>>Dr. Doug Elmore: At this stop we're going
to talk about the history of the Arbuckle
Mountains. And we're going to start with something
called "the Southern Oklahoma Aulacogen."
We are currently in the Southern Oklahoma
Aulacogen. What is an aulacogen? Well, it's
a failed rift. It's a rift where the continents
started to split apart but then it didn't
make it into an ocean. A divergent pit plate
boundary that never was successful.
Well, what happens at divergent plate boundaries?
You start off with volcanic and igneous rocks.
And that's what you have here in southern
Oklahoma. So if you look at this cross section
you can see, this is a cross section of the
Arbuckle Mountains. We're located right here.
[locations highlighted on screen] You can
see the north flank of the Arbuckle Mountains
with the rocks dipping to the north, the south
flank dipping to the south, and then the rocks
in the center here are Igneous Rocks. And
they're rocks that formed during the initial
phases of the Oklahoma aulacogen.
So what I'd like to now is talk about the
history from that point on. So roughly 550
million years ago or so you had these volcanic
rocks and igneous rocks form and then what
happened after that? And I'll ask the students
to help me with this. What would be the next
event after the formation of those igneous
rocks?
>>Ally: They cooled.
>>Dr. Doug Elmore: They cooled. And as things
cool what happens?
>>Ally: They sink.
>>Dr. Doug Elmore and Dustin: They contract
and they sink.
>>Dr. Doug Elmore: So when you sink you produce
a big basin and what do you think that basin
filled up with?
>>Shannon: Carbonated rocks.
>>Dr. Doug Elmore: Carbonated rocks, sandstones,
and shales. As you can see here in the cross
section. And as you can see in the background,
lots of carbonated rocks here. But what else?
What then happened at the end of the Paleozoic
Era? Or toward the end of the Paleozoic Era?
>>Shannon: Well, then you had your mountain
building.
>>Dr. Doug Elmore: Then you had mountain building
event and that was when African South America
hit North America producing the Arbuckle Mountains,
the Arbuckle Anticline, you fold it, and you
fault it and you see the current situation.
Well you almost see the current situation.
What has happened since the deformation in
the late Paleozoic?
>>Dustin: Erosion?
>>Dr. Doug Elmore: Erosion. The rocks have
been eroded down. The Arbuckle Mountains are
an old mountain range. 300 million years old,
they're not as high as the Rocky Mountains.
Unfortunately we don't have ski slopes in
Oklahoma, got to go out to Colorado. Colorado,
the Laramide Orogeny, the Rocky Mountains,
much higher mountains. Why? Because they're
much younger. They're maybe 50 million years
old or 20 or 30 million years old compared
to 300 million years old for the Arbuckle
Mountains. And one other thing I'd like you
to note here in the Arbuckle Mountains, remember
we talked about how these rocks are dipping?
And if you look off in here you can see some
of these dipping rocks. And we call that tombstone
topography. It's where the rocks are dipping
and they stick up from the grass, and they
look like tombstones that are slightly tilted
over. It's called "tombstone topography."
