(Opening Music)
Welcome back geology fans! Today we
imagine you have completed your
background investigations and gotten
your gear together for your trip, and now
you've touched down on your site of
investigation. What should be your next
steps and how should you conduct
yourself to ensure safety and good data
collection? There is no set list of steps
to follow as each location may have to
be approached in novel ways, but you
should have your general strategy mapped
out before arriving in the field. Be
prepared. Your strategy may or may not
involve some of the concepts we will
discuss here, but these ideas are valid
in most cases. I previously suggested
viewing the HBO episode of From the Earth
to the Moon on the Apollo 15 mission
called "Galileo Was Right". A lot of what
I'm going to talk about today is covered
in that episode, and that is no mere
coincidence nor plagiarism. Lee Silver
was the Caltech geologist featured in
that episode, but it should be no
surprise that there were a team of
geologists in the field training the
astronauts, and anyone who knows anything
about the geology of the Apollo missions
knows the name Bill Muehlberger; a
geologist I first encountered as an
undergraduate student at U.T. Austin.
He was my most influential field geology
instructor there, and I hear Bill in that
film telling his students to get to the
high ground to get the big picture first,
to note the usual suite of rocks, but to
keep an eye out for the unusual one.
Always keep an eye on the context of
each individual rock, and be sure your
notes are so detailed that some other
geologists could read it and know
exactly what you meant, for one day you
will be that other geologists wondering
what your vague scribblings meant 30
years ago. Let's start with what you put
in your field notebook. Details, details;
yes you need to note the details. This
includes where you are both physically
and emotionally. Start each mission with
a general header of location and goals,
but each day of the mission should
probably start on a new page with the
date mission goal for that day,
the weather, and how you're feeling. Are
you full of energy and ready to go, or
are you sick, or even worse hungover or
otherwise affected physically or
emotionally? You are the filter through
which the data comes, so, geologist, know
thyself. Be suspicious of data taken
while feeling sick or rundown. Focus on
data from the good days, which you'll
have more of if you've gotten in shape
for your excursions in the weeks before
you get out to your study site. A general
rule is to get the big picture first, and
then work down into the details. In the
old days, this usually meant climbing up
to the highest point to get a good view.
But today we have airplanes and
satellites and Google Earth, which you
should have already looked at before
getting to your field site. So you may be
able to skip hiking up to the highest
point if you feel you have that scale of
the big picture down already. These days
I use drones to get a good overview of a
field location, and to do some other
types of mapping like high-resolution 2d
images, so-so vegetation maps, digital
elevation maps (which we call DEMs), and 3d
maps of the site. The principle of
getting the big picture first holds at
many scales. So, for example, if you
were approaching a rock outcrop, you want
to start by looking at it from a
distance in its context, then moving in
closer to get details. This means if
you're at a road outcrop, you might have
to start out standing on the opposite
side of the road and maybe ask yourself
the following questions, which you could
also ask yourself during your pre field
preparation research. Is there one kind
of rock or many kinds, and do the various
rock structures look as if they continue,
or once continued beyond the edges of
the visible rock outcrop, or do they end
suddenly within the outcrop. And if they
end suddenly; against what? Can you tell
if the rock is truncated by a fault, an
unconformity, an intrusive cross-cutting
feature? Turn your attention to the edges
of the outcrop. Does it end suddenly or
grade into the soil or rock debris, and
do you think that you can see why the
outcrop ends where it does?
Do you think you can tell what kind of
rock it is from the fact that
sedimentary rocks are usually layered
and tabular, while metamorphic and
igneous crystalline rocks have a more
massive or jointed appearance. Sketch the
various rock bodies you see and note how
they control the shape of the outcrop
itself. Try to discern both from a
distance and as you get closer the
nature of the boundaries between the
different rock units. Are the contacts
gradational or sharp, and do they cut
across any prominent patterning or grain
in rock on either side of the boundary?
Does the color or any other prominent
feature change in either of the rocks
approaching the boundary? If the rocks
are layered, describe layer thickness,
lateral continuity, internal structure
that is or is not parallel to the
bounding surfaces (the bounding surfaces
means the main bedding planes of the
layers).
