STUDY ON AUTHIGENIC MINERALS IN SEDIMENTS RECOVERED FROM THE SEA OF MARMARA

Gas hydrate, widely distributing in marine sediments on continental slope and in permanent terrestrial permafrost, attracts worldwide attention because of its environment-friendly property, high energy density and gigantic reserves. There are several conditions for gas hydrate to form: methane saturating pore water and pressure and temperature regime in sediment being in the regime of hydrate stability. In such a condition, the geochemical environment in sediments with hydrate occurrence is generally reductive and acidic, and certain specific authigenic minerals will be formed. The sediment samples for this study were collected from the Western High in the western part and the Cinarcik Basin in the eastern part of Sea of Marmara, and the occurrence of gas hydrate was identified in the former while no hydrate recognized in the latter. The sediment samples were recovered with piston corer for both sites (MRS-CS-13 and MRS-CS-17). Efforts have been made to study the types and morphology of authigenic minerals for the two sites by using XRD and SEM.

Authigenic minerals are mainly gypsum and iron sulfide in the sediments of Core MRS-CS-13 on the Western High, while there are pyrite and calcite in the sediments of Core MRS-CS-17 in the Cinarcik Basin. Greigeite is identified in the sediments of Core MRS-CS-13 on the Western High, indicating an acidic and reduced environment,and there possibly exists gap of methane leak.The erosion on gypsum surface in the sediments of Core MRS-CS-13 also indicates an acidic environment.Moreover,we guess that calcium ions in gypsum in the sediments of Core MRS-CS-13 come from calcite acid dissolution, because calite can be only found in the sediments of Core MRS-CS-17 where the PH of water is nearly neutral.

Key Words: Authigenic mineral; Sediment; Gas Hydrate; Sea of Marmara, Pyrite