Origin and characterization of hydrothermal dolomite in the Western Canada Sedimentary Basin

Regional and localized extensive fluid flow events may have occurred during tectonic thrusting, sediment loading, uplift and compression in the Western Canada Sedimentary Basin (WCSB). These fluids were responsible for the formation of sediment-hosted ore deposits; petroleum migration and dolomitization affecting the majority of Devonian and Mississippian carbonate reservoirs. The timing and origin of these fluid flow events remain a controversial issue. Pre-, syn- and post-Laramide fluid flow events have been invoked in the literature based on a multitude of paleomagnetic, geochemical and other evidence. The composition and evolution of ancient sedimentary fluids have been successfully reconstructed using the techniques of stable and radiogenic isotopes and fluid inclusion analyses. In this contribution, hydrothermal dolomites from several reservoirs in the WCSB will be discussed to show how hydrothermal fluids could have been instrumental in the formation of dolomite. These fluids were mostly focused through fractures and faults generated early and late in the diagenetic history of the basin. These dolomites occur in both Devonian and Mississippian carbonates from Alberta and British Columbia. Earlier hydrothermal incursions occurred in a shallow burial environment during the Tournaisian or Visean, while later hot fluids were generated during and post-Laramide tectonic event. The: composition, temperature and salinity of the hydrothermal fluids produced during these two main events were very different. Earlier, hydrothermal event is characterized by higher salinity, lower temperature values and variable isotopic signatures than later event. (C) 2003 Elsevier Science B.V. All rights reserved.