Deposition of the cretaceous lower mannville group, Drumheller area, Alberta

The Lower Mannville Group of south-central Alberta represent part of an extensive Early Cretaceous drainage system incised into Paleozoic carbonates and shales. Sediments were deposited as debris flows, in bars of low sinuosity, sandy braided rivers, and in shallow fresh to brackish water lakes. Late Aptian-Early Albian transgression of the Moosebar-Clearwater Sea lead to formation of a large estuary in the Drumheller area. Petrographic examination of the basal alluvial sands indicates the existence of 3 lithologically distinct sandstones: (1) a basal immature chert arenite; (2) an immature quartz arenite; and (3) a mature to supermature quartz arenite, correlatable with the Ellerslie Formation. The change from cherty sandstone to quartzose sandstone reflects uplift to the east, of the Sweetgrass Arch and Swift Current Platform. Diagenetic modification of the sandstones include compaction and cementation by siderite, quartz, calcite, dolomite, barite, pyrite, and clay, all of which have reduced initial primary porosity. Secondary porosity was subsequently created through dissolution of early siderite cement. Oil emplacement in the Basal Quartz sands appears to follow cementation by siderite and silica. [Note: Oversize leaves 220-228 (maps) and 232-242 (cross sections) available in Rare Books and Special Collections, Irving K. Barber Learning Centre.]Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat