Petrology of Early Paleogene phosphorite deposits in Hazm Al-Jalamid, Northwest Saudi Arabia

Abstract

Large phosphorite deposits can be found in the Sirhan-Turayf Basin in northwestern Saudi Arabia. These deposits are considered part of the Middle Eastern to North African phosphogenic province of the Late Cretaceous–Paleogene age. Petrographic, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray spectroscopy analyses were conducted to examine phosphorite samples from Hazm Al-Jalamid. Phosphatic grains were primarily present in the forms of pellets and/or peloids, ooids, coprolites, fish bone fragments (BFs), and shark teeth. Phosphatic minerals were collophane, carbonate fluorapatite, and hydroxylapatite accompanied by non-phosphatic particles of quartz, shell fragments, and clay materials. Phosphatic and non-phosphatic particles were bound together by calcite cement. A systematic microscopic study on phosphorite sediments revealed that the pelletal grains were formed via several diagenetic processes. Most grains were formed through growth around a foreign particle (e.g., fish BFs), phosphomicritization of BFs, fragmentation and abrasion of bone and intraclasts, pelletization of aggregates, and phosphatization and fragmentation of fecal pellets. The depositional environment of Hazm Al-Jalamid phosphorite is characterized by paleo-highs and restricted areas created by local tectonics and low topographic swells and basins within the huge syncline of the Sirhan-Turayf sub-basin. Upwelling marine currents would have provided phosphorus, nutrients, and other elements to this restricted/semi-restricted inner shelf. Notably, the phosphorite beds experienced superficial karstic weathering, and leaching of calcareous cements produced calcite nodules and/or geodes.