Thursday, January 31, 2013

Petrified Forest National Park


When I saw that a new geologic map had been made for the Petrified Forest National Park, my thoughts went back to my first visit there when I was just four-years-old; of all my childhood memories, these are among the most vibrant. It wasn’t until I could read that I could go through the “report” on the park published before I was born (I still have it); and not until I was in second grade that my piece of petrified wood from the souvenir shop was glued to a board and included as part of my first science project.

Petrified wood is rare; petrified wood of the quality in the National Park is very very rare. The existence of petrified wood in the area that would be the park was recognized in 1851, and documented in an early scientific study in 1853. First proposed to become a National Park in 1890, even with the help and study of John Muir, the area was initially declared a National Monument by Teddy Roosevelt in 1906, and finally gained National Park status in 1962.

So why is this an “old” park?

The majority of the park’s terrain consists of the upper Triassic Chinle Formation (~215 million years in age), which comprises geologic deposits from a lowland terrestrial environment with meandering river valleys, swamps and lakes. And forests. And dinosaurs. It is not unusual to encounter a Triassic formation, but so great an expanse of preserved surface lands is exceedingly rare. The Chinle is so little deformed, so mildly metamorphosed, that it is like, well, visiting the planet Earth in the Triassic. This is one of the world’s oldest and best preserved “fossil” ecosystems.

Petrified wood as in the Park is the remnant of trees and other vegetation that have been “fossilized” by replacement of plant material slowly via the penetration of silica-bearing waters which then slowly turn the wood into jasper. This jasper, in itself stunningly colored, frequently retains the original structure and appearance of the parent tree: within the park, you can visit conifer stumps with their roots intact; count the tree rings to see how old a tree was when it died in the Triassic; and even observe the borings of Triassic insects into the trees. In some petrified wood, the jasper has crystallized to from quartz crystals including semi-precious stones of citrine and amethyst.

In addition to the ancient geologic setting, the park has abundant petroglyphs, carvings on stone surfaces by native Americans, some dating back to 13,000 years in age. Much of the area referred to as “The Painted Desert” is contained in the National Park, in itself a desert region deserving its own post here on TES.

Thank you for allowing me, through The Earth Story, to revisit a place that holds a special place in my memory. Perhaps if you take your four-year-old to visit the Park, he/she too may become a geoscientist!

Photo: Courtesy National Parks Service
http://3dparks.wr.usgs.gov/pefo/
html2/pf1529.html
The new map and report by the park geologists can be downloaded here:
http://repository.azgs.az.gov/uri_gin/azgs/dlio/1487
I highly recommend the photo gallery of the National Park Service and USGS:
http://www.nps.gov/pefo/index.htm
http://3dparks.wr.usgs.gov/pefo/index.html
Link to my first rock-baby:
http://3.bp.blogspot.com/-PKjt9f2LER4/Ton0QhHZgxI/AAAAAAAABDs/jDdurildeEs/s1600/2%2BPet%2Bwood.jpg



No comments:

There was an error in this gadget