Formation and transformation of mixed-layer minerals by Tertiary intrusives in Cretaceous mudstones, West Greenland

• Published in: Clays and Clay Minerals
• Main Authors: Drits, Victor A., Lindgreen, Holger, Sakharov, Boris A., Jakobsen, Hans Jorgen, Fallick, Anthony E., Salyn, Alfred L., Dainyak, Lidia G., Zviagina, Bella B., Barfod, Dan N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2007
• Subjects: Burial Diagenesis; Greenland; Illite-smectite; Oil-source Rocks; Tobelite; Nuussuaq
• Online Access: https://ddd.uab.cat/record/224784

In the Nuussuaq Basin, West Greenland, a thick succession of Tertiary dolerites has penetrated Upper Cretaceous mudstone. The mixed-layer minerals of mudstone core samples have been analyzed by X-ray diffraction, solid-state Si and Al magic-angle spinning nuclear magnetic resonance, Mössbauer and infrared spectroscopies, thermal analysis, chemical analysis, stable isotopes (O/O), and K/Ar dating. The mixed-layer minerals include for each sample two mixed-layer phases consisting of pyrophyllite, margarite, paragonite, tobelite, illite, smectite and vermiculite layers. The main, 80 m thick intrusion resulted in the formation of pyrophyllite, margarite, paragonite and tobelite layers. However, the tobelite layers are absent in samples <21 m from this intrusion. Furthermore, chlorite was formed and kaolinite destroyed in samples adjacent to minor intrusions and at distances <60 m from the large intrusion. For the first time, the detailed, complex mixed-layer structures formed during contact metamorphism of kaolinitic, oil-forming mudstones have been investigated accurately. The formation of tobelite layers reveals that oil formation has taken place during contact metamorphism. Furthermore, K/Ar dating of mixed-layer minerals from shale indicates that the intrusives are of early Eocene age. The 80 m thick intrusive is responsible for the main mixed-layer transformations, whereas two thin (3 m and 0.5 m thick) intrusions contribute little. Thus, the detailed mixed-layer investigation has contributed significantly to the understanding of the regional geology and the contact metamorphic processes.