| Description |
The upper member of the Guilmette Formation in west-central Utah consists of 600 m of peritidal and subtidal carbonate platform deposits. These rocks are divided into four stratigraphic units whose lithologies are described by ten lithofacies. Facies dominat in (but not exclusive to) each unit include Unit 1 (lowest) containing Facies A (Supratidal) light-colored, silty dolomitic mudstone; Facies B (intertidal to shallow lagoonal) dark gray, peloidal, I aminated/stromatolitic mudstone to wackestone; and Facies C (lower intertidal) medium dark, shelly/oolitic wackestone to grainstone. Unit 3 is dominated by Facies G and H (lagoonal) light and dark colored floatstone to rudstone (Amphipora dominant) ; and Facies I (lagoonal) stromatoporoid floatstone to rudstone. Unit 4 (highest) consists of Facies J 9open marine) olive-to-dark gray, nodular wackestone. Lateral facies associations vary depending on whether they are behind stromatoproidal buildups (low energy, slackwater facies), behind gaps in the buildups (higher energy facies), or according to the geometry, extent, and organism concentration of the buildups. Within the bottom three stratigraphic units, facies are vertically stacked in repeating transgressiver/regressive sequences, normally capped by supratidal facies. Some cycles may have been formed during eustatic sea level rises related to Milankovitch driven climatic fluctuations. An eastward salient developed in a north-south (present-day directions) trending coastline due to a relatively rapid deepening in the center of the study area. Concurrently, a topographic high emerged in the north of the area (related to Stansbury Uplift?). General deepening as reflected in Successive stratigraphic units was probably caused by the widespread Middle to Upper Devonian transgression. Diagenesis of Guilmette rocks includes allochem rim cementation, postcompaction interparticle cementation rim cementation, postcompaction interparticle cementation, and three stages of dolomitization that includes: syngenetic supratidal dolomites, a formationwide overprint dolomitization, and a massive, complete dolomitization controlled by fault systems and by stratigraphy. |
