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!