{"title":"岩溶环境下的磷酸盐沉淀、磷化和碎屑充填动力学:以Quercy(法国西南部)大坝的“磷化<e:1>”为例","authors":"Carine Lézin , Kévin Moreau , Sébastien Fabre , Christian Dupuis , Thierry Pelissié , Patrick Sorriaux , Gilles Escarguel , Maeva Orliac , Pierre-Olivier Antoine , Monique Vianey-Liaud , Romain Weppe","doi":"10.1016/j.chemgeo.2024.122586","DOIUrl":null,"url":null,"abstract":"<div><div>Phosphate rocks are the most important natural source of phosphorus. While a large literature discusses the conditions of their formation in marine environments, few document their formation in a terrestrial context. The Quercy phosphate mines in south-west France, known as <em>phosphatières</em>, are notable for their exceptional Cenozoic palaeontological content and represent a rare example of phosphate precipitation in a non-marine environment. Using the Dams ‘phosphatière’ as an example, this paper reconstructs the conditions under which these terrestrial phosphorites formed during the Eocene-Oligocene interval by analysing karstic sediments (sedimentology, grain size, mineralogy, and geochemistry). It discusses the origin of the karst infills and the processes involved in the genesis of phosphate minerals. The site shows three phases of infill that frame the Eocene-Oligocene transition (EOT). Each deposit contains both a detrital fraction and a phosphate-bearing neo‐formed fraction. The detrital input results from the mass transport of Eocene-Oligocene “siderolithic” sediments (formation of reddish clays with ferruginous concretions) derived from the reworking of lateritic paleosols. This siderolithic material was formed at the surface directly from fresh detrital sediments resulting from the mechanical alteration of the crystalline parent rock, located to the east in the French Massif Central.</div><div>The climatic changes around the EOT seem to be reflected only by the groundwater dynamics recorded in the karst deposits: channels are mainly present during the late Eocene, suggesting galleries well supplied with water, while abundant desiccation cracks indicate intense dry periods during the early Oligocene. Phosphate minerals, mainly fluorapatites and carbonate fluorapatite, are present as precipitated laminated crusts along the karst walls, and as mineralised fossils and phosphatised karst walls showing epigenetic processes. Field data and thermodynamic modelling suggest a major phosphate precipitation phase before karst opening, filling, and subsequent remobilisation. Phosphate rocks and phosphatised bones exhibit a marine geochemical signature, suggesting the contribution of the marine carbonate aquifer as a source of phosphorus (by dissolution of the host rock). However, the geometric relationships of the phosphates with infills derived from reworked alterites, and the enrichment in REE, challenge the influence of pedogenetic activity on phosphatogenesis. The laminated nature of some phosphate crusts would suggest bacterial activity in the phosphate precipitation process.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"676 ","pages":"Article 122586"},"PeriodicalIF":3.6000,"publicationDate":"2024-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Phosphate precipitation, phosphatisation and detrital filling dynamics in karstic contexts: The example of the Dams ‘phosphatière’, Quercy (SW France)\",\"authors\":\"Carine Lézin , Kévin Moreau , Sébastien Fabre , Christian Dupuis , Thierry Pelissié , Patrick Sorriaux , Gilles Escarguel , Maeva Orliac , Pierre-Olivier Antoine , Monique Vianey-Liaud , Romain Weppe\",\"doi\":\"10.1016/j.chemgeo.2024.122586\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>Phosphate rocks are the most important natural source of phosphorus. While a large literature discusses the conditions of their formation in marine environments, few document their formation in a terrestrial context. The Quercy phosphate mines in south-west France, known as <em>phosphatières</em>, are notable for their exceptional Cenozoic palaeontological content and represent a rare example of phosphate precipitation in a non-marine environment. Using the Dams ‘phosphatière’ as an example, this paper reconstructs the conditions under which these terrestrial phosphorites formed during the Eocene-Oligocene interval by analysing karstic sediments (sedimentology, grain size, mineralogy, and geochemistry). It discusses the origin of the karst infills and the processes involved in the genesis of phosphate minerals. The site shows three phases of infill that frame the Eocene-Oligocene transition (EOT). Each deposit contains both a detrital fraction and a phosphate-bearing neo‐formed fraction. The detrital input results from the mass transport of Eocene-Oligocene “siderolithic” sediments (formation of reddish clays with ferruginous concretions) derived from the reworking of lateritic paleosols. This siderolithic material was formed at the surface directly from fresh detrital sediments resulting from the mechanical alteration of the crystalline parent rock, located to the east in the French Massif Central.