EFFECTS OF TROPICAL WEATHERING ON QUARTZ GRAIN SHAPE - AN EXAMPLE FROM NORTHEASTERN AUSTRALIA

Although previous work has provided qualitative evidence that the shap es of quartz sand grains can be modified significantly by postdepositi onal weathering and pedogenesis, the magnitude and rate of such change s have not been quantified. Fourier shape analysis of quartz grains fr om two generations of stabilized parabolic dunes from North Queensland , Australia, has shown that the grains in the older dunes are signific antly more angular than those from the younger dunes. Because the sand s of both dune generations have a similar provenance and transport his tory, the observed shape differences are attributed to postdepositiona l weathering in a humid tropical climate. This interpretation is suppo rted by scanning electron microscope examination of grain surface text ures and by textural analysis which revealed severe chemical etching a nd in situ silt production by disintegration of quartz grains. The obs erved changes in grain shape have been brought about in less than 8000 years.