Regional Diagenesis and Fluid Flow Study of the Early Triassic Montney Formation as Related to H2S Generation
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2021-08
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Abstract
The regional diagenetic evolution of the Early Triassic Montney Formation was investigated using detailed petrographic techniques (optical and SEM/EDXS/CL) and multiple bulk and in-situ isotope geochemical data to address the nature of diagenetic fluids, water/rock interaction, and geological, geochemical, and structural processes controlled the formation of sulfates (anhydrite and barite), sulfides (H2S and pyrite), and carbonates (calcite and dolomite). According to the results of this study, the Montney Formation contains both early and late diagenetic anhydrite and late barite cement mainly formed by the Montney Formation pore water and incursion of structurally-controlled Devonian-sourced hydrothermal sulfate-rich fluids. Three pyrite forms, i.e., framboidal, recrystallized, and coalesced with distinct δ34S values, were identified. The sulfur isotope composition of anhydrite/barite, H2S, and pyrite demonstrates both microbial and thermochemical sulfate reduction (MSR and TSR) controlled the diagenetic sulfur cycle of the Montney Formation. The present-day produced-gas H2S was dominantly originated from the in-situ thermochemical sulfate reduction process and partially migrated from underlying formations. The Montney Formation is also comprised of three and four generations of early to late calcite (C1-C3) and dolomite (D1-D4) cement, respectively. Bulk δ13C and δ18O values, and 87Sr/86Sr isotope ratios of carbonate cement suggest water/rock interaction between hot basinal brines, Precambrian metasediments, and siliciclastics in the basin. Moreover, hydrothermal fluids as well as burial diagenesis appear to have contributed to the formation of carbonate cement. The overall diagenetic evolution of the Montney Formation was controlled by intraformational (Montney Formation pore water), and cross-formational fluid flow driven by hydrothermal activities and tectonic evolution of the Canadian Cordillera.
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Haghnazar Liseroudi, M. (2021). Regional diagenesis and fluid flow study of the early Triassic Montney Formation as related to H2S generation (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.