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1 Division of Continental Geology, Bureau of Mineral Resources, PO Box 378, Canberra, Australia
2 Department of Oceanography, Florida State University, Tallahassee, Florida, USA
3 Department of Geology, East Carolina State University, Greenville, North Carolina, USA
The nature and origin of phosphorites have been a matter of much speculation since were they first discovered more than 150 years ago. They are also of wide scientific interest in that they provide evidence of past changes in the biology and chemistry of the world’s oceans.
In the past ten years or so, due to a considerable extent to the efforts of the many participants in IGCP Project 156, our knowledge and understanding of phosphorites has increased enormously: it is now evident that there were times in earth history when phosphorites were preferentially deposited in many parts of the world. This probably was the consequence of the interaction of a number of factors including oceanography, changes of sea-level, and plate tectonics. Perhaps one of the most intriguing features to have become apparent in recent years is the link between times of phosphogenesis and periods of major evolutionary change. Not only has our knowledge of ancient deposits increased but much information now exists on present-day deposits, such as those off Chile—Peru and the more enigmatic deposits off southern Australia. In addition, there are better data and a greater understanding of some of the details of phosphorite formation and phosphate hardgrounds, on the role of bacteria in phosphogenesis, and on the petrology, mineralogy, geochemistry and biology of phosphorites.
Whilst a great deal has been achieved in the past 10 years, there still remains much to be done: there is scope for grass-root phosphate exploration in countries presently lacking their own sources of phosphate; the nature of the relationship between phosphate and some diagenetic minerals such as zeolites has yet to be elucidated; similarly the link between phosphogenesis and the formation of petroleum source rocks needs to be better understood and much more work is required on Precambrian phosphorites.
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