LAB #1 : Strikes, Dips, Bruntons, Thicknesses, and 'Wall Outcrops'
GEO 309/549 - Spring 2008
Feb. 5, Due: at the START of LAB, Feb. 12
In this lab, you will use a Brunton compass to determine strikes and dips. You will also
look at a few mock outcrops in order to become familiar with measuring dips and thicknesses
and interpreting some basic geometrical relationships - structures - in rocks.
The compasses don’t work indoors, so one part of the lab (determining azimuths) is to be
done outdoors. It will be dark during the evening lab, so you will have to share flashlights.
Make sure to keep metal flashlights away from the compasses while you're trying to read
azimuths!
You will divide into teams of 2 people. Each team will have a Brunton compass. Make
certain that you follow closely the instructions for its use and verify that the magnetic declination
is set properly (these Bruntons are sometimes used in research far from Stony Brook!).
To keep any particular location from becoming too crowded, you should be prepared to
do this lab out of order.
Record your results. Later, transcribe them IN ORDER, NEATLY and CLEARLY
before they are handed in. Each team member should hand in her/his own lab report.
We start in the lab room itself, working in teams (but keep and hand in your own records).....
1.
Measure the strikes and dips of four sloped surfaces (labelled A thru D) on desks in the lab.
Record your results, giving strikes in both azimuthal and quadrantal forms.
2.
In the lab, there are two vertical cardboard surfaces labelled E1 and E2. These are the
upper and lower boundaries of a vertical 'bed'. Measure the thickness of the bed.
3.
In the lab, there are also two inclined cardboard surfaces (F1 and F2). These are the upper
and lower boundaries of an inclined 'bed'.
a) Measure the thickness of the 'bed' directly (using only your ruler). Indicate on a neat
drawing the measurement you have made.
b) Without lifting your ruler off the table, determine the thickness of the bed. To do
this, you will also need to use your calculator and your Brunton (which you may lift off
the table). Neatly draw the 'outcrop' and indicate any measurements you have made.
Also, show your calculations.
4.
There are two inclined surfaces, G1 and G2. These represent the same bed, cropping out on
two limbs of a fold.
a) Take the strikes and dips.
b) Describe this fold, including whether or not it is plunging (and if so, roughly in which
direction).
5.
There are tape marks extending 30 m down the hallway on the 3rd floor. Find a
comfortable, natural stepping pace. Walk between 25 and 30 meters, and divide your
distance by the number of paces (or, if you prefer, steps). Repeat the experiment a few
times and average your result. Show your measurements and calculations.
The next question requires going outdoors....
6.
Starting at the corner of the retaining wall outside and to the right of the fire exit near the
lab, proceed about 18 meters toward azimuth 063°. This is stop 1.
Then, turn toward azimuth 000°, and walk another 38 m. This is stop 2.
Take a bearing of 275° and walk 38 m to stop 3.
Finally, take a bearing of 180° and walk 20 m.
a) Where are you? Draw a map of the 10 m radius around your location. Label it carefully,
indicating any landmarks.
b) What is the bearing and distance to the nearest lamppost?
Now, we look at 'outcrops' indoors.....
The azimuths will be impossible to determine using a Brunton compass (too much metal
and electrical wiring). For the purposes of this problem, assume that the wall connecting
the two 'outcrops' runs exactly N-S, with outcrop 2 (nearer the exit) to the north.
7.
Go to 'outcrop 1', located by the freight elevator near room 115.
NOTE THAT ‘NORTH’ AND ‘SOUTH’ ARE SHOWN ON THE WALL
a)
Measure the two apparent dips. Also express each as a Bearing and Plunge.
b)
What do you think the true dip is?
c)
What do you think the strike is?
d)
Why are (b) and (c) relatively easy in this case?
8.
Go to 'outcrop 2', located down the short hall from 'outcrop 1'.
a)
Measure the two apparent dips. Also express each as a Bearing and Plunge.
b)
Think about what the the true dip is.
Can you tell immediately an angle it must be greater than?
c)
Think about the strike.
Can you tell immediately whether it is closer to N-S or E-W? Explain
d)
Get down on the floor with a clipboard and (with someone’s help) measure the dip
exactly. Also measure the strike, but don’t worry if the answer makes no sense
beacuse of the measurement being indoors.
e)
Why is this problem more complicated than at outcrop 1? Explain.