amsterdam: Elsevier, with permission from Elsevier.

Fig. 76 (A) Core photograph showing rhythmic layers of sand and mud. Middle Pleistocene, Gulf of Mexico. (B) Core photograph showing discrete thin sand layers with sharp upper contacts (top arrow). Traction structures include horizontal laminae, low-angle cross laminae, and starved ripples. Dip of cross laminae to the right suggests current from left to right. Note rhythmic occurrence of sand and mud layers. Middle Pleistocene, Gulf of Mexico. Reproduced from Shanmugam, G., Spalding, T. D. and Rofheart, D. H. (1993). Process sedimentology and reservoir quality of deep-marine bottom-current reworked sands (sandy contourites): An example from the Gulf of Mexico. AAPG Bulletin 77, 1241–1259, with permission from American Association of Petroleum Geologists.


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canyon floors, underwater photographs of canyon floors, photographs and X-radiographs of box cores, seismic profiles, and current–velocity measurements (Dill et al., 1975; Shepard, 1976; Shepard and Dill, 1966; Shepard et al., 1969, 1979). Selected examples of studies that dealt with tidal processes and/or their deposits in modern and ancient deepwater environments have been reviewed by Shanmugam (2003, 2008a). In order to discuss deep-marine tidal bottom currents, one must first establish a clear framework on submarine canyons. This is necessary because tidal currents tend to focus their energy within submarine canyons. Harris and Whiteway (2011), based on ETOPO1 bathymetric grid, had compiled the first inventory of 5849 separate large submarine canyons in the world’s oceans. They have classified canyons into three types, namely, type 1 shelf-incising canyons having heads with a clear bathymetric connection to a major river system, type 2 shelf-incising canyons with no clear bathymetric connection to a major river system, and type 3 blind canyons that incise onto the continental slope. In order to differentiate the role of tidal currents in different types of submarine canyons, I have further subdivided the type 1 into type 1A and type 1B based on the position of canyon head (Fig. 41). Shepard et al. (1979) measured current velocities in 25 submarine canyons worldwide at water depths ranging from 46 to 4200 m by suspending current meters, usually 3 m above the sea bottom (Fig. 77A). Shepard et al. (1979) also documented systematically that up- and down-canyon currents closely correlated with timing of tides (Fig. 77B). These canyons include the Hydrographer, Hudson, Wilmington, and Zaire in the Atlantic Ocean and the Monterey, Hueneme (Fig. 77B), Redondo, La Jolla/ Scripps, and Hawaii in the Pacific Ocean. Maximum velocities of up- and down-canyon currents commonly ranged from 25 to 50 cm s1 (Fig. 77A; Table 12). Keller and Shepard (1978) reported velocities as high as 7075 cm s1, velocities sufficient to transport even coarse-grained sand, from the Hydrographer Canyon. In the Niger Delta area of West Africa, five modern submarine canyons (Avon, Mahin, Niger, Qua Iboe, and Calabar) have been recognized. In the Calabar River, the tidal range is 2.8 m, and tidal flows with reversible currents are common (Allen, 1965). In the Calabar estuary, maximum ebb current velocities range from 60 to 280 cm s1, and flood current velocities range from 30 to 150 cm s1. These velocities are strong enough to transport particles of sand and gravel size. The Calabar estuary has a deepwater counterpart that cuts through sediments of the outer shelf and slope, forming the modern Calabar submarine canyon. Thus, as they do in the Zaire Canyon to the south, tidal currents are likely to operate in the Calabar and Qua Iboe Canyons. Unlike the robust data sets on measured current velocities of deep-marine tidal currents in submarine canyons worldwide (Shepard et al., 1979), there has not been a single published current velocity of highdensity turbidity current in submarine canyons. Sedimentary features indicative of tidal processes in shallow-water environments have been well established (e.g., Allen, 1982; Archer, 1998; Banerjee, 1989; Dalrymple, 1992; Klein, 1970; Nio and Yang, 1991; Reineck and Wunderlich, 1968; Shanmugam et al., 2000; Terwindt, 1981; Visser, 1980). Traction structures that develop in shallow-water estuaries also develop in deepwater canyons and channels with tidal currents (Shanmugam, 2003). Klein (1975), based on studies of DSDP (Leg 30, Sites 288 and 289) cores, suggested that current ripples, micro-cross laminae, mud drapes, flaser bedding, lenticular bedding, and parallel laminae reflect alternate traction and suspension deposition from tidal bottom currents in deep-marine environments. Perhaps, the single most diagnostic structure is the double mud layers (DMLs) in deepwater strata that clearly suggest deposition by tidal bottom currents in offshore Nigeria (Fig. 78A) and Bay of Bengal (Fig. 78B). Submarine canyons are not only unique for providing a protected environment for focusing tidal energy from shallow-marine estuaries to deep-marine canyons but also prone to generating mass movements (e.g., slides, slumps, and debris flows) due to failure of steep canyon walls. Recognition of tidal facies in deepwater sequences is important in understanding sand distribution because deposits of tidal processes and mass-transport processes (i.e., slides, slumps, and debris flows) characterize fills of modern and ancient submarine canyons (Fig. 78C). This complex facies association (Fig. 78C), mimicking both shallow-water and deepwater deposits, has been recognized in the modern La Jolla Canyon box cores (offshore California), ancient Qua Iboe Canyon conventional cores (Pliocene, Edop Field, offshore Nigeria), ancient Pliocene canyon conventional cores (Fig. 78B) (KG Basin, Bay of Bengal), and ancient Annot Sandstone outcrops (Eocene–Oligocene, onshore SE France), among others. It appears that the association of tidal and mass flow facies is unique to canyon environments. Therefore, this facies association may be used as a criterion for inferring submarine canyon settings in the rock record where direct evidence for canyon filling is lacking. Because MTD (i.e., deposits of slides, slumps, and debris flows) can occur both inside and outside submarine canyons, the correct identification of tidal facies in deepwater sequences is extremely critical in establishing the facies association. In channel-mouth environments, downslope turbidity currents are likely to develop depositional lobes (Fig. 78D), whereas bidirectional tidal bottom currents are likely to develop elongate bars (Fig. 78C). Turbidite lobes are aligned perpendicular to channel axis, whereas tidal bars are aligned parallel to channel axis. Depositional lobes are likely to be much larger than channel width (Fig. 78D), whereas tidal sandbars are thought to be much smaller than channel width (Fig. 78D). Deepwater elongate tidal bars are speculated to be analogous to tidal sandbars that develop in shallow-water estuarine environments (see Shanmugam et al., 2000). In frontier exploration areas, an incorrect use of a turbidite lobe model (with sheet geometry), instead of a tidal bar model (with bar geometry), will result in an unrealistic overestimation of sandstone reservoirs.

