Diagenetic Processes and Geochemical Propertiesof the Elika Formation in Gadamgah Anticline in South of Central Alborz

The Elika Formation forms the major part of the Triassic carbonate sediments in the Alborz basin. In this study, diagenetic processes and geochemical properties of this formation in Shahmirzad section with a thickness of 746 meters in the southern part of central Alborz were studied. Cementation, micritization, neomorphism, dissolution, compaction, dolomitization, dedolomitization, fracturing, hematitization, pyritization and silicification affected the carbonate sediments of the Elika Formation in the study area. Based on petrographic studies (grain size and fabric), five different dolomite types including dolomicrites, dolomicrosparites, dolosparites, dolomite cement and saddle dolomite are recognized in the Elika Formation. All dolomite types are formed during very early to late diagenetic processese. Dolomicrite (dolomite type1) is Sabka type dolomite and this is attributed to Sabka model. Dolomite type2 and 3 are probably formed by mixing-zone model and dolomite type 4 and 5 can be related to burial type model. Diagenetic processes occurred in three digenetic environments of marine, meteoric and burial. Elemental and isotopic analysis of studied rocks represented the effect of meteoric and burial diagenesis in a semi-closed diagenetic system. Aragonite is the original mineral in the studied carbonates of the Elika Formation.