Sequential
distribution of trace elements in Middle Eocene limestones, Mokattam area, Cairo, Egypt
Svetlana M. Loukina and Mariem A. ElHefnawi
National Research Center, Cairo, Egypt. |
Forty six samples of Middle Eocene limestones
from Mokattam area near Cairo were studied petrographically, mineralogically and
geochemically. The sequential distribution of trace elements in the rocks shows three
distinct types of associations of these elements. In the whole rock, correlations exist
between Mg and Pb, and between Al and Fe, Mn, Ti, Cu, Co, Zn. In the carbonate fraction,
correlations exist between Mg and Sr, Pb; between Fe and Cu; and between Mn and Co. In the
insoluble residue, correlation exists between Al and Fe, Mn, Ti, Cu, Co, Ni, Zn. This
indicates that only Mg and Sr occur replacing Ca in the calcite structure. Other elements
are associated with the insoluble residue, especially with Fe and Mn oxides adsorbed to
the clay fractions. The carbonate fraction has been depleted in Sr through diagenetic
effects, as been confirmed by microprobe analysis of Nummulites.
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