BRYCE CANYON

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GEOLOGY

UTAH U.S.A

 

Located in the Colorado Plateau, this region of the United States Southwest was once a massive inland sea called the Western Interior Seaway. The region was mostly marine until the Larmanide Orogeny uplifted the western United States, this took part in the vanishing ocean 70 million years ago in the Cretaceous.

 

After the uplift, a foreland basin at the front of the ancestral Rocky Mountains formed, this slowly filled with fresh water from the melt at the top of the mountains. The added freshwater formed a chain of lakes that extended up into Wyoming, 50 million years ago (Paleogene Period, Eocene Epoch) Lake Claron formed in the current state of Utah. 

The latest uplift event around 15 million years ago in the Miocene period was also created by the same tectonic events that several million years prior created the now eroding Rocky Mountains. For 10 million years the landscape would rise almost one vertical mile forming the Colorado Plateau, the uplift formed many deep faults which split up the Plateau at the bedrock which formed seven blocks within the Colorado Plateau.

ROCK LAYERS

Below the Claron Formation is the Pine Hollow Formation which represents the last regression of the Western Interior Seaway in the late cretaceous to Paleocene, it is comprised of very fine-grained to fine-grained clastic sediments. The formation is a mix of purplish-grey to grey red mudstones or claystone along with calcareous and bentonitic mudstones.

 

It also contains argillaceous limestone which includes lenticular interbeds comprised of fine red to grey coarse sandstone and even conglomeratic sandstone that is mostly located at the lower unit, the formation varies from pale lavender to bright red in colour. 

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 slowly expanded.  

The formation is roughly 400-700 feet thick and is subdivided into 2 units, the upper white unit and the lower red unit. 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 pink colour comes from iron oxides while the dark blue to almost purple comes from manganese oxides, the lake water was also heavy in calcium carbonate (dissolved limestone) that connects the small particles together that forms the Claron Formation. 

The name of the Wasatch Formation was abandoned in the 1960s in favour of the Claron Formation.

 

EROSION & Hoodoos

Bryce Canyon is very famous for steep slot canyons, those canyons have been formed from water erosion and ice wedging over the winter. This has been happening for thousands of years as the extent of the erosion is very widespread, the Red Cliffs formed from ancient lake Claron will be the first to erode away leaving deposits from the Western Interior Seaway on the surface. 

Hoodoos are formed from differential erosion, some layers within the Claron Formation are harder and more resistant to weathering and erosion than other layers, this forms the famous hoodoos of Bryce Canyon and Red Canyon. 

NATURAL BRIDGES

Along the Navajo Loop Trail, a few natural bridges are visible called The Two Bridges, These formed from differential erosion as weaker layers eroded out leaving behind the more resistant ones. The Two Bridges were most likely formed from seasonal erosion which takes sediment into the lower valleys, and dissolution where chemicals dissolve the cement that holds the formation together.  

 

Gravity has also affected the natural bridges and arches within Bryce Canyon, where rock falls from the top of and expands the gap below. Ice Wedging also expands the cracks which filled with water over the winter. 

 

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REFEreNCES

Bryce Canyon, National Park Service. (2016, April 13). Natural Bridge - Bryce Canyon National Park (U.S. National Park Service). 

United States Geological Survey (USGS). (n.d.). Geology of Bryce Canyon National Park. 

National Park Service. Bryce Canyon: The story in the rocks

William E. Bowers & United States Department of the Interior. (1972). The Canaan Peak, Pine Hollow, and Wasatch Formations in the Table Cliff Region, Garfield County, Utah. United States Geologic Survey (USGS). 

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