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Lookup NU author(s): Lisa Buckley, Dr Richard Tyson
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The Cretaceous Colorado Group (Albian-Turonian) is a sequence of homogeneous organic-rich shales deposited within the Western Interior Seaway of North America. Bulk geochemical analysis (Rock-Eval, TOC, Total Carbon, Total Sulphur), and palynofacies observations have been conducted on 452 core samples in order to reconstruct the organic facies variations through the Group and along transects across the Canadian portion of the Western Interior Seaway. The Viking and Westgate formations are typified by low percentages of poorly preserved (weakly fluorescent) marine amorphous organic matter (AOM) and abundant terrestrial phytoclasts, associated with low TOC and average measured hydrogen indices of only 106 mgHC/gTOC (Type III kerogen). The Fish Scales and Belle Fourche formations have a transitional organic facies reflecting mixing with better preserved marine AOM, and thus exhibit higher mean TOC and measured HI values (158 and 170 respectively). The Second White Specks Formation and the upper Colorado Group are both dominated by moderate to strongly fluorescent AOM, resulting in a mean measured HI of 320 (Type II kerogen). The mean average HI values of the Type III and Type II kerogen components, computed from the slope of S2 versus TOC trends, are approximately 170 and 500 respectively. The transgressive Albian-Turonian interval is associated with a progressive upward decrease in terrestrial phytoclast supply, and progressive improvement in the preservation of the AOM, related to changing basin redox conditions. Stable carbon isotope analysis has identified a significant (~4 ppt) positive shift in delta 13Corg values in the vicinity of the Belle Fourche-Second White Specks Formation boundary in three WCSB cores. This is interpreted as the regional expression of the isochronous Cenomanian-Turonian (C-T) global isotopic event. The formation boundary apparently becomes older towards the east, where the lower siliciclastic input allows the development of a calcareous facies to occur earlier than in the west.
Author(s): Buckley L, Tyson RV
Publication type: Report
Publication status: Published
Series Title: Summary of Investigations 2003
Year: 2003
Source Publication Date: 01-07-2003
Report Number: Misc. Rept. 2003-4.1
Institution: Energy and Resources Geo-Publications, Government of Saskatchewan
Place Published: Regina, Saskatchewan
