Gravity flows: Types, definitions, origins, identification markers, and problems

2020 ◽  
Vol 37 (2) ◽  
pp. 61-90
Author(s):  
Shanmugam G
Keyword(s):  
Debris Flow ◽  
Deep Water ◽  
Sediment Concentration ◽  
Gravity Flow ◽  
Turbidity Currents ◽  
Hyperpycnal Flows ◽  
Gravity Flows ◽  
Sediment Gravity Flow ◽  
Aeolian Dunes ◽  
C 50

Abstract This review covers 135 years of research on gravity flows since the first reporting of density plumes in the Lake Geneva, Switzerland, by Forel (1885). Six basic types of gravity flows have been identified in subaerial and suaqueous environments. They are: (1) hyperpycnal flows, (2) turbidity currents, (3) debris flows, (4) liquefied/fluidized flows, (5) grain flows, and (6) thermohaline contour currents. The first five types are flows in which the density is caused by sediment in the flow, whereas in the sixth type, the density is caused by variations in temperature and salinity. Although all six types originate initially as downslope gravity flows, only the first five types are truly downslope processes, whereas the sixth type eventually becomes an alongslope process. (1) Hyperpycnal flows are triggered by river floods in which density of incoming river water is greater than the basin water. These flows  are confined to proximity of the shoreline. They transport mud, and they do not transport sand into the deep sea. There are no sedimentological criteria yet to identify hyperpycnites in the ancient sedimentary record.  (2) A turbidity current is a sediment-gravity flow with Newtonian rheology  and turbulent state in which sediment is supported by flow turbulence and from which deposition occurs through suspension settling. Typical turbidity currents can function as truly turbulent suspensions only when their sediment concentration by volume is below 9% or C < 9%. This requirement firmly excludes the existence of 'high-density turbidity currents'. Turbidites are recognized by their distinct normal grading in deep-water deposits.  (3) A debris flow (C: 25-100%) is a sediment-gravity 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. General characteristics of muddy and sandy debrites are floating clasts, planar clast fabric, inverse grading, etc.  Most sandy deep-water deposits are sandy debrites and they comprise important petroleum reservoirs worldwide. (4) A liquefied/fluidized low (>25%) is a sediment-gravity flow in which sediment is supported by upward-moving intergranular fluid. They are commonly triggered by seismicity. Water-escape structures, dish and pillar structures, and SSDS are common. (5) A grain flow (C: 50-100%) is a sediment-gravity flow in which grains are supported by dispersive pressure caused by grain collision. These flows are common on the slip face of aeolian dunes. Massive sand and inverse grading are potential identification markers.  (6) Thermohaline contour currents originate in the Antarctic region due to shelf freezing and  the related increase in the density of cold saline (i.e., thermohaline) water. Although they begin their journey as downslope gravity flows, they eventually flow alongslope as contour currents. Hybridites are deposits that result from intersection of downslope gravity flows and alongslope contour currents. Hybridites mimic the "Bouma Sequence" with traction structures (Tb and Tc). Facies models of hyperpycnites, turbidites, and contourites  are obsolete. Of the six types of density flows, hyperpycnal flows and their deposits are the least understood.

scholarly journals Autogenic influence on the morphology of submarine fans: an approach from 3D physical modelling of turbidity currents

2017 ◽  
Vol 47 (3) ◽  
pp. 345-368
Author(s):  
Cristiano Fick ◽  
Rafael Manica ◽  
Elírio Ernestino Toldo Junior
Keyword(s):  
Deep Water ◽  
Physical Modelling ◽  
Sediment Concentration ◽  
Experimental Series ◽  
Turbidity Currents ◽  
Geometrical Parameters ◽  
Submarine Fans ◽  
Relative Standard ◽  
Length Width ◽  
Depositional Evolution

