The new knowledge is written on sedimentary rocks – a comment on Shanmugam’s paper “the hyperpycnite problem”

Abstract

In a recent contribution G. Shanmugam (2018) discusses and neglects the importance of hyperpycnal flows and hyperpycnites for the understanding of some sediment gravity flow deposits. For him, the hyperpycnal flow paradigm is strictly based on experimental and theoretical concepts, without the supporting empirical data from modern depositional systems. In this discussion I will demonstrate that G. Shanmugam overlooks growing evidences that support the importance of hyperpycnal flows in the accumulation of a huge volume of fossil clastic sediments. Sustained hyperpycnal flows also provide a rational explanation for the origin of well sorted fine-grained massive sandstones with floating clasts, a deposit often wrongly related to sandy debris flows.

Reply to discussions by Zavala (2019) and by Van Loon, Hüeneke, and Mulder (2019) on Shanmugam, G. (2018, Journal of Palaeogeography, 7 (3): 197–238): ‘the hyperpycnite problem’

“…Since the original description of hyperpycnal flows for deltaic settings (i.e., density of river water is greater than density of basin water) by Bates (1953), the basic definition of hyperpycnal flows is still elusive from a fluid dynamic point of view. Zavala (2019) states that, "Clearly, we don't equate turbidity currents (Newtonian turbulent flows) to hyperpycnal flows." This statement only informs the readership what hyperpycnal flows are not.…”

“…The major advantage of experiments is that it allows researchers to measure fluid dynamical properties and observe sedimentary characteristics of deposits. Both Mutti et al (1999) and Zavala (2019) have failed to appreciate the importance of fluid mechanics in defining turbidity currents. In our flume experiments, the distinction between debris flows and turbidity currents in terms of fluid rheology and flow state is inescapable ( Fig.…”

“…1) Group 1 of researchers would recognize the importance of bottom layer with different rheology and flow state (Bagnold 1956;Sanders 1965;Shanmugam 1996). 2) Group 2 would not (Kuenen 1951;Postma et al 1988;Mutti et al 1999;Zavala 2019). Postma et al (1988) would combine both layers and classify them together as "High-density turbidity currents" (Fig.…”

“…Specifically, in proposing his facies models of intrabasinal and extrabasinal turbidites, Zavala has failed to take into account the importance of submarine canyons in advocating submarine fan models (Shanmugam 2018a). Instead of providing empirical data for verification, he cites his own earlier publication as the proof that the facies models must be correct with the following statement (Zavala 2019): "Intrabasinal and extrabasinal turbidites display diagnostic characteristics in their deposits that allow a clear differentiation between them (Zavala and Arcuri 2016)." The issue here is the role of submarine canyons.…”

“…2 Result and discussion: reply to Zavala (2019) 2.1 Paper title Zavala has chosen an awkward title for his discussion, which is "The new knowledge is written on sedimentary rocksa comment on Shanmugam's paper "The hyperpycnite problem". According to the Cambridge Dictionary, the term "knowledge" is defined as follows: "Awareness, understanding, or information that has been obtained by experience or study, and that is either in a person's mind or possessed by people generally".…”