Deep-water Processes by G.
Shanmugam
Defective turbidite paradigm
- Turbidity currents are inherently low in sediment concentration or low in flow density (Figure 1B), and hence, true HDTC cannot exist in nature (Shanmugam, 1996, 2000, 2012).
- 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, 2012).
- No one has ever documented the vertical facies model showing the R1, R2, R3, S1, S2, and S3 divisions in ascending order in modern deep-sea sediments (Shanmugam, 2000, 2012).
- 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, 2012).
- 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 (Sanders, 1965; Shanmugam, 1997; Hsü, 2004; Leclair and Arnott, 2005). 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.”
Figure 1. A. Schematic diagram
showing four common types of gravity-driven downslope processes (slides,
slumps, debris flows, and turbidity currents) that transport sediment into
deep-marine environments. After
Shanmugam et al. (1994). B.
Sediment concentration (% by volume) in gravity-driven processes. Note that
turbidity currents are low in sediment concentration (i.e., low-density flows).
After Shanmugam (2000). C. Based on mechanical behavior of
gravity-driven downslope processes, mass-transport processes are
considered to include slide, slump, and debris flow, but not turbidity currents
(Dott, 1963). D. The prefix “sandy” is used for mass-transport deposits (SMTDs)
that have grain (>0.06 mm: sand and gravel) concentration value equal to or
above 20% by volume. The 20% value is adopted from the original field
classification of sedimentary rocks by Krynine (1948). Figure after Shanmugam
(2012).
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, 2002). In stark contrast to
elusive HDTC in modern oceans, sandy mass-transport processes and their
deposits (SMTD) 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). Given the fact that the very
existence of sandy and gravelly turbidity currents has never been documented in
modern oceans, the outcrop-based turbidite facies models (Bouma, 1962; Lowe,
1982) and their more recent derivatives
with an alternative ensemble of nomenclature (Talling et al., 2012) and explanations (Postma et al., 2014) are unnecessary
distractions for interpreting ancient rock record objectively. The turbidite facies models, which are nothing more than a "groupthink", have suppressed scientific curiosity by averting novel observations and by preventing innovative process interpretations during the past 50 years. Because turbidite facies models tend to promote complacency and intellectual laziness, which undermine one's ability to practice pragmatic process sedimentology, it is imperative
to discard these flawed facies models altogether (Shanmugam, 2012, 2013, and 2014a, b).
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To download PDF, click or copy and paste URL
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