Effects of some macrobiota on the Weipa Bauxite, northern Australia

Abstract

Bioturbation of the Weipa bauxite is effected primarily by termites and tree roots. Termite galleries extend into the Plasmic Zone to a depth of 20 m. Termite nests are constructed from the surrounding soil (averaging 30% kaolinite) and also from kaolinite derived from below the bauxite, with some parts of the nest containing 75% kaolinite. Measurement of termite nest volume from two 1 ha areas indicates nest materials amount to as much as 5 t/ha and that termites bring kaolinite to the surface to the extent of perhaps 10 kg/ha annually. Roots of Eucalyptus tetrodonta, the main forest tree of the region, penetrate the 3–6 m thickness of the bauxite at least as far as the top of the Mottled Zone and commonly some distance further. Penetrating roots displace the loose pisolithic bauxite, and eventually provide channels through the bauxite down which material may fall, thus tending to homogenise the deposit. Evidence of their effect on local redox conditions is revealed in mine faces by zones of variable ferruginous colouration. Tree-fall, mainly the result of cyclones, disturbs the soil and upper bauxite: about 0.5% of a 1 ha area is estimated to have been affected by tree-fall. Small nodules scattered throughout the bauxite, prolate ellipsoidal in shape, averaging 28 × 21 mm, are interpreted as the fossilised pupal cases of ground-dwelling beetle larvae, probably scarabs or weevils.