The Mannville Group (Lower Cretaceous) of Central Alberta

ABSTRACT Relief on the sub-Mannville unconformity, carved by northwesterly-flowing subsequent rivers prior to and during early Mannville time, is of the order of 300 to 400 feet. At the beginning of late Mannville time an Arctic sea transgressed southward. Towards the end of Mannville time the sea withdrew to the north as the basin filled with coarse clastics. Lower Mannville sandstones are quartz-rich lithic sandstones containing less than 25 per cent metamorphic rock fragments, less than 8 per cent orthoclase feldspar, and well rounded tourmaline and zircon as the main heavy minerals. A Precambrian cratonic source is indicated. Upper Mannville sandstones range from lithic sandstone at the base to arkose at the top. Sedimentary and volcanic rock fragments form most of the framework with feldspar becoming abundant towards the top. Carbonate-rich sedimentary rocks, volcanic rocks and perhaps acid igneous masses of the Cordillera were the probable sources.