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Coarse-grained clastic rocks at the top of the Kootenay formation and the base of the Blairmore group are transitional between the Jurassic and Cretaceous systems in the westerly regions of the area.
The subsurface equivalents in the easterly regions of the area occur at the base of the Blairmore or Mannville groups and are known locally as the Basal quartz, Ellerslie, Sunburst, Cutbank and Dina sands, respectively; all are generally considered Cretaceous in age and overlay either the Paleozoic surface or members of the Jurassic Ellis group. Where the Cretaceous overlies the Paleozoic, a residual or detrital bed commonly occurs and is known as the Deville member of the Mannville group.
Petrographic examination of the transitional or basal Cretaceous clastic rocks indicates that there are three main authigenic mineral facies developed largely irrespective of rock type in "residual beds," shales, siltstones, sandstones, and (or) conglomerates.
The three diagnostic authigenic minerals are hematite, siderite, and pyrite; other significant authigenic minerals present are magnetite, iron-rich dolomite, calcite, kaolinite, silica chlorite, and glauconite.
The presence of these authigenic minerals, together with various physical features of the sedimentary rocks, assists in elucidating the intricate paleographic pattern of estuaries, rivers, lakes, and land surfaces.
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