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The Great Unconformity of Powell in the Grand Canyon is a regional unconformity that separates the Tonto Group from the underlying, faulted and tilted sedimentary rocks of the Grand Canyon Supergroup and vertically foliated metamorphic and igneous rocks of the Vishnu Basement Rocks. The unconformity between the Tonto Group and the Vishnu ...
The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ...
Frenchman Mountain is a mountain located east of Las Vegas, Nevada. Made up of rocks similar to those found on the bottom of the Grand Canyon, Frenchman Mountain formed when faulting elevated and tilted the rocks followed by erosion, giving it its sharp triangular profile. The mountain provides an example of the Great Unconformity with the ...
The neighboring Sierra Ancha range has another occurrence of the Great Unconformity, with a sandstone unit that is an analogue of the Tapeats Sandstone. The Arizona 87 highway section south of Pine is where the north Mazatzal Mountains merge into the western region of the Mogollon Rim, as the Rim continues northwest into the Oak Creek Canyon ...
In the Grand Canyon, the Bright Angel Shale is typically a heterogenous, sometimes fossiliferous, mixture of interbedded shale, mudstone, siltstone, fine-grained sandstone, and isolated beds of limestone. The dominant lithology within the Bright Angel Shale is greenish shale that is composed largely of illite and varying amounts of chlorite and ...
Los Angeles Basin. The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east–west trending chains of mountains collectively known as the Transverse Ranges. The present basin is a coastal lowland area, whose floor is marked ...
Sep. 5—A new study led by University of Colorado Boulder researchers sheds light on one of the world's great geological mysteries: a missing chapter of the earth's rock record known as the Great ...
Except where it overlies the Sixtymile Formation, the base of the Tapeats Sandstone is an unconformity underlying Precambrian rocks and is known as the Great Unconformity. In the eastern Grand Canyon, the Tapeats Sandstone uncomfortably overlies a hilly and weathered paleosurface underlain by the Grand Canyon Group and, in one structural basin ...