Layers of Time in The Grand Canyon
by Jon Burch Photography
Title
Layers of Time in The Grand Canyon
Artist
Jon Burch Photography
Medium
Photograph - Digital Capture
Description
The Grand Canyon in the Colorado Plateau exposes uplifted Proterozoic and Paleozoic strata is one of the 19 distinct physiographic sections of the Colorado Plateau province. While the Canyon is known for its visually overwhelming size and its intricate and colorful landscape, the deepest canyon in the world is the Kali Gandaki Gorge in Nepal. Geologically the Grand Canyon is significant because of the thick sequence of ancient rocks that is beautifully preserved and exposed in its walls. These rock layers record much of the early geologic history of the North American continent.
Uplift associated with mountain formation later moved these sediments thousands of feet upward and created the Colorado Plateau. The higher elevation has also resulted in greater precipitation in the Colorado River drainage area, but not enough to change the Grand Canyon area from being semi-arid. The uplift of the Colorado Plateau is uneven, and the Kaibab Plateau that Grand Canyon bisects is over a thousand feet higher at the North Rim than at the South Rim. Almost all of the runoff from the North Rim from the greater amounts of rain and snow flows toward the Grand Canyon, while much of the runoff on the plateau behind the South Rim flows away from the canyon following the general tilt of the land. The result is deeper and longer tributary washes and canyons on the north side and shorter and steeper side canyons on the south side.
The major geologic exposures in the Grand Canyon range in age from the 2 billion year old Vishnu Schist at the bottom of the Inner Gorge to the 230 million year old Kaibab Limestone on the Rim. There is a gap of about a billion years between the 500 million year old stratum and the level below it, which dates to about 1.5 billion years ago. This large unconformity indicates a period of erosion between two periods of deposition.
Many of the formations were deposited in warm shallow seas, near-shore environments such as beaches, and swamps as the seashore repeatedly advanced and retreated over the edge of a proto-North America. Major exceptions include the Permian Coconino Sandstone, which contains abundant geological evidence of aeolian sand dune deposition. Several parts of the Supai Group also were deposited in non-marine environments.
The great depth of the Grand Canyon and especially the height of its strata, most of which formed below sea level, can be attributed to 5 to 10 thousand feet of uplift of the Colorado Plateau, starting about 65 million years ago called the Laramide Orogeny. This uplift has steepened the stream gradient of the Colorado River and its tributaries, which in turn has increased their speed and thus their ability to cut through rock.
Image copyright 2014 Jon Burch Photography
Uploaded
April 10th, 2014
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