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

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Peretyazhko, E. A. Savina, E.A. Gladkochub This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9376046/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract LA-ICP-MS is applied to a sample from Govorov Guyot (Western Pacific Magellan Seamount Trail), which encloses a geode partially filled with biogenic phosphatized carbonate and bears carbonate fluorapatite (CFA), for in situ CFA U-Pb dating, minor and trace element chemistry. 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 ~12–18 Myr older than the previous dates for CFA (77–71 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. Oldest Pacific carbonate fluorapatite Co-rich Fe-Mn crust Turonian–Coniacian phosphatization events Magellan Seamount Trail Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Phosphorus is a main energy carrier in living organisms and the dominant limiting nutrient for oceanic primary productivity, while its biogeochemical cycle influences crucially the global climate and biodiversity (Van Cappellen and Ingall 1996; Slomp and Van Cappellen 2007). The amount of dissolved P in the ocean is controlled by the tradeoff between its supply, mostly from terrestrial weathering, and loss by burial in marine sediments and Fe-Mn crusts, together with organic matter (Föllmi 1996; Planavsky et al. 2010). As a result of sediment diagenesis caused by global deficiency of seawater oxygen (Oceanic Anoxic Event, OAE) and local upwelling of cold bottom water, it is authigenic carbonate fluorapatite (Ca₅(PO₄,CO₃)₃F, CFA) precipitated upon rock surfaces and between Fe-Mn crust layers that becomes a major P sink (Filippelli and Delaney 1996; Hein et al. 1993; Jaing et al. 2020). The periods of enhanced phosphorus accumulation and CFA precipitation are termed phosphatization events . The evolution of phosphogenesis, CFA precipitation, and Fe-Mn crust growth in the oceans was controlled by local upwelling of cold deep bottom water rich in nutrients, the position of the oxygen minimum zone (OMZ), phosphorus cycle dynamics, and bioproductivity patterns. Upwelling increases bioproductivity by supplying oxygen and P-rich cold water to shallow shelves of continental margins and oceanic islands which make natural barriers for underwater currents. A large portion of dissolved phosphorus is consumed by plankton, becomes buried in sediments after the organisms die, and then converts to CFA during diagenesis (Föllmi 1996; Filippelli 2011). Reactions in the OMZ lead to partial dissolution of Fе- and Mn-oxyhydroxides, while the release of the adsorbed phosphorus into the bottom water provides its local P enrichment (Yao and Millero 1996). Suboxic–anoxic conditions favorable for phosphatization of carbonates and CFA precipitation appear at intersections of seamount slopes with the OMZ. Dating of CFA in phosphorites, marine sediments, and Fe-Mn crusts can provide valuable insights into the Cretaceous to modern climates, seawater redox conditions, and phosphorus cycle dynamics (Zhao et al. 2020; Benites et al. 2021; Peng et al. 2024). U-Pb dating of CFA by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been largley used to constrain the length of interruptions in the Fe-Mn crust growth (Josso et al. 2019; Peng et al. 2024). The available biostratigraphic data on intervals of coexisting index species of calcareous nannoplankton bracket the age of Co-rich Fe-Mn crusts from the Western Pacific Magellan Seamount Trail (MST) and other equatorial Pacific areas at ~65–60 Ma (Peretyazhko et al. 2025). Mn- and Fe-oxyhydroxides in the old section of MST Co-rich Fe-Mn crusts (layers R, I-1, and I-2) were phosphatized, with CFA being the major sink of P, Ca, and F. In each phosphatization event, microcrystalline CFA formed pore cement in carbonate sediments and precipitated between Fe-Mn crust layers. As the concentration of phosphorus in seawater was increasing, CFA fully replaced calcite in the carbonate sediments (Cappellen and Berner 1991; Ekamparam and Singh 2020). In this study, a unique sample from MST Govorov Guyot, which contains the oldest Pacific CFA and Fe-Mn crust, is analyzed by SEM-EDS and LA-ICP-MS for CFA in situ U-Pb LA-ICP-MS dating, minor and trace element chemistry. Data and methods The analyzed sample 08D97 (Fig. 1a) was cut from a 31.8 kg (53×27×25 cm) block dredged out from a depth of 1691 m (17°57.8522' N, 151°17.2433' E) near the northeastern slope of MST Govorov Guyot during the 2016-2017 cruise of R/V Gelendzhik , JSC Yuzhmorgeologiya . The sample contains a Co-rich Fe-Mn crust consisting of three texturally different layers (I-1, II and III), 7 to 14 cm of total thickness, which record the Co-rich Fe-Mn ore deposition history, according to the general section of MST Fe-Mn crusts (Peretyazhko et al. 2025). The Fe-Mn crust precipitated upon hyaloclastite mainly composed of replaced volcanic glass (<2–4 mm clasts) and fragments of basaltic rocks cemented with foraminifera-bearing phosphatized biogenic carbonate. The study focused on a 6×3.5 cm geode within sample 08D97 (Fig. 1a), in a section of porous hyaloclastic material which strips several small cavities and geodes of different sizes. The geode is surrounded by phosphatized hyaloclastite coexisting with phosphatized Fe-Mn crust fragments and encloses CFA-replaced biogenic carbonate, layers of massive CFA, and a layer of acicular calcite lining the inner cavity wall (Fig. 1b). SEM-EDS and LA-ICP-MS Analyses were applied to a cut section of the geode polished with diamond pastes. The texture and mineralogy of the geode and the Fe-Mn crust were studied by scanning electron microscopy and energy dispersion spectrometry (SEM-EDS) at the Center for Isotope-Geochemical Studies ( IGC SB RAS , Irkutsk). The contents of minor and trace elements and U-Pb isotopes in СFA were measured by LA-ICP-MS at the Center for Geodynamics and Geochronology ( IEC SB RAS , Irkutsk). The SEM-EDS analyses were performed on a Tescan Mira-3 LMU microscope equipped with an Ultim MAX-40 SDD analyzer and an Aztec Energy XMax 50+ EDS system. The operating conditions were 20 kV accelerating voltage, <0.5 nA beam current, and 30 s count time. The instruments for LA-ICP-MS were an Agilent 7900 quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) coupled to a Photon Machines Analyte Exite 193 nm ArF Excimer laser-ablation platform with a HelEx II active double-volume cell (CETAC Teledyne, USA). LA-ICP-MS analyses were applied to 110 μm CFA spots were ablated using a repetition rate of 10 Hz at a laser fluence of 3.02 J/cm -2 in a flux of He as a carrier gas (Table S1). Isotopes of 51 elements were measured successively, at integration times of 5 to 30 ms: 9 Be, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 39 K, 43 Ca, 45 Sc, 47 Ti, 51 V, 52 Cr, 55 Mn, 57 Fe, 59 Co, 60 Ni, 63 Cu, 66 Zn, 71 Ga, 85 Rb, 88 Sr, 89 Y, 90 Zr, 93 Nb, 95 Mo, 118 Sn, 121 Sb, 133 Cs, 137 Ba, 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 153 Eu, 157 Gd, 159 Tb, 163 Dy, 165 Ho, 166 Er, 169 Tm, 172 Yb, 175 Lu, 178 Hf, 181 Ta, 184 W, 205 TI, 208 Pb, 209 Bi, 232 Th, and 238 U. The data quality was checked against measurements in reference materials: NIST SRM 612 for