The impact of organic matter deposition and pre-oil window diagenetic transformation on commonly utilized thermal maturity indicators
Date
2021-08-19
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Abstract
Despite decades of research on organic matter deposition, alteration, and preservation, the processes affecting and altering organic matter at low maturity are relatively poorly understood. Processes that affect deposition of organic matter, such as wildfires, or influence its preservation after deposition, such as diagenetic clay catalyzed transformation, can reduce the reliability of commonly applied thermal maturity proxies. This thesis integrated organic geochemistry and petrographic examination of samples from the Upper Cretaceous in Western Canada and the Canadian Arctic Islands to better understand processes that altered organic matter during deposition and early diagenetic. Samples from the Upper Cretaceous Kanguk Formation of the Canadian Arctic Islands have abundances of pyrogenic polycyclic aromatic hydrocarbon compounds and combustion-related organic macerals that show a distinct trend of increasing wildfire influence from the Turonian to the Campanian. This trend corresponds with increasing amounts of terrigenous organic matter in the marine Sverdrup Basin, in addition to increasing angiosperm-derived biomarkers. High rates of terrigenous organic matter deposition, accelerated by wildfires, have an important impact on the preservation of organic matter in a marine basin, as observed through degradation trends correlated to elevated primary productivity. A stratigraphically-controlled thermal maturity transect of samples ranging from eogenesis up to the peak of catagenesis was collected from the Upper Cretaceous Western Canadian Sedimentary Basin and examined using integrated organic geochemistry and organic petrology. The diagenetic transformation of hopanoid and steroid compounds was investigated, and key chemical transformations were calibrated to a maturity level. This investigation demonstrated that early clay-catalyzed backbone rearrangement in both hopanoid and steroid compounds has a profound impact on the hopanoid and steroid composition at higher maturity levels as well as on commonly applied thermal maturity indicators. A detailed calibration was completed, producing a correlation between a wide variety of common geochemical and optical thermal maturity indicators. Although each indicator has drawbacks, thirteen proxies are found to be effective, and a multi-disciplinary approach is recommended.
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Organic Geochemistry, Diagenesis, Organic Petrology, Thermal Maturity
Citation
Synnott, D. P. (2021). The impact of organic matter deposition and pre-oil window diagenetic transformation on commonly utilized thermal maturity indicators (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.