Abstract

Detailed rock stratigraphy and petrography of selected sandstone samples in the Markagunt Plateau indicates that the Kaiparowits Formation is not present and the Straight Cliffs and Wahweap Formations are present there. A stratigraphic section about 2,800 feet (~850 meters) thick was measured near Crow Creek (east of Cedar City) in order to correlate it to lithostratigraphic units in the Kaiparowits Plateau. The section overlies the Tibbet Canyon Member of the Straight Cliffs Formation (Upper Cretaceous) and underlies the Claron Formation. The section consists of thin, distinctive marginal marine mudstones overlain by progradational coastal plain rocks.

The lowest strata are 150 ft (46 m) of distinctive, brackish-water, Ostrea-bearing mudstone and thin interbeds of coal, sandstone, and coquina limestone. These strata and others in Interval A (totaling 313 ft, 95 m) clearly correlate to the Smoky Hollow Member of the Straight Cliffs Formation in the Kaiparowits Plateau.

Above the Smoky Hollow Member is more than 1,000 ft (>~310 m) of fluvial, deltaic(?) and lacustrine(?) mudstone and sandstone (Intervals B through F). These strata are mostly mudstone that contains thin, coaly beds, carbonaceous plant material, lensic, fine-grained sandstone, and probably correlate to the John Henry Member of the Straight Cliffs Formation. Interval F, sandstone capped by a conglomerate bed, is tentatively correlated to the Drip Tank Member of the Straight Cliffs Formation. Above the Drip Tank Member(?) to the base of the Claron Formation, and of disputed stratigraphic assignment, is an upward-coarsening succession of fluvial mudstone and sandstone, Intervals G through V inclusive, about 1,480 ft (~450 m) thick, of which the upper 850 ft, (260 m) is mostly fine-grained sandstone, locally silty. The sandstone exhibits variations of yellow-red hue, minor yellow hue, and locally weathers light-brown. We correlate this section to the Wahweap Formation. This uppermost part of the section includes some beds of friable, light-gray and yellowish-gray sandstone that slightly resemble the Kaiparowits Formation. However they are relatively few, are not light-bluish-gray like the typical Kaiparowits Formation, and are less lithic. They generally are sublitharenitic, compositionally closer to rock of the Wahweap Formation than to rock of the Kaiparowits Formation. Counts of quartz-feldspar-lithic (QFL) framework grains in sandstone beneath the Claron from several localities in the Markagunt Plateau show that none match the distinctive litharenite (68–69 percent lithic grains) from the type Kaiparowits Formation on the Kaiparowits Plateau.

High in the measured section on Highway 14, Interval O exposes very pale orange (essentially white), friable, quartzarenite ~140 ft (~43 m) thick. Other workers correlate this sandstone to the Grand Castle Formation (Paleocene). However, palynologic data indicate a Late Cretaceous age for this part of the section and higher. Further study is needed to resolve the conflicting interpretations.

Rocks of a coastal plain facies interfinger in short distances horizontally. Vertically, thick successions of mudstone and sandstone beds repeat without marker beds, making correlation to distant type sections uncertain. A comparison of 48 stratigraphic columns of previous workers shows that boundaries of units in nearby localities were placed at different levels in many cases.