Blackhawk Formation

rdf:langString Blackhawk Formation

rdf:langString Blackhawk Formation

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rdf:langString Coal, sandstones and carbonaceous mudstones of the Blackhawk Formation exposed along U.S. Highway 6, Price Canyon, Carbon County Utah.

rdf:langString Campanian

rdf:langString The Blackhawk Formation is a geological formation in east-central Utah, USA. It was named for the former town of Blackhawk on the east side of the Wastach Plateau, Carbon County. The formation is composed of mostly light-brown, light-gray and brownish-gray, thin- to medium-bedded, fine- to medium-grained quartzose sandstone that is interbedded with shaly siltstone, shale, carbonaceous shale, and coal. There are many thin to thick bituminous coal seams, including several economically important beds, such as the Sunnyside Coal. The formation thickness ranges from about 120 m (400 ft) to about 270 m (900 ft). It conformably overlies the Star Point Sandstone and unconformably underlies the Castlegate Sandstone. The sediments that formed the Blackhawk Formation originated from erosion of the Sevier Uplift in western Utah. This sediment was transported eastwards by rivers and deposited on the western coast of the Cretaceous Seaway. At this time, the Seaway was also withdrawing (regression) eastwards, but this was irregular, with occasional episodes of the sea advancing (transgression) to cover coastal lands. This transgression was partially as a result of fluctuating (eustatic) global sea level changes and partly as a result of the shift position of the deltas. These events created wedges of terrestrial sedimentary rock between wedges of marine sedimentary rock (Mancos Shale). These wedges of the Blackhawk Formation have been given names and many of them contain economically important bituminous coal zones, such as the Kenilworth Coal that is up to 11 m (37 feet) thick. The coast probably resembled the Gulf Coast today, being composed of a broad coastal plain, with meandering rivers that ended in wave-dominated deltas. These deltas were flanked by sandy beaches. Swamps were probably developed on the delta plains and on the floodplain (bottomlands) adjacent to the meandering rivers, rather than in brackish-water of lagoons because of the low sulfur content of the coals.