ABSTRACTThe number of paired horizontal laminae in an ephemeral channel‐fill increases systematically down‐catchment from stream headwaters, and is shown to be functionally related to tributary confluence. Under moving storm conditions, each tributary sub‐catchment delivers a sediment‐laden discharge pulse that finds sedimentary expression in paired laminae of light and heavy minerals. Lamina differentiation is attributed to a congregational sorting mechanism. The direct relationship (r, = 0.903) between paired laminae and confluencing tributaries permits palaeoenvironmental inference of drainage‐net character, and palaeoclimatic va