Geologic and palaeomagnetic constraints on the formation of weathered profiles near Inverell, Eastern Australia

Abstract

We use geologic and palaeomagnetic observations to constrain the timing and duration of weathering of the Oakwood bauxite, which outcrops in the New England region of New South Wales, Australia. The bauxite is developed on and overlain by mafic volcanic flows. Prior geochronologic results from surrounding regions indicate that age of these flows, and thus the age of the bauxite, is most likely between 18 and 26 Ma, though volcanics elsewhere in the Central volcanic province have a much greater range of between 6 and 56 Ma. Similarly, comparison of a new palaeomagnetic pole computed from the bauxite (Pole latitude= 75.4°N, longitude= 311.3°E, N=58, A95=4.4°) with the Australian apparent polar wander path gives estimated ages of 21–27 Ma. Individual samples of the bauxite have both normal and reversed polarity components of magnetization, which, beside providing a positive palaeomagnetic reversal test, suggests that the duration of weathering exceeded 10,000 years and more likely lasted several million years. Our results suggest that the Oakwood region had a palaeoclimate and palaeoenvironment that was conducive for deep weathering over a significant period in a the time interval from the mid-Oligocene to the Early Miocene.