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Welcome to week two of
physical science oceanography. We are going to be talking this week about
marine geology.
And specifically the actual materials that make up the ocean floor
and coastlines.
So what we are going to discuss, this video in particular, are
the rocks that are present. That's what we'll go through in this video.
Video two will go into the different sediments that are present
and then in video three we'll discuss, again,
uplift, gradation
some different
processes that help that gradation
process to happen and then some of the methods that are used to collect these samples.
So materials that make up the seafloor and coastlines. Well we have rocks, solid
particles,
and we have sediment. So we have those loose bits: sands, gravels, muds,
that aren't actually solidified into an actual rock.
The majority of the seafloor
what we find are layers of basalt and gabbro. And we'll
talk about those
in the next few slides. We see some layers of sedimentary rocks. We'll go into
those in a little bit more detail.
Then we also see the thick layers of sediment
and we'll discuss that in the next
video along with what happens along the edges
of the continents. Of that continental margin.
Rocks.
Well we have three major rock types. We have igneous rocks,
metamorphic rocks and sedimentary rocks. And here you can see how
all three of these rock types are actually related to one another.
Igneous rocks.
We have
some type of igneous activity, magma, lava
cooling to a solid.
We have sediments produced when those rocks are actually weathered, broken down into
smaller pieces, dissolved away,
transported from one place to another,
deposited, left
in some kind of a basin and then they get actually
solidified
through lithification
into a solid rock. And then if we take those two sedimentary or igneous rocks
and apply some heat and pressure.
Heat and/or pressure I should say.
We can create a metamorphic rock.
Because we have changed
those rocks through
applying that heat and/or pressure.
So we're going to go into each of these in a little bit more detail.
The first type of rock we're going to discuss, and you're going to see
most of these in lab this week,
are igneous rocks.
These, like I said before, cooled
from magma or lava
to form a solid rock.
And
we can tell by looking at the actual size of the minerals in those rocks
where they cooled. Below the surface or above the surface of the earth.
Those rocks that cool
beneath the surface are insulated by the surrounding rocks. So
they cool inside the earth, they're insulated
and they have larger grain sizes. So all those
little building blocks that are in that magma, that liquid magma,
have a chance to actually find each other and
bond and create those larger minerals.
Those
rocks that have a smaller grain size, they've cooled much faster, the building blocks
didn't have a chance
to find each other
as that
lava was cooling.
And
we have that kind of scenario on the surface of the earth where we have
much more rapid cooling
of that lava.
And you may be wondering
the difference between magma and lava. Well magma is below the surface.
Lava is on the surface.
So when we actually look at rocks in lab this week, you're going to be
comparing the grain size, do you see mineral grains with the naked eye,
or do you not see any.
And then we will also look at the actual color or shade of the rock.
And that color or shade tells you a little bit about what minerals might be present.
So even if you have a fine-grained rock,
the minerals are very small, can't see them with the naked eye,
just by looking at the overall shade, if it's dark , if it's intermediate,
kinda grayish color
or light in color.
You can actually
take an educated guess as to what minerals might be possible
to be present in that rock.
So let's figure here you can see the intrusive rocks cooling around where that
magma chamber below that volcano.
The lava flows on the surface
and then when we have some of these volcanic eruptions you can also get a
variety of different things like, ash
or tephra, really hot
pyraclastic flows, lahars when that hot material mixes with
water or ice on the surface.
So what does some of these the rocks look like? And what do these
grain sizes
actually look like when you're holding a rock sample in your hand.
Well the actual size of the grains and the appearance of that rock we call that
texture. What does it look like?
And so here you can see
coarse
igneous rocks
in the upper
right-hand corner of the screen.
We have rulers here to tell you about how big each of those samples are.
those are
in centimeters.
So in those coarse,
igneous rocks you can see
the different colors. You can see pinks, you can see whites and you can see
the black color of the
different minerals present each of those,
those rocks. So that's telling you because you can see the different minerals, the
different colors.
That's gong to be a coarse, igneous rock cooled
inside the earth.
Because those minerals had a chance to grow
to be that large.
Fine-grained side on the lower right hand corner
there all you see is kinda this black
grayish colored rock.
We don't see
the actual minerals present
but they are there they're just too small for us to see. So that one would have
cooled much faster.
Two
other textures we have here vesicular and glassy.
These two are also going to be in the extra ____. Cooled on
the earth category.
Vesicular
we've got some type of gas
that was present as that magma was erupting on the surface and the rock cooled so that
that lava cooled so quickly
that the gas bubbles didn't have a chance to actually escape from that lava. So they kinda of
get frozen in the rock.
And the bottom there
glassy looks like glass. Same idea
cooled so fast
in this case that minerals barely had a chance to even form at all. So some of these
glassy, igneous rocks
don't have actually have minerals present because they cooled too fast.
So the other side of things are the
composition. So
what's the overall color
of that rock?
So we have light in color, also called felsic.
And light colored rocks are going to have a whitish color. You might see some black minerals,
some browns, but you'll also see pinks.
And pink is technically going to be in that light category even if the pink is a
little bit of a darker pink color.
