PEDOGENESIS, BIOTURBATION AND OPTICALLY STIMULATED LUMINESCENCE

Effects of bioturbation on an 80 cm thick inceptisol in the SE Australian highlands were examined, where we previously estimated soil production using cosmogenic nuclides and burial dates from optical ages of soil samples (Wilkinson et al., 2005). Soil at this ridge crest site may have been ~ 30 cm thinner during the Last Glacial Period (LGP), consistent with sparse vegetation inferred from late Pleistocene aeolian cliff-top deposits nearby (Hesse et al., 2003). Accordingly, a diffuse stonelayer (28 – 55 cm depth) underneath a relatively stone-free horizon may be a former surface lag or a characteristic of a biogenic, three-layered soil. Therefore, current and previous biotic activity was examined and combined with data on the particle size distribution, bulk density and organic material content. Modern biotic activity was assessed by a micromorphology analysis (pedotubules, macula soil, charcoal, litter and living roots) while previous activity was quantified using optical dating.

The results illustrate that modern biotic activity affects the soil profile from the surface to the saprolite. Levels are highest in the E-horizon and decrease exponentially to the saprolite . This activity is consistent with the optical ages that increase exponentially with depth and indicate soil from all depths have previously been exposed to sunlight.

We propose a two-stage history: during the LGP surface deflation prevented topsoil development, however once vegetation cover increased, biotically-mounded soil was retained on slope, and a stone-free topsoil accumulated while the former lag sank to the depth-limit of biotic mining.

References

Hesse, P., Humphreys, G. S., Selkirk, P. M., Adamson, D. A., Gore, D. B., Nobes, D. C., Price, D. M., Schwenninger, J.-L., Smith, B., Tulau, M., and Hemmings, F., 2003, Late Quaternary aeolian dunes on the presently humid Blue Mountains, eastern Australia: Quaternary International, v. 108, p. 13-32.

Wilkinson, M. T., Chappell, J., Humphreys, G. S., Fifield, K., Smith, B., and Hesse, P. P., 2005, Soil production in heath and forest, Blue Mountains, Australia: influence of lithology and palaeoclimate: Earth Surface Processes and Landforms, v. 30, p. 923–934. Erratum: v. 30, p. 1683-1685.