Correlating paleomagnetic, geochemical and petrographic evidence to date diagenetic and fluid flow events in the Mississippian Turner Valley Formation, Moose Field, Alberta, Canada
Mt. Cioppa et al., Correlating paleomagnetic, geochemical and petrographic evidence to date diagenetic and fluid flow events in the Mississippian Turner Valley Formation, Moose Field, Alberta, Canada, SEDIMENT GE, 131(3-4), 2000, pp. 109-129
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.