『Abstract
　In this study, porewater chemistry, solid-phase analysis and microscopic observations were combined to evaluate phosphogenesis in three boxcores located within the intensive oxygen minimum zone of the Arabian Sea. Three parameters, namely a decrease of the dissolved phosphate and fluoride concentrations with depth, saturation with respect to carbonate fluorapatite, and the presence of a solid-phase Ca-phosphate mineral, all indicate that phosphogenesis is currently taking place at all three sites. Authigenic apatite precipitation rates vary between 0.076 and 1.94 μmol P cm^-2 yr^-1, and are of the same order of magnitude as reported for other high productively areas. Precipitation of an intermediate precursor precedes francolite formation in the continental slope sediments on the Karachi Margin. Results of a diagenetic P model indicate that phosphogenesis is induced by high rates of organic matter degradation. Dissolution of fish debris is likely to provide a substantial additional source of phosphate. Redox iron cycling does not influence phosphogenesis in these environments. Model results suggest that sediment mixing is essential in promoting early diagenetic phosphogenesis. The highest rate of francolite formation was observed in a boxcore taken on the Oman Margin, where it contributes to the formation of a Holocene phosphorite deposit. This observation contrasts with previous reports of only old phosphorites in this area. Phosphorites are presently forming on the Oman Margin as a result of: (a) deposition of older, reworked material from the continental shelf, which has undergone an earlier phase of phosphogenesis; (b) a high input of reactive P (fish debris and degradable organic matter); (c) a relatively low sediment accumulation rate; and (d) the absence of winnowing on this location. Holocene phosphorite deposits may be less common on the Oman Margin than in other coastal upwelling areas because of the narrowness of the shelf and the steepness of the slope, which limit the area where phosphorite formation may occur.

Keywords: Phosphogenesis; Phosphorites; Oxygen minimum zone; Arabian Sea; Early diagenesis』

1. Introduction
2. Materials and methods
　2.1. Sediment sampling and core description
　2.2. Porewater analysis
　2.3. Solid-phase analysis
　2.4. Description of the model
3. Results
　3.1. Porewater
　3.2. Solid phase
　3.3. Microscopic observations and calibrated ¹⁴C ages of apatite macro particles in BC484
　　Coated foraminifers
　　Phosphatised pelletes
　3.4. Application of the model
4. Discussion
　4.1. Authigenic apatite formation
　　Porewater phosphate and fluoride concentrations
　　The francolite saturation state
　　Solid-phase authigenic phosphorus
　4.2. Implications of the model
　4.3. Phosphorite formation in BC484
　　4.3.1. Winnowing
　　4.3.2. Redeposition
5. Conclusions
Acknowledgements
Appendix A
References