Lithology
The Colorado Group consists of shale for the most part, and incorporates conglomerate, sandstone and siltstone, and beds of chalk, chalky limestone, coquinas, phosphorite and concretionary beds including calcite, siderite and pyrite.
The lower part includes the following sandstone members: Phillips Sandstone (below the Second White Speckled Shale), Bowdoin Sandstone and Cardium Sandstone in the non-calcareous shale unit. The upper part includes the Martin Sandy Zone and Medicine Hat Sandstone.
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