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Analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm-like oscillatory and combined flow. Experiments were carried out in a large wave tunnel and used a range of sand sizes (fine and very fine), wave periods (10.5 and 8 s), oscillatory velocities (0 to 125 cm/s), and unidirectional velocities (0 to 25 cm/s).At low unidirectional velocities (Յ10 cm/s), addition of an increasing collinear oscillatory flow caused the bed to evolve from small-scale (wavelength Ͻ 20 cm), symmetric, anorbital ripples, to large-scale (wavelength Ͼ 100 cm), symmetric, orbital ripples, to plane bed. At higher unidirectional velocities (Ͼ10 cm/s), a similar trend was noted, but ripples were more asymmetric. Three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions. These diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent.Distinctive features of small-scale asymmetric combined-flow ripples generated are: a 3D planform, round crest, and convex-up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a ''boxy'' appearance. Similarly, large-scale asymmetric combined-flow ripples had broad and round crests, convex-up stoss sides, and ''compressed profiles'' due to scouring at the toe of the stoss side.Hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities. Hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed-form scale and symmetry. Hummocks were more prevalent at longer oscillatory periods and in finer-grained sediment. Stratification produced by ''synthetically'' aggrading hummocky bed profiles closely resembles hummocky cross-stratification. With the introduction of only a small unidirectional-flow component, hummocks evolve into downstream-migrating large-scale asymmetric ripples, and the resultant cross-stratification becomes similar to that produced by unidirectional-flow dunes. Accordingly, these experiments suggest that much of the hummocky cross-stratification observed in the stratigraphic record is produced by storm-generated long-period oscillatory-dominant combined flows. Inasmuch as long-period, high-energy waves require deep, wide basins to form, hummocky cross-stratification may therefore serve as a useful indicator of deposition in unrestricted, open-water conditions.

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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