ABSTRACT: Transmission Electron Microscopic (TEM) Study of Illite-Smectite (I/S) Diagenesis in the Beaufort-MacKenzie Basin, Arctic Canada

VALI, H., R. HESSE, and J. KO, McGill University, Montreal, Quebec, Canada

Samples of progressively illitized I/S mixed-layer clays from two drill holes (Taglu C-42, Reindeer D-27) of the Beaufort-MacKenzie basin were studied with the TEM using novel techniques of ultrathin section treatment with alkylammonium ions and cryofixation and freeze etching. Treatment of expandable mixed-layer clays with

alkylammonium ions of different chain lengths provides characteristic expansions that are stable under the electron beam and allowed the recognition of three types of expandable layers: low-charge smectite, high-charge smectite or vermiculite-like layers, and "expandable illite" layers. At shallow subsurface depths, I/S mixed-layers are random interstratifications with 40-65% I according to XRD results. Alkylammonium-treated ultrathin sections of the same samples show a higher proportion of expandable layers compared to glycolated XRD powders. Smectitic layers are curved and of short length and do not seem to form coherent sequences. Illitic packets are between 2 and 10 layers thick. At intermediate burial depths, R1-ordered I/S observed by XRD is also seen in ultrathin sections. Sing e S layers disappeared. R3- (or R>3-) ordering identified both by XRD and TEM at greater burial depth is associated with thicker particles. In addition, TEM shows the presence of "expandable illite." The high-resolution replicas of cryofixation/freeze-etched dispersions shows dissolution and growth phenomena on surfaces with exceptional clarity.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)