Give a Chick a
Chance (Earthcache)
Welcome to beautiful Chickies
Rock located between the boroughs of Marietta and
Columbia. This 422-acre Lancaster County site is the second largest
regional park and includes Chiques Creek, Donegal Creek, and
selected points of the Susquehanna River. Chickies Rock Park is
replete with colonial and American history, too. The area once had
seven iron furnaces and rolling mills, a canal and a local trolley
line - remnants of which are still visible throughout the
park.
Objective:
1.
The cacher will be
able to demonstrate, through drawing and field sketches,
primary sedimentary features in Chickies metamorphic
rock.
2.
To explain, in
writing, why it is significant that these primary sedimentary
features remain in metamorphic rock.
Background:
This particular location is the type locality of
the Lower (early) Cambrian Chickies Formation. The rock outcroppings that you
will investigate are relatively fresh quartzite and the result of
later undercutting and widening to make way for the Susquehanna
Canal and low-grade bed of the Pennsylvania
Railroad. This
Chickies Quartzite is a metamorphic rock and is very
resistant to erosion.
As a bonus, one of the features you might want
to investigate is an
anticline, or a convex up fold in rock that
resembles an arch like structure with the rock beds (or limbs)
dipping way from the center of the
structure. If you look
closely at the posted coordinates, you will see this
feature. In order to
really appreciate it, you have to step back and look at the big
picture. If you can’t
readily identify it, don’t feel bad, I didn’t catch it the first
time either.
So how did this rock
form? How did it get
here? Good question!
The lithology
(The gross physical
character of a rock or rock formation) of Chickies Rock
originated as sediments or sand deposits of a tidal/near
shore zone of the early Iapetus Ocean. Interfingering with these
sands were lagoonal muds. With the start of closure
marking the end of the Iapetus Ocean, the sands and mud were
buried and altered. The metamorphic processes
(high temperature and pressure deep below the earth) changed
the sands to hard quartzite. These deformations are now found
on dry land.
(They may have been deposited horizontally originally, but
now they can be found dipping at very steep angles up on
end. This is a
matter for another Earthcache.)
In general, Sedimentary rocks are formed by the
deposition of sediment by several processes, either by settling of
sediment particles in a body of water, by chemical precipitation in
water, or by transportation of the particles by water such as
streams and rivers, or by wind. Over time, the sediment eventually
undergoes a conversion from a loose material into a solid rock by
natural processes such as cementation, compaction, desiccation, or
crystallization
Independent
Practice:
Primary Sedimentary Structures in
Some Metamorphic Rocks
I specifically chose this area for an earthcache
because I never saw such a large outcropping of metamorphic rock
which retained so many various sedimentary characteristics. In
lower grade metamorphic rocks, sometimes it is possible to find
primary sedimentary features that can assist a geologist in an
interpretation of the origin of the rock and its original geologic
environment where it was formed. (we have already discussed the
origin of this rock above). Here, at Chickies Rock, it is
very prevalent.
You will need to look for at
least one primary sedimentary features/structure in the metamorphic
rock. Some primary
sedimentary features to look for are:
A)
Rippling –
is a type of feature which
forms on the surface of a bed of sediment. At the time of
formation, the "surface of a bed" is equivalent to the sea floor,
or the bottom of a lake or river. There are undulations of the sediment surface
produced as wind or water moves across sand. Ripples that form in
unidirectional currents (such as in streams or rivers) tend to be
asymmetrical. Crests
of asymmetrical ripples may be straight, sinuous, or lobe-like,
depending on water velocity. Asymmetrical ripples have a steep
slope on the downstream side, and a gentle slope on the upstream
side. Because of this unique geometry, asymmetrical ripples in the
rock record may be used to determine ancient current directions. In
waves or oscillating water, symmetrical ripples
are produced. So why is this
important? This
proves the existence of an ocean or other large body of water
exactly where you will be standing.
B)
Layering - This is the
easiest to see and record. Basically, if you look at
the rock from a profile (cross section view) you will see it
appears to be put together buy several layers of rock, like a
sandwich. This
is important as you can see how the layers of sand were
compressed to form a layer, then compressed again, over and
over until there is a morphed rock, still showing some of the
layers.
C)
Skolithos Tubes – These are
fossil worm burrows, representing traces if life at a time
just before organisms evolved shells and other hard body
parts. These
tubes could not have happened in hard rock which proves that
these rocks came from a softer subcomponent, sandstone, which
allowed these worms to travel around freely and make these
fossilized burrow holes.
D)
Cleavage – The rocks
sometimes separate at parallel planes. This rock seems to have a
tendancy to separate, also another great way to see the
layering.
I would highly recommend finding some pictures
which show examples of the above structures to make it easier on
you, at least until I can figure out how to upload images to the
cache page.
Materials:
To properly complete this cache you should have
with you the following:
1.
Pencil and
eraser
2.
Drawing
paper
3.
This cache
page
4.
Any pictures or
relevant literature review you found to assist you in
sedimentary structure identification
5.
Camera
6.
Clipboard
Assignment:
In order to claim this cache as a find, please
complete the following homework assignment:
1.
Sketch at least one
primary sedimentary feature/structure you found. The more the
better. If you
find two of the same one that is good too. Feel free to wonder around
the area and observe and investigate the features about which
you just learned. Make sure to label clearly
what it is you are drawing and give the drawing a title as
well.
2.
Scan or photograph
(or find some other method you prefer) your field sketch and
include it with your log.
3.
IN
AN E-MAIL TO ME Answer the following: Why is it significant, to
us and to geologists, these metamorphic rocks still retain
such obvious sedimentary features/structures?
4.
Include a picture of
you IN FRONT OF THE "CAVE", your gps
and anything else you find relevant to your
investigations.