Bacterial origin of East Australian continental margin phosphorites

Abstract

Many models of the origin of marine phosphorites require a sediment rich in organic matter, which by decomposition releases phosphorus for the precipitation of carbonate fluorapatite^1–7. This concept is useful in explaining contemporary phosphorite in areas of very high productivity off the coasts of Peru–Chile and South West Africa^8–10 where there are high organic matter fluxes to the sea floor^4–7,11. It does not explain the origin of marine phosphorite deposits which formed in regions of limited oceanic upwelling and productivity^12–14. The East Australian continental margin, an area of phosphogenesis throughout the late Pleistocene and Holocene^13,14, is a modern analogue of an ‘East Coast’ phosphogenic province^15–17 with low productivity over the upper slope region where the most recent phosphorites have been found¹⁸. Evidence is reported here for the carbonate fluorapatite in the East Australian phosphorites being located within bacterial cellular structures, and a model proposed for the origin of these deposits through the slow bacterial assimilation of phosphorus from seawater in an area of restricted sedimentation.