Mineralogical And Geochemical Evaluation Of Upper Cretaceous Black Shales, Safaga District, Egypt.

Abstract

Lithologic and compositional properties of black shale and pyrite from the Upper Cretaceous phosphorite/black shale deposits (Duwi Formation) of Eastern Desert of Egypt indicate similarity in mineralogy, geochemical characters and carbon isotopic ratios with those inferred for modern organic-carbon-rich sediments. Components of the black shale include various clay minerals, silt(grade quartz, organic matter, pyrite, calcareous foraminifera shells and phosphatic nodules. The clay mineralogy of the black shale does not differ significantly from typical Cretaceous black shale (dominance of smectite and illite with minor amounts of kaolinite and chlorite). The trace-element concentrations (Zn, Cu, Ni, Co, U and Pb) show a general enrichment pattern and seem to correlate with enrichment of organic matter. The stable carbon-isotope cratios (from- 22% to - 28.7 %) suggest that the organic matter is of continental and marine origin. The relationship between the total organic carbon and sulfur contents of black shale samples is similar to that of marine sediments, but the pyrite content is probably controlled by the Fe +contents.