A Brief Moment Through the Arbuckles
This past week, I took a road trip to Stillwater, Oklahoma. The drive was fantastic as a person who loves
environments. Our route took us from the
coastal setting of the Florida Panhandle, transitioning to the piedmont of the
southern Appalachians, passing over the timeless Mississippi River, acquainting
with the Ozark Mountains, then crossing the modern “100th Meridian”
into the drier, Great Plains of Oklahoma.
One of the most surprising parts of the trip had nothing to
do with the week in 99° heat nor the shocking juxtaposition of Oklahoma’s agrarian
structure in comparison to Florida’s rampant over-commercialization. It had to do with the trip home. Our return route had us stopping in Austin,
Texas for a night, and the strangest thing occurred on Interstate 35 in southern
Oklahoma.
In the middle of (what I assume to be) the Great Plains, a
mountain range appears. I know what you’re
thinking, “How has nobody noticed a mountain range in the Great Plains?” Well to be fair, “mountain” may be an
exaggeration to the average person. They
would probably be considered hills by those familiar with the likes of the Rockies
or Appalachians, but they were large enough to require a roadcut through them,
exposing the layers of rock on either side of the road. What particularly caught my eye was the degree
of folding and tilting that occurred in the rock layers.
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| Nearly vertical tilting see here, tilt shown with red lines for those who are unfamiliar with seeing rock layers. Captured from Google Maps Street view along I-35 |
Now is time for a little background on physical
geology. When sedimentary rock layers (also
known as “strata”) form, they form in flat layers. Essentially, this is for the same reason that
spills are flat instead of three dimensional whenever you knock over a glass of
water; it is just how gravity works. Now these strata will remain horizontal and
flat, continuously stacking layers and eroding layers away as time goes on
UNLESS a force is applied to it. What
kind of a force? Well, a continental plate hitting another continent would be a
good example, as is the case for the Rockies, the Appalachians, and the
Himalayas (where this is still happening today) as is the case for almost all
mountain ranges.
If you have followed thus far, I will pose a question. Why is there a small mountain range with tilted rocks in the
middle of the continent, in an area that is known for being flat? How can continents collide in the middle of a continent? Well, there is a rich history to the area. We’ll
go back in time to around 1 billion years ago in the Precambrian when the
supercontinent Rodinia (way before Pangaea) existed. Around 750 million years ago, forces caused
the continent to pull itself apart, leading to volcanic flows dominating the
pre-North America continent known as Laurentia.
Sea level rose and flooded the area, leading layers of marine
rocks to deposit over the next 250 million years as seas level fluctuated. Then the continents decided to have a reunion
tour, as pre-South America (relatively gently) collided with Laurentia, completing
Pangaea, and crumbling the sedimentary layers that are seen along Interstate 35
today. Upon getting pushed together, the
rocks had nowhere to go but upwards, being uplifted. This is known as the Ouachita ("wah-chih-taw") Orogoeny. When looking at an aerial view, you see the
thrust belts that are so reminiscent of the great mountain ranges you are more
familiar with (seen below).
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| Aerial view of the Arbuckle Mountains. Thrust belts that look like a crumbled blanket are seen within the white outline. Captured from Google Earth. |
Over the next 250 million years, the Arbuckle Mountains experienced
Pangaea breaking up, incredible erosion, rising seas level flooding the area forming many of the
flat plains around the Arbuckles, and then sea level falling to leave the
plains and mountains exposed. Within the past 100 years, they were blasted with
dynamite to allow an Interstate Highway to be built through them and have a
young scientist ponder how such a feature could occur in an unlikely area.
For even the giants may fall to the deluge of time, but the forces of nature cannot erase their story completely as long as there is a curious mind out there.
-KC
B.S. Geology
Excerpts from:1)Oklahoma Geological Survey Website, 2001, 2002
2) Kenneth S. Johnson, Oklahoma Geological Survey, 1997, Mountains, Streams, and Lakes of Oklahoma: Information Series #1, February 1997
3) USGS/NPS Geology of the Parks Website, 2001
https://web.archive.org/web/20040724221125/http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_oklahoma.html
G. Randy Keller, An Overview of the Structure and Evolution of the Ouachita Orogenic Belt from Mississippi to Mexico. (Oklahoma Geological Survey, 2012)
Robert O. Fay, Geology of the Arbuckle Mountains Along Interstate 35, Carter and Murray Counties, Oklahoma (Norman: Oklahoma Geological Survey, 1995).
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