Thermochemical sulphate reduction in the Upper Devonian Cairn Formation of the Fairholme carbonate complex (South-West Alberta, Canadian Rockies): evidence from fluid inclusions and isotopic data |
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Authors: | VEERLE VANDEGINSTE RUDY SWENNEN SARAH A GLEESON† ROB M ELLAM‡ KIRK OSADETZ§ FRANÇOIS ROURE¶ |
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Institution: | Afdeling Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Heverlee, Belgium (E-mail: ); Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E3; Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride G750QF, UK; Geological Survey of Canada, 3303, 33rd Street N.W., Calgary, AB, Canada; Institut Français du Pétrole, 1&4 avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France |
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Abstract: | The Fairholme carbonate complex is part of the extensively dolomitized Upper Devonian carbonate reefs in west-central Alberta. The studied formations contain moulds (up to 10 cm in diameter), which are filled partially with (saddle) dolomite, quartz and calcite cements. These cements precipitated from a mixture of brines that acquired high salinity by dissolution of halite and brines derived from evaporated sea water. The fluids were warm (homogenization temperature of primary fluid inclusions of 76 to 200 °C) and saline (20 to 25 wt% NaCl equivalent) and testify to thermochemical sulphate reduction processes. The latter is deduced from S in solid inclusions, CO2 and H2S in volatile-rich aqueous inclusions and depleted δ13C values down to ?26‰ Vienna Pee Dee Belemnite. High 87Sr/86Sr values (0·7094 to 0·7110) of the cements also indicate interaction of the fluids with siliciclastic sequences. The thermochemical sulphate reduction-related cements probably formed during early Laramide burial. Another (younger) calcite phase, characterized by depleted δ18O values (?23·9‰ to ?13·9‰ Vienna Pee Dee Belemnite), low Na (27 to 37 p.p.m.) and Sr (39 to 150 p.p.m.) concentrations and non-saline (~0 wt% NaCl equivalent) fluid inclusions, is attributed to post-Laramide meteoric water. |
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Keywords: | Dolomite fluid inclusions stable and radiogenic isotopes thermochemical sulphate reduction Western Canada Sedimentary Basin |
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