>>Dr. Doug Elmore: This is our third stop
on our Arbuckle Mountain field trip. We're
a little south of our last outcrop, which
was the Collins Ranch conglomerate. And there
are a couple things to note here. First, some
of those clasps in the Collins Ranch conglomerate
actually came from this unit which is an Ordovician
limestone called "the Arbuckle group." But
the main reason I wanted to stop at his location
was to show you a sedimentary structure within
the rock and that sedimentary structure, you
can see it right here. Those are mud cracks.
What do they tell us about the history of
this rock? Well, when this rock formed in
the Ordovician, the water depth must have
been very shallow and periodically it must
had desiccated or dried up to produce the
mud cracks. So by looking at sedimentary structures
and rocks, such as mud cracks, we can learn
a lot about the depositional setting and the
processes involved in formation of that particular
rock. You can also see at this outcrop several
holes within the rock. These are holes that
were collected for paleomagnetic studies.
We will be talking about paleomagnetism later
on in the semester. But "paleomagnetism" is
the study of the magnetization in the rocks
and that can also provide a lot of useful
information about the history of the rock,
which we will discuss later on in the semester.