Baroclinic Currents (Internal Waves and Internal Tides) Gill (1982) discussed the basic differences between barotropic (surface) waves that develop at the air–water interface and baroclinic (internal) waves that develop at the water–water interface (Fig. 79). Fluid parcels in the entire water column move together in the same direction and with the same velocity in a surface wave, whereas fluid parcels in shallow and deep layers of the water column move in opposite directions and with different velocities in an internal wave (Fig. 79). The surface displacement and interface

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Fig. 77 (A) Conceptual diagram showing cross section of a submarine canyon with ebb and flood tidal currents (opposing arrows). Shepard et al. (1979) measured current velocities in 25 submarine canyons at water depths ranging from 46 to 4200 m by suspending current meters commonly 3 m above the sea bottom. Measured maximum velocities commonly range from 25 to 50 cm s1. (B) Time–velocity plot from data obtained at 448 m in the Hueneme Canyon, California, showing excellent correlation between the timing of up- and down-canyon currents and the timing of tides obtained from tide tables (solid curve). 3mAB, velocity measurements were made 3 m above sea bottom. (A) Reproduced from Shanmugam, G. (2003). Deep-marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons. Marine and Petroleum Geology 20, 471–491, with permission from Elsevier. (B) Modified from Shepard, F. P., Marshall, N. F., McLoughlin, P. A. and Sullivan, G. G. (1979). Currents in submarine canyons and other sea valleys. AAPG Studies in Geology 8, 173, with permission from American Association of Petroleum Geologists.

displacement are the same for a surface wave, while the interface displacements are large for internal wave. Although the free surface movement associated with the baroclinic mode is only 1/400 of the interface movement, this is still sufficient for baroclinic motions to be detectable by sea-surface changes (Wunsch and Gill, 1976). Apel (2002), Apel et al. (2006), and Jackson (2004a) had published comprehensive accounts of internal waves and tides worldwide. A sedimentologic and oceanographic review is provided by Shanmugam (2013a). Internal waves are gravity waves that


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Table 12 Selected examples of maximum velocities of up- and down-canyon currents measured at varying water depths by suspending current meters 3 m above sea bottom Water depth (m)

Submarine canyon and location

Mean tidal range (m)

Up-canyon current velocity (cm s1)

Down-canyon current velocity (cm s1)

348 375 400 448 458 914 1445 1737 1904

Hydrographer, Atlantic, the United States La Jolla, Pacific, the United States Zaire (Congo), West Africa Hueneme, Pacific, the United States Santa Monica, Pacific, the United States Wilmington, Atlantic, the United States Monterey, Pacific, the United States Kaulakahi, Pacific Islands Río Balsas, Mexico

1.6 2.5 1.3 2.4 2.7 1.8 2.0 0.9 0.7

39 19 22 32 27 20 30 26 21

52 18 13 32 30 21 30 24 21

Compiled from Shepard, F. P., Marshall, N. F., McLoughlin, P. A., Sullivan, G. G. (1979). Currents in submarine canyons and other sea valleys. AAPG Studies in Geoloy 8, 173.

oscillate along oceanic pycnoclines (Fig. 80). Internal tides are internal waves with a tidal frequency. Internal solitary waves (i.e., solitons), the most common type, are commonly generated near the shelf edge (100–200 m in bathymetry) and in the deep ocean over areas of seafloor irregularities, such as mid-ocean ridges, seamounts, and guyots. Empirical data from 51 locations (Fig. 81) in the Atlantic, Pacific, Indian, Arctic, and Antarctic Oceans reveal that internal solitary waves travel in packets (Fig. 82). Internal waves commonly exhibit (1) higher wave amplitudes (5–50 m) than surface waves (