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Fossil Forests of Eastern Washington - Page 5 of 10 There are several indications that the Vantage logs were preserved in a water environment, including the water-worn appearance of the fossil wood exterior and the fact that limbs, bark, and roots are rarely found (figure 3 shows an example of Vantage wood). These features indicate that the logs were carried to the ancient lake by water currents, which eroded external features from the wood as it was carried down river. Also, the logs are typically found in a horizontal orientation in the lava flows and have accumulated in large rafts, implying that they had been carried from the original source and have been concentrated. Additional evidence for the preservation of logs in a water environment is provided by the presence of "pillow basalts" in the fossil wood deposits. This type of basalt forms when molten lava contacts water and solidifies into large rounded lobes reminiscent of pillows (Beck, 1935). Figure 3: Section of a petrified log from Vantage Once the wood was encased in solidified basalt, hot water present in and around the wood dissolved silica minerals from the basalt. These minerals penetrated into the wood and gradually replaced components in the wood structure. Since silicon is chemically similar to carbon, it preferentially replaced the carbon in the cell walls of the waterlogged wood. This resulted in petrifaction of the wood giving us the beautifully preserved fossils we see today. The Fossil Forests Deposits of petrified wood associated with the basalt flows appear in many areas throughout southeastern Washington besides Vantage (figure 4). These deposits are collectively known as the Russell Forests in honor of I. C. Russell, the geologist who first published accounts of the fossils (Beck, 1945). Figure 4: Major petrified wood deposits in southeastern Washington. ©2004 - 2001 Evolving Earth Foundation. All rights reserved |
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