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Geochemical evidence of microbial activity within ooids
Author(s) -
Diaz Mara R.,
Swart Peter K.,
Eberli Gregor P.,
Oehlert Amanda M.,
Devlin Quinn,
Saeid Amel,
Altabet Mark A.
Publication year - 2015
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/sed.12218
Subject(s) - leachate , carbonate , geology , ooid , organic matter , environmental chemistry , total organic carbon , calcite , microbial mat , nitrogen , carbon fibers , isotopes of carbon , geochemistry , mineralogy , chemistry , paleontology , materials science , sedimentary depositional environment , bacteria , organic chemistry , cyanobacteria , structural basin , composite material , composite number
Ooid formation remains elusive despite their importance as palaeoclimatic indicators and important contributors to global carbonate budget. Based on stable isotopes, nutrient and elemental analyses on solid components and ooidal leachates, this study supports the notion of microbial involvement in the development of ooids from Great Bahama Bank. Carbon and nitrogen isotopic analyses on organic fractions identified geochemical signatures of microbial activity. The δ 13 C values for organic carbon in the bulk (−11·9 to −16·9‰); intercrystalline/intracrystalline (−11·9 to 16·7‰); and intracrystalline phases (−12·4 to −17·7‰) were similar and, except for the more enriched values of ooids from Butterfly Beach, were within the range of photosynthesisers. The δ 15 N values for the bulk (+0·5 to −0·2‰); intercrystalline/intracrystalline (−0·3‰ to −0·7‰) and intracrystalline organic matter (−0·3 to −1·7‰) showed a narrow range consistent with nitrogen fixation. While positive δ 15 N and δ 18 O values of the NO 3 − leached from the ooids provided evidence of denitrification, the carbonate associated sulphate δ 34 S CAS of the bulk sediments (+19·2 to +19·6‰) and δ 34 S of the leachates (+16·6 to +18·3‰) provided weak indication of sulphate reduction, suggesting either that high concentrations of isotopically enriched S are overriding bio‐signatures of sulphate reduction or that microbes are preferentially using NO 3 − as an electron acceptor. In contrast, the elevated sulphate concentrations of the leachates suggest the occurrence of microbial sulphide oxidation within ooids. The high Mg/Ca of the leachates and scanning electron microscope analyses provide putative evidence of amorphous calcium carbonate and a formative role in CaCO 3 precipitation. Together, these findings indicate that a redox dependent microbial consortium may influence CaCO 3 precipitation in the form of ooid accretion, cementation and micritization. It is also inferred that ooid deposits are not suitable indicators of palaeoclimate because ooids are affected throughout their life by a complex chain of abiotic and biological processes which can lead to large geochemical offsets.