Iron Sources and Cycling During Diagenetic Transformations of Negev Phosphorites (Israel)

The Late Cretaceous Negev area in the Levant was influenced by high productivity upwelling in southern Tethys, leading to massive deposition of phosphorites. The phosphorites occur in two facies: (a) pristine phosphorites with low phosphorous (P) content, formed under low-energy, high-productivity conditions, and (b) reworked phosphorites with high P content, formed during high-energy episodes. Although paleoenvironmental settings leading to the Negev phosphorite depositions have been previously studied, questions remain regarding redox conditions and processes governing phosphogenesis and reworking. We combined iron (Fe) speciation, chemistry and total organic carbon (TOC) to enhance understanding of phosphorite environmental conditions. In pristine phosphorites, no significant correlation was found between Fe and P contents, suggesting distinct sources. Their Fe speciation is consistent with anoxic, ferruginous water column conditions, which were highly unlikely during Negev phosphorites formation. Aeolian transport of Fe-rich dust is proposed as the source of highly reactive Fe (Fe_HR) in pristine layers. Also, high concentrations of Fe_HR (>0.05%) and TOC (>2.0%) strongly correlate, while low contents show weak correlation reflecting more oxygenated conditions during early diagenesis. Reworked phosphorites exhibit higher Fe_HR/total Fe ratios than pristine ones, attributed to preferential removal of low-density minerals, containing poorly reactive Fe during high-energy reworking events. These findings clarify the interactions between P, Fe, and environmental conditions during phosphorite deposition, highlight the role of early diagenesis to geochemical signatures, and underscore the significance of aeolian Fe-rich dust as the primary source of highly reactive Fe in pristine phosphorites, offering broader interpretation of phosphorite formation in similar geologic settings.