Modern internal waves and internal tides along oceanic pycnoclines: Challenges and implications for ancient deep-marine baroclinic sands: Discussion

Dunham, John B.; Saller, Arthur H.

doi:10.1306/09111313081

Cited by 9 publications

(2 citation statements)

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“…baroclinites) (Gao and Eriksson 1991;Gao et al 1998;He et al 2011;Gao et al 2013). However, these interpretations and related issues were the subjects of lively debates (He et al 2012;Pomar et al 2013;Shanmugam 2012bShanmugam , 2013bShanmugam , 2014aShanmugam , 2014bGao et al 2014;Dunham and Saller 2014). At present, our understanding of the origin of traction structures in deep-water environments is in a state of flux.…”

Section: Academic Discussionmentioning

confidence: 99%

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

Shanmugam

2021

J. Palaeogeogr.

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The 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.

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Section: Academic Discussionmentioning

confidence: 99%

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

Shanmugam

2021

J. Palaeogeogr.

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“…Basic requirements, principles, and methods of this discipline are: (1) a knowledge of physics, with emphasis on soil mechanics and fluid mechanics (Sanders, 1963;Brush, 1965), (2) the application of uniformitarianism principle, (3) the pragmatic, accurate, precise, and consistent description of the rock, (4) the preservation of absolute distinction between descrip-tion and interpretation, (5) the documentation of excruciating details in sedimentological logs, (6) the interpretation of processes using exclusively primary sedimentary structures, (7) the mandatory consideration of alternative process interpretations, (8) the total exclusion of facies models, (9) the quantification of depositional facies, and (10) the routine use of common sense. A major problem in sedimentological studies is the failure to adopt the basic principles of process sedimentology, which has prompted lively debates on the deep-water petroleum-producing reservoirs of the Kutei Basin, Indonesia (Figure 1) (Dunham and Saller, 2014;Saller et al, 2006;Shanmugam, 2008aShanmugam, , 2014a.…”

Section: Process Sedimentologymentioning

confidence: 99%

The landslide problem

Shanmugam

Wang²

2015

Journal of Palaeogeography

147

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The synonymous use of the general term "landslide", with a built-in reference to a sliding motion, for all varieties of mass-transport deposits (MTD), which include slides, slumps, debrites, topples, creeps, debris avalanches etc. in subaerial, sublacustrine, submarine, and extraterrestrial environments has created a multitude of conceptual and nomenclatural problems. In addition, concepts of triggers and long-runout mechanisms of mass movements are loosely applied without rigor. These problems have enormous implications for studies in process sedimentology, sequence stratigraphy, palaeogeography, petroleum geology, and engineering geology. Therefore, the objective of this critical review is to identify key problems and to provide conceptual clarity and possible solutions. Specific issues are the following: (1) According to "limit equilibrium analyses" in soil mechanics, sediment failure with a sliding motion is initiated over a shear surface when the factor of safety for slope stability (F) is less than 1. However, the term landslide is not meaningful for debris flows with a flowing motion.(2) Sliding motion can be measured in oriented core and outcrop, but such measurement is not practical on seismic profiles or radar images. (3) Although 79 MTD types exist in the geological and engineering literature, only slides, slumps, and debrites are viable depositional facies for interpreting ancient stratigraphic records. (4) The use of the term landslide for highvelocity debris avalanches is inappropriate because velocities of mass-transport processes cannot be determined in the rock record. (5) Of the 21 potential triggering mechanisms of sediment failures, frequent short-term events that last for only a few minutes to several hours or days (e.g., earthquakes, meteorite impacts, tsunamis, tropical cyclones, etc.) are more relevant in controlling deposition of deep-water sands than sporadic long-term events that last for thousands to millions of years (e.g., sea-level lowstands). (6) The comparison of H/L (fall height/runout distance) ratios of MTD in subaerial environments with H/L ratios of MTD in submarine and extraterrestrial environments is incongruous because of differences in data sources (e.g., outcrop vs. seismic or radar images). (7) Slides represent the pre-transport disposition of strata and their reservoir quality (i.e., porosity and permeability) of the provenance region, whereas debrites reflect post-transport depositional texture and reservoir quality. However, both sandy slides and sandy debrites could generate blocky wireline (gamma-ray) log motifs. Therefore, reservoir characterization of deep-water strata must be based on direct examination of the rocks and related process-specific facies interpretations, not on wireline logs or on seismic profiles and related process-vague facies interpretations. A solution to these problems is to apply the term "landslide" solely to cases in which a sliding motion can be empirically determined. Otherwise, a general term MTD is appropriate. This decree is not just ...

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

Shanmugam¹

2018

Reference Module in Earth Systems and Environmental Sciences

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Modern internal waves and internal tides along oceanic pycnoclines: Challenges and implications for ancient deep-marine baroclinic sands: Discussion

Cited by 9 publications

References 13 publications

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

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

The landslide problem

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

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