Abstract

The upper member of the Guilmette Formation in west-central Utah consists of more than 600 m of peritidal and subtidal carbonate-platform deposits. Constituent facies range from supratidal dolomitic laminites to subtidal lagoonal stromatoporoidal floatstones, and open marine wackestones. These facies occur in a repetitive series of transgressive-regressive and shallowing upward cycles that persist throughout much of the member and range in thickness from 3 to 44 m, averaging 11 m.

The upper member of the Guilmette Formation is divided into four informal units whose lithofacies indicate deepening environments upsection. Unit 1 is dominated by supratidal facies, Unit 2 by intertidal facies, Unit 3 by subtidal, lagoonal facies and Unit 4 by subtidal, open-marine facies. Cycles are present only in the lower three units.

Correlation of units, cycles and distinctive beds between measured sections in the study area indicates major differences between the southernmost section and those to the north. The southern section has more regularly spaced cycles, consistently shallower environments and lower sediment accumulation/subsidence rates. These features indicate that the southern section was on the edge of the developing Pilot basin and possibly closer to the paleostrandline.

Thick cycles (> 19 m) probably indicate deepening events and may be related to similar events documented elsewhere. Some cycles may have been formed during eustatic sea level rises related to Milankovitch cycles.