>>Dr. Doug Elmore: This our second stop on
our field trip to the Arbuckle Mountains,
and here we have an outcrop of the Collins
Ranch conglomerate you can see it right here.
This is the conglomerate that was sitting
on top of the angular unconformity at our
last stop, the first stop on the field trip.
So what I'd like to do at this stop is to
talk about how this particular rock formed.
And to do that we first need to describe the
characteristics of this rock. So I'm going
ask the students to help me with that so Shannon,
tell me something about this rock, describe
it.
>>Shannon: There's a large grain size variation
in it. Some of the cobbles are really large
and some of them are really tiny.
>>Dr. Doug Elmore: And what does that say
about the sorting? We use the term "sorting",
which is the range of sizes. So would it be
poorly sorted or well sorted?
>>Shannon: Poorly sorted.
>>Dr. Doug Elmore: Poorly sorted, okay. Dustin
tell me something else.
>>Dustin: The clasps are somewhere between
sub-angular and sub-rounded. Some of them
more rounded then others.
>>Dr. Doug Elmore: Okay there are some rounded
claps but clearly there are some that are
not okay. All right, what about interpretation?
What can we say about the depositional processes
that form this particular rock? And then the
depositional environment that the rock formed
in?
>>Shannon: You have to have really high energy
to move these large claps.
>>Dr. Doug Elmore: Absolutely, you have to
have high energy. What moved the clasps do
you think?
>>Dustin: Water.
>>Dr. Doug Elmore: Water, okay. What kind
of environment do you think it was?
>>Shannon: Alluvial fan?
>>Dr. Doug Elmore: Maybe an alluvial fan.
Okay, how far do you think it was from the
source? In other words what was the source
of these cobbles? Think of the rounding and
the angularity. As you move away from the
source what happens to rounding? It increases,
right? So here we have some fairly poorly
rounded clasps, so that would suggest that
we're probably pretty close to the source.
And in fact at our next stop we're going to
go look at the source for the clasps in this
conglomerate. Now one last thing I'd like
to do at this outcrop is to look across the
highway, but before I do that I need a little
prop. I want you to notice here that these
beds are dipping, okay? In this direction.
Alright you can see the bedding. Not dipping
very steeply, but they are still dipping.
Why are they dipping? Well, that's when rocks
become deformed. For example, using this notebook
if I squeeze the rocks I can fold the rocks
into a syncline like this where the rocks
dip down or I can do an anticline where the
rocks are like this. This is actually one
limb of a syncline like this. And if you look
across the highway you can see the whole syncline
dipping to the north and then dipping to the
south. And of course that's this situation
caused by compression. So after the rocks
were deposited they were then deformed into
the syncline.
