Week six :Sedimentary

RockArches National Park

The story

• The story of Arches begins roughly 65 million years ago. At that time, the area was a dry seabed spreading from horizon to horizon. If you stood in Devils Garden then, the striking red rock features we see today would have been buried thousands of feet below you, raw material as yet uncarved. Then the landscape slowly began to change.

Slow deposition of rock

• Over 300 million years ago, the area where Arches National Park is was covered by a sea, which left a salt bed that is thousands of feet thick in places. The salt bed was covered with erosion from surrounding areas, forming the Navajo Sandstone (Early Jurassic) and then that was covered by the Entrada Sandstone.

This diagram shows layers of rock in

Arches National Park

Salt domes formation

• Younger sediment had been both deposited and eroded since then. The weight of the different layers caused the salt layer to liquefy, which deformed layers of rock into salt domes.

Salt dome-Arches National Park

Example of faulting

• That, along with faulting, which in some places almost turned the rock on it's edge, set the perfect stage for arches to develop. Erosion worked away the younger rock and through water weathering the rock (Entrada and Navajo Sandstone) and then wind working its erosion magic, some large chunks of rock fell off and small particles have been sandblasted off as well, until we have the arches in the park, including Delicate Arch.

Sedimentary Structures: The bedding is regular and horizontal and ripple marks are common.

Location

Arches National Park is located in southeast Utah, 5 miles north of Moab, Utah and 236 miles south of Salt Lake City, UT.

The beauty of the park.

The night sky

Sources

• Geology.com

• Public domain pictures

• Arches National park.gov