Many geologists have attempted to explain the origin and lithification of the Pleistocene calcareous sediments of the western coastal plain of Egypt. The present study is an interpretation of the origin and lithification of the Pleistocene carbonates from the Salum area. The oldest deposit (Tyrrhenian limestone) consists of grains which lack any concentric structure, but instead have developed micritic calcite envelopes. They are interpreted as detrital grains of recycled carbonates. The younger deposits (Late Monasterian and Main Monasterian limestones) have a well developed oolitic texture probably formed in shallow, agitated marine waters. It is believed that the existing textures and mineralogy are the result of diagenesis which proceeded under subaerial conditions. Three stages of diagenesis are recognized, each exhibiting its own peculiar textural, mineralogical and geochemical characteristics. The decrease in strontium content as related to aragonite inversion to calcite is shown to be a reliable diagenetic guide.