Microstructure and geochemistry studies on Messinian gypsum deposits from the Northern Coast of Egypt |
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| Authors: | Ahmed Melegy Ismael S Ismael |
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| Institution: | 1. Department of Geological Sciences, National Research Center, Dokki, Cairo, Egypt
2. Faculty of Science, Suez University, Suez, Egypt
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| Abstract: | Messinian gypsum deposits from Dir El-Baraqan area, Northern Coast of Egypt, were investigated by stable sulfur isotope method, X-ray diffraction, infrared spectroscopy, optical microscopy, and scanning electron microscopy to differentiate features formed under substantial microbial influences as indicator of paleoenvironments. Petrographically, gypsum deposits were classified into three types: biolaminated gypsum, disordered selenite, and swallow-tail selenitic crystals. Biolaminated gypsum is characterized by regular alternating dark and light laminae, which were formed due to the seasonal environmental changes in Dir El-Baraqan area. Stable sulfur isotope data show that the gypsum deposits are characterized by δ34S values ranging from +18.1 to +28.1 ‰. In swallow-tail gypsum, the δ34S values are characterized by a narrow range (from +20.0 to +20.2 ‰) which is considered as the primary phase. In biolaminated gypsum, the δ34S values ranged from +22.8 to +28.1 ‰ which is considered as the secondary phase. However, the white laminae are characterized by δ34S values ranging from +22.8 to +24.1 ‰, while dark laminae are characterized by δ34S values ranging from +27.2 to +28.1 ‰. The high δ34S values of dark laminae revealed the increasing activity of sulfate-reducing bacteria. |
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