Rapid gravity flow transformation revealed in a single climbing ripple

Sediment gravity flows demonstrate a wide range of rheological behaviors, and past work has shown how transformations between flow types generate spatiotemporal changes in the resultant sedimentary successions. We used the geometrical characteristics of a single climbing ripple to demonstrate how such flows can transform from a turbulent to a quasi-laminar plug flow, with the transitional clay flow sequence being manifested by abnormally large heterolithic sand-clay current ripples with small backflow ripples, and then abundant clay deposition associated with smaller ripples. Analysis of ripple size, angle of climb, grain size, internal erosional surfaces, and soft-sediment deformation suggests that transformation in the rheological character of the sediment gravity flow was rapid, occurring over a period of tens of minutes, and thus probably over a spatial scale of hundreds of meters to several kilometers. Our study indicates how the character of flow transformation can be elucidated from the details of a small-scale sedimentary structure.