calibration; NIST SRM 610 as a secondary (Pearce 1997); and the contents of Ca (average SEM-EDS values at CFA ablation spots) as an in-house standard. The standard samples were measured after every four analyzed samples. U-Pb dating U-Pb LA-ICP-MS analyses of CFA were conducted at a 50 μm spot size and were ablated using a repetition rate of 10 Hz for single spot analysis (Table S2). The reference materials were the glass standard NIST SRM 610 as a primary reference material (Pearce 1997), McClure Mountain Syenite (MMS) apatite (Schoene et al. 2006) and Otter Lake (Barfod et al. 2005) apatite as secondaries. Each spot analysis consisted of a 20 sec background acquisition and 40 sec sample data acquisition followed by 40 sec for cleaning the sample cell and tubing. Every 4 samples analyzed were followed by one measurement of NIST SRM 610, MMS and Otter Lake apatites. Analytical results were processed using Iolite 4.10.5 software (Paton et al. 2011). The measured U–Pb LA-CP-MS data need correction for inter-element fractionation on 238 U/ 206 Pb ratios, due to matrix difference between apatite samples and standards (NIST SRM 610, MMS and Otter Lake apatites). Analytical procedure and subsequent processing of the primary data were performed according to the method described in (Li et al. 2014) and references therein. Correction of the ²⁰⁷Pb/²⁰⁶Pb ratio was carried out using NIST SRM 610 glass. The ²³⁸U/²⁰⁶Pb ratio was calibrated using the MMS apatite as a primary matrix-matched standard, whose age was calculated considering the initial ²⁰⁷Pb/²⁰⁶Pb of 0.882, determined by ID-TIMS total U-Pb isochron (Schoene et al. 2006), to account for the matrix effect. U-Pb ages (Fig. S1) and their uncertainties were calculated from Tera-Wasserburg concordia lower intercepts of the calculated regression line using the IsoplotR software (Vermeesch 2018). Results SEM-EDS The geode was studied in several fragments along cracks that crosscut gray phosphatized biogenic carbonate (Bio region, 11–12 mm), yellowish layers of dense chemogenic CFA (Chem region, 9–10 mm), and translucent acicular calcite lining (Cal region, 2–4 mm) (Figs. 1b,2). The biogenic region, with numerous foraminifers and other organic fossils (Fig. 2b,e), is composed of CFA replacing the carbonate material. The chemogenic region consists of a microcrystalline CFA aggregate with a porous top above dense massive material (Fig. 2a,c,d). Up the section, there follows a porous CFA aggregate bearing <1–2 µm barite grains and a 2–4 µm calcite zone overlain by a <5 mm layer of acicular calcite with sporadic barite and CFA inclusions (Fig. 2a). Compared to CFA Chem from the layered region, CFA Bio has lower average contents of Ca (35.2 against 36.3 wt.%, SEM-EDS data), P (12.7 against 13.3 wt.%), F (3.6 against 4.6 wt.%), but shows greater enrichment in Mg and Sr (both 0.3 against 0.1 wt.%), at approximately same amounts of S (0.8 wt.%), Na (0.7 wt.%), and impurities (Si, Al, Fe, K) making < 0.7 wt.% in total (Tables S3, S4). LA-ICP-MS The concentrations of minor (Si, Ti, Fe, Mn, Mg, Na, K, P, Al) and trace (Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Nb, Mo, Sn, Sb, Cs, Ba, Hf, Ta, W, Tl, Pb, Bi, Th, U, REE, Y) elements were determined at 18 ablation spots along geode sections (Fig. 1b; Table S5): 5 spots for CFA Bio (bio-1,-3,-5,-6), 10 spots for CFA Chem (slv-2,-7–15), and 3 spots in the calcite layer (cal-18–20). Figure 3 shows the concentrations of some elements relative to Al which is times higher in CFA Bio than in CFA Chem (1500–4500 ppm against 500–900 ppm, respectively). CFA Bio is enriched in Si, Fe, K, Rb, Ti, Zr, Sb, and Ga, while CFA Chem is depleted in Mn, P, Ba, Sr, Pb, U, Zn, and V. CFA throughout the geode contains 10 to 200 ppm REE and Y in total (Tables S3, S4). The REE+Y contents in CFA Bio are lower than in CFA Chem, except for bio-1 spot (Fig. 4). The PAAS-normalized REE+Y patterns are typical of CFA from marine sediments and hydrogenetic Fe-Mn crusts (Jiang et al. 2020), with a moderate HREE enrichment over LREE, a negative Ce anomaly (Ce* 0.1–0.4), and a positive Y anomaly. Calcite is generally depleted in minor and trace elements (average contents, ppm): 4103 Mg, 996 Si, 291 P, 203 Fe, 104 Sr, 51 Na, 45 Mn, 27 K, 16 Ba, 10 Cr, 8 Zn, 4 Ti, <0.n–0.0n REE and Y, (Table S3). The average total of all impurities is 6073 ppm. U-Pb dating The U-Pb isotope measurements in the geode were performed in three 300–400 µm areas of CFA Bio (bio-3,-5,-6) near the LA-ICP-MS spots, as well as near bio-7 spot from the surrounding biogenic phosphatized carbonate in hyaloclastite (Fig. 1b). Discordant ages of CFA Bio were determined from 25–26 analyses: 82.8 ± 6.5 Ma (bio-3), 87 ± 6.5 Ma (bio-5), and 83 ± 18 Ma (bio-6) at initial 207 Pb/ 206 Pb of 0.834 ± 0.008, 0.84 ± 0.03, and 0.843 ± 0.012, respectively (Fig. S2; Table S5). The initial 207 Pb/ 206 Pb values calculated for CFA Bio from an unanchored Tera-Wasserburg upper intercept differ slightly from the two-stage crustal Pb evolution model (Stacey and Kramers 1975) but are within the deep ocean range (Ben-Israel et al. 2014). The similarity of initial 207 Pb/ 206 Pb (0.834–0.843) allowed us to use the data for CFA Bio (spots bio-3,-5,-6) jointly and calculate the discordant U-Pb age from 76 analyses: 88.8 ± 1.9 Ma at initial 207 Pb/ 206 Pb 0.8440 ± 0.0036 and MSWD 1.7 (Fig. S2a). Note that the 207 Pb/ 206 Pb and 238 U/ 206 Pb values for 25 analyses from bio-7 spot (Fig. 1b) show greater variance, but they lie near or on the discordia line (Fig. S2a). Therefore, CFA Bio from the geode and from phosphatized hyaloclastite are coeval. U-Pb LA-ICP-MS data were also obtained for CFA Chem near spots (slv-7,-12,-15), in 200–300 µm areas (Figs. 1b, S3). Discordant ages of lower accuracy were calculated for three different combinations of 25 to 51 analyses of CFA Chem, at initial 207 Pb/ 206 Pb > 0.8: 72 ± 17 Ma (slv-7), 53.5 ± 9.1 Ma (slv-12 + slv-15), and 61 ± 19 Ma (slv-15), at initial 207 Pb/ 206 Pb 0.828 ± 0.032, 0.804 ± 0.017, and 0.814 ± 0.026, respectively (Fig. S3). Thus, chemogenic CFA precipitated much later than CFA Bio replacing carbonate in the biogenic region. Discussion The early deposition episodes of the MST Co-rich Fe-Mn сrust occurred in a shallow shelf at <500–600 m seawater depths, in the Campanian–Maastrichtian, and Late Paleocene (relict layer R, <65–60 Ma), Late Paleocene–Early Eocene (layer I-1, ~60–48 Ma) and in the Middle–Late Eocene (layer I‐2, ~48–38 Ma) (Peretyazhko et al. 2025). By analogy with the dated phosphorites from equatorial Pacific seamount deposits (Hein et al. 1993), the precipitation of CFA in the old crust layers R, I-1 and I-2 was inferred to span two phosphatization events: Late Eocene–Early Oligocene (39–34 Ma, with a peak at ~37 Ma) and Late Oligocene–Early Miocene (27–21 Ma, with a peak at ~25 Мa) (Peretyazhko et al. 2025). Meanwhile, recent U-Pb ages of CFA from Co-rich Fe-Mn crusts sampled at Pacific and Atlantic seamounts revealed a longer time span of phosphogenesis in the deposition history of oceanic CFA. It apparently lasted from ~72 to 7 Ma and included six episodes coinciding with growth hiatuses in the Co-rich Fe-Mn crusts (Peng et al. 2024). The 56–54 Ma phosphatization event was concurrent to a stage of global