A constructional carbonate platform and a generally north-trending shelf margin in Utah and southwestern Idaho were bordered on the west by a starved basin, flysch trough, and orogenic highland during Kinderhookian to middle Meramecian time. The Antler orogeny produced epeirogenic movements, which resulted in sea-level changes that caused the carbonate platform episodically to prograde and retreat. At different times the shelf was bordered either by a narrow foreslope or by a broad ramp. The sequential history is as follows: (1) Late Devonian thrusting raised the continental margin to produce the Antler orogenic highlands, which in earliest Mississippian time had a low eastern coastal plain that bordered a narrow, shallow marine basin lacking a distinct eastern shelf. (2) Widespread marine inundation of the craton on the east was followed by a stillstand, during which a low shelf margin that turned abruptly eastward in Montana was developed and deposition of clinoform micritic limestone beds occurred in moderately deep water across a very broad ramp. (3) Increased downwarping produced an incipient starved basin, separated by a shallow carbonate bank from the flysch trough on the west and by a broad ramp from the northeast-trending shelf margin on the east; coarse encrinites were deposited alternately with micrites on the ramp. (4) Maximum deepening and expansion of the starved basin were accompanied on the west by deepening of the carbonate bank and on the east by westward progradation of a carbonate platform with a narrow, steep foreslope. (5) Lowering o sea level produced a karst plateau on the former carbonate platform and caused cratonic sands to be carried westward into the basin. Meanwhile, filling of the flysch trough allowed an eastward spillover of distal flysch sediments into the basin. The starved-basin sediments, which have organic-carbon values as high as 7% in outcrop, are considered to be source rocks. Coarse sediments of the carbonate platform, particularly where dolomitized, may serve as petroleum reservoirs.

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