Geochemical and Isotope Characteristics of Carbonates from Ejecta of Mud Volcanoes of the Kura Basin, Azerbaijan

Аннотация

This paper is devoted to the vein and dispersed carbonates from ejecta of mud volcanoes of Azerbaijan. The vein calcites are morphologically diverse and related to the healing of fracture systems. Most of them have δ¹³C (from –4 to +2‰) and δ¹⁸O (from +20 to +26‰) typical of marine carbonates. Some volcanoes contain fragments of the vein calcites enriched in light carbon (δ¹³C from –49.2 to –6‰), which could be formed in methane seep discharge sites during the Caspian Sea highstand period. In the dispersed carbonates from the clay pulp, the values of δ¹³C and δ¹⁸O change from –6.1 to +11.9‰ and from +23.8 to +32.7‰, respectively. It is shown that the studied carbonate matter has no genetic relation with the modern mud volcanic waters, which are characterized by high concentrations of \({\text{HCO}}_{3}^{-}\) (up to 8 g/L) and values of δ¹³C(TDIC) (δ¹³C_av= +20.0‰) and δ¹⁸O(H₂O) (δ¹⁸O_av= +4.0‰). Based on isotope characteristics and REE patterns, the vein calcites can be ascribed to the products of seawater-assisted postsedimentation transformation of sedimentary carbonates. The obtained data revealed a complete hydrodynamic isolation of mud volcanic channels from aquiferous complexes of host rocks.