warming (Paleocene/Eocene Thermal Maximum, Fig. 5), while the other episodes correspond to transitions between cold and warm climates (Campanian–Maastrichtian boundary event, 72–71 Ma; Eocene/Oligocene Warm–Cool transition, 35–34 Ma; and Oligocene/Miocene Cool transition, 25–23 Ma) and to two Late Miocene cooling events (11–10 and 8–7 Ma). These episodes of oceanic phosphatization correlate with the respective events in continental settings (Pufahl and Groat 2017). Volcaniclastic fragments in sample 08D97 (Fig. 1a) represent the substrate on which layers I-1, I-2, and III of the Co-rich Fe-Mn crust formed. The interstices between small clasts of replaced volcanic glass in hyaloclastite and fragments of basaltic rocks in sample 08D97 are filled with phosphatized biogenic carbonate containing abundant foraminifers and other unidentified fossils. CFA has fully replaced biogenic carbonate in the geode and in the surrounding hyaloclastite. Euhedral crystal morphology, especially in the chemogenic region (Fig. 2a,f,g), indicates authigenic CFA precipitation. The PAAS-normalized REE+Y patterns of CFA in both biogenic and chemogenic regions lack the Eu anomaly and are similar to those for deep-seawater (Fig. 4). This is reliable evidence that CFA originated from seawater, without the effect of hydrothermal fluids on its crystallization and carbonate phosphatization (Piepgras and Jacobsen 1992; Klinkhammer et al. 1994). The CFA-replaced phosphatized biogenic carbonate hosts foraminifers and calcareous nannoplankton (Fig. 2b,f). The obtained U-Pb age of 88.8 ± 1.9 Ma for CFA Bio, with good statistics (Fig. S2a; Table S5), is ~12–18 Myr older than the previous determinations of 77–71 Ma for CFA from the lowermost Pacific and Atlantic Fe-Mn crust layers (Josso et al. 2019; Peng et al. 2024). Thus, the geode we analyzed stores the oldest known oceanic CFA precipitated during the Late Cretaceous phosphatization of the Pacific sediments. Biogenic carbonate in the geode was deposited and replaced by CFA during the hottest and longest climate event of the Cretaceous thermal maximum (Fig. 5). The Turonian–Coniacian (~ 94–86 Ma) Pacific climate and regional system was one of the most extreme periods of the Cretaceous hot greenhouse, when the Earth lacked polar ice caps and the oceans were the warmest. It was the time of global oceanographic, tectonic, and magmatic events associated with active plate motions in the Pacific and the Atlantic spreading (Huber et al. 2018). The Cenomanian–Turonian OAE2 (~94 Mа, Gangl et al. 2019) and Coniacian–Santonian OAE3 (87–84 Ma, Mansour and Wagreich 2022) anoxic conditions were the most recent global-scale catastrophic events in the geological history, when the oceanic and continental cycles of CO 2 , O, S, Fe, and P changed dramatically (Selby et al. 2009). The extreme warming conditions, with oceanic water surface temperatures ranging between 36 °C in the tropic latitudes and at least 20 °C in middle latitudes (Huber et al. 2018), continued till the Turonian–Coniacian boundary. The Cretaceous hot greenhouse effect apparently resulted from a combination of several paleo-geodynamic events, including large-scale volcanism with voluminous release of greenhouse gases. Furthermore, the time span between OAE2 and OAE3 corresponded to magmatic activity in several Large Igneous Provinces (LIPs), e.g., the Ontong Java LIP in the areas of the spreading Izanagi, Farallon, and Phoenix plates during the formation of the Pacific Plate fragment that accommodates the MST volcanic edifices (Seton et al. 2012; Hochmuth et al. 2015). Till recently, the oldest age of 99–92 Ma (Cenomanian–Turonian, early Late Cretaceous) was assigned to the Fe-Mn crust from the Tropic Seamount in the Canary Island Province, Atlantic Ocean (Marino et al. 2018). However, the crust growth event was timed using empirical Co-chronometry (Manheim and Lane-Bostwick 1988) which yields underestimated growth rates and thus overestimates the ages (Josso et al. 2019; Peretyazhko et al. 2025). According to an updated age model of Josso et al. (2019) based on cross-validation of Co-chronometry and 187 Os/ 188 Os isotope ratio, the Atlantic Fe-Mn crust rather started growing between 77 and 72 Ma. Meanwhile, the Fe-Mn crust fragments from the analyzed sample must be older than the phosphatization event (88.8 ± 1.9 Ma), given that biogenic carbonate was deposited at several sites on the geode wall surrounded with the crust (Fig. 1). Therefore, with its age apparently exceeding 90 Ma, it may be one of the oldest oceanic Fe–Mn crusts. Judging by the inner structure of the geode (Fig. 1b), its chemogenic region composed of microporous CFA postdates biogenic carbonate and its phosphatization. The subparallel layers in the geode were produced by CFA precipitation from seawater. Chemogenic CFA possibly crystallized in response to changes in bottom seawater: temperature, pH , contents of dissolved Ca, P, Ba, and S, as well as adsorption of phosphorus on the sediment-water interface, etc. (Filippelli 1997; Nishi et al. 2017; Jiang et al. 2020 and references therein). CFA precipitated together with barite and calcite in the upper part of the chemogenic region (Fig. 2a), and the crystallization sequence was completed by acicular calcite lining the inner cavity (Fig. 1b). The successive change of chemogenic phases CFA → (CFA + barite + calcite) → (CFA + calcite) → calcite apparently resulted from variations in some physical and chemical parameters of bottom seawater under different paleoclimatic conditions during phosphatization of MST rocks in the ~72–54 Ma time span (dating of CFA Chem, Fig. S3; Table S5). Conclusion The reported analyses of CFA in the sample from Govorov Guyot revealed the earliest (88.8 ± 1.9 Ma) phosphatization event of biogenic carbonate that interrupted the deposition of Fe-Mn crusts during one of the most extreme Turonian–Coniacian (~ 94–86 Ma) period of the Cretaceous hot greenhouse. The obtained oldest age of Pacific CFA, which has fully replaced biogenic calcite in the geode, is ~12–18 Myr older than the previous dates for CFA (77–71 Ma) in the Atlantic and Pacific Co-rich Fe-Mn crusts. The sequential deposition of CFA, barite, and calcite in the geode's chemogenic section may result from variations in physical and chemical parameters of bottom seawater under different paleoclimatic conditions during the phosphatization of Magellan Seamount rocks through the Cretaceous–Cenozoic history of the Pacific Ocean. The ages of chemogenic CFA can be updated in the future and complemented by dating calcite and CFA from the oldest Fe-Mn сrust around the geode. Further studies of CFA in MST rocks and Fe-Mn crusts will reveal potential older phosphatization events and provide more rigorous constraints on the duration of the known episodes in which Pacific sediments were phosphatized in different Cretaceous through Cenozoic paleoclimatic conditions. Declarations Acknowledgements We thank the crew members of R/V Gelendzhik , JSC Yuzhmorgeologiya for support during the cruises. We appreciate assistance of our colleagues from IGC SB RAS, Irkutsk: O.Yu. Belozerova for SEM-EDS analyses and I.A. Vlasyuk for sample preparation. Author contributions ISP spearheaded the research, conceptualized the study and crafted the initial draft of the manuscript. EAS and EAG and revised the text, contributed to creating figures and tables. All authors participated in interpreting the results and engaging in discussions. Funding The study was funded by grant 25–17–00128 from the Russian Science Foundation. Availability of data and materials Data is provided within the manuscript and supplementary file. References Alibo DS, Nozaki Y (1999) Rare earth elements in seawater: particle association, shale- normalization, and Ce oxidation. 