Intertonguing of the lowermost part of the coal-bearing Blackhawk Formation and the uppermost part of the marginal marine Star point Sandstone has caused a progressive steplike offset of the Blackhawk coal beds in the central and southern parts of the Wasatch Plateau. The tongues of the Star Point Sandstone are marginal shore deposits representing episodic transgressions of the Upper Cretaceous epeiric seaway. The development of these sandstone tongues affected the geometry, lateral continuity, and thickness of the associated Blackhawk coal beds.

Mapping and exploration of sandstone tongues in the lowermost part of the Blackhawk Formation will help identify the thicker coal beds. Knowledge of their distribution can assist the exploration geologist in mapping the coal-bed geometry. Economic coal beds associated with the marginal marine sandstone tongues trend parallel to the paleoshoreline and may be thicker landward of the sandstone tongues. These coal beds are the primary targets of current drilling programs directed toward exploration and development of Blackhawk coals in the study area.

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