A caller survey led by the University of Colorado Boulder reveals the analyzable past down 1 of the Grand Canyon's astir well-known geologic features: A mysterious and missing spread of clip successful the canyon's stone grounds that covers hundreds of millions of years.
The probe comes person to solving a puzzle, called the "Great Unconformity," that has perplexed geologists since it was archetypal described astir 150 years ago.
Think of the reddish bluffs and cliffs of the Grand Canyon arsenic Earth's past textbook, explained Barra Peak, pb writer of the caller survey and a postgraduate pupil successful geological sciences astatine CU Boulder. If you standard down the canyon's stone faces, you tin leap backmost astir 2 cardinal years into the planet's past. But that textbook is besides missing pages: In immoderate areas, much than 1 cardinal years' worthy of rocks person disappeared from the Grand Canyon without a trace.
Geologists privation to cognize why.
"The Great Unconformity is 1 of the archetypal well-documented geologic features successful North America," Peak said. "But until recently, we didn't person a batch of constraints connected erstwhile oregon however it occurred."
Now, she and her colleagues deliberation they whitethorn beryllium narrowing successful connected an reply successful a insubstantial published this period successful the diary Geology. The squad reports that a bid of tiny yet convulsive faulting events whitethorn person rocked the portion during the breakup of an past supercontinent called Rodinia. The resulting havoc apt tore up the world astir the canyon, causing rocks and sediment to lavation distant and into the ocean.
The team's findings could assistance scientists capable successful missing pieces of what happened during this captious play for the Grand Canyon -- contiguous 1 of North America's foremost earthy wonders.
"We person caller analytical methods successful our laboratory that let america to decipher the past successful the missing model of clip crossed the Great Unconformity," said Rebecca Flowers, coauthor of the caller survey and a prof of geological sciences. "We are doing this successful the Grand Canyon and astatine different Great Unconformity localities crossed North America."
Beautiful lines
It's a enigma that goes backmost a agelong way. John Wesley Powell, the namesake of today's Lake Powell, archetypal saw the Great Unconformity during his famed 1869 expedition by vessel down the rapids of the Colorado River.
Peak, who completed a akin probe rafting travel done the Grand Canyon successful outpouring 2021, said that the diagnostic is stark capable that you tin spot it from the river.
"There are beauteous lines," Peak said. "At the bottom, you tin spot precise intelligibly that determination are rocks that person been pushed together. Their layers are vertical. Then determination there's a cutoff, and supra that you person these beauteous horizontal layers that signifier the buttes and peaks that you subordinate with the Grand Canyon."
The quality betwixt those 2 types of rocks is significant. In the occidental portion of the canyon toward Lake Mead, the basement chromatic is 1.4 to 1.8 cardinal years old. The rocks sitting connected top, however, are conscionable 520 cardinal years old. Since Powell's voyage, scientists person seen grounds of akin periods of mislaid clip astatine sites astir North America.
"There's much than a cardinal years that's gone," Peak said. "It's besides a cardinal years during an absorbing portion of Earth's past wherever the satellite is transitioning from an older mounting to the modern Earth we cognize today."
A continent splits
To research the transition, Peak and her colleagues employed a method called "thermochronology," which tracks the past of vigor successful stone. Peak explained that, erstwhile geologic formations are buried heavy underground, the unit gathering connected apical of them tin origin them to get toasty. That heat, successful turn, leaves a hint successful the chemistry of minerals successful those formations.
Using this approach, the researchers conducted a survey of samples of stone collected from passim the Grand Canyon. They discovered that the past of this diagnostic whitethorn beryllium much convoluted than scientists person assumed. In particular, the occidental fractional of the canyon and its eastbound information (the portion that tourists are astir acquainted with) whitethorn person undergone antithetic geologic contortions passim time.
"It's not a azygous artifact with the aforesaid somesthesia history," Peak said.
Roughly 700 cardinal years ago, basement stone successful the westbound seems to person risen to the surface. In the eastbound half, however, that aforesaid chromatic was nether kilometers of sediment.
The quality apt came down to the breakup of Rodinia, a gigantic onshore wide that began to propulsion isolated astatine astir the aforesaid time, Peak said. The researchers results suggest that this large upheaval whitethorn person torn astatine the eastbound and occidental halves of the Grand Canyon successful antithetic ways and astatine somewhat antithetic times -- producing the Great Unconformity successful the process.
Peak and her colleagues are present looking astatine different sites of the Great Unconformity successful North America to spot however wide this representation mightiness be. For now, she's excited to ticker geologic past play retired successful 1 of the country's astir picturesque landscapes.
"There are conscionable truthful galore things determination that aren't contiguous anyplace else," she said. "It's a truly astonishing earthy lab."
Other coauthors of the caller survey included John Cottle and Francis Macdonald of the University of California, Santa Barbara.
English (US) ·