Australia: The Land Where Time Began

A biography of the Australian continent 

Southern Yilgarn Craton - Aeolian Influence on Landforms and Soils, Southwestern Australia

Strong evidence has been found of prior aeolian activity within a landscape that has been developed on the dominantly granitic rocks, that are deeply weathered, on the Yilgarn Craton, southwestern Australia. Clay dunes or lunettes formed of multiple layers of arrays of clayey saltation deposits that extend up to 5 km to the southeast of playas, and in a 2-km wide band extending 10 km southeast of the ephemeral creek line, quartzose sand dunes and sheets are present. Within some clayey lunettes parabolic dunes are present. The winds responsible for the formation of these geomorphic entities were blowing from the northwest, as suggested by the parallel orientation of these diverse features and the elliptical shape of the playas. In this paper the authors¹ report multiple arrays of lunettes with up to 7 members that have not previously been reported from this region.

Evidence has been found indicating a more widespread, though subtle, aeolian influence on soils, with deposits of dust covering arras of the landscape that are inferred to be coeval with the clayey saltation deposits. Though they do not appear as a discrete layer, evidence has been found, including a plume of calcareous and lithic soils to the southeast of the major playa, in a landscape that otherwise is characterised by acidic, kaolinitic soils. There is a similar occurrence on soils that are deep and sandy, on slopes with a southeasterly aspect, is suggested to possibly indicate that topography interferes with transport of saltating sands during an arid phase of the climate. There are implications for agricultural management, mineral exploration and interpretations of ecological gradients in similar undisturbed landscapes.

In this landscape salinisation and erosion dominates in current desertification. The authors¹ suggest a means of interpreting responses to previous climate change is provided by aeolian deposits, a key to the prediction of possible outcomes of desertification and climate change. If it is assumed that Bowler's theory, that an adjacent formation of a salinised playa bed is required by clay dunes is correct it is indicated by the arrays of clayey lunettes, together with vegetated former playas, that the landscape has undergone multiple cycles of salinisation and recovery. Therefore, lunettes may provide the means of predicting the hydrological responses of the landscape to the widespread removal of natural vegetation for farming. To provide a timescale for these landscape processes dating of the various sequences is required.

Sources & Further reading

1. Harper, R. J., and R. J. Gilkes. "Aeolian Influences on the Soils and Landforms of the Southern Yilgarn Craton of Semi-Arid, Southwestern Australia." Geomorphology 59, no. 1–4 (4/2/ 2004): 215-35.