Sedimentology, stratigraphy, and shallow burial alteration of the Upper Jurassic Swift Formation, southeastern Alberta

The Upper Jurassic (Oxfordian) Swift Formation in southeastern Alberta unconformably overlies Bathonian calcareous shales of the Rierdon Formation, and in turn is overlain by Lower Cretaceous sandstone, siltstone, and mudstone of the Basal Quartz Formation (Lower Mannville Group). The Swift comprises two unconformably bounded sequences: the shale member and ribbon sandstone. The shale member consists dominantly of shale with uncommon hummocky-cross-stratified siltstone. Comprising at least four parasequences that show a subtle upward-fining stacking pattern, it was deposited in an overall deepening, fully marine environment during the fourth Jurassic transgression across the Western Interior of North America. Deposition of Sequence 1 was terminated by a fall of relative sea level.; During the following lowstand, multiple, northeast-southwest trending meandering channels incised along the top of the subaerially exposed shale member. During a subsequent rise of relative sea level and transgression, lowstand deposits were thoroughly reworked by wave ravinement, which deposited a thin chert pebble lag. At the same time, lowstand channels were most probably widened. Associated also with transgression were significant changes in the physical and chemical conditions of the marine basin in the study area. (Abstract shortened by UMI.)...