Kaibab Limestone (Geology of The Grand Staircase)
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Exposure:
The Kaibab Limestone forms the caprock of most of the Grand Canyon. Great exposures exist west of Zion National Park.
Age: Early Permian, 250 million years ago.
Depositional Environment: Shallow Marine Shelf Deposit.
Paleogeography: Sediment deposition was influenced by the Uncompahgre Uplift (ancestral Rocky Mountains), but by the end of the Permian, the Uncompahgre mountains had been worn down and was not longer a major sediment source.
Tectonics: Collision of the Gondwana Plate with the Northern Plate resulted in the Uncompahgre highland.
Climate: Warm current winds
Features: The Kaibab Limestone is composed of impure cherty limestone and dolomite that interfinger with the White Rim Sandstone below it (Mathis, 2000). The Kaibab rocks range in color from gray, buff, and brown, to yellow/brown dolomite. Some sandy, carbonate beds are very fossiliferous (Condon, 1997). Invertebrate fossils include brachiopods, pelecypods, gastropods, crinoids, and bryozoans. The Kaibab formation in Capitol Reef National Park is only 0-200’ thick and but thickens to 300-500’ in the Grand Canyon (Morris, 2003). The difference in thickness is attributed to erosion. The environmental setting for the Kaibab Limestone was a shallow marine shelf deposit that represents the time of maximum eastward transgression of the Kaibab Sea (Condon, 1997). The Kaibab Sea began to withdraw by the Middle Permian, which left these sediments exposed to be subject to erosion (Condon, 1997). The Kaibab Limestone is visible at the Goosenecks Overlook in Capitol Reef National Park.
Description:
The Kaibab Limestone is a complex sedimentary package of interbedded and interfingering gypsum, limestone, dolomite, chert, siltstone, and sandstone that is 300–400 ft (91–122 m) thick. Erosion-resistant layers of limestone and dolomite form steep cliffs and the rims of the Grand Canyon and its tributary canyons. They also underlie most of the expansive surface of the Kaibab Plateau surrounding the Grand Canyon. Less erosion-resistant sandstones, siltstones, and cherts form distinct recesses along cliff faces.
As previously noted, the Kaibab Limestone is currently subdivided into two members, the Fossil Mountain Member and the underlying Harrisburg Member, in the Grand Canyon area. Eastward, both members become more sandy, silty, and clayey at the expense of limestone, dolomite, and chert, until both members consist uniformly of interbedded and interfingering sandstone, sandy limestone, and sandy dolomite that that cannot be subdivided into individual members.
The Fossil Mountain Member consists largely of light gray, cherty, thick-bedded limestone. It is named for its type locality at Fossil Mountain, which lies just east of the Bass Trail in Grand Canyon National Park, Arizona. The Fossil Mountain Member forms a continuous and promimemt cliff overlying the slope-forming Woods Ranch Member of the Toroweap Formation. The distribution of chert is argued to reflect the original occurrence and abundance of siliceous sponges and accumulation of their spicules. In the western part of the Grand Canyon region, it consists predominately of fossiliferous limestone. Eastward, it grades eastward into nondescript sandstone, sandy carbonate, and dolomite and thins from approximately 250–300 ft (76–91 m) thick to about 200 ft (61 m) thick at Fossil Mountain along the south rim.
The Harrisburg Member, formerly known as either the alpha or Harrisburg gypsiferous member, consists of interbedded light-red to pale-gray limestone and dolomite, siltstone, sandstone, and gypsum. These strata form a sloping surface with projecting ledges of limestone and dolomite. It is named for exposures at Harrisburg Dome, its type locality in southwestern Utah. The Harrisburg Member is about 160–300 ft (49–91 m) thick. East of a line running roughly north-south from near Page to east and south of Flagstaff, the Harrisburg Member grades into calcareous sandstone and becomes in separatable from overlying Fossil Mountain Member. East of that line, the Kaibab Limestone is known as the Kaibab Formation.
The Big Maria and Little Maria mountains in Riverside County, California expose strongly deformed and overturned metasedimentary strata. These cratonic metasedimentary rocks stratigraphically correlate with Paleozoic and Mesozoic strata exposed in the Grand Canyon region. They have been highly metamorphosed to upper middle to upper greenschist grade. These metasedimentary strata are preserved as roof pendants surrounded by Late Cretaceous dioritic and granitic plutons. The uppermost Paleozoic metasedimentary strata in the Big Maria region have been designated and mapped as the Kaibab Marble. It consists of calcitic and subordinate dolomitic marbles, metachert, quartzite, and minor anhydrite schist. The Kaibab Marble shows a variety of colors including white, gray, buff, yellow, pink, and brown. Commonly, these colors are striped by dark-weathering metachert. Exposures of the Kaibab Marble typically exhibits spectacular isoclinal folds, recumbent folds, and disrupted structures on all scales. Because of tectonic deformation, it ranges in thickness from 2–300 ft (0.61–91.44 m). It Likley consists of metamorphised, undifferentiated limestones and dolomites of both the Toroweap Formation and Kaibab Limestone.
Modern Analog to Utah’s Middle Jurassic
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Paleogeography or Depiction of Utah during Middle Jurassic
What is the Grand Staircase?
The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.
The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.
