Petrified Wood

What is special about petrified wood in Oklahoma?

Oklahoma can boast that it has the oldest and youngest petrified wood of any state in the nation, even though not blessed with the abundance or beautiful colors of petrified wood from many other western states. Our oldest wood is about 375 million years (m.y.) old and formed from the most primitive true trees that grew on the Earth, and our youngest wood, probably about only 15 m.y. old, grew along rivers that were eroding the Rocky Mountains. Some of our most spectacular specimens of ancient trees, although not "technically" petrified wood, are associated with eastern Oklahoma's coal beds that were deposited about 310 m.y. ago. No other state has the diversity of ancient wood that Oklahoma does.

How does petrified wood form?

Petrified wood from Jenks, Oklahoma.

Petrified wood forms when wood is quickly buried in sand or mud, typically in a river channel during a flood. In some cases, however, wood can be buried in a beach or rafted into a deep-marine environment. Under the right conditions, silica (SiO₂) dissolved in groundwater is "templated" on the organic material in the wood; in addition, some silica crystallizes within the pore spaces in the wood. Depending on the timing of the various processes and the degree to which they progress, the wood can be fragile and splintery or completely solid, and the cellular structure of the wood can be perfectly preserved or completely destroyed.

Some "fossil wood" in Oklahoma, while it looks and "feels" like petrified wood is, in fact, not petrified wood. Rather, it is a "cast" that forms when wood buried in sediment decays, leaving a mold that preserves many of the features present on the outside of the wood. If the mold fills with sediment which then hardens, the cast that forms resembles petrified wood but did not form as a result of silica-templating or pore-filling of organic material.

Where does petrified wood occur in Oklahoma?

The oldest is called Callixylon and occurs in the Devonian-age Woodford Shale in the Arbuckle Mountains and near Ada. A superb specimen can be seen at the entrance to East Central University in Ada. Most Pennsylvanian (about 320 to 300 m.y. ago) wood in Oklahoma are casts that, while not as spectacular as the one on the display at the Canadian County Historical Society's museum in El Reno, can also be found in some sandstone beds in LeFlore, Latimer, Haskell, and Pittsburg Counties. Some true Pennsylvanian petrified wood occurs near Ada and near the coal beds of northeastern Oklahoma. Permian petrified wood about 280 m.y.old is associated with some of the state's small, uneconomic copper deposits in Payne and Noble Counties. Cretaceous (145 to 65 m.y. ago) wood is Oklahoma's most common and is found in the same age rocks as many of the state’s dinosaurs, particularly the Antlers Formation in southeastern Oklahoma; some buildings in Ardmore are built of Antlers petrified wood. The same-age rocks near Kenton once had tree trunks as large as 2.5 feet in diameter and 85 feet long, but these have long since been removed by collectors. The youngest petrified wood in Oklahoma is in the mostly Miocene (25 to 5 m.y. ago) Ogallala Formation of Beaver, Harper, and Ellis Counties.

OGS Publications on Petrified Wood

Suneson, N.S., 2010, Petrified Wood in Oklahoma: Oklahoma Geological Survey Information Series, IS-14, 16 p. (PDF)

Petrified Wood in Oklahoma. Slideshow presentation given by Neil Suneson at the Tahlequah Rock and Mineral Society on July 21, 2009. (PDF)

Petrified Wood from Ada, Oklahoma.

Acknowledgments

Petrified wood information and photos provided by Oklahoma Geological Survey geologist Neil Suneson.