ABSTRACT: Autogenic controls have significant influence on deep-water fans and depositional lobes morphology. In this work, we aim to investigate autogenic controls on the topography and geometry of deep-water fans. The influence of the sediment concentration of turbidity currents on deep-water fans morphology was also investigated. From the repeatability of 3D physical modeling of turbidity currents, two series of ten experiments were made, one of high-density turbidity currents (HDTC) and another of low-density turbidity currents (LDTC). All other input parameters (discharge, sediment volumetric concentration and grain size median) were kept constant. Each deposit was analyzed from qualitative and quantitative approaches and statistical analysis. In each experimental series, the variability of the morphological parameters (length, width, L/W ratio, centroid, area, topography) of the simulated deep-water fans was observed. Depositional evolution of the HDTC fans was more complex, showing four evolutionary steps and characterized by the self-channelizing of the turbidity current, while LDTC fans neither present self-channelizing, nor evolutionary steps. High disparities on the geometrical parameters of the fans, as characterized by the elevated relative standard deviation, suggest that autogenic controls induced a stochastic morphological behaviour on the simulated fans of the two experimental series.

scholarly journals The gravity flow dynamics of submarine fan sedimentation in the Magura Basin of the Western Carpathians (Magura Nappe, Slovakia)

2010 ◽  
Vol 61 (3) ◽  
pp. 201-209 ◽  
Author(s):  
František Teťák
Keyword(s):  
Deep Water ◽  
Flow Dynamics ◽  
Western Carpathians ◽  
Gravity Flow ◽  
Submarine Fan ◽  
Sedimentary Structures ◽  
Gravity Flows ◽  
Bed Thickness ◽  
Change Position ◽  
Current Arrangement

The gravity flow dynamics of submarine fan sedimentation in the Magura Basin of the Western Carpathians (Magura Nappe, Slovakia)This article deals with the dynamics of the deep-water gravity flows sedimentation within the Magura Formation. This investigation is based on analysis of the Magura sandstone sedimentary structures studied on the outcrops. The final comparison of the sedimentary structures and cycles with the paleocurrent directions provided an interpretation of the gravity flows dynamics and helped to restore the migration of the sandy lobes in space and time. Three modes of sedimentation are recorded: regular cyclic sedimentation from the lobe, irregular sedimentation from the immature lobe and pelitic sedimentation on the basin plane without the lobe influence. We compared the occurrence of some sedimentary structures with the changes of the current directions and bed thickness. The following interpretations of gravity flow fan dynamics are results of this comparision: the fan consists of one or several lobes, the lobe branches out into branches with the radial current arrangement, the lobes laterally change position and the lobes suddenly die out.

scholarly journals Rapid gravity flow transformation revealed in a single climbing ripple

Geology ◽  
2020 ◽  
Author(s):  
Jaco H. Baas ◽  
Jim Best ◽  
Jeff Peakall
Keyword(s):  
Plug Flow ◽  
Gravity Flow ◽  
Small Scale ◽  
Geometrical Characteristics ◽  
Gravity Flows ◽  
Sediment Gravity Flow ◽  
Wide Range ◽  
Sediment Deformation ◽  
Rheological Character ◽  
Current Ripples

Sediment gravity flows demonstrate a wide range of rheological behaviors, and past work has shown how transformations between flow types generate spatiotemporal changes in the resultant sedimentary successions. We used the geometrical characteristics of a single climbing ripple to demonstrate how such flows can transform from a turbulent to a quasi-laminar plug flow, with the transitional clay flow sequence being manifested by abnormally large heterolithic sand-clay current ripples with small backflow ripples, and then abundant clay deposition associated with smaller ripples. Analysis of ripple size, angle of climb, grain size, internal erosional surfaces, and soft-sediment deformation suggests that transformation in the rheological character of the sediment gravity flow was rapid, occurring over a period of tens of minutes, and thus probably over a spatial scale of hundreds of meters to several kilometers. Our study indicates how the character of flow transformation can be elucidated from the details of a small-scale sedimentary structure.

scholarly journals The turbidite-contourite-tidalite-baroclinite-hybridite problem: orthodoxy vs. empirical evidence behind the “Bouma Sequence”

