MICROFACIES AND DIAGENESIS OF CRETACEOUS/
TERTIARY CHAIKS, NORTHEAST SINAI, EGYPT
NADIA M.S. ABD EL MAGUID AND
1OCTAVIAN CATUNEANU
Department of Geology ,Faculty of Sciences,Menoufia University ,Egypt;
1Department of Earth & Atmospheric Science, Faculty of science, Alberta University, Canada |
Petrographic and geochemical evaluation of Upper
Cretaceous/Lower Tertiary chalks from El- Qussaima and Bir El-Maien areas, northeast Sinai, Egypt was conducted to investigate their particulate constituents, chemical composition. depositional environment and diagenetic history.
Petrographic studies revealed the occurrence of nine microfacies: Packed Nummulitic biomicrite, foraminiferal biomicrite, packed foraminiferal biornicrite. dolomicrite. sparse
cherty foraminiferal biomicrite, packed biomicrite, packed algal sandy biomicrite, dolomitized biomicrite, and packed algal biosparite. SEM investigation indicates that primary skeletal fabrics (coccolith and foraminifera) of El- Qussaima chalks are well preserved. In contrast, primary skeletal fabrics of Bir El-Maien chalks are pervasively altered.
Chemically, the analyzed chalks have a high calcium oxide content (avg. 56.52 and 56.06%, respectively) and a low magnesium content. Thc trace elements of these chalks show a good contrast in
composition in the two studied localities. El-Qussaima chalk proved to be higher in Sr and Ba contents (1382 and 1232 ppm., respectively relative to those in Bir El-Maien chalk (590 and 770 ppm., respectively). This may indicate that the pelagic micrite of El-Qussaima are richer in biogenic skeletal grains than those of Bir ElMaien chalk. The difference in microfabric and elemental chemistry of the pelagic micrite El-Qussaima and Bir El-Maien are point that the former were deposited under deeper water conditions, lower rate of sedimentation, and higher influence of diagenetic processes than the latter.
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