Sequoia affinis (fossil giant redwood tree trunk) (Florissant Formation, Upper Eocene; Florissant Fossil Beds National Monument, Colorado, USA) 121

Sequoia affinis Lesquereux, 1876 - fossil giant redwood tree trunk in the Eocene of Colorado, USA.

"Petrified wood" refers to fossil wood that, while buried in sediments, had its microscopic porosity filled with minerals as groundwater percolated through. This fossilization process is technically known as permineralization ("petrified" is a horrible term - never use it in a scientific context). Permineralization can also occur with fossil bones. The most common permineralization mineral is quartz (~pure silica - SiO2), which is the most common mineral in the Earth's crust.

The permineralized fossil tree trunk seen here is an extinct giant redwood. Redwoods and sequoias are famous giant trees living in modern California. This Colorado fossil demonstrates that they used to live in the Rocky Mountains, when the climate was different.
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From park signage:

Stumps of Stone

These fossilized tree stumps are remnants of an ancient catastrophe. In the Late Eocene Epoch, about 34 million yeas ago, the Florissant valley was buried by eruptions from a cluster of volcanoes known as the Guffey Volcanic Center. Huge volcanic mudflows spread into this forested valley with great speed, destroying all but the largest trees.

The bases of giant redwoods were buried in place in 15 feet of mud. The trees died and the unburied portions fell over and rotted away. Casings of volcanic mud created the special conditions that turned the buried stumps into stone.

Wood Becomes Rock

Entombed in silica-rich volcanic mud, these ancient redwood stumps slowly turned to stone through a process called permineralization. Dissolved minerals seeped into the wood, filling in the microscopic spaces within cells. After the solution precipitated silica within the cells of the wood, a stone replica remained. This preserved both the general outer appearance of the tree as well as its inner cellular structure.

Redwoods in Colorado?

The Rocky Mountain region was once much warmer. Thirty-four million years ago, summers were wet and the winters mild. The Florissant region was forested with towering redwoods, cedars, pines, mixed hardwoods, and ferns. Streams flowed through the valley. Insects, birds, mammals, and fish all thrived in this environment.

Fossil leaves serve as ancient thermometers for reading the temperature of the past. By comparing fossil plants with modern vegetation, scientists estimate that the mean annual temperature at Florissant during the Late Eocene was about 56 degrees Fahrenheit (13 degrees Celsius), similar to San Francisco today.

Climate Signals

The lobed, toothed leaf of the fossil maple Acer florissantii indicates warm-temperate growing conditions. The smooth-edged Cape mahogany, Trichilia florissantii, with its extended "drip tip", is a leaf design common to wetter, subtropical climates.

These warmer climates no longer exist at Florissant, where extreme winter temperatures can reach -35 degrees Fahrenheit (-37 degrees Celsius). As the climate changed, the plants of the Eocene then adapted, became extinct, or dispersed to other parts of the Earth.
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Classification: Plantae, Spermatophyta, Pinophyta, Pinopsida, Cupressales, Cupressaceae

Stratigraphy: Florissant Formation, Upper Eocene

Locality: Petrified Forest Loop Trail, Florissant Fossil Beds National Monument, central Colorado, USA
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Info. at:
www.nps.gov/flfo/learn/nature/sequoia-affinis.htm
and
en.wikipedia.org/wiki/Sequoia_affinis

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Taken on: July 28, 2007

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Sets appears in: • Colorado Rocks, Minerals, Fossils • Eocene Rocks, Minerals, Fossils more » • Fossil Preservation Styles - Permineralization • Plant Fossils • Florissant Lagerstätte fossils (Florissant Formation, Upper Eocene; Florissant area, central Colorado, USA) « less

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