From Turbid to Lucid: A Straightforward Approach to Sediment Gravity Flows and Their Deposits

Abstract

Deepwater sediment gravity flows are categorized on the basis of a combination of four parameters – sediment concentration, sediment-support mechanism, flow state (laminar or turbulent), and rheology. Because there is no agreement among sedimentologists about which of these parameters should be the decisive one, one school’s turbidites become another school’s debrites, and vice-versa. Except for rheology, all of these parameters change gradationally from one end member to another.Therefore, rheologi- cal classification of sediment gravity flows should be the most straightforward and the least controversial.These flows can be either Newtonian (i.e., turbidity currents), or non-Newtonian (i.e., debris flows).However, identification of flow rheology by examining the deposits may not be easy.Although we may confidently identify some rocks as tur- bidites and others as debrites, there are some transitional deposits, here called densites, that share both the characteristics of turbidites and debrites. Densites are the deposits of dense flows, which are rheologically stratified flows having a composite rheology of Newtonian fluids and non-Newtonian fluids. Moreover, the absence of a general term for all types of sediment gravity flow deposits has resulted in overuse and misuse of the term turbidite.The term ‘gravite’ is proposed here for deposits of any kind of sediment gravity flow, irrespective of their depositional environment. INTRODUCTION