David Stoelzel
Educational Research
Final Daft Research Proposal
Statement of purpose:
The purpose of the study is to explain the types of evidence of impact craters and
to elaborate any correlations between three different impact sites. Peer-reviewed
articles along with professional Geologist will be included in this research for
optimal knowledge of impact craters.
Rational:
I believe it is important to study the natural world around us to make this world a
better and safer place to live. When studying impact craters, it is important to
know that these craters were made by celestial objects that crashed into planet
Earth and that there is a good chance it will happen again sometime in the future.
I believe it is extremely important to correlate impact sites because
understanding how and what celestial objects can do to the Earth is vital for
future generations to come. Scientists must research impact craters to be able to
correlate all types of impacts craters to make any viable contributions on celestial
objects and how they affect planet Earth.
Critical questions:
Is there any correlation that impact craters show the same lines of evidence or are
the types of evidence random?
Is the methodology of the data collection accurate or are there lines of error when
collecting?
What do the different types of evidence found at multiple sites tell us about the
magnitude of an impact?
Literacy review:
When looking at science literature, most reputable sources are found in peer
reviewed journal articles. This is where I found the bulk of my resources. Using
SUNY Oswego’s online library, I searched in two different search engines which
included geo ref and science direct. I found 16 peer-reviewed journal articles that
I used in this literacy review. Geo ref had some good articles but was only
available by Iliad. I did find a few peer-reviewed articles in which I ordered
through Iliad that I used in this literature review. I found the bulk of my peerreviewed journal articles through the science direct search engine. Many of the
articles were from science journals including Tectonophysics, Earth and
Planetary Science, and Chemie der Erde. I found so much information that I
couldn’t even use it all. Using key words such as impact crater, Chicxulub,
Vredefort crater and shocked quartz, I found numerous journal articles through
Penfield library. Searching using the key word impact crater produced 1357
results in the geo ref search engine. I found that many of these journal articles
had no link to the full papers so I had to order them from Iliad. When using the
Science direct search engine, I found many viewable articles. I skimmed through
many articles and chose the best ones that pertained to my investigation. I then
narrowed my results using key words such as shocked quartz and locations such
as Vredefort and Chicxulub crater. It is amazing on the amount of information in
the two search engines and both were very helpful in writing this literacy review
on impact craters.
Background information:
The purpose of this review is to understand the processes involved with impacts
on the Earth and to examine the types of evidence found at impact sites so one
can better understand what consequences come with them. During this review, I
will examine what occurs during an impact and the evidence they leave behind. I
will also look at evidence found at three different impact sites along with the
techniques scientists in the field use in determining the evidence. Celestial
objects have been bombarding Earth for millions and millions of years.
Understanding what occurs during impacts on Earth is important to Earth’s
dominating species, Human Beings. The fact is that it’s more than likely another
celestial object will hit the Earth in the future. Impact structures and impact
metamorphism (change in rock chemistry) go hand-in-hand with impact craters.
During the main processes of the initial impact, metamorphism takes place due
to the extreme heats and pressures. Impact metamorphism occurs when meteors
slam into the Earth causing extremely high pressures and temperatures. This is
also known as shock metamorphism because the rates of strain are so high that
this results in passing high speed shock wave creating cataclastic fabrics (changes
in the rocks structure), high-Pressure phases, local melting and the production of
pseudotachylite. Pseudotachylites are dark fine-grained to glassy rocks. Impact
metamorphism usually corresponds with meteor craters and for good reason too.
When put into perspective, imagine a colossal ball of heavy iron rock the size of
New York with speeds of upwards of 17 Km/s crashing into the Earth. This causes
extreme heat and pressure of the rock that it’s almost unimaginable. Bjorrnerud
states, those events such as meteor impacts are considered to be very brief
deformational events (M.G. Bjornerud, 97). Scientists have made breakthroughs
in finding impact craters, mostly with the aid of satellites. One important idea to
remember is that over time impact craters will undergo geologic processes such
as burial by sediment or walls collapsing. So it is important to keep in mind that
impact metamorphism can help identify places on earth were there might have
been impacts in the past. For example, shocked rocks (metamorphic rocks) would
be a good indicator that some sort of impact metamorphism has taken place.
