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Cyclic zoning in authigenic saddle dolomite-ankerite: Indications of a complex interplay between fault-rupturing and diagenetic alteration
Chemical Geology ( IF 3.6 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.chemgeo.2020.119831 Pengjie Ma , Chengyan Lin , Jens Jahren , Chunmei Dong , Lihua Ren , Helge Hellevang
Chemical Geology ( IF 3.6 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.chemgeo.2020.119831 Pengjie Ma , Chengyan Lin , Jens Jahren , Chunmei Dong , Lihua Ren , Helge Hellevang
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Abstract Zoned authigenic minerals reflect temporal changes in fluid composition and can shed light on the dynamic evolution of sedimentary systems. The chemistry of the zoned saddle dolomite-ankerite from the Bohai Bay Basin, China, changes in a cyclic way from core to rim, reflecting a dynamic system perturbated several times from thermodynamic steady-state. The distribution of the dolomite-ankerite close to faults suggests that the cyclic evolution may be related to the faulting. Oxygen isotope ratios, relatively high precipitation temperatures (80–160°C), and association with late-stage pyrite cementation, suggest that dolomite-ankerite formation may be connected to thermochemical sulphate reduction within the hydrocarbon reservoir. The chemical zones alternate between low and high Fe-content, and show evidence of corrosion before each growth stage. The complex relation between the silicate, carbonate, and sulphur/sulphide systems can be explained in terms of open-system diagenesis, where fault rupturing triggers an influx of CO2 and thermogenic H2S. Pyrite scavenges both H2S and Fe, until all H2S is exhausted, and the aqueous Fe then builds up again from slow silicate dissolution. The Fe-content of dolomite-ankerite growth after such a perturbation therefore depends on the rate of Fe-supply from the silicate dissolution, and the length of time between the chemical perturbations. If such a relation exists between time and the coupled mineral reactions, then the Fe-content of the carbonates may provide an indication of the length of time between the fault-triggered chemical perturbations of a system. This must be regarded as a working hypothesis for further detailed studies on the relation between faulting and the silicate-sulphur/sulphide‑carbonate system.
更新日期：2021-01-01
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