| Rock composition and origin of the Duwi Formation calcareous rocks, Upper Egypt |
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| 作者姓名： | Baioumy H. M. Attia A. M. Boulis S. N. Hassan M. S. Helmy M. E. |
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| 作者单位： | [1]Central Metallurgical Research and Development Institute, 87 Helwan, Cairo, Egypt [2]Geology Dept. Faculty of Science, Ain Shams University, Abbasia, Cairo, Egypt |
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| 摘 要： | Upper Cretaceous phosphorite beds of the Duwi Formation, Upper Egypt, are intercalated with limestone, sandy limestone, marl, calcareous shales, and calcareous sandstone. Calcareous intercalations were subjected to field and detailed petrographic, mineralogical and geochemical investigations in order to constrain their rock composition and origin. Mineralogically, dolomite, calcite, quartz, francolite and feldspars are the non-clay minerals. Smectite, kaolinite and illite represent the clay minerals. Major and trace elements can be classified as the detrital and carbonate fractions based on their sources. The detrital fraction includes the elements that are derived from detrital sources, mainly clay minerals and quartz, such as Si, Al, Fe, Ti, K, Ba, V, Ni, Co, Cr, Zn, Cu, Zr, and Mo. The carbonate fraction includes the elements that are derived from carbonates, maily calcite and dolomite, such as Ca, Mg and Sr. Dolomite occurs as being dense, uniform, mosaic, very fine-to-fine, non-ferroan, and non-stoichiometrical, suggesting its early diagenetic formation in a near-shore oxidizing shallow marine environment. The close association and positive correlation between dolomite and smectite indicates the role of clay minerals in the formation of dolomite as a source of Mg^2＋ -rich solutions. Calcareous rocks were deposited in marine, oxidizing and weakly alkaline conditions, marking a semi-arid climatic period. The calcareous/argillaceous alternations are due to oscillations in clay/carbonate ratio.
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| 关 键 词： | 岩石 埃及 石灰质 白云石 成岩作用 |
| 收稿时间： | 23 June 2009 |
Rock composition and origin of the Duwi Formation calcareous rocks, Upper Egypt |
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| Baioumy H. M. Attia A. M. Boulis S. N. Hassan M. S. Helmy M. E..Rock composition and origin of the Duwi Formation calcareous rocks, Upper Egypt[J].Chinese Journal of Geochemistry,2005,24(4):316-326. |
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| Authors: | H M Baioumy A M Attia S N Boulis M S Hassan M E Helmy |
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| Institution: | (1) Central Metallurgical Research and Development Institute, 87 Helwan, Cairo, Egypt;(2) Geology Dept. Faculty of Science, Ain Shams University, Abbasia, Cairo, Egypt |
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| Abstract: | Upper Cretaceous phosphorite beds of the Duwi Formation, Upper Egypt, are intercalated with limestone, sandy limestone, marl, calcareous shales, and calcareous sandstone. Calcareous intercalations were subjected to field and detailed petrographic, mineralogical and geochemical investigations in order to constrain their rock composition and origin.Mineralogically, dolomite, calcite, quartz, francolite and feldspars are the non-clay minerals. Smectite, kaolinite and illite represent the clay minerals. Major and trace elements can be classified as the detrital and carbonate fractions based on their sources. The detrital fraction includes the elements that are derived from detrital sources, mainly clay minerals and quartz, such as Si, Al, Fe, Ti, K, Ba, V, Ni, Co, Cr, Zn, Cu, Zr, and Mo. The carbonate fraction includes the elements that are derived from carbonates, maily calcite and dolomite, such as Ca, Mg and Sr. Dolomite occurs as being dense, uniform, mosaic, very fine-to-fine, non-ferroan, and non-stoichiometrical suggesting its early diagenetic formation in a near-shore oxidizing shallow marine environment. The close association and positive correlation between dolomite and smectite indicates the role of clay minerals in the formation of dolomite as a source of Mg 2 -rich solutions.Calcareous rocks were deposited in marine, oxidizing and weakly alkaline conditions, marking a semi-arid climatic period. The calcareous/argillaceous alternations are due to oscillations in clay/carbonate ratio. |
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| Keywords: | calcareous Duwi Egypt dolomite diagenesis |
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