Friday, August 30, 2013

[Geology2] Zion National Park Shows Evidence Of Earthquakes That Rattled Dinosaurs

Zion National Park Shows Evidence Of Earthquakes That Rattled Dinosaurs

Date: Aug 29, 2013 | Author: Joelle Renstrom 

A new study conducted by scientists at the University of Nebraska in Lincoln confirms that the red cliffs of Zion National Park in Utah were the result of an earthquake that ripped through North America during the early Jurassic period. That was just under 200 million years ago, if you're counting, or more importantly, the period often characterized by the presence of dinosaurs.

This massive earthquake tore through the expansive sand sea of North America (which at that time was part of Pangaea, the single supercontinent), disturbing the water-soaked sand buried below and causing it to erupt through the sand like a volcano or geyser. Archaeologists have found evidence of these blowouts in the Navajo Sandstone of the American Southwest. The sand sea, or Jurassic dune field, occupied nearly 250,000 square miles, from Wyoming to California, for roughly 15 million years.

Navajo Sandstone in Grand Staircase-Escalanta National Monument (Utah)

Navajo Sandstone in Grand Staircase-Escalanta National Monument (Utah)

While scientists have known about the quake and resulting blow-outs for a while, the new study reveals intricacies and more detailed information than ever before. The affected sandstone remains impressively intact, to the point that scientists can spot patterns in it that correspond to seasons. In Zion National Park, scientists identified sand pipes — indications of the quake-induced sand eruptions — that reveal a year's worth of shifting and spewing that most likely corresponds to the main earthquake and its aftershocks. "The exposure is so complete you can see every detail," said David Loope, lead study author and sedimentologist.

The dunes were affected by monsoons and high winds, which helped form mud and limestone that have preserved fossils from Jurassic times. It's thought that these rains helped form the water-saturated sand that erupted after the massive earthquake. The dunes moved southeast by approximately three feet per year due to winds caused by Pangaea splitting up. As they pushed southeast, the dunes caused sand avalanches that buried and preserved the sand pipes and formations recently discovered.

sand pipes

Sand pipes in the Navajo Sandstone are evidence of earthquakes during the Jurassic period, scientists say.

Scientists still aren't quite sure what caused the earthquake. Earth's plates collided and overlapped in something called the "subduction zone," which is their best guess as to the cause of the quake, but that zone is roughly 300 miles west of Zion National Park, so the geographical areas don't quite match up.

I think there's a way to get a definitive answer to this question, and Michael Crichton's already thought of it. Once cloned and restored to a nice corner of the earth, all we have to do is teach dinosaurs to communicate (I think the T-Rex is a good candidate for sign language) and then they can tell us what happened. Though we should be ready to treat their PTSD.


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