--> Distribution of Coals in Upper Cretaceous Highstand Deposits of the Kaiparowits Plateau, Utah, by R. D. Hettinger; #90986 (1994).

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Abstract: Distribution of Coals in Upper Cretaceous Highstand Deposits of the Kaiparowits Plateau, Utah

R.D. Hettinger

Extensive low-ash coal deposits of the Kaiparowits Plateau, Utah, are contained within highstand systems tracts of two unconformity-bounded sequences. The sequences are within a 250 m-thick interval of Coniacian and Santonian strata of the Straight Cliffs Formation. Coals are in a 40 km-wide belt of coastal-plain strata that parallel a thick stack of shoreface parasequences.

Correlation of data from 80 coal test holes reveals the distribution of coal-bearing strata. The thickest coals are 5-20 km inland from the coeval shoreface stack. Individual coal beds are up to 9 m thick, and cumulative coal thicknesses are as much as 65 m; coal comprises up to 25% of each highstand deposit. Although some beds can be traced as far as 15 km, most split and thin in less than 5 km. Coals thin near the seaward edge of the coastal plain and form distinct zones separated by shoreface strata. Along the landward margin of the coastal plain, coal is interbedded with alluvial strata and total coal accumulation is less than 10 m. Facies analysis of core retrieved from areas of thicker coals indicates that about 60% of the clastic strata was deposited under some tidal influence. This suggests that the coastal plain was dissected by tidal creeks and estuaries, and the thick coals formed in mires that persisted for long periods of time with limited clastic input from either fluvial or marine realms. The close association of low-ash coal (less than 8%) with higher energy tidal and shoreface environments helps confirm previous conclusions that the mires were of a raised form.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994