Field Exercise I
The following is what is required for Fieldtrip 1. Obviously, as
this is a computer based exercise you will not be able to complete all
that is required. Use common sense and answer as much as you can
(i.e. you cannot measure orientation of strucutr, but you should be able
to get some indicatiuon of rock type from the photos).
All data obtained on this field trip should be detailed in your notebook.
At each stop, make sure to record information about rock type, important
features, the orientations of structures (make sure you write down what
structure you have measured), and sketches illustrating important relationships.
Sketches should be carefully labeled and should include a scale and a directional
arrow or other indication of the viewing direction. You should be
able to return to your notebook in a year or ten years and be able to understand
everything you have written today.
Photos can be accesses in 2 ways
-
linked from an image map (Arroyo
del tajo image map). Arrowheads on the map indicate the approximate
location where the photo was taken, and the direction in which the photo
was taken. The large arrows, in general, indicate a larger field
of view, whereas the smaller arrows indicate a more detailed view of the
outcrop. Click on an arrow to open a photo in a new window.
-
from the list below. .
Arroyo del Tajo (Map)
In addition to the data you would typically put in your notebook,
you should answer the questions relating to each stop. Record bedding
measurements on the appropriate spots on your map. As we work through
our traverse, we would like you to make a schematic cross-section from
the information recorded on your map and your sketches.
The section line drawn on the map is approximately 700m long.
You can assume that the strike of bedding is approximately normal to the
section line. When drawing your schematic cross-section assume flat
topography along the section line.
Stop 1 (Photos a,b,c,d):
Identify the rock types present in this outcrop. Do you see any primary
structures? Measure the orientations of bedding and the fracture
or joint sets. Fractures may intersect, causing blocks of rock to
be easily separated from an exposure. When the exposure is in a mine,
such blocks can be extremely dangerous to workers and machinery.
Could rockfall be a problem in a mine placed in this area? Explain
your answer.
Stop 2 (Photos a,b,c,d,e,f):
What are the rock types? Do you see any primary structures?
Measure the orientations of bedding planes. What’s happening to bedding
here? Draw a sketch in your notebook. Photos 2a-d represent
an E-W traverse across stop 2.
Stop 3 (Photos a,b,c):
Identify lithologies. Do you see any primary structures? Can
they be used as way-up indicators? Are the beds here right-side-up
or overturned? Don’t forget to measure the bedding. Photos
3a and b are seperated by ca. 30 metres.
Stop 4 (Photos a,b,c,d):
What kinds of rocks are here? Do you see any way-up indicators?
Measure bedding!
What kind of structure is this? Does it look different from the wash
than from the top of the hill to the south? Sketch the structure
from the top of the hill to the south looking north. Take the minimum
number of bedding measurements you believe are necessary to complete your
cross section. Do you see any veins here? What is the relationship
between veins and bedding? What kind of fractures might these veins
be filling?
Finally draw a schematic cross-section through the area. A suggested
cross-section line is indicated on the map.
Nameless Arroyo (Photos a,b)
Sketch the structures exposed in this wash. looking toward the south.
There are two types of fault here. What are they? Which is
the youngest? Why?
Do you see repetition of bedding due to faulting? Mark
examples on your drawing.
Based on what you have learned from this outcrop and the features
at Arroyo del Tajo, write a brief (one paragraph) geologic history for
this area.
Geology
353 home page
Structural
Geology at New Mexico Tech
Dept of Earth and Environmental Science,
New
Mexico Tech