Hydrocarbon gases in deposits from mud volcanoes in the Sorokin Trough, north-eastern Black Sea

• Published in: Geo-marine letters 2003-12, Vol.23 (3-4), p.250-257
• Main Authors: Blinova, V N, Ivanov, M K, Bohrmann, G
• Format: Article
• Language: English
• Subjects: Brackish; Ethane; Gases; Hydrocarbons; Landslides & mudslides; Methane; Mud; Unsaturated hydrocarbons; Volcanoes
• ISSN: 0276-0460; 1432-1157
• DOI: 10.1007/s00367-003-0148-8

Hydrocarbon gases were determined in sediments from three mud volcanoes in the Sorokin Trough. In comparison to a reference station outside the mud volcano area, the deposits are characterized by an enrichment of high-molecular hydrocarbons (C sub(2)-C sub(4)), an absence of unsaturated homologues, a predominance of iso-butane in comparison with n-butane, and the presence of gas hydrate. The molecular composition of the hydrocarbon gases suggests their deep sources and thermogenic origin. In the pelagic sediments at the reference station, the methane concentration is relatively low (up to 49 ml/l); maximum concentrations are reached in deposits of the Dvurechenskii mud volcano (up to 400 ml/l). It was the first time that gas hydrate was sampled at the Dvurechenskii mud volcano. The gas extracted by dissociation of hydrate samples was dominated by methane (99.5%) with low amounts of ethane and propane (less than 0.5%). The isotopic composition of the methane varies between -62 and -66 PDB in delta super(13)C, and between -185 and -209 SMOW in delta D, indicating a mainly biogenic origin with an admixture of thermogenic gas.