Sediment gravity flows possess a wide range of rheological behaviors and past work has shown how transformations between flow types generate patiotemporal changes in the resultant sedimentary successions. Herein, the geometrical characteristics of a single climbing ripple are used 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 suggest 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. The present study indicates how the character of flow transformation can be elucidated from the details of a small-scale sedimentary structure.