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
G. Shanmugam
Keyword(s):  
Deep Water ◽  
General Term ◽  
Bottom Current ◽  
Turbidity Currents ◽  
Facies Model ◽  
Bottom Currents ◽  
Gravity Flows ◽  
Slope Flow ◽  
Baroclinic Currents ◽  
Facies Models

AbstractThe underpinning problems of deep-water facies still remain unresolved. (1) The Tb, Tc, and Td divisions of the turbidite facies model, with traction structures, are an integral part of the “Bouma Sequence” (Ta, Tb, Tc, Td, Te). However, deposits of thermohaline contour currents, wind-driven bottom currents, deep-marine tidal currents, and baroclinic currents (internal waves and tides) also develop discrete rippled units, mimicking Tc. (2) The application of “cut-out” logic of sequences, which was originally introduced for the “Bouma Sequence”, with sharp basal contacts and sandy divisions containing well-developed traction structures, to muddy contorts with gradational basal contacts and an absence of well-developed traction structures is incongruent. (3) The presence of five internal divisions and hiatus in the muddy contoured facies model is in dispute. (4) Intersection of along slope contour currents with down slope sediment-gravity flows, triggering hybrid flows, also develops traction structures. (5) The comparison of genuine hybrid flows with down slope flow transformation of gravity flows is inconsistent with etymology of the term “hybrid”. (6) A reexamination of the Annot Sandstone at the Peira Cava type locality in SE France fails to validate either the orthodoxy of five internal divisions of the “Bouma Sequence” or their origin by turbidity currents. For example, the “Ta” division is composed of amalgamated units with inverse grading and floating mudstone clasts, suggesting a mass-transport deposit (MTD). The “Tb” and “Tc” divisions are composed of double mud layers and sigmoidal cross bedding, respectively, which suggest a tidalite origin. (7) Although it was reasonable to introduce a simplistic “Bouma Sequence” in 1962, at a time of limited knowledge on deep-water processes, it is obsolete now in 2021 to apply this model to the rock record amid a wealth of new knowledge. (8) The disconnect between 12 observed, but questionable, modern turbidity currents and over 10,000 interpreted ancient turbidites defies the doctrine of uniformitarianism. This disconnect is attributed to routine application of genetic facies models, without a pragmatic interpretation of empirical data. (9) A suggested solution to these problems is to interpret traction structures in the sedimentary record pragmatically on the basis of empirical field and experimental evidence, without any built-in bias using facies models, such as the “Bouma Sequence”. (10) Until reliable criteria are developed to distinguish traction structures of each type of bottom currents based on uniformitarianism, a general term “BCRS” (i.e., bottom-current reworked sands) is appropriate for deposits of all four kinds of bottom currents.

Stratigraphy and sedimentology of the Hamill Group in the northern Selkirk Mountains, British Columbia: evidence for latest Proterozoic – Early Cambrian extensional tectonism

1989 ◽  
Vol 26 (3) ◽  
pp. 515-533 ◽  
Author(s):  
William J. Devlin
Keyword(s):  
British Columbia ◽  
Fault Scarp ◽  
Gravity Flow ◽  
Tectonic Activity ◽  
Turbidity Currents ◽  
Early Cambrian ◽  
Shallow Marine ◽  
Sedimentary Characteristics ◽  
Sediment Gravity Flow ◽  
Selkirk Mountains

