Stable isotope study of carbonate-cemented rocks from the Pobitite Kamani area, north-eastern Bulgaria

Abstract

The Precipitation of carbonate cements in the Pobitite Kamani area (Lower Eocene) began during early diagenesis of sediments. There is evidence, however, that calcite is still forming today.

The negative δ¹³C values to −29.2‰ suggest that the carbonate formed during degradation of ¹²C-enriched organic matter (perhaps partly from oxidation of methane). The δ¹⁸O values of −0.9 to −1.6‰ reflect the marine origin of the early diagenetic carbonate cements. Most of the carbonates, however, formed during late diagenesis (at approximately 1300 m burial depth) and/or recently (after uplift) from percolating groundwaters. These carbonates have an isotopic composition characteristic of carbonates which precipitated from meteoric waters under normal sedimentary temperatures in isotopic equilibrium with ¹²C-enriched soil carbon dioxide.