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Case Studies Assessing Timing of Fluid Flow Events |
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada
Six distinct fluid events, which span a time frame from syndeposition (Cambrian-Devonian) to the last stages of the Laramide Orogeny (early Tertiary), have been identified in the MacKenzie Mountain range of the northern Canadian Rocky Mountains. The earliest event was a sedimentary exhalative event associated with the expulsion of brines onto the seafloor along extensional faults associated with a Silurian sedimentary basin. This was followed by a widespread diagenetic dolomitization event that affected the majority of carbonates from the early Devonian and older. The third event produced the stratigraphically restricted but regionally extensive Manetoe Facies dolomites, host to Mississippi Valley-type mineralization and reserves of natural gas. The formation of the Manetoe Facies dolomites is interpreted to have resulted from late diagenetic fluid flow in the late Devonian to early Carboniferous, possibly driven by the Antler Orogeny. The fourth fluid event, the vug-fill event, is constrained by low
D values to being early Cretaceous, or later in age. Features produced by this event are in turn cut by veins associated with the Laramide Orogeny (early Cretaceous to early Tertiary). The final recorded fluid event in this region is the calcite-barite event, interpreted to have been deposited by inflowing meteoric water. This study represents one of the most complete records of the fluid history of an area that has seen many palaeohydrogeological events. The combination of field and geochemical observations allows us to estimate the age, as well as the origin, of each event described.
