Authigenic Formation of Phosphorites

There is no consistent definition for the use of the term phosphorites. Suggestions reach from a limiting P content of 6 wt.% (van Cappellen and Berner 1988) to a threshold value of 18 wt.% P O, as representative for authigenic and biogenic phosphate minerals (Jarvis et al. 1994). However, the formation of secondary P phases from initially more labile-P in marine sediments (see above) is one major sink for phosphoms on Earth, because this general process results in sequestration of P from the nutrient cycle in the water column (e.g. Compton et al. 2000). 

Research on the benthic phosphoms cycle and phosphorites formation in particular was intensified especially in the seventies to early nineties of the last century (e g. Burnet 1977 Burnett and Froelich 1988 Burnett and Riggs 1990 Nolton and Jarvis 1990 Follmi 1996 Gleim et al. 2000). All present result clearly substantiate that the process of phosphogenesis (= the authigenic formation of carbonate fluorapatite - CFA) is highly complex and not completely understood. However, hydroxy-apatite may be the primary authigenic P- 

or the stable isotopic composition of sedimentary apatite reflecting the variability of environmental conditions (e g. summarized in Kolodny and Luz 1992). Nevertheless, control factors of phosphogenesis in different environments are still under debate, particularly with regard to the overall benthic C-cycle. 

---