Stable isotope of some selected Egyptian pectinids and their paleoenvironmental implications

Eight pectinid shells were collected and subjected to quantitative study using δ18O and δ13C isotopic analysis in order to study the paleoenvironment which prevailed during their calcification. The scalerochronological variations in δ18O and δ13C values, among these shells are also discussed. The Early Miocene pectinid shells display highly depleted δ18O and δ13C signature as a result of paleo-meteoric water with heavy rainfall that was produced by Tropical Cyclones when the Mediterranean Sea was open. The Early Pliocene pectinid shells reveal depleted δ18O values, related to the influx of fresh water influenced by monsoonal activity following the formation of the Tibetan Plateau. Their enrichment in the δ13C isotopic excursion is referred to high productivity of the Indian Ocean, which was the main source of the Red Sea water. The Pleistocene pectinid shell shows highly depleted δ18O and δ13C signature with obvious diagenetic shell structure, indicating that a wetter humid climate prevailed during the Early–Middle Pleistocene and long sub-arial exposure of the shell. The Recent Mediterranean pectinid shell displays slight enrichment in δ18O and δ13C values referring to deeper inhabitation of this species with a low temperature and high salinity environment. The scalerochronological variations in both δ18O and δ13C values, along these shells is referred to seasonal variations or kinetic effects.

Research highlights
► The calcitic pectinid shells can yield faithful records of their paleoenvironments.
► Their shell has high preservation potential and relatively immune to dissolution.
► δ18O and δ13C analysis of their shells is used to track the paleoenvironment.
► Scalerochronological profile of the shell reveals the seasonal changes.