</div><div>The climatic changes around the EOT seem to be reflected only by the groundwater dynamics recorded in the karst deposits: channels are mainly present during the late Eocene, suggesting galleries well supplied with water, while abundant desiccation cracks indicate intense dry periods during the early Oligocene. Phosphate minerals, mainly fluorapatites and carbonate fluorapatite, are present as precipitated laminated crusts along the karst walls, and as mineralised fossils and phosphatised karst walls showing epigenetic processes. Field data and thermodynamic modelling suggest a major phosphate precipitation phase before karst opening, filling, and subsequent remobilisation. Phosphate rocks and phosphatised bones exhibit a marine geochemical signature, suggesting the contribution of the marine carbonate aquifer as a source of phosphorus (by dissolution of the host rock). However, the geometric relationships of the phosphates with infills derived from reworked alterites, and the enrichment in REE, challenge the influence of pedogenetic activity on phosphatogenesis. The laminated nature of some phosphate crusts would suggest bacterial activity in the phosphate precipitation process.</div></div>\",\"PeriodicalId\":9847,\"journal\":{\"name\":\"Chemical Geology\",\"volume\":\"676 \",\"pages\":\"Article 122586\"},\"PeriodicalIF\":3.6000,\"publicationDate\":\"2024-12-24\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Chemical Geology\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0009254124006661\",\"RegionNum\":2,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemical Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0009254124006661","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Phosphate precipitation, phosphatisation and detrital filling dynamics in karstic contexts: The example of the Dams ‘phosphatière’, Quercy (SW France)
Phosphate rocks are the most important natural source of phosphorus. While a large literature discusses the conditions of their formation in marine environments, few document their formation in a terrestrial context. The Quercy phosphate mines in south-west France, known as phosphatières, are notable for their exceptional Cenozoic palaeontological content and represent a rare example of phosphate precipitation in a non-marine environment. Using the Dams ‘phosphatière’ as an example, this paper reconstructs the conditions under which these terrestrial phosphorites formed during the Eocene-Oligocene interval by analysing karstic sediments (sedimentology, grain size, mineralogy, and geochemistry). It discusses the origin of the karst infills and the processes involved in the genesis of phosphate minerals. The site shows three phases of infill that frame the Eocene-Oligocene transition (EOT). Each deposit contains both a detrital fraction and a phosphate-bearing neo‐formed fraction. The detrital input results from the mass transport of Eocene-Oligocene “siderolithic” sediments (formation of reddish clays with ferruginous concretions) derived from the reworking of lateritic paleosols. This siderolithic material was formed at the surface directly from fresh detrital sediments resulting from the mechanical alteration of the crystalline parent rock, located to the east in the French Massif Central.
The climatic changes around the EOT seem to be reflected only by the groundwater dynamics recorded in the karst deposits: channels are mainly present during the late Eocene, suggesting galleries well supplied with water, while abundant desiccation cracks indicate intense dry periods during the early Oligocene. Phosphate minerals, mainly fluorapatites and carbonate fluorapatite, are present as precipitated laminated crusts along the karst walls, and as mineralised fossils and phosphatised karst walls showing epigenetic processes. Field data and thermodynamic modelling suggest a major phosphate precipitation phase before karst opening, filling, and subsequent remobilisation. Phosphate rocks and phosphatised bones exhibit a marine geochemical signature, suggesting the contribution of the marine carbonate aquifer as a source of phosphorus (by dissolution of the host rock). However, the geometric relationships of the phosphates with infills derived from reworked alterites, and the enrichment in REE, challenge the influence of pedogenetic activity on phosphatogenesis. The laminated nature of some phosphate crusts would suggest bacterial activity in the phosphate precipitation process.
期刊介绍:
Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry.
The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry.
Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry.
The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.