ZION NATIONAL PARK

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ROCK LAYERS

GEOLOGY

UTAH U.S.A

 

The Zion Canyons were once a flat basin close to sea level during the late Paleozoic Era, roughly 544 - 240 million years ago. Streams and rivers carried fluvial deposits of sand and silt into the basin from the surrounding mountains, this placed the sediment down in layers. The weight of the layered rock material caused the basin to sink, this meant that the basin always remained close to sea level.  

 

The landscape changed over the course of millions of years, from shallow seas, to a coastal plain and to the once-massive sand-covered desert that expanded over most of the Colorado plateau during the early Jurassic.

 

Mineral Laced water slowly filtered through the compacted basin sediment, this acted as cementing agents along with the pressure from overlying rock material. Over several million years the deposits were turned into stone.  

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The Zion Narrows 

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The Zion Narrows 

LITHIFICATION

During the Lithification process, different layers of sediment changed into different rock types. This was partly because of the Cementing agents that were filtered through the sediment over a prolonged period of time.

Cementing Agents

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1. Iron-Oxides - Formed from precipitation from Iron-Enriched groundwater, Iron-Oxide pigments are made up of ferric oxides and a mix of impurities. The impurities are usually Clay, Manganese, and Organics, sometimes even a mix of all 3, this is what changes the colour of the rocks it's affected. 

2. Calcium Carbonate (CaCo3) -  Comprises more than 4% of the earth's crust, it has many natural forms, like limestone and the metamorphic variant of Marble. In chemical terms, all its forms are identical but all its varieties are slightly different, outside factors change how its viewed in the natural world. Calcium Carbonate is produced by the decay and sedimentation of marine life such as shells and coral over the course of millions of years.  

3. Silica (SiO4(4-) - Silica is never found in its natural state but in a combination with Oxygen. Majority of minerals in the earth's crust contain silica. The structural components of silica are Si04(4-), this shows as a tetrahedron and can be represented in many different ways. The most known mineral in the silica group is Quartz, but others include Feldspar and Obsidian.   

 

Echo Canyon ... Iron Oxide colouring (Navajo Sandstone)

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Observation Point Trail ... Iron Oxide colouring (Navajo Sandstone)

FORMATION OF Exfoliation Joints

Canyon carving in Zion National Park is strongly controlled by the joints of weakness coursed by the relaxation of compressional forces. So most canyons follow straight joints that are roughly parallel and uniform in distance, this is because the joints are perpendicular to the original compression of the rock. 

During the past process of Lithification, the Navajo Sandstone became very hard and brittle. When the late Cenozoic Eon rolled around the landscape began to rise in elevation, this was because of the tectonic events affecting the West coast. The North American plate was clashing with parts of the Pacific Ocean plate, the west coast became active once again with a new mountain building episode. This force in elevation put stress on the rocks below creating points of weakness and faulting in the sedimentary layers below. 

 

Weathering and erosion have revealed these Joints and exploited them to form the slot canyons visible in the park today.    

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Arial View of Joint zones ... Canyon Junction to Angels Landing - (NASA Earth Observatory)

FRACTURES & SLOT CANYONS

The correlation between exfoliation joint zones and slot canyons is visible all through the park, from the Zion Narrows to Echo Canyon. The track of the Virgin River has exploited many of the weak joint zones and faults in the rock strata, Erosion has moved the sediment downstream into another basin just like the one Zion National Park started from. This continuation of erosion has formed the spectacular slot canyons visible in Zion today.  

 

Heading out the park along the Zion-Mount Carmel Highway shows an amazing side view of the fractures and joints including the visible Springdale Member of the Kayenta formation along with spectacular towers and temples made of Navajo Sandstone.

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Zion-Mount Carmel Highway ... Zion National Park - Joints

ISOLATED JOINTS

Isolated joints in the Navajo Sandstone are so closely spaced they look like joint zones. The spacing is much closer than typical bedded sedimentary rocks, Isolated Joints don't tend to erode as slot canyons like Exfoliation Joints. 

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Exfoliation Joints (Left) - Observation Point Trail 

Isolated Joints (Left) - Observation Point Trail

Checkerboard Mesa

Checkerboard Mesa has one of the best examples of crossbedding in the world. The crossbedded Navajo Sandstone allows for the past Jurassic wind direction to be preserved as well, the most predominant wind direction was left to right. To work out the wind direction a compass reading of the dipping larminae is needed.  

The crossbedded pattern has a lot to do with the Navajo sandstone and its past environment. As stated in the introduction the Colorado plateau was coved by a massive desert. During the time the Navajo Sandstone was being deposited North America was very close to the equator and stuck in the dry trade winds belt. Sand dunes were around 150 feet high, the sand deposit eventually reached a maximum thickness of around 2,200 feet deep and over 100,000 miles squared in distance.  

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WEEPING ROCK

A series of interconnected diagonal Fractures in the overlying rock above the alcove allows water to flow through gaps and down to the base of the canyon. The reason water so easily flows through the Navajo Sandstone is that it's relatively porous and permeable. The lowest unit of the Navajo Sandstone is much thinner and less permeable than the upper units. The Kayenta Formation delays the downward movement of groundwater.

The layer of Kayenta mudstone forces the water to be rerouted to a lateral flow toward the canyon wall, the water then runs into another set of fractured rock which forces the water down towards the alcove. 

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REFERENCES

Potter, Michael J., 2003, Iron Oxide Pigments: U.S. Geological Survey Minerals Yearbook, P.41.1-41.3.

"Zion Geology"

National Park Service 

Zion National Park Utah 

last updated: June 13, 2015

Minerals Education Coalition (MEC)

Minerals Database

Silica

"geologic Trail Guides to Zion National Park, Utah"

Robert F. Biek, Grant C. Wills, Michael D. Hylland and Hellmut H. Doelling

Utah Geological Survey 

Salt Lake City, Utah

"NPS Geodiversity atlas - Zion National Park, Utah"

National Park Service

Last update - December 14th, 2018 

(Joint Controlled Canyons)

Science Direct - Ferric Oxide

(Dyeing With Mineral Colours)

(Construction Steel) - Building Materials in Civil Engineering

"What is Calcium Carbonate?"

Industrial Minerals Association - North America  (IMA-NA)

ima-na.org 

 

"Kinematic implications of joint zones and isolated joints in the Navajo Sandstone at Zion National Park, Utah: Evidence for Cordilleran relaxation"

Christie M. Rogers, Douglas A. Myers, Terry Engelder

24 January 2004

AGU100 - Tectonics

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001TC001329