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Day 6: Specimen Ridge
Petrified Wood, Creationism, Waterfalls, Volcanism…and
More
Petrified Forest Site
• Up on a very steep ridge• Consists of 27 layers of many buried forests• Located near a glacial basin with a river
flowing through it
• What is petrification? How is it different from fossilization and replacement?
What We Were Looking For
• Vertical stumps
• Log Alignment
• Sedimentary structure
• Types of Trees
• Roots, Branches, Leaves, etc.
• Ripple Marks and indications of flow
>> These all give indications of how petrification occurred.
What we Found• Vertical stumps, horizontal logs and one instance of
both combined.• No alignment; very few horizontal specimens• MSC found; sandstone found around roots.• We don’t know what types of trees were petrified.• Large root system found. Some branches found.• Small indications of cross-bedding. No other flow
marks found. • So some trees were most likely transported in a mud
flow or similar event; some may not have been.
Dating Method
• Older Method
• Carbon 14
• Cosmogenic
• Life
• Relative Dating
Erosion of Trees
• Tree on hill - outside petrified, inside eroded• Outside could be mineralized first, inside more
slowly; not as stable so erodes quickly– Could be from inside rotting, not completely petrified– Animals live in root holes, also help to erode
• Explains the erosion gradient; couplets of rings– Light ring petrified, dark not– Could be wood (50million yrs old)
Waterfalls
• Recall the changing nature of rivers
• Base level rise
• Base level drop
Relative Dating and the Canyon
• Rhyolite deposits from Dave’s speech • Dike intrudes; younger than the deposit• Fault line; younger than the dike • Top layer usually sedimentation• This allows for relative dating
Application to the Canyon
• Radioactive dating- two different ages on different sides of the canyon
• Broad valley- lava flow into it; thick• Rising of river- eroded part of valley and retreated
– Three river valleys
• New basalt and gravel flow fills in other side– Discussed possibility of two different lava flows
(relatively same dates)– Glaciation on top
Hoodoos
• Towers of rock, usually along a riverbed
• Formed with a erosion-resistant rock cap
• Column of more erodable rock beneath it is shielded by the tough rock cap by the river
• Can also be eroded by wind instead of water
Merry Yellowstone Christmas!