A new study led by the University of Colorado Boulder reveals the complex story behind one of the Grand Canyon's most famous geological features - a mysterious and lost time interval in the canyon's rock record, spanning hundreds of millions of years. This research is closer to solving a problem called the 'great unconformity' that has plagued geologists since it was first described nearly 150 years ago. Think of the red cliffs and cliffs of the Grand Canyon as a textbook of the history of the earth, explained Barra Peak, the lead author of the new study and a graduate student of geological sciences at CU Boulder. If you shrink the canyon's rocky walls, you can go back to Earth's last nearly 2 billion years. But that textbook is also missing pages: in some areas, rocks over a billion years old have disappeared from the Grand Canyon without a trace. Geologists want to know why. “The Great Unconformity is the first well-documented geological feature in North America”, Pique said. “But until recently, we didn't have too many restrictions on when or how it happened”. Now, she and her colleagues believe that they might narrow the scope of the answer in an article published this month in the journal Geology. The team reported that during the disintegration of the ancient supercontinent named Rodinia, a series of small but violent faults may have shaken the area. The resulting chaos may tear the land around the canyon, causing rocks and sediments to overflow into the ocean. The team's findings can help scientists fill in the missing parts of what happened during this critical period in the Grand Canyon, which is today one of the most important natural wonders in North America. Rebecca Flowers, a co-author of the new study and professor of geological sciences, said: “Our laboratory has new analytical methods that allow us to decipher in the missing window of time through the large unconformity. This story”. “We are doing this work in the Grand Canyon and other major unconformity locations in North America”.
Graceful Lines
This is a mystery that can be traced back a long time ago. John Wesley Powell, today's Lake Powell of the same name, first saw the great unconformity during his famous 1869 boat expedition along the rapids of the Colorado River. Pique completed a similar Grand Canyon rafting study in the spring of 2021, and he said the feature is clear enough to be seen from the river. “There are beautiful lines”, Pique said. “At the bottom, you can see very clearly that there are rocks gathered together. Its layers are vertical. Then there is a boundary. Above the boundary, you have these beautiful horizontal layers that make up your connection to the Grand Canyon. Hills and peaks”. The difference between these two types of rocks is significant. In the western part of the canyon facing Lake Mead, the base stone is between 140 and 1.8 billion years old. However, the rock at the top is only 520 million years old. Since Powell's trip, scientists have seen evidence of a similar waste of time in places in North America. “More than a billion years have passed”, said Pique. “This is also a billion years in an interesting part of the earth's history. The earth is in transition from ancient earth to modern earth as we know it today”.
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Continent Division
To explore this transition, Peak and his colleagues used a method called 'thermochronology', which tracks the history of heat in rocks. Pique explained that when geological structures are buried deep in the ground, the pressure built up on them will heat them up. In turn, this heat will leave traces on the mineral chemistry in these formations. Using this method, the researchers examined rock samples collected throughout the Grand Canyon. They found that the history of this feature may be more complicated than scientists thought. Especially the western half of the canyon and its eastern part (the most familiar part of visitors) may have experienced different geological distortions over time. “This is not a single block with the same temperature history”, Pique said. About 700 million years ago, the bedrock in the west seemed to have surfaced. However, in the eastern half, the same stones were deposited in the sediments for miles. Pique said this difference may have been caused by the split of Rodinia, a huge piece of land that began to separate at about the same time.
Conclusion
The researchers' results indicate that this large unconformity may have torn the eastern and western halves of the Grand Canyon in different ways and at slightly different times, and in the process produced a large unconformity. Pique and his colleagues are now studying other major unconformities in North America to understand the universality of the image. Now, you are happy to see geological history staged in one of the most beautiful landscapes in the country. “There are many things that are not available elsewhere”, he said. “This is an amazing natural laboratory”.
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