Ten turbidite myths

Abstract

During the past 50 years, the turbidite paradigm has promoted many myths related to deep-water turbidite deposition. John E. Sanders (1926–1999), a pioneering process sedimentologist, first uncovered many of these turbidite myths. This paper provides a reality check by undoing 10 of these turbidite myths. Myth No. 1: turbidity currents are non-turbulent flows with multiple sediment-support mechanisms. Reality: turbidity currents are turbulent flows in which turbulence is the principal sediment-support mechanism. Myth No. 2: turbidites are deposits of debris flows, grain flows, fluidized flows, and turbidity currents. Reality: turbidites are the exclusive deposits of turbidity currents. Myth No. 3: turbidity currents are high-velocity flows and therefore they elude documentation. Reality: turbidity currents operate under a wide range of velocity conditions. Myth No. 4: high-density turbidity currents are true turbidity currents. Reality: Ph. H. Kuenen (1950) introduced the concept of “turbidity currents of high density” based on experimental debris flows, not turbidity currents. High-density turbidity currents are sandy debris flows. Myth No. 5: slurry flows are high-density turbidity currents. Reality: slurry-flows are debris flows. Myth No. 6: flute structures are indicative of turbidite deposition. Reality: flute structures are indicative only of flow erosion, not deposition. Myth No. 7: normal grading is a product of multiple depositional events. Reality: normal grading is the product of a single depositional event. Myth No. 8: cross-bedding is a product of turbidity currents. Reality: cross-bedding is a product of traction deposition from bottom currents. Myth No. 9: turbidite facies models are useful tools for interpreting deposits of turbidity currents. Reality: a reexamination of the Annot Sandstone in SE France, which served as the basis for developing the first turbidite facies model, suggests a complex depositional origin by plastic flows and bottom currents. Myth No. 10: turbidite facies can be interpreted using seismic facies and geometries. Reality: individual turbidity-current depositional events, commonly centimeters to decimeters in thickness, cannot be resolved in seismic data. All turbidite myths promote falsehood and should be abandoned.