SEDIMENTOLOGY AND DIAGENESIS OF POST EOCENE
LACUSTRINE "PALUSTRINE" CARBONATES ALONG THE
EASTERN SIDE OF THE NILE VALLEY, EASTERN DESERT,
EGYPT
SAYED E. GHARIEB
Department of Geology, Faculty of Science, Cairo University
(Beni Suef Branch), Beni Suef Egypt
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The Post Eocene lacustrine carbonates exposed at different localities along the eastern side of the Nile Valley, Eastern Desert of Egypt consist of distal, open and marginal lacustrine facies. Some evaporites were recorded on top of the sections indicating a short hypersaline phase in the lake history.
The lacustrine carbonates and associated facies show a dark blue color under a cathodoluminesence microscope. The carbon and oxygen stable isotope analysis of these rocks shows negative values indicating a non marine origin. The high negativity of the stable isotopes is due to the input of light meteoric oxygen and light organic carbon isotopes. The co-occurrence of calcrete horizons and karst solution cavities appears to indicate a contemporaneous carbonate precipitation and dissolution in the subaerial regime. Petrography and geochemistry, as well as megascopic and mesoscopic relation of the marginal lacustrine carbonate facies show strong indications of pedogenetic and subaerial diagenetic modification. The intensity of modification is highly variable depending on the climate and length of time of emergence. So, the term palustrine carbonates could be applied to describe these deposits.
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