Regional elemental and organic geochemical character of the Devonian/Mississippian Exshaw Formation across Alberta, Canada.


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A regional geochemical study of the Devonian/Mississippian Exshaw shale across Alberta was conducted to test the hypothesis that the shale has widespread organic matter richness accompanied by redox-sensitive trace metal enrichment and biomarker ratios reflecting widespread, consistent anoxia. Our dataset enables a multi-proxy investigation of depositional environments and thermal maturity using whole-rock samples taken from 20 locations across southern and central Alberta. Rock-Eval 7S, Handheld XRF and GCMS are used in concert to conclude that the Exshaw shale is within the oil window for much of its geographical area. The organic matter is oil-prone, marine producer-sourced, moderately sulfur-rich (Type IIS, HI>400), and of excellent kerogen quality (TOC>2%, S2>10) where not overmature. Biomarker ratios and trace metal concentrations suggest that although reducing conditions were consistent throughout deposition, anoxia varied across the basin. Biomarker thermal maturity proxies generally agree with Tmax values that thermal maturity increases southwestward.



Exshaw. Shale. Anoxia. WCSB.