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ABSTRACT: Replacement Dolomitization in the Upper Devonian Leduc and Swan Hills Formations, Previous HitCarolineNext Hit Area, Alberta, Canada

LAFLAMME, ANDRE K., Husky Oil, Calgary, Alberta, Canada

A petrographic and geochemical study was undertaken to better constrain the origin and the timing of the diagenetic fluids responsible for the pervasive dolomitization of the Upper Devonian Leduc and Swan Hills formations in the Previous HitCarolineTop area of Alberta, Canada. Dolomitization in these formations is replacive, obliterates most of the limestone fabric, and is responsible for the well-developed pore systems. This replacement type of dolomite has similar characteristics in both formations. These similarities include an abundance of inclusions, a xenotopic texture, and a red cathodoluminescence response. However, the Leduc and Swan Hills dolomites have different responses when observed under fluorescence. The Leduc dolomite fluoresces yellow, whereas the Swan Hills dolomite fluoresces gre n. Trace element and stable isotope data are also comparable in both formations and overlap for the most part. Diagenetic fluids derived from seawater or slightly modified seawater are supported by average Carbon 13 (1.8o/oo; 2.8o/oo), Oxygen 18 (-4.2o/oo; -5.0o/oo) and 87Sr/86Sr (0.7082; 0.7086) values in the Leduc and Swan Hills dolomites, respectively. The timing of dolomitization is difficult to determine, but the petrographic and geochemical evidence may suggest a relatively early origin for these dolomites. The yellow fluorescent signature and some specific pyrolysis parameters characterizing the Leduc dolomite may indicate that mature organic compounds could have been incorporated during the initial crystallization or, more likely, during a subsequent recrystallization event.


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