Death Valley geology field trip
Amargosa Chaos |
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L. F. Noble, a pioneering Death Valley geologist, studied the jumbled rocks of the Virgin Spring area in the Black Mountains in the 1930's. He found this region so complexly faulted and folded, that he named this part of Death Valley the ‘Amargosa chaos'. Later researchers found this area equally perplexing. It was not until geologists learned that this region had suffered from extraordinary tension that pulled great blocks of crust apart, that the background was laid to understand the intricate structure of the Amargosa Chaos. Modern geologists have documented four major events (deformational events) that faulted and folded the Amargosa Chaos. The first event metamorphosed Death Valley's Precambrian basement rocks and was quite ancient, possibly occurring as long as 1,700 million years ago. The second event began while layered younger Precambrian sediments were being deposited on top of the beveled surface of older metamorphic basement rocks. This deformational event shifted the crust vertically, creating thinning and thickening of some sedimentary layers as they were being deposited. The two events responsible for the chaotic appearance of the Amargosa Chaos didn't occur until over half a billion years later, during Mesozoic or Early Tertiary time. This third event folded the layered Precambrian and Cambrian sedimentary rocks. The fourth and final event occurred quite recently, geologically speaking. This phase of deformation coincided with severe crustal stretching that created the deep valleys and high mountains of this part of the Basin and Range Province. In just a few million years, during Late Miocene to Pliocene time, older rocks were intensely faulted and sheared. In some areas all that remains of some thick rock layers are lens-shaped pods of rock bounded on all sides by faults. Other layers have been sliced out of their original sequence altogether! |
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