Carbonates in Jurassic deposits in the southeast of the Nyurol'ka depression (Tomsk Region)

We studied the morphology, composition, occurrence, and sizes of deposits of secondary carbonates in Jurassic sedimentary rocks in the southeast of the Nyurol'ka depression (Tomsk Region). We have established a significant difference in the mineralogical and structural compositions of the carbonates as a result of their different genesis and the effect of oil and gas fluids during the formation and destruction of hydrocarbon pools. Diagenetic carbonates have a nearly stoichiometric composition and a nearly ideal structure and are least recrystallized. Carbonates that underwent catagenesis have larger crystals and a more isomorphous and defect structure. In the marginal zones of oil deposits the minerals are most crystallized. Siderite has the most defect structure, and dolomite is similar in structure to calcite, from which it might have formed.