An exciting new study has just been conducted on the Sixtymile Formation of the Grand Canyon that has shown the sandstone analyzed to be not nearly as old as had been assumed in the past, when it was mistakenly believed that this area belonged to the Precambrian Grand Canyon Supergroup.
Scientists have been conducting intense geological investigations around the Grand Canyon for the past 140 years and the last study conducted on any new formations was during the 1970s. This has changed as research is now being done on the Eastern region of the Grand Canyon that can be found directly below the Great Unconformity, as Phys.org report.
The University of New Mexico’s Laura Crossey explained that the new discovery occurred after much investigation into parts of the Grand Canyon that are normally inaccessible and quite difficult to traverse.
“Unraveling this science tale was an adventure in discovery, and involved serendipity, deep insight, and persistence – with a good dose of state-of-the-art geochronology and extreme fieldwork including several water/rock, heavily laden backpack treks along significant stretches of the Horsethief Trail among other remote locations in Grand Canyon.”
What is known as the Sauk marine Transgression can be dated as having occurred from between 600 to 500 million years ago. Zircons were created at this point after a dramatic rise in sea levels, and it is these zircons that allow scientists to date the small amounts of uranium and thorium mineral deposits in them.
— Phys.org (@physorg_com) June 1, 2018
As it turns out, it was the true age of the Tonto Group of the Grand Canyon, which lies above the Sixtymile Formation, that led researchers to the new discovery. After dating the detrital zircon grain here, it was determined that these were actually much younger than the sand grains around it, which are approximately 505-million-years-old.
As scientist Karl Karlstrom noted, even though the new discovery contradicted everything that had been learned about the fossils that had been found, it was determined that flooding in North America occurred over a relatively short period of time, and between just 505 to 500 million years ago.
“At first, it seemed to contradict fossil evidence, but, using new global constraints, we document that Tonto Group trilobites lived on Earth 505- 500 Ma million years ago such that the precise new geochronology and fossil evidence are in mutual agreement. Thus, flooding of the North American continent took place within a geologically short interval between 505 and 500 million years ago – more recently and much more rapidly than previously thought.”
After such an important discovery, the Sixtymile Formation of the Grand Canyon can no longer be thought of as belonging to the Precambrian Period of 650 million years ago, according to Laura Crossey.
“Sixtymile Formation was long considered Precambrian, but precise new dating of zircon sand grains from this rock using the U-Pb radioactive decay ‘clock’ shows it to be younger than once thought. New dating shows that its youngest detrital grains are 508.6 ± 0.5 Ma, hence the Sixtymile Formation sandstone must have been laid down after that, and the overlying Tonto Group after that.”
After further work was conducted by numerous individuals, it was determined that the Sixtymile Formation of the Grand Canyon can more accurately be dated now to belonging to around the middle or end of the Cambrian Period.
“This research, which involved an amazing group of collaborators, and the support of many graduate students, provides a marked revision of classic Grand Canyon stratigraphy by showing that the Sixtymile Formation is not Precambrian, but is middle to late-Cambrian.”
The study on the new dating of the Sixtymile Formation of the Grand Canyon can be read in Nature.