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 T urner Valley Formation provide constraints on diagenesis and fluid how even ts in the Western Canada Sedimentary Basin. Paleomagnetic plugs and compani on geochemical samples were taken from two drillcores, with Fullbore MicroI mage log orientations. Dolomite from both wells yielded two magnetization d irections. The low-temperature, low-coercivity direction is a drilling-indu ced remanence rather than a viscous remanent magnetization. The high-temper ature, high-coercivity remanence direction is Cretaceous, and there is no s ign of a primary Mississippian direction. Geochemical analyses of matrix do lomite yield delta(18)O values ranging from 0.65 to -3.34 parts per thousan d (VPDB standard) and delta(13)C values ranging from 1.77 to 3.05 parts per thousand VPDB. The least depleted samples have stable isotope values consi stent with, or only slightly depleted from, postulated Mississippian dolomi te values. The remaining sample values exhibit a negative covariant trend c onsistent with either mixing with another diagenetic fluid or recrystalliza tion during burial. Petrographic analysis reveals the presence of a recryst allization event that caused zoning and a gradual increase size of the dolo mite crystals. This event is thought to have caused both the Cretaceous pal eomagnetic remanence and the altered geochemical values. The minor enrichme nt in Sr radiogenic isotopes, relative to coeval seawater values, suggests that both an extrabasinal source for any fluid and large-scale fluid how ar e unlikely. The results also indicate that magnetic remanences are very sen sitive to visually minor changes in carbonate recrystallization from heat o r pressure, so that great care must be taken in correlating paleomagnetic a nd geochemical data. (C) 2000 Elsevier Science B.V. All rights reserved.