The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Friday, August 15, 2014

August 15. Coconino Formation







By early Permian time, about 260 million years ago, what is now southwestern United States, around the Grand Canyon area today, was becoming pretty arid. The Coconino sandstone represents an extensive dune terrane, essentially a Permian desert that formed there. Wind-borne or eolian sand in dunes forms sloping dune faces, and when these are preserved in the sandstone, the sloping forms are called cross-beds, angular curving beds within a single package of sand. We can infer wind direction from the orientation of cross-beds.

The Coconino is typically a white, almost pure sandstone 60 to 100 feet thick. It is so resistant that it forms near vertical cliffs in places, and makes for some of the most difficult passages down into the Grand Canyon today. I climbed through it on a route in the western part of the canyon back in 1987 – a 70-foot section that required the use of ropes to descend.

The Coconino is extensive and forms prominent landscapes across much of southern Utah as well as northern Arizona.

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On August 15, 1950, an 8.6-magnitude earthquake in Assam, eastern India, reportedly killed more than 30,000 people, but other estimates give much smaller death tolls. This quake was definitely related to the ongoing collision between India and Eurasia, pushing up the Himalayas. There are other consequences to that collision, and this location, in northeastern India and adjacent Tibet, is essentially at the corner of the collision, so mountain belts and fault zones change direction here from about east-west to more north-south.
—Richard I. Gibson
See also The Earth Story's report on the Coconino

Photo by Richard Gibson

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