Impact processes and characteristics of material are important basic
understandings of impact structures and metamorphism. Examining these ideas
and methods will help better understand the processes and effects of impact
structures on a more geological scale.
According to Grieves, there are three main impact processes that are recognized
by (Grieve, 2006) contact/compressive, excavation, and modification which are
on impact. The initial stage is the impact but then a huge amount of other
materials play a role as the process progresses (G.L.H McCall, 2008). The initial
projectile creates a shock wave in which kinetic energy is transferred. The rock
then deforms on contact and the shock wave passes through the body of rock,
deforming it by compression. So at that very second the meteor has only
penetrated slightly. The shock wave is then reflected back as a rarefaction wave
and melting then occurs. As the wave moves through the body at supersonic
speeds the rocks are driven downward and then outward. Discharges of materials
of the rocks are thrown into the air and this creates the transient crater. This is
considered by Grieve to be the end of the contact/compression stage and the
beginning of the excavation stage. What is left after the contact/compression
stage is a dome shaped crater. This is because of the lining of the interior walls
have collapsed inward which creates an interior breccia lens, of allochthonous
rocks, made up of shocked, unshocked, melted and unmelted material (McCann
2008). During the excavation stage the melts are occurring in the central part of
the crater. As time passes the transient cavity is formed and the end of the
excavation stage has taken place. The last process is the modification stage.
Modification is the result of the passing of the rarefaction wave and release of
ambient pressure. Grieves tells that not all pressure and volume work is
recovered on the release of the rarefaction wave process, so any leftover work is
manifested as wasted heat (Grieve, 2006). The ejecta blanket has now fallen over
and lay on the side of the crater. The final crater contains melted material, uplift
rim and breccias lenses. All of this is the direct result from the meteor impact and
creates these dome shapes into the target body of rock.
Types of evidence:
The first lines of evidence of impacts on Earth are impact breccias. Impact
breccias are evidence that indicates that there once was some sort of impact,
usually by an asteroid or comet. Breccias are rock composed of angular fragments
of minerals or rocks in a matrix. Impact breccias form during the process of
impact cratering. Breccias of this type may be present on or underneath the floor
of the crater, in the rim, or in the ejecta expelled beyond the crater. Monomictic
and polymictic breccias are two of the most well known macroscopic features in
impact structures. There are many phases in the cratering process. One is when
they can be formed in the rock mass flow behind the shock and in the front
starting from the impact point, during the excavation and the formation of the
transient crater (Dressler, Sharpton, 1997). Another is during the ejection of the
excavated material, on landing of the ejecta and their emplacement. Melosh tells
that mixing with local material and during the collapse of the transient cavity in
the modification stage wrap up the many phases (Melosh, 1989). In this process,
breccias may incorporate earlier formed breccias, which leads to breccias-withinbreccias and even to multiple breccia generations mainly unknown from other
geological proccesses. After the intial impact and from the rebound of the central
crater basement the crater walls will collapse inward. This is the main proccess
that creates these impact breccias. Dressler and Sharpton looked at the Slate
island impact crater in Canada. This crater is 50,000 years old with a diameter of
1.2Km. This crater is one of the most studied inpact craters in the world. So much
is understood about impact craters because of this famous sight. These craters
are filled in by breccias and by partial melts (Dressler, Sharpton, 1997).
Polymictic clastic matrix breccias are the most common at the Slate island
craters. These are irregular shaped dikes that have sharp contacts with the host
rock. At Slate island, the exposers of breccia are anywhere from 10-30 meters in
width(Dressler, Sharpton, 1997). What is intreresting at the Slate sight is that
there has been up to seven different target rock fragment types in a single breccia
occurence. This shows use that there has been a mixing of the components
around the crater. Whats great about most impact crater sights is that we can
observe shock metamorphic features in breccias. This tells use a little about the
shock pressures that has happened at a specific crater. According to Frenth and
Koeberl, the understanding of breccias is important to the study of impact
structures and impact metamorphism for the fact that structural interpitations
can be made such as how many impacts were there at a sight or how much
erosion has taken place(B.M. French, Koeberl 2010). Breccias are found at most
impact strucures and provide evidence of some sort of impact. The study of
breccias continue to be a very important tool into understanding inpact
structures and impact metamorphism.
