This depth is coincident with the trees' rooting depth, and mixing has led to homogenisation of the topsoil here, because surface sorting by rainwash is inhibited by persistent vegetation cover, and tree turnover is capable of exhuming a large range of particle sizes.
Humphreys GS, Mitchell PB (1983) A preliminary assessment of the role of bioturbation and rainwash on sandstone hillslopes in the Sydney Basin.
It is inferred from the evidence of stable binding mechanisms that the root mat protected the mineral soil from the action of rainsplash and rainwash, and trapped sediment washed into the leaf litter from upslope.
If the above hypothesis is correct, the presence of fabric Type 4 in association with maculae suggests that proteoid roots can reduce the effectiveness of rainwash and cause the re-incorporation of fine material deposited at the soil surface by bioturbation.
In addition to the winnowing effect of bioturbation and rainwash proposed by Humphreys and Mitchell (1983), proteoid root mats actively retain medium-to-coarse material.
The arguments for proteoid roots mitigating the effectiveness of rainwash and contributing to the development of texture contrast initially appear contradictory.