PHOSPHOGENESIS AROUND THE PROTEROZOIC PHANEROZOIC TRANSITION

There was a very significant and widespread phosphogenic event around the Proterozoic-Phanerozoic transition. This is reflected in the occurrence of many major and minor latest Proterozoic and Cambrian phosphate deposits (phosphorites) in Asia, Australia, Africa and South America, as well as minor occurrences in many other parts of the world. The major peak in phosphogenesis was in the Tommotian, with lesser events in the Ediacaran and the Lenian, bracketed by other minor though significant events. Recent evidence on the timing of Proterozoic phosphogenesis does not now support the suggestion of a phosphogenesis-glaciation link. These peaks in phosphogenesis are taken as evidence that there was a marked increase in the phosphate content of the shallow seas at about this time, possibly as a result of the circulation of deep, phosphorus-rich ocean waters into the photic zone. Not only was this responsible for the formation of phosphorites but it also had a profound effect on the biota, and may have been a driving mechanism for the Cambrian faunal 'explosion' and the initiation of biomineralization.