| Summary: | Nearly 3000 continuous metres of Eureka Sound Formation sandstones, shales and coals were examined in outcrop along Kanguk Peninsula, Axel Heiberg Island, N.W.T., in the present study. From these rocks, diagenetic parameters such as illite crystrallinity, 1.0 nm peak sharpness ratios, proportion of illite in illite/smectite mixed layers, and sandstone cement paragenesis have been used in combination with thermal modelling to make inferences about the thermochemical evolution of the strata and their contained pore waters. The findings from both the thermal modelling and sandstone petrology suggest that a syn- or post-tectonic heat flow anomaly existed whereby heated Na⁺-enriched waters passed from diapir cores (where halite dissolution occurred) into laterally adjacent permeable lithologies such as coals and arenites. This concept is supported by an offset in the plot of vitrinite reflectance versus depth whereby the upper segment (based primarily on coals) has higher reflectance values than the lower segment (based mainly on phytoclasts), and on the formation of the sodium rich phase dawsonite as the last authigenic phase precipitated in the pores of the sandstones. An examination of the chemical conditions under which halite dissolves and dawsonite precipitates suggests that the Na⁺ concentration may have been as high as 105 g I⁻¹. Clay mineral analyses suggest that the major part of the clay variation in the Eureka Sound Formation can be attributed to changes in detrital minerals rather than to diagenetic reactions between the clay minerals and their chemical environment. Textural relationships between the six principal authigenic sandstone cements (calcite, ankerite, siderite, dawsonite, kaolinite and quartz overgrowths) and dissolution features in the aluminosilicates suggest that at least 7 episodes of changing pore fluid chemistry have occured since the strata were deposited. Science, Faculty of Earth, Ocean and Atmospheric Sciences, Department of Graduate
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