Another type of evidence of impacts on Earth are Pseudotachylites.
Pseudotachylites are dark fine-grained to glassy rocks normally formed by
frictional heating along a fault during seismic deformation (E.C. Ferre, M.S.
Zechmeister, J.W. Geissman, N. Mathanasekaran, and K. Kocak 2005). It can
also be formed by impact metamorphism. Many Geologists believe that
pseudotachylites are only produced by tectonic friction. Not all occurrences of
pseudotachylite are narrow veins, as one would expect if they were directly
produced by friction. Large pockets with angular and rounded inclusions of
country rock on scales up to meters wide have been found in impact structures.
Occurrences of thick veins, in some cases up to 500 m wide and 11 km long, of
pseudotachylite, have been described at the Sudbury impact structure (Spray and
Thompson 1995). As (Melosh, 1995) describes, there are three stages of impact
crater formation which are contact and compression, excavation, and collapse.
Contact and compression, the stage in which the kinetic energy of the
meteor/asteroid is changed into heat and kinetic energy, is unrelated to shear
zone formation so long as the impact speed exceeds a few km/sec (R.L. Gibson,
W.U. Reimold, T. Wallmach, 1997). The excavation stage includes the shock wave
and the opening of the crater. During this stage, extremely high strain rates
occur. Strong vibrations enhance the pseudotachylite formation.
Another important line of evidence of impact craters is shocked quartz. Shocked
quartz happens when deformation occurs to existing quartz minerals. Under
extreme pressure and temperature, the quartz gets deformed and its crystalline
structure changes. Shocked quartz goes hand in hand with impact craters for the
fact that impacts are only one of two known ways of making shocked quartz.
Trepmann states, that the other way is nuclear bombs. It takes so much heat and
pressure to deform quartz that impacts from celestial bodies are the only things
that produce that kind of heat and pressures (C.A. Trepmann). Finding shocked
quartz is a key indicator that some sort of impact has occurred.
Vredefort Dome, Southern Africa:
A good example of pseudotachylites is the Vredefort dome in southern Africa. It
is a 45k/m diameter core of granitic rock. The dome is comprised of green schist
facies all the way to granulite facies rocks. Facies are a body of rock with specified
characteristics. These facies are of mid to high temperature and pressure
metamorphic rocks. The interesting discovery about this dome is that the grades
increase to the center of the zone (R.L. Gibson, W.U. Reimold, T. Wallmach,
1997). At the Vredefort dome, pseudotachylite veins have been found in most
lithologies throughout the rock outcrops. Veins and dikes range from a few
meters to the kilometer scale. The thickness of the pseudotachylite does not go
over a few centimeters (R.L. Gibson, W.U. Reimold, T. Wallmach, 1997). It is fair
to say that the most likely cause of the pseudotachylite is from an impact of some
sort. Magnetic measurements were also taken at the Vredefort dome to check for
magnetic anomalies due to an impact crater. The magnetic anomalies have been
long disputed because of the stratigraphy of the dome. B. Ivanov disputes the
findings at the Vredefort dome because of the crust surrounding the dome (B.
Ivanov, 2007). Modeling of the magnetic profiles across the transition zone
shows those vertical layers of magnetized rock can best account for the magnetic
variations so there is dispute of this evidence at the dome. Melt rocks are another
line of evidence at the Vredefort dome. Melt rocks are caused by the
metamorphism of the surrounding target rocks after impact has occurred.
According to W.U Riemold and R.L. Gibson, the Vredefort impact crater is
famous for its granophyeric metamorphic rock (W.U. Teimold, R.L. Gibson,
2005). Granophyric rock is rock that has a certain texture due to an impact of
some sort. This texture is found all over the Vredefort dome area. The Vredefort
Dome is not the only place geologist find pseudotachylite and melt rocks.
