BRYCE - UTAH, USA
MAR 25TH 2020
Bryce Canyon national park is located close to Red Canyon and exhibits some of the same hoodoo-like formations, those hoodoos are also formed from the same Claron Formation as Bryce Canyon. Both are apart of a staircase configuration of cliffs climbing in altitude, Red Canyon resides in the Pink Cliffs which are the highest and will be the first to erode away.
The location is placed within the Paunsaugunt Plateau which is bordered by the Sunset Cliffs, Pink Cliffs and Bryce Canyon. The top and bordering slopes of the region are considered apart of the larger Colorado Plateau. The area rises to an altitude of 6,000-8,000 feet above sea level with an average of 8,000.
All the steps in the staircase were formed by the middle to late cretaceous Western Interior Seaway, those cliffs begin with the lowest set, the Chocolate Cliffs then the Vermillion Cliffs, White Cliffs and Grey Cliffs which all climb in altitude. The Pink cliffs are apart of an ancient lake system and not the Seaway as the region was uplifted and currently remains at the top of the staircase.
The Paunsaugunt Plateau is defined by angular mesas, vertical Cliffs and straight-sided-canyons, the plateau is characterised by flat layers of slightly tilted sedimentary rocks that lie between two faults. Those two faults named the Sevier/Toroweap and the Paunsaugunt faults define the edges of the plateau.
The Western Side of the Sevier/Toroweap Fault Zone is comprised of Basaltic Volcanic Talus, the Eastern side is comprised of the sedimentary Claron Formation. The volcanics have been displaced around 200 meters across the fault. A small outcrop of the Mount Dutton Volcanic Sediment is visible next to Mafic Volcanic Sediments to the West and Clastic Talus to the East next to the Fault Zone along the Hanging Wall.
A Volcanic Field is located further North along the Hanging Wall of the Fault Zone, it was previously unknown until studies in 1989. The volcanic vent system consists of several spatter cones and cinder cones, they were eroded so far back they went unrecognized.
The name of the Wasatch Formation was abandoned in the 1960s in favour of the Claron Formation. The Claron Formation is a mix of fluvial sediment and lacustrine formed by sediment at the bottom of an ancient lake, which also consisted of sediment from the eroding mountain ranges. Conglomerate, sandstone and limestone are also apart of the rock layers that make up the Formation.
Lake Claron was the southernmost lake which was apart of a chain of lakes that extended into Wyoming 50 million years ago. By the time the lakes were being deposited the Western Interior Seaway had vanished due to uplift by the subducting Farallon Plate 70 million years ago which triggered the Larmanide Orogeny, during that time the Sevier Orogeny was winding down. The uplift built the Rockies and formed a basin which the lakes slowly formed in by meltwater accumulating in a marsh which later expanded.
The formation is roughly 400-700 feet thick and is subdivided into 2 parts, the upper white part and the lower red part. The base layer of the formation was possibly deposited in the Late Cretaceous or Paleocene, while the younger part of the formation was deposited in the Eocene and the Oligocene only 33-23 million years ago.
The Fault Zone visible in Red Canyon goes by two names, the Sevier Fault zone in Utah and the Toroweap Fault Zone in Arizona. The two different names represent the same fault Zone, which is called the Sevier/Toroweap Fault Zone by the USGS. Further to the north, there is another fault regarded as the Sevier Fault, not to be confused with the Sevier Section of the Sevier/Toroweap Fault Zone in Red Canyon. The Sevier/Toroweap fault zone is the only visible major fault in Red Canyon, it does get mislabeled as the Sevier fault on occasion.
Section (A) of the Sevier / Toroweap Fault Zone
The Sevier Fault is poorly understood and lies in the western section of the Sevier Plateau, it is on-trend with and south of the Late Quaternary Annabella faults. The Sevier Plateau is defined by external bounding cliffs and internal alluvium-filled valleys that follow north-trending fault lines and grabens.
The Sevier Fault is split into the southern and northern portions separated by a 50-km-wide unfaulted gap, differences in displacement style and age of the most recent movement. The northern and southern sections are two simple faults rather than a sectioned fault.
The main fault is comprised of mostly a dip-slip series of faults, some are also comprised of strike-slip displacement. It has a slip rate of less than 0.2 mm/yr so its very slow. The last movement of the Sevier Fault was during the Quaternary (<1.6 ma), the movement was worked out by the association of the Quaternary Annabella faults towards the north. The Sevier Fault is not visible on the map below as it lies further to the north.
Sevier/Toroweap Fault Zone
The Fault goes by two names, the Sevier Fault in Utah and the Toroweap Fault in Arizona. The fault zone is divided into 4 sections which have been mapped out by recent rupture history along the strike, and changes in geomorphic expression. The Northern section is entirely in Utah while the Southern section is located in Arizona.
The fault zone extends towards the North-Northeast. The fault zone has substantial Cenozoic Movement which has formed a west-facing escapement on the eastern side of the Toroweap and Prospect Valleys in Arizona and beside Long Valley in Utah.
A 50-kilometre long section of the fault zone centred on the Colorado River ruptured during the middle to late Holocene (1,600 years ago to current). The same section of the fault also shows evidence of late Quaternary displacement events, the fault section shows a linear fault escapement which continues for roughly 10-kilometres south of the most recent rupture.
The movement suggests that the southernmost section of the fault zone has been relatively active during the Quaternary period, the northernmost section in the Kanab Plateau has most likely been less active as there is minimal topographic relief across the fault but that doesn't rule out late Quaternary movement.
SEVIER / TOROWEAP
Thomas H. Morris, Scott M. Ritter, Dallin P. Laycock
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