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Supplementary Files GLResearchLettersSupInfPeretyazhkoetal2026.pdf Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 16 Apr, 2026 Editor assigned by journal 13 Apr, 2026 Submission checks completed at journal 13 Apr, 2026 First submitted to journal 10 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9376046","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":626066576,"identity":"357b423c-cbbb-41aa-820a-1ad22d3c8e70","order_by":0,"name":"I.S. Peretyazhko","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuElEQVRIiWNgGAWjYJCCA0Asx8DA2HiAJC3GQC0NxGsBgcQGqF7CwJx/deLBLxX30te2H244wLjnMGEtljPebjgsc6Y4d9uZRKDDnhGhxeDG2Q2HJdsScrcdAGk5QIKWdLPzD4nVcr53w8GPbQkJZjeItcVyBu+GwwxnEgy33QDaknAgnbAWc/6zmz/+qEiQNzuf/vDBhwPWRDhMIoGBmQfGSyCsAaiF/wAD4w9iVI6CUTAKRsHIBQBaA0ry/405TAAAAABJRU5ErkJggg==","orcid":"","institution":"Vinogradov Institute of Geochemistry","correspondingAuthor":true,"prefix":"","firstName":"I.S.","middleName":"","lastName":"Peretyazhko","suffix":""},{"id":626066580,"identity":"d5e0cf64-0e12-4ab0-9440-b25eec173178","order_by":1,"name":"E. A. Savina","email":"","orcid":"","institution":"Vinogradov Institute of Geochemistry","correspondingAuthor":false,"prefix":"","firstName":"E.","middleName":"A.","lastName":"Savina","suffix":""},{"id":626066583,"identity":"8d94ff96-afde-45c4-afe0-ea0cb5a5a2f9","order_by":2,"name":"E.A. Gladkochub","email":"","orcid":"","institution":"Institute of the Earth’s Crust","correspondingAuthor":false,"prefix":"","firstName":"E.A.","middleName":"","lastName":"Gladkochub","suffix":""}],"badges":[],"createdAt":"2026-04-10 07:38:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9376046/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9376046/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107869138,"identity":"3a9be25b-ca39-45cd-bcc2-55e2b4455f62","added_by":"auto","created_at":"2026-04-27 07:36:12","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":708324,"visible":true,"origin":"","legend":"\u003cp\u003eSample\u003cstrong\u003e \u003c/strong\u003e08D97 (a) and enlarged geode section (b) with phosphatized biogenic carbonate, layers of chemogenic CFA, and a lining of acicular calcite. The geode is surrounded by phosphatized hyaloclastite, biogenic carbonate, and the Fe-Mn crusts. Numerals are numbers of LA-ICP-MS spots. Cal = calcite, Brt = barite.\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/af42a549cdd37e486bef1f14.jpeg"},{"id":108006114,"identity":"c46452f4-7050-4df4-a234-2766f1c57a3a","added_by":"auto","created_at":"2026-04-28 12:53:30","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":641497,"visible":true,"origin":"","legend":"\u003cp\u003eBSE (a-d) and SE (e-g) images of geode fragments. (a) Upper part of the layered chemogenic section. (b,e) Biogenic region with foraminifera remnants. (f) Contact of biogenic and chemogenic regions. (g) euhedral crystals of chemogenic CFA, arrows point to nannoplankton imprints.\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/1615781595d76301bf1dfc14.jpeg"},{"id":107755038,"identity":"20dcf91d-bfe5-4221-8187-a951ae443708","added_by":"auto","created_at":"2026-04-24 18:41:35","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":164130,"visible":true,"origin":"","legend":"\u003cp\u003eVariations in the concentrations of Al relative to Mn, P, Si, Fe, Ba, Sr, K, Rb, Pb, U, Ti, Zr, Zn, V, Sb and Ga from the geode in sample 08D97. r = significant correlation coefficient value at the 95% confidence level.\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/d0c0b78158135f755e7d3655.jpeg"},{"id":107870172,"identity":"891e42c6-d8f7-41d0-ae05-d932ef2d0959","added_by":"auto","created_at":"2026-04-27 07:39:00","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":190367,"visible":true,"origin":"","legend":"\u003cp\u003ePAAS-normalized REE+Y patterns of CFA from the biogenic and chemogenic regions in the geode. Data of deep-seawater (1502 m) from the North Pacific (Alibo and Nozaki 1999).\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/c78dc3b31ef609c46029e74a.jpeg"},{"id":107755041,"identity":"1b05a2ce-e739-479e-a27d-b6f6b30c3603","added_by":"auto","created_at":"2026-04-24 18:41:35","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":365531,"visible":true,"origin":"","legend":"\u003cp\u003eCretaceous and Paleogene changes in global climatic states, modified after Huber et al. (2018). The foraminiferal oxygen isotope values for southern high latitude deep-sea oceanic drill sites, OAE and сlimatic events: Aptian/Albian Boundary Interval (AABI), Cretaceous Thermal Maximum (СTM), Paleocene/Eocene Thermal Maximum (PETM), and Middle Eocene Climatic Optimum (MECO).\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/1c94dec2f75dbffb3e4b0d14.jpeg"},{"id":108490772,"identity":"100cd5f0-67ef-4ba4-8571-be0eb62fb47e","added_by":"auto","created_at":"2026-05-05 09:48:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2301313,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/79eb120d-7160-4214-b764-d059378c0b1f.pdf"},{"id":107755036,"identity":"605599d7-5cda-4150-a1a4-d0e0cc3fd4e2","added_by":"auto","created_at":"2026-04-24 18:41:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2193550,"visible":true,"origin":"","legend":"","description":"","filename":"GLResearchLettersSupInfPeretyazhkoetal2026.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9376046/v1/93bd1eb556dd4efb34245d74.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The oldest Pacific carbonate fluorapatite and Fe-Mn crust: а new episode of Turonian–Coniacian phosphatization event","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePhosphorus is a main energy carrier in living organisms and the dominant limiting nutrient for oceanic primary productivity, while its biogeochemical cycle influences crucially the global climate and biodiversity (Van Cappellen and Ingall 1996; Slomp and Van Cappellen 2007). The amount of dissolved P in the ocean is controlled by the tradeoff between its supply, mostly from terrestrial weathering, and loss by burial in marine sediments and Fe-Mn crusts, together with organic matter (F\u0026ouml;llmi 1996; Planavsky et al. 2010). As a result of sediment diagenesis caused by global deficiency of seawater oxygen (Oceanic Anoxic Event, OAE) and local upwelling of cold bottom water, it is authigenic carbonate fluorapatite (Ca₅(PO₄,CO₃)₃F, CFA) precipitated upon rock surfaces and between Fe-Mn crust layers that becomes a major P sink (Filippelli and Delaney 1996; Hein et al. 1993; Jaing et al. 2020). The periods of enhanced phosphorus accumulation and CFA precipitation are termed \u003cem\u003ephosphatization events\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe evolution of phosphogenesis, CFA precipitation, and Fe-Mn crust growth in the oceans was controlled by local upwelling of cold deep bottom water rich in nutrients, the position of the oxygen minimum zone (OMZ), phosphorus cycle dynamics, and bioproductivity patterns. Upwelling increases bioproductivity by supplying oxygen and P-rich cold water to shallow shelves of continental margins and oceanic islands which make natural barriers for underwater currents. A large portion of dissolved phosphorus is consumed by plankton, becomes buried in sediments after the organisms die, and then converts to CFA during diagenesis (F\u0026ouml;llmi 1996; Filippelli 2011). Reactions in the OMZ lead to partial dissolution of Fе- and Mn-oxyhydroxides, while the release of the adsorbed phosphorus into the bottom water provides its local P enrichment (Yao and Millero 1996). Suboxic\u0026ndash;anoxic conditions favorable for phosphatization of carbonates and CFA precipitation appear at intersections of seamount slopes with the OMZ.