Extreme values of δ³⁴S: +105.3 ‰, +105.2 ‰, +87.9 ‰, +87.2 ‰ and +79.7 ‰ were determined in barite concretions from the Aptian-Lower Albian marly limestone of the Krizna Nappe of the Western Carpathians, Slovakia. The phases relation in inclusions from these concretions, and the results of thermo-vacuometric impulse decrepitation analyses indicate temperatures of 50–60 °C, which correspond mostly to secondary inclusions. For the purpose of comparison, barite concretions from Rohoznik, Slovakia, from Gaiseltal, Germany, and from Havana, Cuba, were analyzed. Barite concretions with extremely high δ³⁴S values were formed during late diagenesis of organic matter-rich sediment in the depth range of very low pore water sulphate concentrations, below the sulphate reduction zone.