Microbially induced dolomite precipitates in Eocene lacustrine siliciclastic sequences in the Dongying depression, Bohai Bay Basin, China: Evidence from petrology, geochemistry, and numerical modeling
Autor: | Kenneth A. Eriksson, Yingchang Cao, Benben Ma |
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Rok vydání: | 2020 |
Předmět: |
Anhydrite
Evaporite 020209 energy Dolomite Geochemistry Energy Engineering and Power Technology Geology 02 engineering and technology engineering.material Troilite Petrography chemistry.chemical_compound Fuel Technology chemistry Geochemistry and Petrology 0202 electrical engineering electronic engineering information engineering Earth and Planetary Sciences (miscellaneous) engineering Carbonate Siliciclastic Pyrite |
Zdroj: | AAPG Bulletin. 104:2051-2075 |
ISSN: | 0149-1423 |
Popis: | This study investigates the origin of dolomite by examining thick lacustrine sequences of evaporites, mudstones, and deep-water sublacustrine fan sandstones in the lower unit of the fourth member of the Eocene Shahejie Formation (Es4x) in Bohai Bay Basin, China. This petrographic, geochemical, and numerical modeling study recognizes evidence for microbially mediated dolomite precipitates in the Es4x sandstones, including the following: (1) spherical or elliptical dolomite aggregates consisting of submicrometer-sized crystals; (2) negative δ13CVPDB (VPDB refers to Vienna Peedee belemnite) values of the dolomite cements (–6.56‰ to –3.35‰); (3) relatively low precipitation temperatures of dolomite cements (39°C–65°C [102°F–149°F]) based on δ18OVPDB values from –8.76‰ to –4.65‰; and (4) negative 34SVCDT (VCDT refers to Vienna Canon Diablo troilite) values of associated framboidal pyrite (–3.9‰ to +5.7‰) with respect to an anhydrite precursor (+21.2‰ to +37.8‰). One-dimensional reactive transport modeling incorporating biodegradation kinetics was conducted to evaluate the link between biodegradation of organic matter and geochemical reactions of inorganic minerals during microbial sulfate reduction (MSR). Microbial metabolism in the model creates favorable geochemical conditions for dolomite precipitation by increasing pH, carbonate alkalinity, and Mg2+/Ca2+ ratio. The modeling results reproduce petrographic observations associated with the MSR process and indicate that the kinetics of microbial growth can significantly modify the geochemistry of simulated waters and enhance microbially mediated dolomite precipitation. Therefore, this study illustrates the effect of MSR in dolomite precipitation in a semiclosed and reducing continental lacustrine basin. |
Databáze: | OpenAIRE |
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