Correlating paleomagnetic, geochemical and petrographic evidence to date diagenetic and fluid flow events in the Mississippian Turner Valley Formation, Moose Field, Alberta, Canada

Petrographic, geochemical and paleomagnetic analyses of the Mississippian Turner Valley Formation provide constraints on diagenesis and fluid flow events in the Western Canada Sedimentary Basin. Paleomagnetic plugs and companion geochemical samples were taken from two drillcores, with Fullbore MicroImage log orientations. Dolomite from both wells yielded two magnetization directions. The low-temperature, low-coercivity direction is a drilling-induced remanence rather than a viscous remanent magnetization. The high-temperature, high-coercivity remanence direction is Cretaceous, and there is no sign of a primary Mississippian direction. Geochemical analyses of matrix dolomite yield δ 18O values ranging from 0.65 to −3.34‰ (VPDB standard) and δ 13C values ranging from 1.77 to 3.05‰ VPDB. The least depleted samples have stable isotope values consistent with, or only slightly depleted from, postulated Mississippian dolomite values. The remaining sample values exhibit a negative covariant trend consistent with either mixing with another diagenetic fluid or recrystallization during burial. Petrographic analysis reveals the presence of a recrystallization event that caused zoning and a gradual increase size of the dolomite crystals. This event is thought to have caused both the Cretaceous paleomagnetic remanence and the altered geochemical values. The minor enrichment in Sr radiogenic isotopes, relative to coeval seawater values, suggests that both an extrabasinal source for any fluid and large-scale fluid flow are unlikely. The results also indicate that magnetic remanences are very sensitive to visually minor changes in carbonate recrystallization from heat or pressure, so that great care must be taken in correlating paleomagnetic and geochemical data.