The study of post depositional history in the Chehel Kaman formation, in the eastern regions of Kopet-Dagh, North-East Iran

The Chehel Kaman Formation of the upper Paleocene age formed from carbonate and siliciclastic sediments is located, in the Kapeh Dagh Sedimentary Basin. Two sections where considered for the purpose of research into the effective diagenetic processes of this formation. The Cheshmeh Qorban section with a thickness of 270.8m located 140km down the Mashhad – Sarakhs Highway while the Shourlog Section with a thickness of 288.3m is situated 130km down the Mashhad – Mozduran – Sarakhs Highway. 120 samples were taken from these sections and 100 thin cross sections produced from these samples. The carbonate rocks of this formation have been affected by diagenetic processes such as cementation, micritization, neomorphism, dissolution stress and porosity. These processes have taken place at the four marine diagenetic stages of the underground and surface sweet water. All cross sections were investigated using a gypsum bladein order to identify any extant porosity. All changes including type and percentage were plotted for each section. The results of the investigations indicated that in the Cheshmeh Qorban section of the Chehel Kaman Formation the lowest porosity content with a 3% rate of recurrence was related to microporosities while the greatest accumulation of porosity with a 7% recurrence rate in porosity was due to fracture porosity. In the Shourlog section meanwhile the lowest porosity content with a 2% recurrence rate was related to microporosities and the greatest accumulation with a recurrence rate of 6% was due to vuggy porosity.