|
''For the similarly named structure on the RMS Titanic, see Grand Staircase of the Titanic'' ''For the stairs in the White House see Grand Staircase (White House)'' The Grand Staircase refers to an immense sequence of sedimentary rock layers that stretch south from Bryce Canyon National Park through Zion National Park and into the Grand Canyon. In the 1870s, geologist Clarence Dutton first conceptualized this region as a huge stairway ascending out of the bottom of the Grand Canyon northward with the cliff edge of each layer forming giant steps. Dutton divided this layer cake of Earth history into five steps from the youngest (uppermost) rocks: *Pink Cliffs, *Grey Cliffs, *White Cliffs, *Vermilion Cliffs, and *Chocolate Cliffs. Since then, modern geologists have further divided Dutton's steps into individual rock formations. Formations in the Grand Staircase starting with the youngest (uppermost) rocks:〔http://www.nature.nps.gov/geology/inventory/publications/reports/brca_gre_rpt_view.pdf〕 *Claron Formation *Kaiparowits Formation *Wahweap Formation *Straight Cliffs Formation *Tropic Shale *Dakota Sandstone *Carmel Formation *Temple Cap Formation *Navajo Formation *Kayenta Formation *Moenave Formation *Chinle Formation *Moenkopi Formation *Kaibab Limestone *Toroweap Formation *Coconino Sandstone *Hermit Shale *Supai Group *Surprise Canyon Formation *Redwall Limestone *Temple Butte Limestone *Muav Limestone *Bright Angel Shale *Tapeats Sandstone ==Geology== The major sedimentary rock units exposed in the Grand Canyon range in age from 2000 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world. See geology of the Grand Canyon area for details. The oldest exposed formation in Zion National Park is the youngest exposed formation in the Grand Canyon – the ~240‑million-year-old Kaibab Limestone. The Bryce Canyon area to the northeast continues where the Zion area leaves off by presenting Cenozoic-aged rocks that are 100 million years younger. In fact the youngest formation seen in the Zion area is the oldest exposed formation in Bryce Canyon – the Dakota Sandstone. There are, however, shared rock units between all three, creating a super-sequence of formations that geologists call the Grand Staircase. Bryce Canyon's formations are the youngest known units in the Grand Staircase. Younger rock units, if they ever existed, have been removed by erosion. See geology of the Zion Canyon area and geology of the Bryce Canyon area for details. These layers have undergone 5000 to 10,000 feet (1500 to 3000 m) of uplift starting about 66 million years ago with the Laramide orogeny which has increased the ability of the Colorado River to cut its channel to make individual plateaus out of the Colorado Plateaus region. The major canyons of the region did not start to form until about five to six million years ago when the Gulf of California opened up and thus lowered the river's base level (its lowest point). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Grand Staircase」の詳細全文を読む スポンサード リンク
|