University:
Arizona State University
Course:
ABS 370 | Ecology
Academic year:

2024
Views:

469

Pages:

2
Author:

Thuyoul US

OROGORI LARAMIDE Beginning about 80 million years ago, much of western North America was uplifted. The entire Rocky Mountain Region (Figure 165) from northern Mexico to Canada rises nearly a mile above sea level. This episode of mountain building called Laramide orogeni results from the subduction of oceanic crust beneath the West Coast of North America, causing an increase in crustal buoyancy. The Canadian Rockies consist of successive wedges of sedimentary rock detached from the underlying underground rock and pushed eastward on top of each other. A region between the Sierra Nevada and the southern Rockies took bursts of uplift over the past 20 million years, increasing the area by more than 3,000 feet. Since the end of the Cambrian, the future Rocky Mountain region has been near sea level. Further west within about 400 miles of the coast, a mountain belt comparable to the current Andes formed over a subduction zone 80 million years before Laramide. It appears to be responsible for the Cretaceous Sevier orogeny that created the Overthrust Belt in Utah and Nevada A region from eastern Utah to the Texas panhandle that changed shape during the orogeny of the late Paleozoic Rockies completely eroded by the time Laramide.The Rocky Mountain foreland region receded by as much as 2 miles between 85 million and 65 million years ago and then rose well above sea level, It gained its current height about 30 million years ago. To the west of the Rockies, many parallel faults slice through the Basin and Range Provinces between California's Sierra Nevada and Utah's Wasatch Mountains.This resulted in a series of 20 north-south trend blocks of mountain blocks. The Basin and Range includes southern Oregon, Nevada, western Utah, southeastern California, and southern Arizona and New Mexico.The crust bounded by the fault is literally broken up into hundreds of steep sloping blocks and lifted nearly a mile above the basin, forming nearly parallel mountains up to 50 miles in length. Death Valley (Figure 166), at 280 feet below sea level, is the lowest place on the North American continent. The region was originally elevated several thousand feet higher during the Cretaceous.The area collapsed when the continental crust thinned from extensive blocks of faults, with one block of crust lying under the other. The Great Basin area is the remnant of a vast mountain belt and plateau that later collapsed after the crust was pulled apart following Laramide. The Wasatch Range rising in north-central Utah (Fig. 167) is an excellent example of a series of north-trend faults, one below the other. The fault block extends for 80 miles, with a possible clean slip along the west side of 18,000 feet. The western Wyoming Teton was broken along the east flank and broken west. The rest of the Rocky Mountains evolved by an upthrusting process similar to plate collisions and subduction that uplifted the Central and South American Andes.The Andes continue to rise due to increased crustal buoyancy caused by the subduction of the Nazca plate beneath the South American plate.