Reply to the Discussion of He et al. (2011, Geo-Marine Letters) Evidence of internal-wave and internal-tide deposits in the Middle Ordovician Xujiajuan Formation of the Xiangshan Group, Ningxia, China

He, Yixin; Jinxiong, Luo; Gao, Zhenzhong; Zhan, Wenfeng

doi:10.1007/s00367-012-0290-2

Cited by 7 publications

(1 citation statement)

References 23 publications

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

Shanmugam¹

2018

Reference Module in Earth Systems and Environmental Sciences

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Comment on “Internal waves, an under-explored source of turbulence events in the sedimentary record” by L. Pomar, M. Morsilli, P. Hallock, and B. Bádenas [Earth-Science Reviews, 111 (2012), 56–81]

Shanmugam

2013

Earth-Science Reviews

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Reply to the Discussion of He et al. (2011, Geo-Marine Letters) Evidence of internal-wave and internal-tide deposits in the Middle Ordovician Xujiajuan Formation of the Xiangshan Group, Ningxia, China

Cited by 7 publications

References 23 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”

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

Comment on “Internal waves, an under-explored source of turbulence events in the sedimentary record” by L. Pomar, M. Morsilli, P. Hallock, and B. Bádenas [Earth-Science Reviews, 111 (2012), 56–81]

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