The Kaiparowits Formation
(LATE CRETACEOUS)
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In the Cretaceous of southern Utah the Kaiparowits formation constitutes a distinctive belt of rock just beneath the rim of the Markagunt, Paunsaugunt, and Kaiparowits Plateaus. In eastern Southwest Utah it is exposed in two roughly defined areas in which contrasted topographic forms and colors reflect differences in composition, texture, and mode of deposition.
1. Between Navajo Lake and the southern branches of Ashdown Creek, and particularly in the drainage basins of Deep Creek and Coal Creek, the prevailing topographic features of the Kaiparowits formation are gently inclined slopes, mounds, and moderately broad, shallow valleys. The general tone of the rocks is dark-gray and green-gray and thus readily distinguishable from the light-gray and buff Cretaceous rocks below and the pink Tertiary rocks above. Within this area casual views leave the impression that the Kaiparowits is a sequence of weakly cemented dark-colored shales interrupted by beds of white sandstone, but measured sections show that the prevailing rock is thinly stratified sandstone, highly irregular in texture and composition. Some of the sandstone beds are evenly laminated and consist of well-rounded and assorted grains that average about 0.40 millimeters in diameters, but the most common beds are lenticular, cross-bedded, and made up of small spherical, subangular, and sharply angular grains of quartz (70 to 90 per cent of the rock), feldspar, mica, magnetite, chert, and chips of clay shale and hard sandstone. Interbedded with the dominant sandstone are lenses of vari-colored calcareous, ferruginous, and sandy shale, limestone, conglomerates, and lignites. Sheets and concretionary balls of ironstone are common. The cement-iron, lime, and gypsum-is weak and, where exposed at the surface, the rock, particularly the thin-bedded sandstone, disintegrates so rapidly that only in road cuts and at the bottom of newly made gulches can the formation be examined in detail. South of Navajo Lake, within an area of about 9 square miles, the Kaiparowits formation has been almost entirely stripped away from the more resistant Straight Cliffs sandstone, leaving flat lands known as "The Plains." Thus in essential physical features the bulk of the Kaiparowits along the southwestern edge of the Markagunt Plateau closely resembles that along the southern edge of the Markagunt and Paunsaugunt Plateaus and differs little from the type section in the Kaiparowits Plateau. A noticeable departure from its normal expression is the presence of coarse-grained, generally massive, roughly stratified, white sandstone, containing fossil wood and turtle bones-beds which in places constitute the upper fourth, or nearly half, of the formation.
2. In contrast to its continuity, its miscellaneous make-up and its extreme friability, in the valley of Coal Creek and eastward the Kaiparowits formation in the drainage basin of Parowan Creek is represented by detached masses brought into view by faulting, and its characteristic erosion forms are cliffs, steep canyon walls, and sharply outlined mesas, ridges, and picturesque pinnacles. In general view the formation in this area appears as thick irregular beds of sandstone and huge lenses of conglomerate, white or yellow-gray in color. Measured sections reveal evenly laminated friable sandstone like that elsewhere characteristic of the Kaiparowits formation and also small amounts of shale and lignite. The general arrangement of the component materials as displayed in the canyon branches of Parowan Creek is shown in the following section.
| Eocene (Claron/Wasatch formation) | Feet |
|
|
|
|
|
|
| Cretaceous (Kaiparowits formation) | |
|
10-40 |
| Unconformity | |
|
170-210 |
|
30-80 |
| Unconformity | |
|
8+ |
Generally along branches of Parowan Canyon and upper Summit Canyon the conglomerate forms lenses and wedges 50 to 1,000 feet long and 10 to 200 feet thick, with very irregular outlines. They lie within bedded standstone and in vertical sections occupy two or more positions. In some lenses the conglomerate at the center grades laterally into gravel, then to coarse sand and of the surrounding rock; in others, masses of cobbles as much as 6 inches in diameter are replaced within a few feet along strike by sandstone of medium fineness. Wherever observed, the upper contact is gradational; the lower abruptly unconformable. Though the assignment of these peculiar strata to the Kaiparowits seems reasonably satisfactory, proof of their strati-graphic position was not obtained.
Analysis of the conglomerate at outcrops within an area of several square miles shows substantial likeness. The chief component pebbles are quartz-clear, cloudy, crystalline, amorphous; quartzite-white, gray, brown, massive, and minutely banded; sandstone and arkose-massive, laminated, fine and coarse-grained; limestone-gray, black, crystalline, amorphous. Some pebbles of limestone and of fine dense sandstone contain fragmentary Paleozoic corals. In shape the pebbles that compose the conglomerate are dominantly oblong or cubical, with rounded edges and corners; very few are spherical or highly polished. About 40 per cent of the constituent pebbles exceed 1 inch in diameter; 10 percent, 3 inches; and 1 percent, 5 inches. Some little abraded flat slabs of sandstone measure 8 to 15 inches in long diameter. The matrix of the pebbles is fine conglomerate and coarse, arkosic sandstone; the ultimate cement, impure lime and ferruginous clay. Generally the cementing material is resistant and the conglomerate weathers into domes, round-topped towers, and forms locally called "castles," but in places the cement is so weak that surface weathering and ground water seepage have produced "honeycombs" and small caves within which hawks make their nests.
SOURCE
-from Geology of Eastern Iron County, Utah by Herbert E. Gregory
