Diagenetic Trends In The Pleistocene Calcareous Ridges, Mersa Matruh Area, Egypt

Abstract

Ooids are a major constituent of the Pleistocene carbonates along the northwestern coastal ridges of Egypt. For a detailed diagenetic study of the rocks, the Mersa Matruh area was selected. Petrographic examination shows that the rocks are partly consolidated ooid grainstones with low-Mg calcite cement in granular voids. 818O, 813C, and Sr values were determined on whole rock samples, on the manually separated ooids and calcite cements. Oxygen isotopic and Sr values for the whole rock (+0.5%o PDB; 9,300 ppm) are consistent with data on limestones of the same age. In contrast, oxygen isotopic values for ooids (average +0.5%o PDB) are heavier relative to values for low-Mg calcite cement (average -\A%o PDB) and Sr contents are higher for ooids (10.000 ppm). In addition, 813C values are identical for the whole rock and ooids (average + 4.5%o PDB) and heavier relative to 813C values of the calcite cements (ranging from +4.1 to +3.8%O PDB). These data may suggest that calcite cements are formed in non-diluted pore-water under relatively high rock/water ratios.