Photos from
Structural GeologyPhotos from
Structural Geology
Port
Clinton
- looking at slatey cleavage and bedding, trying to locate the
axes of large scale folds
So is this an
anticline or a syncline? My friend the geoarcheologist Bill
Chadwick for scale.
Slatey
cleavage at an angle to bedding. The angle between slatey
cleavage and bedding is different in different parts of the fold and
can be used to help you locate yourself within large structures.
A fault is simply a crack in the rock
along which the two blocks of rock slide past one another. Slickenlines are mineral growths that are
aligned with the direction of slip along a fault. Studying
slickenlines thus allows us to determine the direction of movement
along a fault (and thus deduce the forces/stresses that caused the
deformation!)
Me standing on
a tilted angular unconformity. Prior to folding during the
Permian Allegheny orogeny that formed the modern Appalachian mountains,
the boundary between the old, eroded surface of the Ordovician
Martinsburg Formation (450 million years old) and the younger, Silurian
age Shawangunk Formation (425 million years old) on which I'm
"standing" would have been horizontal.
There is a nice
bed of conglomerate at the base of the Shawangunk Formation - very
typical of angular unconformities.
Pencil
cleavage in slate at the nose of a fold at the Whale Back (Big Bear
Coal Mine). Slatey cleavage causes the rock to break
perpendicular to bedding in the nose of folds because slatey cleavage
forms perpedicular to the direction of maximum compression (sigma
1). Breaks along both bedding and slatey cleavage form long
pencil-shaped pieces typical of the noses of folds.
In lab, we
wanted to learn to distinguish between the effects of pure strain and
simple shear. We tried using homemade playdough models to measure
the change of angles and lengths of reference axes.
Amane and Lea
prepare their playdough models.
Amane works in Nevada now, and Lea went off to graduate school at the
University of Alaska in Fairbanks to study geophysics. Both of
them were always great at math!
Simple shear
changes angles
between marker axes
After studying
the effects of strain, we made three
dimensional geologic structures (folds, faults, etc.) to see what map
patterns would develop as erosion cut down into the models. Three
dimensional visualization is a strength with geologists.
.
Knowing where
you are on the map is essential for a geologist. We learned to
use high resolution differential GPS (Global Positioning System)
instruments for this purpose.
We have two
Trimble GPS units, so we split up into two groups. Rich here was
given the assignment to teach himself how to use the instrument and
then teach six of his peers. It's important to be able to teach
yourself things!
.
.
Geologists
often work with drillers to get rock samples beneath the surface.
We had an engineering geology consulting company drilling on site to
plan for some new buildings. We visited them several times to
learn how to log the types of rock that come out of the drillhole and,
more germain to structural geology, measure the rock fracture
characteristics. 
.
Drill core is
stored in nice
wooden boxes - a whole lot fancier than what I've been used to working
in some mines.
Colleen really
liked core because she could clearly see the different vein types and
their relative ages. I feel the same way - core is great! 
Colleen was an
education major preparing to teach earth sciences in a high
school. She'll do a great job - she was always very enthusiastic
and learned her lessons well.
Marking the
footage (depth in the hole) on the core box
Measuring the
length of core and degree of fracturing.
The geologist
who showed us
her work was smart and enthusiastic. It is a very nice job!
..
The consulting
engineer explains RQD measurment (a way of quantifying rock fracture
characteristics of the bedrock)
.
More fieldwork
mapping folds in the Appalachian Mountains. We were working near
a very busy road, so everyone's wearing reflector vests (except the
gentlman who had to sit things out in the vans!)
I use a white
board in the field so I can still sketch maps, outcrop drawings, Mohr
circles, etc. It's small enough that it doesn't cause me trouble
unless I'm climbing in a place that I probably shouldn't have students,
so... no problem!
