- Kayenta Formation
The Kayenta Formation is a geologic layer in the
Glen Canyon Group that is spread across theColorado Plateau province of theUnited States , including northernArizona , northwestColorado ,Nevada , andUtah . This rock formation is particularly prominent in southeastern Utah, where it is seen in the main attractions of a number of national parks and monuments. These includeZion National Park ,Capitol Reef National Park , theSan Rafael Swell , andCanyonlands National Park . The Kayenta Formation frequently appears as a thinner dark broken layer belowNavajo Sandstone and aboveWingate Sandstone (all three formations are in the same group). Together, these three formations can result in immense vertical cliffs of convert|2000|ft|m or more. Kayenta layers are typically red to brown in color, forming broken ledges.outhwest Utah
The red and mauve Kayenta
siltstones andsandstones that form the slopes at base of theNavajo Sandstone cliffs record the record of low to moderate energy streams. Poole (1997) has shown that the streams still flowed toward the east depositing from 150 to 210 m (500 to about 700 feet) ofsediment here. The sedimentary structures showing the channel andflood plain deposits ofstreams are well exposed on switchbacks below the tunnel in Pine Creek Canyon.In the southeastern part of Zion National Park a stratum of cross bedded
sandstone is found roughly halfway between the top and bottom of the Kayenta Formation. It is a "tongue" of sandstone that merges with the Navajo formation east ofKanab , and it shows thatdesert conditions occurred briefly in this area during Kayenta time. This tongue is the ledge that shades the lower portion of the Emerald Pool Trail, and it is properly called Navajo, not Kayenta.Fossil mud-cracks attest to occasional seasonalclimate , and thinlimestones and fossilized trails of aquaticsnails orworm s mark the existence ofponds andlakes . The most interesting fossils, however, are thedinosaur tracks that are relatively common in Kayenta mudstone.These vary in size, but all seem to be the tracks of three-toed
reptiles that walked upright, leaving their tracks in the muds on the flood plains. Unfortunately, so far no bone materials have been found in the County that would enable more specific identification.Apparently during Kayenta time Zion was situated in a climatic belt like that of
Senegal with rainy summers and dry winters at the southern edge of a great desert. The influence of thedesert was about to predominate, however, asNorth America drifted northward into the arid desert belt.outheast Utah
In most sections that include all three
geologic formation s of theGlen Canyon group the Kayenta is easily recognized. Even at a distance it appears as a dark-red, maroon, or lavender band of thin-bedded material between two thick, massive, cross bedded strata of buff, tan, or light-red color. Its position is also generally marked by a topographic break. Its weak beds form a bench or platform developed by stripping the Navajo sandstone back from the face of the Wingate cliffs. The Kayenta is made up of beds of sandstone,shale , and limestone, all , uneven at their tops, and discontinuous within short distances. They suggest deposits made by shiftingstream s of fluctuating volume. The sandstone beds, from less than convert|1|in|mm|sing=on to more than convert|10|ft|m thick, are composed of relatively coarse, well-roundedquartz grains cemented by lime andiron . The thicker beds are indefinitely cross bedded. The shales are essentiallyfine-grained , very thin sandstones that include limeconcretions and balls of consolidatedmud . The limestone appears as solid gray-blue beds, a few inches to a few feet thick, and as lenses of limestone conglomerate. Most of the limestone lenses are less than convert|25|ft|m long, but two were traced for nearly convert|500|ft|m and one for convert|1650|ft|m.Viewed as a whole the Kayenta, is readily distinguished from the geologic formations above and below it. It is unlike them in composition, color, manner of bedding, and sedimentary history. Obviously the conditions of sedimentation changed in passing from the Wingate Sandstone formation to the Kayenta and from the Kayenta to the Navajo sandstone, but the nature and regional significance of the changes have not been determined. In some measured sections the transition from Wingate to Kayenta is gradual; the material in the basal Kayenta, beds seems to have been derived from the Wingate immediately below and redeposited with only the discordance characteristic of fluviatile sediments. But in many sections the contact between the two formations is unconformable; the basal Kayenta consists of conglomerate and lenticular sandstone that fills depressions eroded in the underlying beds. In
Moqui Canyon near Red Cone Spring nearly convert|10|ft|m of Kayenta limestone conglomerate rests in a long meanderingvalley cut in Wingate. Likewise, the contact between the Kayenta and the Navajo in places seems to be gradational, but generally a thin jumbled mass of sandstone and shales, chunks of shale and limestone, mud balls, and concretions of lime and iron, lies at the base of the fine-grained, cross bedded Navajo. Mud cracks, a fewripple marks , and incipient drainage channels were observed in the topmost bed of the Kayenta onRed Rock Plateau ; and in west Glen Canyon, wide sand-filled cracks appear at the horizon. These features indicate that, in places at least, the Wingate and Kayenta were exposed toerosion before their overlying geologic formations were deposited, are it may be that the range in thickness of the Kayenta thus in part (is) accounted for.Grand Canyon
The Kayenta Formation is approximately convert|400|ft|m thick and consists of a fine-grained sandstone interbedded with layers of siltstone. The alternation of these units generally produces a series of ledges and slopes between the cliffs of the Navajo and [http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/moenave.htm Moenave formation] s. Dinosaur tracks are fairly common in the siltstone, and
fresh water mussels andsnail s occur but are rare. The Kayenta Formation is colored pale red and adds to the splendor of theVermilion Cliffs . It accumulated as deposits of rivers.ee also
*
List of fossil sites "(with link directory)"
*Kayenta, Arizona
*List of dinosaur-bearing rock formations References
* Geology of Eastern Iron County, Utah by Herbert E. Gregory
* The San Juan Country - A Geographic and Reconnaissance of Southeastern Utah by Herbert E. Gregory
* Geology Studies Vol. 15 Part 5 1968External links
* [http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/ U.S.G.S Lexicon of Colorado Plateau Stratigraphy]
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