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDating of CFA in phosphorites, marine sediments, and Fe-Mn crusts can provide valuable insights into the Cretaceous to modern climates, seawater redox conditions, and phosphorus cycle dynamics (Zhao et al. 2020; Benites et al. 2021; Peng et al. 2024). U-Pb dating of CFA by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been largley used to constrain the length of interruptions in the Fe-Mn crust growth (Josso et al. 2019; Peng et al. 2024).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe available biostratigraphic data on intervals of coexisting index species of calcareous nannoplankton bracket the age of Co-rich Fe-Mn crusts from the Western Pacific Magellan Seamount Trail (MST) and other equatorial Pacific areas at ~65\u0026ndash;60 Ma (Peretyazhko et al. 2025). Mn- and Fe-oxyhydroxides in the old section of MST Co-rich Fe-Mn crusts (layers R, I-1, and I-2) were phosphatized, with CFA being the major sink of P, Ca, and F. In each phosphatization event, microcrystalline CFA formed pore cement in carbonate sediments and precipitated between Fe-Mn crust layers. As the concentration of phosphorus in seawater was increasing, CFA fully replaced calcite in the carbonate sediments (Cappellen and Berner 1991; Ekamparam and Singh 2020).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this study, a unique sample from MST Govorov Guyot, which contains the oldest Pacific CFA and Fe-Mn crust, is analyzed by SEM-EDS and LA-ICP-MS for CFA\u003cem\u003e\u0026nbsp;in situ\u003c/em\u003e U-Pb LA-ICP-MS dating, minor and trace element chemistry.\u0026nbsp;\u003c/p\u003e"},{"header":"Data and methods","content":"\u003cp\u003eThe analyzed sample 08D97 (Fig. 1a) was cut from a 31.8 kg (53\u0026times;27\u0026times;25 cm) block dredged out from a depth of 1691 m (17\u0026deg;57.8522\u0026apos; N, 151\u0026deg;17.2433\u0026apos; E) near the northeastern slope of MST Govorov Guyot during the 2016-2017 cruise of R/V \u003cem\u003eGelendzhik\u003c/em\u003e,\u003cem\u003e\u0026nbsp;JSC Yuzhmorgeologiya\u003c/em\u003e. The sample contains a Co-rich Fe-Mn crust consisting of three texturally different layers (I-1, II and III), 7 to 14 cm of total thickness, which record the Co-rich Fe-Mn ore deposition history, according to the general section of MST Fe-Mn crusts (Peretyazhko et al. 2025). The Fe-Mn crust precipitated upon hyaloclastite mainly composed of replaced volcanic glass (\u0026lt;2\u0026ndash;4 mm clasts) and fragments of basaltic rocks cemented with foraminifera-bearing phosphatized biogenic carbonate. The study focused on a 6\u0026times;3.5 cm geode within sample 08D97 (Fig. 1a), in a section of porous hyaloclastic material which strips several small cavities and geodes of different sizes. The geode is surrounded by phosphatized hyaloclastite coexisting with phosphatized Fe-Mn crust fragments and encloses CFA-replaced biogenic carbonate, layers of massive CFA, and a layer of acicular calcite lining the inner cavity wall (Fig. 1b).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSEM-EDS\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;and\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eLA-ICP-MS\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnalyses were applied to a cut section of the geode polished with diamond pastes. The texture and mineralogy of the geode and the Fe-Mn crust were studied by scanning electron microscopy and energy dispersion spectrometry (SEM-EDS) at the Center for Isotope-Geochemical Studies (\u003cem\u003eIGC SB RAS\u003c/em\u003e, Irkutsk). The contents of minor and trace elements and U-Pb isotopes in СFA were measured by LA-ICP-MS at the Center for Geodynamics and Geochronology (\u003cem\u003eIEC SB RAS\u003c/em\u003e, Irkutsk).\u003c/p\u003e\n\u003cp\u003eThe SEM-EDS analyses were performed on a Tescan Mira-3 LMU microscope equipped with an Ultim MAX-40 SDD analyzer and an Aztec Energy XMax 50+ EDS system. The operating conditions were 20 kV accelerating voltage, \u0026lt;0.5 nA beam current, and 30 s count time. The instruments for LA-ICP-MS were an Agilent 7900 quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) coupled to a Photon Machines Analyte Exite 193 nm ArF Excimer laser-ablation platform with a HelEx II active double-volume cell (CETAC Teledyne, USA).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLA-ICP-MS analyses were applied to 110\u0026nbsp;\u0026mu;m\u0026nbsp;CFA\u0026nbsp;spots were ablated using a repetition rate of\u0026nbsp;10\u0026nbsp;Hz\u0026nbsp;at a laser fluence of\u0026nbsp;3.02 J/cm\u003csup\u003e-2\u003c/sup\u003e in a flux of He as a carrier gas (Table S1). Isotopes of 51 elements were measured successively, at integration times of 5 to 30 ms:\u003csup\u003e\u0026nbsp;9\u003c/sup\u003eBe, \u003csup\u003e23\u003c/sup\u003eNa, \u003csup\u003e25\u003c/sup\u003eMg, \u003csup\u003e27\u003c/sup\u003eAl,\u003csup\u003e\u0026nbsp;29\u003c/sup\u003eSi, \u003csup\u003e31\u003c/sup\u003eP, \u003csup\u003e39\u003c/sup\u003eK, \u003csup\u003e43\u003c/sup\u003eCa, \u003csup\u003e45\u003c/sup\u003eSc, \u003csup\u003e47\u003c/sup\u003eTi, \u003csup\u003e51\u003c/sup\u003eV, \u003csup\u003e52\u003c/sup\u003eCr, \u003csup\u003e55\u003c/sup\u003eMn, \u003csup\u003e57\u003c/sup\u003eFe, \u003csup\u003e59\u003c/sup\u003eCo, \u003csup\u003e60\u003c/sup\u003eNi, \u003csup\u003e63\u003c/sup\u003eCu, \u003csup\u003e66\u003c/sup\u003eZn, \u003csup\u003e71\u003c/sup\u003eGa,\u003csup\u003e\u0026nbsp;85\u003c/sup\u003eRb, \u003csup\u003e88\u003c/sup\u003eSr, \u003csup\u003e89\u003c/sup\u003eY, \u003csup\u003e90\u003c/sup\u003eZr, \u003csup\u003e93\u003c/sup\u003eNb, \u003csup\u003e95\u003c/sup\u003eMo,\u003csup\u003e\u0026nbsp;118\u003c/sup\u003eSn,\u003csup\u003e\u0026nbsp;121\u003c/sup\u003eSb, \u003csup\u003e133\u003c/sup\u003eCs, \u003csup\u003e137\u003c/sup\u003eBa, \u003csup\u003e139\u003c/sup\u003eLa, \u003csup\u003e140\u003c/sup\u003eCe, \u003csup\u003e141\u003c/sup\u003ePr, \u003csup\u003e146\u003c/sup\u003eNd, \u003csup\u003e147\u003c/sup\u003eSm, \u003csup\u003e153\u003c/sup\u003eEu, \u003csup\u003e157\u003c/sup\u003eGd, \u003csup\u003e159\u003c/sup\u003eTb, \u003csup\u003e163\u003c/sup\u003eDy, \u003csup\u003e165\u003c/sup\u003eHo, \u003csup\u003e166\u003c/sup\u003eEr, \u003csup\u003e169\u003c/sup\u003eTm, \u003csup\u003e172\u003c/sup\u003eYb, \u003csup\u003e175\u003c/sup\u003eLu, \u003csup\u003e178\u003c/sup\u003eHf, \u003csup\u003e181\u003c/sup\u003eTa,\u003csup\u003e\u0026nbsp;184\u003c/sup\u003eW,\u003csup\u003e\u0026nbsp;205\u003c/sup\u003eTI,\u003csup\u003e\u0026nbsp;208\u003c/sup\u003ePb, \u003csup\u003e209\u003c/sup\u003eBi, \u003csup\u003e232\u003c/sup\u003eTh, and \u003csup\u003e238\u003c/sup\u003eU. The data quality was checked against measurements in reference materials: NIST SRM 612 for calibration; NIST SRM 610 as a secondary (Pearce 1997); and the contents of Ca (average SEM-EDS values at CFA ablation spots) as an in-house standard. The standard samples were measured after every four analyzed samples. \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eU-Pb dating\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eU-Pb LA-ICP-MS analyses of CFA were conducted at a 50 \u0026mu;m spot size and were ablated using a repetition rate of 10 Hz for single spot analysis (Table S2). The reference materials were the glass standard NIST SRM 610 as a primary reference material (Pearce 1997), McClure Mountain Syenite (MMS) apatite (Schoene et al. 2006) and Otter Lake (Barfod et al. 2005) apatite as secondaries. Each spot analysis consisted of a 20 sec background acquisition and 40 sec sample data acquisition followed by 40 sec for cleaning the sample cell and tubing. Every 4 samples analyzed were followed by one measurement of NIST SRM 610, MMS and Otter Lake apatites. Analytical results were processed using Iolite 4.10.5 software (Paton et al. 2011). The measured U\u0026ndash;Pb LA-CP-MS data need correction for inter-element fractionation on \u003csup\u003e238\u003c/sup\u003eU/\u003csup\u003e206\u003c/sup\u003ePb ratios, due to matrix difference between apatite samples and standards (NIST SRM 610, MMS and Otter Lake apatites). Analytical procedure and subsequent processing of the primary data were performed according to the method described in (Li et al. 2014) and references therein. Correction of the \u0026sup2;⁰⁷Pb/\u0026sup2;⁰⁶Pb ratio was carried out using NIST SRM 610 glass. The \u0026sup2;\u0026sup3;⁸U/\u0026sup2;⁰⁶Pb ratio was calibrated using the MMS apatite as a primary matrix-matched standard, whose age was calculated considering the initial \u0026sup2;⁰⁷Pb/\u0026sup2;⁰⁶Pb of 0.882, determined by ID-TIMS total U-Pb isochron (Schoene et al. 2006), to account for the matrix effect. U-Pb ages (Fig. S1) and their uncertainties were calculated from Tera-Wasserburg concordia lower intercepts of the calculated regression line using the IsoplotR software (Vermeesch 2018).\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eSEM-EDS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe geode was studied in several fragments along cracks that crosscut gray phosphatized biogenic carbonate (Bio region, 11\u0026ndash;12 mm), yellowish layers of dense chemogenic CFA (Chem region, 9\u0026ndash;10 mm), and translucent acicular calcite lining (Cal region, 2\u0026ndash;4 mm) (Figs. 1b,2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe biogenic region, with numerous foraminifers and other organic fossils (Fig. 2b,e), is composed of CFA replacing the carbonate material. The chemogenic region consists of a microcrystalline CFA aggregate with a porous top above dense massive material (Fig. 2a,c,d). Up the section, there follows a porous CFA aggregate bearing \u0026lt;1\u0026ndash;2 \u0026micro;m barite grains and a 2\u0026ndash;4 \u0026micro;m calcite zone overlain by a \u0026lt;5 mm layer of acicular calcite with sporadic barite and CFA inclusions (Fig. 2a). Compared to CFA Chem from the layered region, CFA Bio has lower average contents of Ca (35.2 against 36.3 wt.%, SEM-EDS data), P (12.7 against 13.3 wt.%), F (3.6 against 4.6 wt.%), but shows greater enrichment in Mg and Sr (both 0.3 against 0.1 wt.%), at approximately same amounts of S (0.8 wt.%), Na (0.7 wt.%), and impurities (Si, Al, Fe, K) making \u0026lt; 0.7 wt.% in total (Tables S3, S4).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLA-ICP-MS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe concentrations of \u0026nbsp;minor (Si, Ti, Fe, Mn, Mg, Na, K, P, Al) and trace (Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Nb, Mo, Sn, Sb, Cs, Ba, Hf, Ta, W, Tl, Pb, Bi, Th, U, REE, Y) elements were determined at 18 ablation spots along geode sections (Fig. 1b; Table S5): 5 spots for CFA Bio (bio-1,-3,-5,-6), 10 spots for CFA Chem (slv-2,-7\u0026ndash;15), and 3 spots in the calcite layer (cal-18\u0026ndash;20). Figure 3 shows the concentrations of some elements relative to Al which is times higher in CFA Bio than in CFA Chem (1500\u0026ndash;4500 ppm against 500\u0026ndash;900 ppm, respectively). CFA Bio is enriched in Si, Fe, K, Rb, Ti, Zr, Sb, and Ga, while CFA Chem is depleted in Mn, P, Ba, Sr, Pb, U, Zn, and V.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCFA throughout the geode contains 10 to 200 ppm REE and Y in total (Tables S3, S4). The REE+Y contents in CFA Bio are lower than in CFA Chem, except for bio-1 spot (Fig. 4). The PAAS-normalized REE+Y patterns are typical of CFA from marine sediments and hydrogenetic Fe-Mn crusts (Jiang et al. 2020), with a moderate HREE enrichment over LREE, a negative Ce anomaly (Ce* 0.1\u0026ndash;0.4), and a positive Y anomaly.\u003c/p\u003e\n\u003cp\u003eCalcite is generally depleted in minor and trace elements (average contents, ppm): 4103 Mg, 996 Si, 291 P, 203 Fe, 104 Sr, 51 Na, 45 Mn, 27 K, 16 Ba, 10 Cr, 8 Zn, 4 Ti, \u0026lt;0.n\u0026ndash;0.0n REE and Y, (Table S3). The average total of all impurities is 6073 ppm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eU-Pb dating\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe U-Pb isotope measurements in the geode were performed in three 300\u0026ndash;400 \u0026micro;m areas of CFA Bio (bio-3,-5,-6) near the LA-ICP-MS spots, as well as near bio-7 spot from the surrounding biogenic phosphatized carbonate in hyaloclastite (Fig. 1b). Discordant ages of CFA Bio were determined from 25\u0026ndash;26 analyses: 82.8 \u0026plusmn; 6.5 Ma (bio-3), 87 \u0026plusmn; 6.5 Ma (bio-5), and 83 \u0026plusmn; 18 Ma (bio-6) at initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb of 0.834 \u0026plusmn; 0.008, 0.84 \u0026plusmn; 0.03, and 0.843 \u0026plusmn; 0.012, respectively (Fig. S2; Table S5). The initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb values calculated for CFA Bio from an unanchored Tera-Wasserburg upper intercept differ slightly from the two-stage crustal Pb evolution model (Stacey and Kramers 1975) but are within the deep ocean range (Ben-Israel et al. 2014). The similarity of initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb (0.834\u0026ndash;0.843) allowed us to use the data for CFA Bio (spots bio-3,-5,-6) jointly and calculate the discordant U-Pb age from 76 analyses: 88.8 \u0026plusmn; 1.9 Ma at initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb 0.8440 \u0026plusmn; 0.0036 and MSWD 1.7 (Fig. S2a). Note that the \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb and \u003csup\u003e238\u003c/sup\u003eU/\u003csup\u003e206\u003c/sup\u003ePb values for 25 analyses from bio-7 spot (Fig. 1b) show greater variance, but they lie near or on the discordia line (Fig. S2a). Therefore, CFA Bio from the geode and from phosphatized hyaloclastite are coeval.