Petrography and geochemistry of dolomites of the Jamal Formation, north of Bajestan- southuest Razavi Khorasan

The study area is located in Central Iran zone in the Gharavol Mountain (10 Km from north of Bajestan). Jamal Formation in studied section is 349m thick and composed of limestone and dolomite. This formation overlies disconformably the Sardar Formation. Based on petrographical studies, 5 types of dolomites were identified including: fine crystal dolomite (Xenotopic A), fine to medium crystal dolomite (Idiotopic P), euhedral medium crystal dolomite (Idiotopic E), medium and coarse crystal dolomite (Idiotopic S) and idiotopic C. In these dolomites, Sr content varies between 40 to 160 ppm and Na is between 13990 to 40580 ppm. These values are more than values expected for dolomites formed in marine environments. Fe content varies between 1020 to 3770 ppm and Mn is about 140 to 580 ppm. Based on petrographic and elemental analysis, these dolomites formed during early diagenesis (marine water) and shallow to medium burial depth. Origin of Mg2+ for type 1 dolomites was marine water, whereas for others were from pore water, shale diagenesis associated with limestones or probably shales of Sardar Formation.