Origin and significance of mud‐filled incised valleys (Upper Cretaceous) in southern Alberta, Canada

摘要: Seven mud-filled incised valleys (MFIVs) in the paralic facies of Dinosaur Park and Horseshoe Canyon formations (Upper Cretaceous) southern Alberta were studied to better understand their morphology, geometry depositional histories an estuarine context. Two preservational geometries occur: simple, U-shaped forms; internally complex forms. Both types MFIV record deposition central zone low energy (turbidity) setting. Simple, MFIVs have sharp basal erosional surfaces consist mudstone-dominated heterolithic fills channel-wide, concave-up laminae. Associated fossil assemblages are marine brackish. Each simple records a cut-and-fill history associated with cycle relative sea-level drop rise. Low-energy settings, loss channel form during infilling, shoreface deposits, as well absence clear tidal indicators suggest coastal plain setting, along wave-dominated, barred coastline. Complex rarer, imbricated, wedge-shaped sets inclined-to-horizontal strata. Tidal deposits and/or nonmarine-to-marine macrofossils occur locally. Complex infilled meandering reaches tide-dominated estuaries. Their rarity compared freshwater palaeontological content that they contiguous landward extensive fluvial channels. A near Onefour comprises three in-channel cycles. consists surface overlain by lateral accretion bedding conformable transition vertically aggraded reflects event under control changes culminated overbank flooding. All formed low-gradient settings (≤0.03%) where zones stretched out over many tens kilometres. Tide-dominated estuaries apparently exhibited straight-to-meandering upstream transitions penetration (≥200 km) backwater effects. Few modern serve adequate analogues these ancient, estuaries. Radiometric data indicate cycles 100 000-400 000 years maximum duration thus, equivalent 4th order However, negative evidence tentatively suggests took place time intervals 1-2 orders magnitude smaller (5th or higher cycles).