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eU-Pb LA-ICP-MS data were also obtained for CFA Chem near spots (slv-7,-12,-15), in 200\u0026ndash;300 \u0026micro;m areas (Figs. 1b, S3). Discordant ages of lower accuracy were calculated for three different combinations of 25 to 51 analyses of CFA Chem, at initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb \u0026gt; 0.8: 72 \u0026plusmn; 17 Ma (slv-7), 53.5 \u0026plusmn; 9.1 Ma (slv-12 + slv-15), and 61 \u0026plusmn; 19 Ma (slv-15), at initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb 0.828 \u0026plusmn; 0.032, 0.804 \u0026plusmn; 0.017, and 0.814 \u0026plusmn; 0.026, respectively (Fig. S3). Thus, chemogenic CFA precipitated much later than CFA Bio replacing carbonate in the biogenic region.\u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe early deposition episodes of the MST Co-rich Fe-Mn сrust occurred in a shallow shelf at \u0026lt;500\u0026ndash;600 m seawater depths, in the Campanian\u0026ndash;Maastrichtian, and Late Paleocene (relict layer R, \u0026lt;65\u0026ndash;60 Ma), Late Paleocene\u0026ndash;Early Eocene (layer I-1, ~60\u0026ndash;48 Ma) and in the Middle\u0026ndash;Late Eocene (layer I‐2, ~48\u0026ndash;38 Ma) (Peretyazhko et al. 2025). By analogy with the dated phosphorites from equatorial Pacific seamount deposits (Hein et al. 1993), the precipitation of CFA in the old crust layers R, I-1 and I-2 was inferred to span two phosphatization events: Late Eocene\u0026ndash;Early Oligocene (39\u0026ndash;34 Ma, with a peak at ~37 Ma) and Late Oligocene\u0026ndash;Early Miocene (27\u0026ndash;21 Ma, with a peak at ~25 Мa) (Peretyazhko et al. 2025). Meanwhile, recent U-Pb ages of CFA from Co-rich Fe-Mn crusts sampled at Pacific and Atlantic seamounts revealed a longer time span of phosphogenesis in the deposition history of oceanic CFA. It apparently lasted from ~72 to 7 Ma and included six episodes coinciding with growth hiatuses in the Co-rich Fe-Mn crusts (Peng et al. 2024). The 56\u0026ndash;54 Ma phosphatization event was concurrent to a stage of global warming (Paleocene/Eocene Thermal Maximum, Fig. 5), while the other episodes correspond to transitions between cold and warm climates (Campanian\u0026ndash;Maastrichtian boundary event, 72\u0026ndash;71 Ma; Eocene/Oligocene Warm\u0026ndash;Cool transition, 35\u0026ndash;34 Ma; and Oligocene/Miocene Cool transition, \u0026nbsp; 25\u0026ndash;23 Ma) and to two Late Miocene cooling events (11\u0026ndash;10 and 8\u0026ndash;7 Ma). These episodes of oceanic phosphatization correlate with the respective events in continental settings (Pufahl and Groat 2017).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVolcaniclastic fragments in sample 08D97 (Fig. 1a) represent the substrate on which layers I-1, I-2, and III of the Co-rich Fe-Mn crust formed. The interstices between small clasts of replaced volcanic glass in hyaloclastite and fragments of basaltic rocks in sample 08D97 are filled with phosphatized biogenic carbonate containing abundant foraminifers and other unidentified fossils. CFA has fully replaced biogenic carbonate in the geode and in the surrounding hyaloclastite. Euhedral crystal morphology, especially in the chemogenic region (Fig. 2a,f,g), indicates authigenic CFA precipitation. The PAAS-normalized REE+Y patterns of CFA in both biogenic and chemogenic regions lack the Eu anomaly and are similar to those for deep-seawater (Fig. 4). This is reliable evidence that CFA originated from seawater, without the effect of hydrothermal fluids on its crystallization and carbonate phosphatization (Piepgras and Jacobsen 1992; Klinkhammer et al. 1994).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe CFA-replaced phosphatized biogenic carbonate hosts foraminifers and calcareous nannoplankton (Fig. 2b,f). The obtained U-Pb age of 88.8 \u0026plusmn; 1.9 Ma for CFA Bio, with good statistics (Fig. S2a; Table S5), is ~12\u0026ndash;18 Myr older than the previous determinations of 77\u0026ndash;71 Ma for CFA from the lowermost Pacific and Atlantic Fe-Mn crust layers (Josso et al. 2019; Peng et al. 2024). Thus, the geode we analyzed stores the oldest known oceanic CFA precipitated during the Late Cretaceous phosphatization of the Pacific sediments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBiogenic carbonate in the geode was deposited and replaced by CFA during the hottest and longest climate event of the Cretaceous thermal maximum (Fig. 5). The Turonian\u0026ndash;Coniacian (~\u0026nbsp;94\u0026ndash;86 Ma) Pacific climate and regional system was one of the most extreme periods of the Cretaceous hot greenhouse, when the Earth lacked polar ice caps and the oceans were the warmest. It was the time of global oceanographic, tectonic, and magmatic events associated with active plate motions in the Pacific and the Atlantic spreading (Huber et al. 2018). The Cenomanian\u0026ndash;Turonian OAE2 (~94 Mа, Gangl et al. 2019)\u0026nbsp;and Coniacian\u0026ndash;Santonian OAE3 (87\u0026ndash;84 Ma, Mansour and Wagreich 2022) anoxic conditions were the most recent global-scale catastrophic events in the geological history, when the oceanic and continental cycles of CO\u003csub\u003e2\u003c/sub\u003e, O, S, Fe, and P changed dramatically (Selby et al. 2009). The extreme warming conditions, with oceanic water surface temperatures ranging between 36 \u0026deg;C in the tropic latitudes and at least 20 \u0026deg;C in middle latitudes (Huber et al. 2018), continued till the Turonian\u0026ndash;Coniacian boundary. The Cretaceous hot greenhouse effect apparently resulted from a combination of several paleo-geodynamic events, including large-scale volcanism with voluminous release of greenhouse gases. Furthermore, the time span between OAE2 and OAE3 corresponded to magmatic activity in several Large Igneous Provinces (LIPs), e.g., the Ontong Java LIP in the areas of the spreading Izanagi, Farallon, and Phoenix plates during the formation of the Pacific Plate fragment that accommodates the MST volcanic edifices (Seton et al. 2012; Hochmuth et al. 2015).\u003c/p\u003e\n\u003cp\u003eTill recently, the oldest age of 99\u0026ndash;92 Ma (Cenomanian\u0026ndash;Turonian, early Late Cretaceous) was assigned to the Fe-Mn crust from the Tropic Seamount in the Canary Island Province, Atlantic Ocean (Marino et al. 2018). However, the crust growth event was timed using empirical Co-chronometry (Manheim and Lane-Bostwick 1988) which yields underestimated growth rates and thus overestimates the ages (Josso et al. 2019; Peretyazhko et al. 2025). According to an updated age model of Josso et al. (2019) based on cross-validation of Co-chronometry and \u003csup\u003e187\u003c/sup\u003eOs/\u003csup\u003e188\u003c/sup\u003eOs isotope ratio, the Atlantic Fe-Mn crust rather started growing between 77 and 72 Ma. Meanwhile, the Fe-Mn crust fragments from the analyzed sample must be older than the phosphatization event (88.8 \u0026plusmn; 1.9 Ma), given that biogenic carbonate was deposited at several sites on the geode wall surrounded with the crust (Fig. 1). Therefore, with its age apparently exceeding 90 Ma, it may be one of the oldest oceanic Fe\u0026ndash;Mn crusts.