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Pedogenic‐phreatic carbonates on a Middle Devonian (Givetian) terrigenous alluvial‐deltaic plain, Gilwood Member (Watt Mountain Formation), northcentral Alberta, Canada
Author(s) -
WILLIAMS C. A.,
KRAUSE F. F.
Publication year - 1998
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.1998.00192.x
Subject(s) - geology , geochemistry , carbonate , trough (economics) , paleosol , sedimentary depositional environment , terrigenous sediment , dolomite , paleontology , tufa , sedimentary rock , economics , metallurgy , macroeconomics , materials science , structural basin , loess
In the Muskeg Trough of northcentral Alberta the Gilwood Member contains widespread carbonate deposits that formed within terrigenous mudstone and sandstone hosts. Stratigraphic, depositional and petrographic relationships indicate that these carbonates represent calcretes and dolocretes. Calcretes, observed best with cathodoluminescence, display microcrystalline alpha fabrics, circumgranular cracks, root networks, displacive growth fabrics, elongate channel voids and rare coloform growths with flower spar. Similarly, dolocretes have microcrystalline alpha fabrics, brecciation, gradational contacts with host mudstones, extensive layered nodular horizons and are associated with anhydrite and pyrite. δ 13 C values range between −7‰ to +1‰ and –6‰ to +3‰ for calcretes and dolocretes, respectively. Oxygen isotopes are more variable and differ with host lithologies. δ 18 O of calcretes ranges between −11‰ to −8‰ for sandstones and −8‰ to −3‰ for mudstones, whereas δ 18 O of dolocretes ranges between −3‰ to 1‰ for marine mudstones and −6‰ to −2‰ for pedogenic mudstones. Regional mapping indicates that calcretes thicken towards the deepest parts of the Muskeg Trough. Widespread dolocretes extend beyond the eastern and western limits of Muskeg Trough and are useful marker intervals for regional correlations. Dolocretes of restricted lateral extent are found within gleyed palaeosol mudstones next to calcretized channel sandstones. Calcrete isotopic values are interpreted as indicative of carbonate precipitation from waters with meteoric water input. However, the higher δ 18 O values in dolocretes are indicative of a contribution from an isotopically heavier source such as seawater. Stratigraphically, calcretes are most common along the western and northern edges of Muskeg Trough; thus, calcrete accumulation was further controlled by meteoric water in‐flow from the highland to the west and sluggish groundwater flow in Muskeg Trough. In contrast, regionally widespread dolocrete horizons appear to have formed from mixing of fresh waters derived from the highland to the west and seawaters introduced from the east. Regionally restricted dolocretes which are found next to channel sandstones formed from groundwater out‐flow from the permeable channel sandstones which resulted in calcretization in channel proximal mudstones and dolomitization in channel distal mudstones.