Characterization and Paleoenvironmental Implications of Phosphorite-Bearing Deposits in Dakhla Oasis, Western Desert, Egypt

Abstract

The current study presents an integrated investigation of petrographical, mineralogical, and geochemical data from Upper Cretaceous phosphorite-bearing strata west of the Abu-Tartur Plateau in the Western Desert of Egypt. Fifty-five samples representing phosphorite and associated rocks were collected from six outcrops. Three facies are identified: phosphorites, carbonates, and siliciclastics. The mineralogy of the samples was quantified via X-ray diffraction (XRD) as follows: fluorapatite, dolomite, calcite, pyrite, quartz, and smectite species. Atomic absorption spectrophotometry (AAS) permitted the quantification of the major oxides: SiO₂, Al₂O₃, MgO, Fe₂O₃, CaO, K₂O, Na₂O, P₂O₅, and SO₃ as well as F and loss of ignition (LOI). The statistical analysis of these geochemical data revealed three significant controlling factors during and after the deposition of the studied phosphorite and associated rocks. These factors represent the effects of the diagenesis of phosphorites, argillaceous marine rocks, and alumino-silicates in descending order of their relative strength. Trends of the analyzed major elements for the study samples are documented. Phosphorite, phosphatic rocks, dolomitized rocks, and siltstone-mudstone are recognized lithologies on the basis of the chemical compositions of the analyzed major oxides. The principal diagenetic processes affecting the phosphorite-bearing rocks included dolomitization, pyritization, silicification, bone dissolution, and micritization.