The Petrified Forest
Petrified Forest National Park in Arizona is one of the best places to see petrified wood. Other fossils include a crocodile-like reptile, a phytosaur (seen above). A lot can be learned about the environment 225 million years ago when these rocks were deposited.
Amazing But True!
- Rock layers in Petrified Forest National Park are Upper Triassic shales and siltstones of the Chinle Formation.
- Volcanic eruptions deposited silica-rich ash.
- Downed trees accumulated in river channels. The trees were buried by sediment including the silica-rich volcanic ash.
- Groundwater dissolved silica from ash and carried it into logs. Quartz crystals replaced the organic material. This is permineralization.
- At least nine species of fossil trees are found in the park. All are extinct.
- Other fossils were created by other processes including compression. Among the many fossils are ferns, cycads, ginkgoes, snails, clams, giant reptiles called phytosaurs, large salamander-like amphibians Buettneria and early dinosaurs.
- The sediments and fossils were buried, and then re-exposed during 35 million years of uplift and erosion.
With the links below, learn more about The Petrified Forest, Arizona. Then answer the following questions.
- 58NationalParks, Petrified Forest National Park: https://www.youtube.com/watch?v=068GcVD3VaE
- Wikipedia, Petrified Forest National Park: http://en.wikipedia.org/wiki/Petrified_Forest_National_Park#Geology
- What was the environment of northeastern Arizona like when the Chinle Formation was deposited?
- Why is it important that the logs were buried by sediment before permineralization?
- Why are the petrified logs so colorful?
- What processes led to the petrified logs just sitting on the ground?