The origin of horizontal laminae in ephemeral stream channel-fill

The 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 variability.