Remember that distinguishing bounding
surfaces from cross bed surfaces is very
important when you measure cross bedded
sediments. Keep asking these questions
and see if any of your answers change as
you approach the outcrop. What was the
color or any other feature from far away
and as you approach? When finally up
against the rock outcrop, collect samples
from the various rock bodies and any
other variable parts. Sometimes you can
just scoop some up or pluck it by hand,
but this is often where the hammer comes
in. Listen to your hammer hitting the
rock. Does the rock crumble or crack? Does
the hammer hit with a thud of softer
rock like shale, or ring like a
metamorphic or igneous crystalline rock.
I often say I don't do geology from
pictures as it robs me of four of my
five senses. Don't forget to smell that
rock for sulfur or petroleum, taste it
for salts, or see if that clay or bone
sticks to your tongue. Feel its texture
and weight. Experience your field site in
every way you can, and pay attention to
what you're sensing, be it the typical or
the unusual. And while listening to the
sound your hammer makes on the rock, go
ahead and break it. Geologists are one of
the leading causes of mechanical
weathering. The outside of a rock is it's
weathering rind and you
to crack it open to see it's fresh
original face. Rocks are
like children; they lie, so we beat them,
and then they tell the truth. Use that
hand lens to get details on both
weathered and fresh faces. Try some
hydrochloric acid to test for
effervescence, or even put some water on
to clean the rock surface ,or see how
well the rock absorbs the water. Start
noting all you can, or at least all you
think is important. This could be overall
rock weathering or mineral alteration,
porosity, grain size, and all those other
primary and secondary sedimentary
features we mentioned earlier in this
series, crystal size, any fabric (that is
preferred direction to the crystals or
grains). And, if you can tell mineralogy,
try to estimate percent volume of the
various minerals in the rock. Give the
best guess to the name of the rock
getting as specific as possible. Are
there any signs of deformation in the
rock at all? Maybe you saw some folding
from a distance, or maybe you can only
see signs of deformation as you get in
closer. Measure faults and joints.
Specifically note major faults and
principal fault and joint directions.
Minor faults are also noted, as with
their spacing an individual throw (throw
being the distance the rocks on either
side of the fault moved relative to each
other). If you find a nice sample you want
to collect, sample bags come in handy.
While collecting samples, don't get too
focused on the odd outliers. Collecting
samples of the typical can help you back
at camp or in the less inspirational
office as well. Getting a good idea of
the typical lets you better see the
unusual. You'll get really good at
noticing the unusual rock and often
calculate the weight / distance to base /
energy / and water left, to tell if you're
gonna haul it back or just take pictures.
And if you take pictures, taking notes
about these pictures so you can properly
identify them later. Rocks can be really
heavy so don't misjudge and carry
something a kilometer or more that
you're just gonna drop later in the day,
thus wasting energy.
Since most rocks you'll be interested in
will be too large
to carry, break-off a smaller piece, or
draw and take pictures with notes of
location, direction you are facing, and
details, and context. I am no artist,
that's for sure,
but practice sitting down a distance
from a rock outcrop and drawing in every
detail you can. You might be surprised.
And if you're not the fossil whisperer,
as I am NOT, nor most of my colleagues,
draw or take a picture and send that to
your paleontologist buddy to identify
for you, or refer to a handy reference
book. Once all these issues have been
noted, and you're still out in the field,
this is a good point to pause and go
over all your notes so far and congeal
your ideas. Now you may have a good idea
of what more specific observations and
notes you may want to take, also keeping
in mind how much more ground you want to
cover and the time that you have. So
let's say you've wrapped up at your
first rock exposure and are ready to set
off of your next exposure. Don't consider
a path to the next goal useless ground.
You shouldn't have to come back to an
area you've already covered, so if you
see something of interest or something
you can measure as you're walking
between point A and point B, put it down
in your book and map it while you're
there. Be consistent in how you measure,
don't drop your guard, and be confident
as well. Do not be shy to ink your map in
the field as it is the best place to do
so. The hotel or tent that night is
seriously inferior, though that's orders
of magnitude better than back in the
office a week later. Again, be a confident
geologist. Never say "I can't" but "I will
try" or "I can't yet". After all, you're
smart and determined enough to be
watching this series, so please don't be
hesitant to commit to your mapping in
the field. It is the best place to do it,
and don't expect any angels of
enlightenment to come down on you later.
But to put another angle on
enlightenment, we're going to look at how
to use what is known as a Jacob's Staff,
and measuring rock sections in
constructing stratigraphic columns, when
we come back next time, here on Earth
Explorations!
