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Formation of low‐magnesium calcite at cold seeps in an aragonite sea
Author(s) -
Feng Dong,
Roberts Harry H.,
Joye Samantha B.,
Heydari Ezat
Publication year - 2014
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12081
Subject(s) - calcite , aragonite , geology , seawater , carbonate , cold seep , dissolution , carbonate minerals , mineralogy , mineral , brine , geochemistry , petrography , precipitation , oceanography , chemistry , methane , physics , organic chemistry , meteorology
This study investigates the conditions of occurrence and petrographic characteristics of low‐Mg calcite ( LMC ) from cold seeps of the Gulf of Mexico at a water depth of 2340 m. Such LMC mineral phases should precipitate in calcite seas rather than today's aragonite sea. The 13 C‐depleted carbonates formed as a consequence of anaerobic oxidation of hydrocarbons in shallow subsurface cold seep environments. The occurrence of LMC may result from brine fluid flows. Brines are relatively Ca 2+ ‐enriched and Mg 2+ ‐depleted (Mg/Ca mole ratio <0.7) relative to seawater, where the Mg/Ca mole ratio is ~5, which drives high‐Mg calcite and aragonite precipitation. The dissolution of aragonitic mollusk shells, grains and cements was observed. Aerobic oxidation of hydrocarbons and H 2 S is the most likely mechanism to explain carbonate dissolution. These findings have important implications for understanding the occurrence of LMC in deep water marine settings and consequently their counterparts in the geological record.