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eJudging by the inner structure of the geode (Fig. 1b), its chemogenic region composed of microporous CFA postdates biogenic carbonate and its phosphatization. The subparallel layers in the geode were produced by CFA precipitation from seawater. Chemogenic CFA possibly crystallized in response to changes in bottom seawater: temperature, \u003cem\u003epH\u003c/em\u003e, contents of dissolved Ca, P, Ba, and S, as well as adsorption of phosphorus on the sediment-water interface, etc. (Filippelli 1997; Nishi et al. 2017; Jiang et al. 2020 and references therein). CFA precipitated together with barite and calcite in the upper part of the chemogenic region (Fig. 2a), and the crystallization sequence was completed by acicular calcite lining the inner cavity (Fig. 1b). The successive change of chemogenic phases CFA \u0026rarr; (CFA + barite + calcite) \u0026rarr; (CFA + calcite) \u0026rarr; calcite apparently resulted from variations in some physical and chemical parameters of bottom seawater under different paleoclimatic conditions during phosphatization of MST rocks in the ~72\u0026ndash;54 Ma time span (dating of CFA Chem, Fig. S3; Table S5).\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe reported analyses of CFA in the sample from Govorov Guyot revealed the earliest (88.8 \u0026plusmn; 1.9 Ma) phosphatization event of biogenic carbonate that interrupted the deposition of Fe-Mn crusts during one of the most extreme Turonian\u0026ndash;Coniacian (~\u0026nbsp;94\u0026ndash;86 Ma) period of the Cretaceous hot greenhouse. The obtained oldest age of Pacific CFA, which has fully replaced biogenic calcite in the geode, is ~12\u0026ndash;18 Myr older than the previous dates for CFA (77\u0026ndash;71 Ma) in the Atlantic and Pacific Co-rich Fe-Mn crusts. The sequential deposition of CFA, barite, and calcite in the geode\u0026apos;s chemogenic section may result from variations in physical and chemical parameters of bottom seawater under different paleoclimatic conditions during the phosphatization of Magellan Seamount rocks through the Cretaceous\u0026ndash;Cenozoic history of the Pacific Ocean.\u003c/p\u003e\n\u003cp\u003eThe ages of chemogenic CFA can be updated in the future and complemented by dating calcite and CFA from the oldest Fe-Mn сrust around the geode. Further studies of CFA in MST rocks and Fe-Mn crusts will reveal potential older phosphatization events and provide more rigorous constraints on the duration of the known episodes in which Pacific sediments were phosphatized in different Cretaceous through Cenozoic paleoclimatic conditions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the crew members of R/V \u003cem\u003eGelendzhik\u003c/em\u003e, \u003cem\u003eJSC Yuzhmorgeologiya\u003c/em\u003e for support during the cruises. We appreciate assistance of our colleagues from IGC SB RAS, Irkutsk: O.Yu. Belozerova for SEM-EDS analyses and I.A. Vlasyuk for sample preparation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eISP spearheaded the research, conceptualized the study and crafted the initial draft of the manuscript. EAS and EAG and revised the text, contributed to creating figures and tables. All authors participated in interpreting the results and engaging in discussions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was funded by grant 25\u0026ndash;17\u0026ndash;00128 from the Russian Science Foundation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData is provided within the manuscript and supplementary file.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlibo DS, Nozaki Y (1999) Rare earth elements in seawater: particle association, shale- normalization, and Ce oxidation. 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Geochem Geophys Geosyst 16(11):3789\u0026ndash;3807. https://doi.org/10.1002/2015GC006036 \u003c/li\u003e\n\u003cli\u003eHuber BT, MacLeod KG, Watkins DK, Coffind MF (2018) The rise and fall of the Cretaceous Hot Greenhouse climate. Glob Planet Change\u003cem\u003e \u003c/em\u003e167:1\u0026ndash;23. https://doi.org/10.1016/j.gloplacha.2018.04.004 \u003c/li\u003e\n\u003cli\u003eJiang XD, Sun XM, Chou YM, Hein JR, He GW, Fu Y, Li DF, Liao JL, Ren JB (2020) Geochemistry and origins of carbonate fluorapatite in seamount Fe-Mn crusts from the Pacific Ocean. Mar Geol\u003cem\u003e \u003c/em\u003e423:106135. https://doi.org/10.1016/j.margeo.2020.106135 \u003c/li\u003e\n\u003cli\u003eJosso P, Parkinson I, Horstwood M, Lusty P, Chenery S, Murton B (2019) Improving confidence in ferromanganese crust age models: A composite geochemical approach. 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Nat Commun 11:2232. https://doi.org/10.1038/s41467-020-15673-3 \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"geoscience-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"gosl","sideBox":"Learn more about [Geoscience Letters](https://geoscienceletters.springeropen.com/)","snPcode":"40562","submissionUrl":"https://submission.springernature.com/new-submission/40562/3","title":"Geoscience Letters","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Oldest Pacific carbonate fluorapatite, Co-rich Fe-Mn crust, Turonian–Coniacian phosphatization events, Magellan Seamount Trail","lastPublishedDoi":"10.21203/rs.3.rs-9376046/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9376046/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"LA-ICP-MS is applied to a sample from Govorov Guyot (Western Pacific Magellan Seamount Trail), which encloses a geode partially filled with biogenic phosphatized carbonate and bears carbonate fluorapatite (CFA), for in situ CFA U-Pb dating, minor and trace element chemistry. 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 ~12–18 Myr older than the previous dates for CFA (77–71 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.","manuscriptTitle":"The oldest Pacific carbonate fluorapatite and Fe-Mn crust: а new episode of Turonian–Coniacian phosphatization event","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-24 18:41:31","doi":"10.21203/rs.3.rs-9376046/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-04-16T13:33:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-14T03:51:13+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-13T10:51:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Geoscience Letters","date":"2026-04-10T07:25:36+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"geoscience-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"gosl","sideBox":"Learn more about [Geoscience Letters](https://geoscienceletters.springeropen.com/)","snPcode":"40562","submissionUrl":"https://submission.springernature.com/new-submission/40562/3","title":"Geoscience Letters","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5b591893-8f7d-489a-9471-2ecd6c444430","owner":[],"postedDate":"April 24th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-24T18:41:31+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-24 18:41:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9376046","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9376046","identity":"rs-9376046","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}