Sunday, October 01, 2006

Fossil fun

My post-defense vacation included a trip to Eastern Oregon to witness the most complete range of Tertiary fossils found anywhere - the John Day Fossil Beds. Rocks ranging from 44 million to 7 million years old contain an amazing assemblage of plants and animals. The rocks and fossils bear witness to evolutionary processes, changing climatic and environmental conditions, and vast volcanic environments. While various Tertiary rocks span much of eastern Oregon, a wide array are concentrated within the three units of the John Day Fossil Beds National Monument. The units are widely spaced, so visiting all three in one day would be impossible (we actually only managed a drive-by of the Clarno unit on our 3 day trip), but the main visitor center is brand new and has an incredibly informative display of fossils, complete with painted murals and ambient sounds.

On the first day, our destination was the Painted Hills Unit. The red bands on the hills (below) are fossil woodland soils , while the yellow bands are fossil soils from open woodlands or wooded grasslands. The black streaks represent fossil soils that formed in water-logged environments.
At the Painted Hills Unit, the Bridge Creek Flora is exposed. It is a 34 million year old assemblage of fossil plants preserved in volcanic ash claystones. The assemblage is dominated by broad-leaved deciduous plants (alder, beech, etc.) along with roses, grapes, and dawn redwood, and most of the genera are no longer found in the Pacific Northwest. Instead, these forest types are now found in China - where the climate is warmer and wetter than eastern Oregon.

The next day we explored the Sheep Rock Unit of the Monument, spending several hours at the excellent visitor center and then wandering the Blue Basin trail through a fossil-rich badlands environment (below). The Blue Basin exposes the Turtle Cove formation, dating from 28-33 million years ago, when the area was covered by woodland and wooded grassland. This formation is fossiliferous and mammals, turtles, snails, and hackberries are just a few of the remains that have been found in these layers. Winter rains and summer thunderstorms erode the sediment layers exposing new fossils on a regular basis. Once exposed to the elements, however, the fossils degrade fairly quickly. Although the area is rich in fossils, they are hard to spot from the trail, and I made the one and only find of the hike. Two small fragments of fossil wood are directly below and below-right of my extra memory card.
After the hike, we drove to the town of Fossil (their gas station is called Fossil Fuel), where you can collect fossils (for a nominal fee) behind the local high school. We spent ~3 hours digging and looking at all sorts of wonderful flora from the Bridge Creek Flora and came away with some nice specimens of metasequoia, alder, and sycamore leaves and wood prints.
Our final adventure was to visit some living trees - a disjunct population of Alaskan cedar (above). Disjunct means that these trees are isolated from the main range of their species, and are able to survive only because of very special environmental conditions. These trees towered up to 100 feet over us and got up to 4 feet in diameter. We wandered through the natural cathedral and contemplated climate change on a range of time scales.

35 million years ago, eastern Oregon was warm and wet - today it is a desert with frigid winters. 15,000 years ago glaciers covered the area where we visited the cedars, and they were left in a pocket of cold air drainage as the climate warmed into the Holocene. And what will happen to the cedars as climate warms even further, thanks to CO2 levels that haven't been experienced in the past 25 million years?

References: various NPS brochures, signs, and exhibits; Trees to Know in Oregon, 2005 (OSU extension service); Oregon Geology, 1991, v. 53, p. 75-80

4 comments:

phd me said...

This non-science person really enjoyed reading this post. Thanks for the pictures, too!

volcano girl said...

Great post! And welcome back :).

B said...

oooH thanks for the photos! I have really wanted to visit these parks but live too far away. Thanks!

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