The oldest Pacific carbonate fluorapatite and Fe–Mn crust: а new episode of Turonian–Coniacian phosphatization event

Abstract Phosphatization events (intervals of enhanced authigenic carbonate fluorapatite, CFA, precipitation) interrupt Fe–Mn crust growth in the ocean and record key transitions in the paleoclimate and phosphorus cycle, yet the oldest such events in the Pacific Ocean remain poorly constrained. Here we report in situ U-Pb dating and trace element chemistry of CFA from a unique geode in sample 08D97 (Govorov Guyot, Western Pacific Magellan Seamount Trail), determined by LA-ICP-MS. Dating of the oldest Pacific CFA reveals a previously unknown event of phosphatization (88.8 ± 1.9 Ma) of biogenic carbonate that interrupted the deposition of Co-rich Fe–Mn crusts during one of the most extreme Turonian–Coniacian (~ 94–86 Ma) period of the Cretaceous hot greenhouse. The age of CFA replacing biogenic carbonate is ~ 18 Myr older than the previous dates for CFA (72–71 Ma) in the Atlantic and Pacific Co-rich Fe–Mn crusts. Thus, the sample from Govorov Guyot represents the oldest oceanic CFA, as well as one of the oldest oceanic Fe–Mn сrusts, apparently exceeding 90 Ma in age. The successive mineral assemblage change of CFA → (CFA + barite + calcite) → (CFA + calcite) → calcite along the geode’s layered chemogenic section may result from variations in bottom seawater temperature, pH , dissolved Ca, P, Ba, and S, along with phosphorus adsorption on the sediment-water interface, under different paleoclimatic conditions during the phosphatization of Magellan Seamount rocks through the Cretaceous–Cenozoic history of the Pacific Ocean.