Multiple fluid flow events and the formation of saddle dolomite: case studies from the Middle Devonian of the Western Canada Sedimentary Basin

In Western Canada Sedimentary Basin (WCSB), large scale and focused fluid flow that caused hydrothermal dolomitization have been suggested with different timing and intensity. In this study, we conducted a petrographic and geochemical comparison between the Middle Devonian Sulphur Point and Slave Point carbonates from northwestern Alberta. The results demonstrate the presence of both an early fluid flow event associated with the Late Devonian to Mississippian Antler Orogeny as well as a later event coincident with the Late Cretaceous to Early Tertiary Laramide Orogeny. Early fluid flow event is characterized by high salinity fluids, and high temperatures and oxygen isotopic values of marine or slightly enriched values, as demonstrated in saddle dolomite from the Slave Point Formation. In contrast, later fluids that caused the precipitation of saddle dolomite in the Sulphur Point formation are characterized by having slightly saline values, comparable homogenization temperatures but more enriched delta(18)O values and slightly depleted delta(13)C signatures. Geochemical data indicate that this later hydrothermal fluid was mixture of Middle Devonian brines and radiogenic basement fluids. (C) 2002 Elsevier Science Ltd. All rights reserved.