Document Type : Original Article
National Iranian Oil Company, Exploration Directorate
Exploration Directorate, National Iranian Oil Company, Tehran, Iran
Islamic Azad University, North Branch of Tehran
A thick succession of pyroclastic and volcanic rocks interbedded with trigenous, carbonate and evaporate sediments of Eocene age are exposed in southeast of Nizar, Qom. Carbonate deposits of E5 lithozone were investigated in this study. The most important identified diagenetic phenomena was silicification in these sediments proved by petrography studies on thin sections. In these sediments silice is present as calsedoni, microquartz and megaquartz and silisification mainly observed as replacements and filling of vugs. Conducted studies reveal that skeletal factors play an important role in amount and manner of bioclasts silicification, so that silicification is more common in hyaline foraminifera. No silicification was observed in foraminifera with porcelanous test. Foraminifera with same hyaline test were affected differently by silicification. The most silicification is observed in Assilina and Nummulites genera. This phenomenon did not have any effect or observed rarely in some foraminifera with hyaline test such as Discocyclina, Operculina and Rotalia.