Pseudotachylites and melt rocks are formed from both impact metamorphism
and frictional tectonics. This is proven from a number of cater sites throughout
the world and continues to be one line of evidence of impacts on the Earth.
Lake Hummeln, Southeast Sweden:
There are still places on Earth where scientists are at odds whether or not certain
locations are impact sights. One such place is Lake Hummeln in southeast
Sweden. Lake Hummeln contains an approximately 1.2-km-wide sub circular
depression. Although different suggestions of this depression have been debated,
the impact theory has presented the best explanation. The geological setting of
this area consists of crystalline bedrock and is covered by Cambro–Ordovician
aged sediments (J. Ormo, E. Sturkell, G. Blomqvist, R. Tornberg, 1999).
Geophysical methods were used at this site such as magnetometry.
Magnetometry is an instrument used for measuring the magnitude and direction
of the magnetic field. This technique was used at the Lake Hummeln site. What
was found was that the fractured region below the proposed crater had values
that where very similar to impact breccias. The values were 100 times lower than
the surrounding rock meaning that the samples showed very low remnant to
induced magnetization. The main cause of deviations in the response curve,
generated by the bodies in the magnetic models, are edges and inclined surfaces
(J. Ormo, E. Sturkell, G. Blomqvist, R. Tornberg, 1999). Special 2.5D interactive
software GMM (Gravity and Magnetic Modeling) by Geo-Vista AB was used.
What this software did was map a gradient map of the magnetic field in the area.
Many other geophysical techniques were used at this site including gravimetry,
resistivity and fissure frequency analysis. What was found a low resistivity zone
which corresponds with the area of higher fissure frequency. The conclusions
made from this data provide great evidence that there was an impact at some
point in Lake Hummeln’s history. The geophysical investigations made it possible
to reconstruct the original shape of the crater and in turn can be used to compare
with other impact craters. These techniques are used on many other impact
sights. For example, more giant impact structures such as the Chicxulub and
Vredefort craters. These geophysical techniques give use insight into important
structural features of impact zones. They can tell how big a particular site used to
be and erosional levels. Geophysical techniques are important tools for geologists
in determining features at a given site.
Chicxulub crater:
The chicxulub crater is believed to be the result of an asteroid impact which is
estimated between 10 to 20 kilometers in width. The crater is located in the
northwest coastline of the Yucatan peninsula in Mexico. This impact has been
long discussed as a main reason for the extinction of the dinosaurs. At the time of
impact (Around 65 million years) the site was flooded by the shallow sea.
Recovered lithologies in breccias near the crater propose a basement composed
of schist, gneisses, amphibolite, and granitoids (D.A Kring, 2004). A lithology is a
rock unit is a description of its physical characteristics visible at outcrop Much
like other impact sites the chicxulub crater has breccias and large amounts of
impact melts. Since the crater sight is mostly covered in shallow sea water
geologist had to gather their evidence in other ways. Drill samples were taken
from the sight. What was found was Bunte-type polymict breccias has been
reported in wells beyond the rim of the crater (Urrutia Fucugauchi et al., 1996;
Sharpton et al., 1996, 1999; Rebolledo,Vieyra et al., 2000). The Bunte-type
breccia is dominated by carbonate and anhydrite materials, but contains a small
fraction (~5%) of silicate material (Sharpton, 1999). Impact melts have been
found around 50 kilometers from the center of the crater. Several melt dikes have
also been discovered in which it crosscuts the cretaceous aged rocks that underlie
the impact melt and impact melt-bearing breccias (Dressler, 2003). Shocked
quartz is well-known at the chicxulub impact crater which is direct result of the
impact. Extremely high heat and pressures changes the physical and
mineralogical characteristics of the silica by impact or shock metamorphism.
