Earths Science Logging Questions
To log this EarthCache as found, please email or message the CO with answers to the following questions. Do not post answers in your log.
At this location you will find a large fossilised stump on display. Your task is to examine the stump closely and interpret the geological processes that brought it into its current stone form. Please do not touch or climb on the specimen.
1. Structure Observe the fossilised stump.
Describe at least one feature that still resembles wood (e.g., rings, bark pattern, internal grain).
What features do you see?
2. Mineralisation What colour(s) do you observe in the fossilised stump?
Based on these colours, what minerals do you think may have replaced the wood?
3. Photo Requirement
Take a photo with you or a personal item with in the location in the background.
Do not include the stump or give away answers in your photo.
Fossilized (Petrified) Stump
At this location you will find a beautifully preserved fossilised tree stump, a window into an ancient landscape that existed long ago. This stump tells the story of lost forests, rapid burial, mineral-rich waters and provides a rare look into the geological processes that transform living trees into durable rock over immense spans of time.
How Petrified Wood Forms
Petrified wood is a fossil. It forms when plant material is buried by sediment and protected from decay due to a lack oxygen and organisms. Petrified wood forms through a process known as permineralisation. Over millions of years:
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a tree dies and is rapidly buried, often by volcanic ash, mud, or flood sediments.
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groundwater carrying dissolved minerals seeps through the buried wood.
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the organic tissues slowly are filled with silica, quartz, calcite, or opal.
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over millions of years, the wood is completely replaced by stone, yet the structure, rings, and surface textures remain.
Geological Setting of the area
Coonabarabran is well known for its volcanic history and silica-rich deposits, making it an ideal environment for petrified wood to form. Around 17 to 13 million years ago, the Warrumbungle region was dominated by a large volcanic complex. This activity produced thick layers of volcanic ash and lava flows rich in silica (especially rhyolite). These ash layers are crucial because they can rapidly bury vegetation. So conditions ideal for fossilisation existed here:
: rapid burial by ash or mud preserved tree trunks before they rotted.
: silica-rich groundwater from volcanic rocks slowly replaced the wood tissue.
: erosion has since exposed many fossilised logs and stumps in the region.
Colours in Petrified Wood and the Minerals Behind Them
Petrified wood comes in a wide range of colours, and each colour is caused by specific minerals that replaced the original wood during fossilisation. The minerals dissolved in the groundwater control the final colours. In volcanic regions like the Warrumbungles, the silica-rich volcanic ash and groundwater often carried:
: Iron → red, orange, brown
: Manganese → black streaks
: Clean silica → white/grey zones
Respect the Site
Fossilised wood is scientifically valuable and irreplaceable. Please:
: do not collect chips or fragments
: avoid climbing on the stump
: leave the site exactly as you found it