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Clays and Clay Minerals; June 2007; v. 55; no. 3; p. 260-283; DOI: 10.1346/CCMN.2007.0550304
© 2007 Clay Minerals Society
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FORMATION AND TRANSFORMATION OF MIXED-LAYER MINERALS BY TERTIARY INTRUSIVES IN CRETACEOUS MUDSTONES, WEST GREENLAND

Victor A. Drits1, Holger Lindgreen2,*, Boris A. Sakharov1, Hans Jorgen Jakobsen3, Anthony E. Fallick4, Alfred L. Salyn1, Lidia G. Dainyak1, Bella B. Zviagina1 and Dan N. Barfod4

1 Geological Institute, Russian Academy of Science, Pyzhevsky per D7, 119017 Moscow, Russia
2 Clay Mineralogical Laboratory, Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
3 Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark
4 Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, Glasgow G75 0QF, UK

* E-mail address of corresponding author: hl{at}geus.dk

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 29Si and 27Al magic-angle spinning nuclear magnetic resonance, Mössbauer and infrared spectroscopies, thermal analysis, chemical analysis, stable isotopes (18O/16O), 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.

Key Words: Burial Diagenesis • Greenland • Illite-smectite • Oil-source Rocks • Tobelite






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