Shocked Quartz grains are formed at the release of the compression stage. The
chicxulub crater is one of the biggest craters in the world and has been studied
repeatedly. Many of the techniques I’ve mentioned earlier have been used in
determining what metamorphic affects have taken place, how big was the initial
impact and the effect on the planet 65 million years ago. The question is still
argued today whether or not the chicxulub impact was the cause of the end
cretaceous mass extinction. With its enormous size I would say it at least played
some kind of role.
Conclusion:
Much of the literature I looked at came from experts in their respected fields of
science. Being a Geologist myself, I understand the dedication and time put into
working in the field. Some of these scientists spend decades putting together
what occurred at some of these locations. So I tend to accept what these scientists
say in their articles. I have also come across opposing views during this literature
review that argue the methodological methods used. I also understand that
sometimes evidence found in the field or the techniques used in the field can be
wrong or disputed because of human error or the techniques used. Impact craters
are interesting to study for the fact that it is fairly a new subject of discussion as is
with the Science of Geology. Much is left to be discovered about impact craters. I
learned through the literacy review that there are many different types of
evidence of impact craters. There are also many types of methods and techniques
to finding evidence of impact craters. There are many other issues of impact
craters that can be studied in the future such as the angle of impact and how that
affects the surrounding environment or looking at how the size of the object
affects the evidence of impact craters. This is an exciting science that will surely
be studied in the future.
Theoretical framework:
I chose a phenomenological approach to my research. For the sake of this study,
the phenomenological approach attempts to understand the meaning of events
and connections. My research is attempting to understand certain events and
connect them together using multiple perspectives from scientists, so I believe
this is the perfect framework
Data Collection Plan:
Typical data collection for geologic events usually has some sort of collection of
data from the event site. Geologists tend to like to go and do their own
investigating and come up with their own conclusions. For the sake of my
research, I will go the other route and interview experts on each crater site. All
three of the impact sites have been studied much in the past. This gives me a
chance to compact a lot of data by interviewing the experts and coming up with
my own conclusions.
My detailed plan consists of interviewing two experts from each of the three
impact sites. The data I will collect will be tape-recorded interviews along with a
field notebook for reflective observations. The first site I will collect data is from
the Vredefort crater in South Africa. I will go to this site for one week to observe
the actual impact site and to conduct my interviews with two different experts. I
will interview one expert for two days and the other for two days. The first
interview will be held at the choice of the interviewee. The second interview will
occur at the actual impact site. The next site I will visit is Lake Hummeln impact
site in Southeast Sweden. Again, I will stay for one week to interview two experts
on the Lake Hummeln impact site. Again, I will conduct the first interview at the
choice of the interviewee. The second will be conducted at the lake Hummeln
crater site. The last impact site I will travel too is the world famous Chicxulub site
in northwest coastline of the Yucatan peninsula in Mexico. I will follow the same
interview strategy as with the other two impact sites.
The strategy I enlisted above is best for my research because interviewing experts
for each site will give me the best direct information. With all the information
that I receive from the experts, I will be able to make the best possible inferences
for my research on impact craters and their evidence left behind.
Data Analysis strategy:
The data analysis for this proposal consists of two main steps. The first step is
data analysis while in the field analysis. The second step is post data analysis. The
first steps of analysis while in the field consist of multiple strategies. First, I will
bring my developed analytical questions so that I will stay focused to the data
collection which will help me stay focused while in the field. I will also keep a
field notebook for observer’s comments. This will help me record important
insights that come to me. It will also help me critically think about what I see and
can help me in my post instruction. I will also use pictures and record video while
in the field. This will assist me in visualizing my surroundings for data analysis in
the future. Step two consists of using the appropriate computer program for post
analysis. Using my field notebook, I will develop coding categories that will
correlate with my data collection. I will interpret all important writings,
published studies, interviews and speculations during my post analysis.
References:
R.L. Gibson, W.U. Reimold, T. Wallmach. Origin of pseudotachylite in the lower
Witwatersrand supergroup, Vredefort dome (South Africa). Tectonophysics
283(1997) 241-262
C.A. Trepmann, Shock effects in quartz: Compression versus shear deformation.
