동해에서 산출한 메탄관련 자생탄산염: 광물, 지화학적 특성

Abstract

Authigenic carbonates related to gas hydrates were discovered from the cores in the Ulleung Basin, East Sea. Carbonateconcretions range from 3 to 6 cm in diameter, and display irregular shapes. The inside of concretions issometimes porous and shows internal layering. Concretions are composed of aragonite or high Mg-calcite, or thecombination of both. Calcite crystals are micritic and include planktonic foraminifers, diatoms, silt-sized, detritalquartz grains, and authigenic framboidal pyrites. Ultra-textural examination reveals that acicular aragonites grewas cements between micritic calcite crystals, and this suggests that micritic calcite precipitated prior to aciculararagonite. Oxygen and carbon isotopic compositions of carbonate concretions range from +2 to +5 per mil (PDB)and from -44 to -39 per mil (PDB), respectively. These depleted carbon isotopic compositions indicate that thecarbon source for the formation of authigenic carbonates were gas hydrates below, and the carbonates were formedby the oxidation of methane. Relatively narrow range of carbon isotope values, compared to those of other authigeniccarbonates reported elsewhere, indicates similar diagenetic environments of formation for these concretions.Distinctive clusters of stable isotope values regardless of mineralogy imply that carbonate concretions formed in aclosed-diagenetic system.