Key Future Directions For Research On Turbidity Currents and Their Deposits

Abstract

Turbidity currents, and other types of submarine sediment density flow, redistribute more sediment across the surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The deposits of these flows are of societal importance as imperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understanding field observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than , 0.6u. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low (, 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces

Facies architecture of submarine channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents

“…Data from full‐scale natural flows in submarine channels, however, are limited to velocity profiles [e.g., Xu , ], and Talling et al . [] state that a key future research direction is the direct measurement of density stratification in natural turbidity currents.…”

The Stratigraphic Record of Submarine-Channel Evolution

“…Sediment-gravity flows have rarely been directly observed in the ocean (Talling et al, 2015). However, recent monitoring data record the hourly to annual interaction between submarine channels and sediment-gravity flows (e.g., Zeng et al, 1991;Xu et al, 2004;Paull et al, 2010;Conway et al, 2012;Cooper et al, 2013;Sumner and Paull, 2014;Talling et al, 2015;Hughes Clarke, 2016). These data underscore the short-term transience of seafloor geomorphology and multi-phase bed reworking, local deposition, and bypass of sediment-gravity flows active during channel initiation, maintenance, and filling (e.g., Covault et al, 2014).…”

Development of cutoff-related knickpoints during early evolution of submarine channels

“…Submarine channel deposits also form important petroleum reservoirs. A clear understanding of the controls and processes that create submarine channels remains elusive, because there are few direct measurements of turbidity currents that shape them and limited documentation of their longer term morphodynamic evolution (Talling et al, 2015). Instances of highly sinuous channels are especially puzzling where, in contrast with rivers, there is no obvious evidence of bend expansion and sinuosity development (e.g., Kolla et al, 2001; Deptuck et al, 2012, their figure 13b).…”