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University of Colorado Boulder has revealed the complicated history of one of Grand Canyon's most famous geologic features. It is a mysterious, missing space in canyon's rock record that spans hundreds of millions of year.
This research is closer to solving the puzzle known as "Great Unconformity", which has baffled geologists for nearly 150 years.
Barra Peak is a graduate student at CU Boulder in geological sciences and the lead author of this new study. You can reach back nearly 2 billion years in the past if you scale down canyon's rock faces. However, this textbook has many missing pages. In some areas, over 1 billion years worth of rocks disappeared without a trace from Grand Canyon.
Geologists are interested in understanding why.
Peak stated that the Great Unconformity was one of the most well-documented geologic features found in North America. "But, until recently we didn't have many constraints on when or where it happened."
She and her colleagues now believe they are closer to an answer with a paper that was published in Geology this month. According to the team, a series small but powerful faulting events could have rocked the area during the breaking up of Rodinia, an ancient supercontinent. The resultant havoc may have caused the earth to shake around the canyon, which likely led to sediment and rocks being washed away into the ocean.
Scientists could use the team's findings to fill in gaps about what happened during this crucial period of Grand Canyon's history, which is today one of North America's most famous natural wonders.
Rebecca Flowers, coauthor and professor of geological sciences, said that she has new analytical tools in her lab that enable them to decipher history in the Great Unconformity's missing window. We are doing it in the Grand Canyon as well as other Great Unconformity locations across North America.
Beautiful lines
It is a mystery that has a long history. John Wesley Powell (named after today's Lake Powell) first saw the Great Unconformity on his famous 1869 expedition that took him down the Colorado River rapids by boat.
Peak completed a similar research trip through the Grand Canyon by rafting in spring 2021. Peak said the Grand Canyon is so stark that it can be seen from the river.
Peak stated, "There are beautiful traces." "At the bottom you can clearly see that there are rocks which have been pushed together. They are all vertical. There is a cutoff and then there are these beautiful horizontal layers which form the buttes or peaks you associate with Grand Canyon."
It is important to note the differences between these two types of rock. The basement stone, which is located in the canyon's western end towards Lake Mead, is between 1.4 and 1.8 billion years of age. However, the rocks on top are only 520 million years old. Scientists have found evidence that similar periods of time were lost at other sites in North America since Powell's expedition.
Peak stated that there are more than a billion years left. It's also a billion year in an interesting period of Earth's past, when the planet is transitioning to the new Earth we know today from an older environment.
A continent splits
Peak and her colleagues used a technique called "thermochronology" to explore the transition. This method tracks the history heat in stone. Peak explained that pressure can make geologic formations toasty if they are deep underground. This heat can cause a trace in the chemistry and composition of minerals within those formations.
The researchers used this method to survey rock samples taken from the Grand Canyon. Scientists may not have realized the complexity of this feature's history. The canyon's western portion and its eastern section (the one most tourists know) could have experienced different geologic changes over time.
Peak stated, "It's no single block with the exact temperature history."
The west's basement rock seems to have reached the surface around 700 million years ago. However, the same stone was found in the eastern half of the country, but it was covered by kilometers of sediment.
Peak stated that the difference could have been due to Rodinia's collapse, which was a huge land mass that started to separate at the same time. According to the researchers, this massive upheaval could have caused the Grand Canyon's eastern and western halves to be ripped apart in slightly different ways at different times. This may explain the Great Unconformity.
Peak and her coworkers are currently looking at other locations of the Great Unconformity North America to determine how broad this picture may be. She is excited to see geologic history unfold in one of the most beautiful landscapes in the country.
She said, "There are so many things there that you won't find anywhere else." It's an amazing natural laboratory.
Continue reading Researchers investigate case of geologic amnesia
More information: B.A. Peak et al., Zircon, U-Th/He thermochronology reveals pregreat unconformity paleotopography, Grand Canyon region, USA Geology (2021). Information from Geology B.A. Peak et al., Zircon (U–Th)/He thermochronology reveals preGreat Unconformity paleotopography within the Grand Canyon region of the USA,(2021). DOI: 10.130/G49116.1
