DO PHOSPHORITES REPRESENT HEAVY ZN ISOTOPE SINKS?

All living things depend critically on zinc (Zn), a transition metal that is a component of all six kinds of enzymes. The isotopic composition of zinc in geological reservoirs can display the mechanism of diverse geological processes and events as well as the geochemical cycle of zinc in nature. In this research, various geochemical proxies derived from trace elements and rare earth elements (REEs) are used to monitor the effect of depositional parameters on the fractionation and accumulation of δ⁶⁶Zn in modern and Permian phosphorite deposits. Two different age phosphorite samples are investigated for their Zn isotope fractionation. In modern phosphorites, the lighter δ⁶⁶Zn encountered except Seamounts which are marked by heavier δ⁶⁶Zn with wide ranges. The variations of δ⁶⁶Zn values in Permian phosphorites are very diverse with wider ranges. Phosphogenesis during the Permian most likely had a place in mid-and outer-ramp conditions where organic geochemical indicators, nutritional trace-element proxies, and phosphorite percentages are all high. Despite being in considerably shallower waters in the Permian, it functions similarly to the modern ocean (relatively deep). During the deposition of modern and Permian phosphorites, various depositional factors including redox conditions, salinity, climate, productivity, and hydrodynamic conditions strongly influence the fractionation and abundance of δ⁶⁶Zn. Additionally, our results indicate that when the enrichment of REEs increases then the values of δ⁶⁶Zn also become heavier in the modern and Permian phosphorites. Based on our detailed interpretations, we can argue that the modern phosphorites act as sinks for lighter δ⁶⁶Zn with a low range (0.38-0.95‰), while Permian phosphorites are the sinks for heavier δ⁶⁶Zn concentration with a wider range (0.14-1.11‰). Meanwhile, the δ⁶⁶Zn values decrease during upwelling while non-upwelling zones fairly increase the values of δ⁶⁶Zn in modern and Permian phosphorites. The evolution of the Zn isotope in modern and Permian phosphorites endorses that the Zn isotope has great potential to be a global proxy of the oceans throughout the earth's history.