So pinks, whites are going to be in the light
category.
Next we have gray or intermediate.
In this one you have
mostly grey color. Maybe some larger black minerals and larger white minerals present.
And then if we have all dark minerals
we have a dark grey color for our rock
we call that mafic
or dark in color. And that's referring to the actual minerals present.
Then if you see any greens
or really dark blacks you're going to have what's called an ultra mafic rock.
So these are the different
compositional categories.
We are going to break these igneous rocks into.
So in lab, we're gonna to be focusing mostly on igneous rocks. We'll look at a
few sedimentary rocks.
So make sure you're familiar with these
before you come to lab
So the next category of rock are sedimentary rocks.
And these are made from eroded sediment. So we have
chunks of other rocks that have been broken down into smaller pieces or dissolved through
different types weathering.
And those sediments get transported from one place to another through
rivers, through glaciers,
through groundwater
all different
ways to
move material from place to place. Once they're deposited into
some kind of a low basin area where you can actually build up layers of these
sediments, And
once they get buried enough
they start to compact a little bit so all those grains start to kinda settle into one another.
And eventually those grains get cemented together.
This is that what we call lithification.
These
million dollar words you can bring up at parties and wow your friends.
So this term lithification means that
converting
sediments into a solid rock and that involved compacting the
sediments together
and then cementing those particles to one another.
Kind of gluing it together.
Here you can see two pictures. We have sediment.
In the lower left corner and then the actual rock that might be produced once
those sediments are actually solidified together.
Now just like igneous rocks, we can look at the grain size. So we can see
um... we can look at and say alright do we see minerals or sediments in
this rock. Or do we not.
The categories, the sizes are clay,
superfine.
And when you feel that rock with your hand it feels very very smooth to the touch
because those particles extremely fine-grained can't see them with the
naked eye.
And they tend to stack up in
layers. So that
rock that has clay particles,
will break off into nice flat sheets.
Silt's a little bit coarser.
These one's might feel a little gritty to the touch.
Sands you will be able to see these with the naked eye.
Also be gritty feel like sandpaper.
Pebbles
a little bit larger.
Cobbles would be about the same size as this rock sample.
And then boulders just actually huge.
Could be the size of a car.
Theses are the different sizes of particles that you can see.
And then just like
our igneous rocks we can also look at the composition so do we see minerals,
do we see rocks, do we see fossils.
For example, here we've got some examples of the different grain sizes.
You can see the pebble sized grains
in
those sedimentary rocks. The sand sized particles we can kinda see the different shiny
bits of quartz in that sand. Silt,
can't really see the particles but if you were to feel that rock, it would feel a little bit
gritty.
And then clay is very smooth and you can see how those break off into those nice,
flat layers.
So composition,
do we see minerals such as halite, which would be salty.
Quartz, which would be harder than glass. You can take that sample and actually
scratch it on a glass plate and it should scratch the glass because quartz
is harder than glass.
And then we can see things like feldspars, which are pink in color.
So whenever you see seen pinks or u see something that's kinda clearish, shiny almost glassy
you're going to want to test that on
a glass plate to see if you actually have quartz present.
And then softer minerals like halite,
soft, not going to scratch glass. That will be salty.
Another one, which I don't actually have a picture of on here, would
be if there are calcite present. And calcite actually reacts
to acid. So if you drop a little bit of weak hydrochloric acid on the
rock and it starts to
fizz or effervesce quite rapidly, that's going to tell you
that you have calcite present. And then,
do we see fossils,
and this can be fossils of any type. Shells,
plants, animals,
all different
types of fossils can present in your rocks. And a lot of these,
especially the shell
material,
is made up of calcite and will also react to acid.
So our third category are metamorphic rocks we might look at a few of these in lab but
not a lot of these located on the ocean floor.
But I just wanted you to be familiar with
what metamorphic rocks are. So these are, you take
any of the three rock types, igneous, sedimentary, metamorphic. And we change them
by applying heat, pressure or hot fluid. So we put them in a new environment, those
minerals aren't stable
in those new conditions
so they change.
That's what that term meta that
prefix means.
So what we tend to see in these metamorphic rocks are
things called foliation. The minerals start to align themselves
and you can see in those two un-labeled pictures there. Well, you can kind of see these
kind of a horizontal trend to the the pattern in those rocks and
that's the foliation of the minerals.
And then we have banding where the minerals act to break out into different color bands.
And then if we don't have different minerals, we have all the same type of mineral in
the rock, those grains actually gets fused together so instead of having
two grains next to each other cemented to one another like you would have in a
sedimentary rock.
We apply that heat and pressure and that grain boundary
disappears. They actually get
blended together.
And a lot of times those will have a kind of sugary
look to them.
So these are our major rock types: igneous, sedimentary, and metamorphic. We're
going to be focusing mostly on igneous with a
little bit of sedimentary in lab this week. So make sure you're familiar
with identifying those.
So we'll sign off in this video and we'll come back and talk about the
different sediments that we see on the ocean floor and on the actual
coastline of
the continents.
So see you in video two.