Mixed-layer illite/smectite diagenesis in the rift and post-rift sediments of the Jeanne d'Arc Basin, offshore Newfoundland, Canada

• Main Author: Abid, Iftikhar A.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1996
• Subjects: Canada; Newfoundland
• Online Access: https://research.library.mun.ca/6619/; https://research.library.mun.ca/6619/1/IftikharAbid.pdf; https://research.library.mun.ca/6619/3/IftikharAbid.pdf

Mixed-layer illite/smectite (I/S) clays were analyzed from 22 deep exploration wells from the Jeanne d'Arc Basin, where large commercial hydrocarbon reserves have been discovered. This basin has been subdivided into 4 areas (Southern, Trans-Basin Fault, Northern, and Outer Ridge Complex) based on general geology and characteristics of I/S-depth profiles. -- The mineralogy of fine-grain clays (<0.1μm) consists of mainly mixed-layer I/S with minor amounts of kaolinite, illite, and chlorite. Smectite and/or smectite-rich I/S clays were supplied to the Jeanne d'Arc Basin during Upper Jurassic to Tertiary time. At present smectite-rich I/S clays occur only in shallow samples irrespective of their geologic age. The proportion of illite-layers, as well as their ordering in I/S, increase with depth and temperature. The random to R1-ordered I/S transition occurs between depth intervals of 1940m to 3720m and crosses several stratigraphic boundaries. The R1 to R3-ordered I/S transition is generally observed below 4000m depth. Basin-wide I/S data indicate that smectite-rich I/S clays have been illitized in both rift and post-rift sediments of the Jeanne d'Arc Basin due to diagenesis. -- The majority of I/S clays in samples with vitrinite reflectance (R₀) values less than 0.5% are highly expandable and randomly interstratified. However, for R₀ values greater than 0.66% only illite-rich ordered I/S is observed. The random to R1-ordered I/S transition generally occurs within the upper "oil window" level of organic maturity (0.50-0.66%R₀). The relationships observed in this study should be expected in other wells of the Jeanne d'Arc Basin and may provide useful information to investigate the thermal maturity of sediments. -- The δ¹⁸O values of I/S clays range from 17.9‰ to 25.8‰ (SMOW), and calculated pore-fluid compositions vary from 1.5‰ to 11.6‰. In the Trans-Basin Fault area, high δ¹⁸O pore-fluid values are present at shallower depths and coincide with a narrow transition from random to R1-ordered I/S and reflect ...