Three informal stratigraphic divisions are recognized in the uppermost Proterozoic – Lower Cambrian Hamill Group in the northern Selkirk Mountains of British Columbia. These informal divisions include a lower sandstone unit, a greenstone–graded-sandstone unit, and an upper sandstone unit. Both the lower and upper sandstone units display sedimentary characteristics that are uniform along strike and indicate a shallow-marine environment of deposition. As is typical of other exposures of the Hamil Group in southeastern British Columbia, the lower sandstone unit is coarser grained and more poorly sorted than the mature quartz arenites of the upper sandstone unit.The greenstone–graded-sandstone unit is a complex assemblage of mafic metavolcanic rocks and associated sandstone facies. This unit is highly variable along strike but essentially consists of a thick succession of subaqueous extrusive rocks overlain by a variety of sediment gravity-flow deposits. These latter deposits include resedimented conglomerates, debris-flow deposits, and trubidites (deposited from both high- and low-density turbidity currents). Stratigraphic sections of this unit are described in detail from three different localities and are examined in terms of their transport and depositional mechanisms.The stratigraphic succession of the Hamill Group indicates that deposition of the shallow-marine sands of the lower sandstone unit was abruptly interrupted by a period of volcanism, the creation of a paleoslope, and the deposition of a large volume of sediment gravity-flow deposits of the greenstone–graded-sandstone unit. These relations are attributed to an episode of syndepositional normal faulting. The inferred fault(s) could have served as the conduit for the extrusion of the volcanics. Offset along the fault(s), the tilting of fault blocks, and the consequent formation of an unstable slope adjacent to a fault scarp created an environment favorable for deposition of the sediment gravity flows. In general, deposition of proximal, base-of-slope deposits was followed by an aggradational basin-fill phase of sedimentation. With the waning of tectonic activity and the filling of the fault-bounded basin, depositon of shallow-marine sands resumed (the upper sandstone unit). The stratigraphic relations of the Hamill Group in the northern Selkirk Mountains are considered direct evidence for an episode of latest Proterozoic – Early Cambrian extensional tectonism. The evidence for an episode of rift-related tectonism in the northern Selkirk Mountains supports inferences concerning the timing of this event as derived from tectonic subsidence analyses of post-rift strata of the Cordilleran miogeocline.

scholarly journals Depositional Models of Deep-Water Gravity-Flow in Lacustrine Basin and Its Petroleum Geological Significance—A Case Study of Chang 6 Oil Group in Heshui Area, Ordos Basin, China

2022 ◽  
Vol 9 ◽  
Author(s):  
Yiming Yang ◽  
Jun Peng ◽  
Zhaobing Chen ◽  
Xiaoying Zhou ◽  
Yao Zeng ◽  
...  
Keyword(s):  
Particle Size ◽  
Spatial Distribution ◽  
Debris Flow ◽  
Deep Water ◽  
Ordos Basin ◽  
Gravity Flow ◽  
Dynamic Mechanisms ◽  
Genetic Types ◽  
Sand Bodies ◽  
Depositional Models

Gravity-flow can carry a large number of sediments and organic matters from shallow water to deep lakes with its strong transporting energy, directly or indirectly facilitating the formation of deep-water tight reservoirs and shale reservoirs. Therefore, studying the genetic types, dynamic mechanisms, and depositional models of gravity-flow deposits is essential in the exploration of unconventional petroleum in large lacustrine basins. This research studied the genetic types, dynamic mechanisms, and sedimentary models of the gravity-flow deposits of the Chang 6 oil group in the Heshui Area, Ordos Basin, China, aiming to reveal its petroleum geological significance. Core observation, microscopic thin section identification, particle size analysis, and determination of rare earth elements were carried out. As a result, three types of gravity-flow deposits are detected, namely, slide-slump, sandy debris flow, and turbidity current. A certain slope gradient in bed form is the necessary geomorphic condition for gravity flow formation, and determines its development level, distribution range, and flow transformation efficiency. Sufficient provenance lays the material foundation and determines its depositional composition and development type. Other factors include earthquakes, volcanoes, and floods, which serve as triggering forces. In addition, fragmentation, liquefaction, and fluid mixing are the main dynamic mechanisms driving flow transformation. Based on the flow type of gravity flow, particle size characteristics, gravity-flow transformation relations, development mechanism, and spatial distribution pattern, we distinguished two depositional gravity-flow models, i.e., slump turbidite body and sublacustrine fan. Re-portrait the spatial distribution of deep-water gravity flow in the study area. From the perspective of sedimentology, explain the genesis of sand bodies in the northeast and southwest. The sandy debris flow in the middle fan braided channel microfacies of the sublacustrine fan sways the development of thick massive sand bodies in the study area. Hybrid event beds formed by the fluid transformation in a slump turbidite are the potential dessert area for deep-water tight oil and gas.