Earth and Planetary Science Letters 267 (2008) 322–332)
B.O. Dressler, V.L. Sharpton. Breccia formation at a complex impact crater: Slate
islands, Lake Superior, Ontario, Canada. Tectonophysics 275(1997) 285-311
H. Henkel, W.U. Reimold. Intergraded geophysical modeling of a giant, complex
impact structure: anatomy of the Vredefort structure, South Africa.
Tectnophysics287 (1998)1-20
W.U. Teimold, R.L. Gibson. 2005 The melt rocks of the Vredefort impact
structure – Vredefort Granophyre and pseudotachylitic breccias: Implications for
impact cratering and the evolution of the Witwatersrand Basin. 2005. Chemie der
Erde 66 (2006) 1–35
J.Ormo, E. Sturkell, G. Blomquist, R. Tornberg. Mutually constrained
geophysical data for the evaluation of a proposed impact structure: Lake
Hunneln, Sweden.Tectonophysics(1999)155-177
(B. Ivanov, Magnetic imaging of the Vredefort impact crater, South Africa, 2007).
Earth and Planetary Science Letters 273 (2008) 397–399
Y.A. Popov, V.P. Pimenov, L.A. Pevzner, R.A. Romushkeuch, E. Popov.
Geothermal characteristics of the Vorotilovo deep borehole drilled into the
Puchezh-Katunk impact structure. Tectonophysics 291(1998) 205-223
N. Nakamaro, Y. Iyeda. Magnetic properties of Paleointensity of pseudotachylites
from the Sudbury structure. Tectonophysics 402(2005) 141-152
M.G. Bjornerud. Superimposed deformations in seconds: breccias from the
impact structure at Kentland, Indiana. Tectonophysiccs 290(1998) 259-269
B.M. French, C. Koeberl. The convincing identification of terrestrial meteorite
impact structures. Earth-Science reviews 98(2010) 123-170
D. Kring. Hypervelocity collisions into continental crust composed of sediments
and an underlying crystalline basement. Chemie Der Erde 65(2005) 1-46
McCall, G.J.H., 2008. Icy spy. Geoscientist 18 (1), 5.
J.G. Spray. Pseudotachylite controversy. Geology 23, 1119-1122
H.J. Melosh. Impact cratering: A geologic process. Oxford university press (1998)
245pp
D.A. Kring / Chemie der Erde 65 (2005)
Appendix:
Definition of terms:
Impact craters- Any depression, natural or manmade, resulting from the high
velocity impact of a projectile with a larger body.
Celestial objects-A natural object which is located outside of Earth's atmosphere,
such as an asteroid.
Chicxulub crater- Crater sight located in the northwest coastline of the Yucatan
peninsula in Mexico.
Vredefort crater-Crater sight in southern Africa.
Hummeln crater-A proposed crater sight that contains an approximately 1.2-kmwide sub circular depression in Sweden.
Impact metamorphism- is the solid-state recrystallization of pre-existing rocks
due to changes in physical and chemical conditions, primarily heat, pressure, and
the introduction of chemically active fluids.
Impact breccias- is a rock composed of angular fragments of minerals or rocks in
a matrix
Pseudotachylites- are dark fine-grained to glassy rocks normally formed by
frictional heating along a fault during seismic deformation.
Shocked quartz- deformation to existing quartz minerals.
Consent form:
I, David Stoelzel am conduction a research project on Impact Craters and their
evidence. I am requesting your participation in this study due to your expert
knowledge in the subject. There will be two interviews on the days that fit your
schedule. The first interview will be formal in that will we sit down and simply
talk. The second interview will occur at the impact crater and will be more
informal. Confidentiality of information will be protected. You will be credited
will all provided information unless unwanted.
Participation in the research will be highly appreciated. Your vast knowledge of
Geology and impact craters is the reason I chose you and I will owe you a life time
of knowledge. You also have the right to not participate in this research study. I
understand that your time is precious and schedules change. Should you have any
questions feel free to call me anytime at (555-555-5555). Thank you for your time
and knowledge.
Authorization: I_________________________, have read and agree to the
above statement and agree to participate in the described research project.
Date: Signature: