^{Comment on “A new classification system for mixed (turbidite-contourite) depositional systems: Examples, conceptual models and diagnostic criteria for modern and ancient records” by S. Rodrigues, F.J. Hernández-Molina, M. Fonnesu, E. Miramontes, M. Rebesco, D. C. Campbell [Earth-Science Reviews (2022), https://doi.org/10.1016/j.earscirev.2022.104030]}

Abstract

Rodrigues et al. (2022) have proposed a new classification for mixed turbidite-contourite depositional systems based on their notion that there is only one type of tubidite and that there is only one type of contourite in deep-marine systems. However, there are at least 36 turbidite types and 4 contourite types in the published literature. Furthermore, they have used the term “bottom current” to represent a single unique current, which flows along-slope. Nevertheless, there are 4 major types of bottom currents (thermohaline contour currents, tidal currents, baroclinic currents, and wind-driven currents). With the exception of contour currents, the other three currents do not and cannot flow along-slope. The problem here is that the authors have failed to provide a clear and precise definition of the terms “turbidite”, “contourite”, and “bottom current” Consequently, their classification has added a new layer of confusion to an already muddled domain of turbidite-contourite research. Importantly, their review article suffers from failing to cite pioneering and seminal works on turbidites (e.g., Kuenen, 1957; Bouma, 1962; Bagnold, 1962,; Middleton, 1967; Sanders, 1965; among others) and on contourites (e.g., Hollister, 1967). In seeking clarity, the purpose of this discussion is to identify specific issues with 14 questions under the following topics: (1) the turbidite problem, (2) the contourite problem, (3) the bottom-current problem, and (4) the seismic geometry vs. process sedimentology problem. Hopefully, the authors would respond with necessary definitions, empirical data, and references.

Introduction

In developing a new classification system for mixed (turbidite-contourite) depositional systems, the first and foremost step is to provide a clear and precise definition of the terms “turbidite”, “contourite”, and “bottom current”, the three basic terms that form the foundation of the paper. Disappointingly, Rodrigues et al. (2021) did not define these three basic terms. Consequently, the entire article is a confusing maze of case studies, figures, and assertions without clarity. In articulating this foundational problem, I have identified specific issues with 14 questions under the following topics: (1) the turbidite problem, (2) the contourite problem, (3) the bottom-current problem, and (4) the seismic geometry vs. process sedimentology problem. Hopefully, the authors would avail this opportunity in providing clarity.