scholarly journals Forward Modelling for Structural Stratigraphic Analysis, Offshore Sureste Basin, Mexico

2021 ◽  
Vol 9 ◽  
Author(s):  
Donald N. Christie ◽  
Frank J. Peel ◽  
Gillian M. Apps ◽  
David “Stan” Stanbrook
Keyword(s):  
Deep Water ◽  
Sediment Supply ◽  
Computational Method ◽  
Gravity Flow ◽  
Model Output ◽  
Seafloor Topography ◽  
Relative Contribution ◽  
Sediment Gravity Flow ◽  
Reduced Complexity ◽  
Stratal Architecture

The stratal architecture of deep-water minibasins is dominantly controlled by the interplay of two factors, structure growth and sediment supply. In this paper we explore the utility of a reduced-complexity, fast computational method (Onlapse-2D) to simulate stratal geometry, using a process of iteration to match the model output to available subsurface control (well logs and 3D seismic data). This approach was used to model the Miocene sediments in two intersecting lines of section in a complex mini-basin in the deep-water Campeche Basin, offshore Mexico. A good first-pass match between model output and geological observations was obtained, allowing us to identify and separate the effects of two distinct phases of compressional folding and a longer-lasting episode of salt withdrawal/diapirism, and to determine the timing of these events. This modelling provides an indication of the relative contribution of background sedimentation (pelagic and hemipelagic) vs. sediment-gravity-flow deposition (e.g. turbidites) within each layer of the model. The inferred timing of the compressional events derived from the model is consistent with other geological observations within the basin. The process of iteration towards a best-fit model leaves significant but local residual mismatches at several levels in the stratigraphy; these correspond to surfaces with anomalous negative (erosional) or positive (constructive depositional) palaeotopography. We label these mismatch surfaces “informative discrepancies” because the magnitude of the mismatch allows us to estimate the geometry and magnitude of the local seafloor topography. Reduced-complexity simulation is shown to be a useful and effective approach, which, when combined with an existing seismic interpretation, provides insight into the geometry and timing of controlling processes, indicates the nature of the sediments (background vs. sediment-gravity-flow) and aids in the identification of key erosional or constructional surfaces within the stratigraphy.

Benthic foraminiferal zonation in deep-water carbonate platform margin environments, northern Little Bahama Bank

1988 ◽  
Vol 62 (01) ◽  
pp. 1-8 ◽  
Author(s):  
Ronald E. Martin
Keyword(s):  
Deep Water ◽  
Benthic Foraminifera ◽  
Carbonate Platform ◽  
Sedimentary Facies ◽  
Depositional Environments ◽  
Near Surface ◽  
Sediment Gravity Flows ◽  
Gravity Flows ◽  
Platform Margin ◽  
Water Carbonate

The utility of benthic foraminifera in bathymetric interpretation of clastic depositional environments is well established. In contrast, bathymetric distribution of benthic foraminifera in deep-water carbonate environments has been largely neglected. Approximately 260 species and morphotypes of benthic foraminifera were identified from 12 piston core tops and grab samples collected along two traverses 25 km apart across the northern windward margin of Little Bahama Bank at depths of 275-1,135 m. Certain species and operational taxonomic groups of benthic foraminifera correspond to major near-surface sedimentary facies of the windward margin of Little Bahama Bank and serve as reliable depth indicators. Globocassidulina subglobosa, Cibicides rugosus, and Cibicides wuellerstorfi are all reliable depth indicators, being most abundant at depths &gt;1,000 m, and are found in lower slope periplatform aprons, which are primarily comprised of sediment gravity flows. Reef-dwelling peneroplids and soritids (suborder Miliolina) and rotaliines (suborder Rotaliina) are most abundant at depths &lt;300 m, reflecting downslope bottom transport in proximity to bank-margin reefs. Small miliolines, rosalinids, and discorbids are abundant in periplatform ooze at depths &lt;300 m and are winnowed from the carbonate platform. Increased variation in assemblage diversity below 900 m reflects mixing of shallow- and deep-water species by sediment gravity flows.

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