Dolomitization of the Devonian Swan Hills Formation, Rosevear Field, Alberta, Canada

• Published in: Sedimentology
• Main Authors: KAUFMAN, JONATHAN, HANSON, GILBERT N., MEYERS, WILLIAM J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1991
• Subjects: canada basin
• Online Access: http://dx.doi.org/10.1111/j.1365-3091.1991.tb01854.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3091.1991.tb01854.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3091.1991.tb01854.x

ABSTRACT The Swan Hills Formation (Middle‐Upper Devonian) of the Western Canada Basin is host to several NW‐SE‐trending gas fields developed in massive replacement dolostone. One of these, the Rosevear Field, contains two major dolostone trends along opposing margins of a marine channel that penetrates into a platform‐reef complex. Dolostones consist predominantly of branching and bulbous strdmatoporoid floatstones and rudstones with well‐developed moldic and vuggy porosity. Replacement dolomite is coarsely crystalline (100‐600 μm), inclusion‐rich, composed of euhedral through anhedral crystals and has a blotchy to homogeneous red cathodoluminescence. Geochemically, replacement dolomite is characterized by (i) nearly stoichiometric composition (50.1‐51.1 mol% CaCO 3 ), (ii) negative δ 18 O values (mean=‐7.5‰, PDB) and (iii) variable 87 Sr/ 86 Sr ratios ranging from values similar to Late Devonian‐Early Mississippian seawater (∼0.7082) to radiogenic compositions comparable to saddle dolomite cements (>0.7100). Dolomitization began after widespread precipitation of early, equant calcite spar and after the onset of pressure solution, implying that replacement dolomite formed in a burial environment. Oxygen isotope data suggest that dolomite formed at 35‐75°C, temperatures reached during burial in Late Devonian through Jurassic time, at minimum depths of 450 m. The linear NW‐SE orientation of most dolomite fields in the Swan Hills Formation is suggestive of fault control on fluid circulation. Two models are proposed for fault‐controlled circulation of dolomitizing fluids at the Rosevear Field. In the first, compaction‐driven, updip fluid migration occurred in response to basin tilting commencing in the Late Palaeozoic. Deep basinal fluids migrating updip were focused into channel‐margin sediments along fault conduits. The second model calls upon fault‐controlled convective circulation of (i) warm Devonian‐Mississippian seawater or (ii) Middle Devonian residual evaporitic brines. The overlap in 87 Sr/ 86 Sr and δ ...