Hi guys and welcome to Field Notes. Now
when i first started learning geology
one of the things that confused me the
most was how you even begin to look at a
hunk of rock and determine what happened
to get it there
how would you know that those cracks are
not man made and how can you determine
the line one rock starts and another
rock ends? and what do you do when you
have found it
some of this comes from stratigraphic
hierarchy or how we divide rocks into
units it's much like how we divide
plants and animals into King Philip came
over for good spaghetti kingdom phylum
genus what is it to kingdom phylum class
order family genus species? By doing this
this gives us a starting point as to how
we divide the massive amounts of rocks
on earth so to start this is what the
hierarchy looks like. This hierarchy is
dependent on being able to tell when rock
composition or rock properties have
changed. A lot of the time you will have
an actual list of all the different
rocks that you are going to be expected
to see, like say if you were out mapping,
but you're still going to spend a lot of
time hunched over one rock determining
if it's a limestone or a dolomite
sometimes it is really obvious, and other
times it is way more blurry. here is
a list.
Here's one such lists you see it it's a
list of all of the different rock types
that you will find near Red Lodge
Montana this is the only example i have of it
look at it so dirty so to get started
learning about this hierarchy we need to
know that the base term is formation
like we've seen many times before
geology can be kinda wishy-washy so
there's no hard and fast rule for what
qualifies a new formation and is
dependent on how complex the geology of
the area is in other words what
qualifies as a new formation in Illinois
may not be the same as what qualifies
for a new formation in Montana. So past
the formation ranking
we can get larger and we can get smaller
let's get larger first. If there are two
or more formations that seem to share
some sort of characteristic, either they
are the same kind of rock or they have
the same distinctive fossil within them
we can group them together in a group
and if there are two or more groups that
seem to go together we can group them
into the less common but still a thing
super group. Super groups are not really
common but they do exist so they're a
good thing to keep in mind now going the
opposite way getting smaller from
formations we have members there's no
real standard for separation for a
member basically if you think this hunk
of rock is different enough in the
formation you can have a member and then
finally the last two that I want to
mention are bed and flow. Bed is the
smallest formal unit. Only distinctive beds
are given formal names and really all a
bed does is help you determine where you
are within a member or a formation and
finally a flow is kind of what it sounds
like it is a volcanic event that you can
see in a member or in a formation and much
like members these are only given names
if it is distinctive and widespread. So
while these generic terms are all well
and good
sometimes things just get too blurry and
too complicated to divide anything past
a formation and honestly sometimes you
just look at it and go well there's a
lot of different things going on here
but it's generally the same kind of rock
so you put it into a group a great
example of something that is just too
complex to divide any further is the
Madison limestone group now i have
heard this called the Madison limestone
formation i have heard this called the
medicine limestone supergroup i have
personally been taught that it is the
Madison limestone group. The Madison
limestone is a rock that is found out west it
is found all over the place out west if
you see a humongous hunk of limestone
were probably looking at the Madison
limestone.
So the Madison LS is not only limestone it has
interbedded shale sections it has
sections where it is more fossiliferous
but then it will switch back to this
original limestone so instead of
dividing each of these tiny sections of
shales and tiny sections of different
types of limestone geologists have kind
of grouped this whole thing together into
one big limestone group
ok so now that we've got these basic
terms down how do we use it in active
geology, active geology as opposed to
that sedentary geology
Oh that all reeks of a bad geology pun doesn't it?
The two main ways are going to be in stratigraphic columns and in
mapping stratigraphic columns are basically
vertical column representations of
layers of rocks and really they deserve
their own videos so that's all we're
going to say about that but you'll
notice that they're labeled with the
names of the rocks and that each of
those rocks sections are of varying
thicknesses which corresponds to how
thick the unit actually is when you saw
it again depending on whether you're
doing a snapshot of a huge depth or
simply 10 meters is going to determine
how far you break the units down. If you're
doing a column all the way down to
bedrock then you might just stick to
labeling groups and formations but if
you're looking at one group in
particular you'll probably label members
beds and flows.
Next we use these names as well as the
strat columns for the age-old geology
pastime of mapping now mapping with a
strat column and determining where the
original breaks are in a rock are pretty
similar with typical mapping that you
will do for classes and research you
probably are already going to have a
strat column with all the names of rocks
that you should expect to see but like I
said you're probably going to spend a
decent amount of your time just bending
over a rock determining what it is. Just
like somebody would have when they were
first making the list so that is all
we've got for an introduction of
stratigraphic hierarchy. Something else
that is really helpful when you're
dealing with these is to remember Steno's
Laws i have a whole video whole separate
video on Steno's Laws, it's really quick
be sure to check it out remember that field notes is now
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be sure to leave any questions that you
might have in the comments i try to get
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like the video if you liked it subscribe
if you would like to see more and i will
see you guys next time.  Mr. bug i'm going
to save you
Drew does not believe me that you're in here.
I found a bug. now supergroups are not
super common
