In the summer of 2009, 13 interns (one funded by a Fellowship Program at Carleton College) spent 8-10 weeks in the Department of Geology and Geophysics. The research projects were supplemented by optional field trips including a day on Lake Superior aboard the Blue Heron Research Vessel; two trips to northern Minnesota to look at the Duluth complex on the north shore and the Proterozoic and Archean rocks exposed in the northeast part of the state; then to southeastern Minnesota to look at karst and cave features. (field trip and other photos).
Again this year, the interns presented posters of their research at the end of the program. Photos from the poster session.
Left to Right. Front row: Chelsea Willett, Julie Greene. Second row: Rebecca Smith, Alissa Morson, Masaru Nobu. Back row: Erik Larson, Nate Ryan, Benjamin Tutolo, Mike Philben, Angela Huston. In action, discussing his poster with our department head is Michael Mournier. Not pictured: Elizabeth Erickson and Will Nachlas.
2009 Interns' Project Descriptions
Elizabeth Erickson, Cornell College
Advisor: Randy Calcote, LRC
Fire history recorded in charcoal in lake sediments can be used to determine different climate conditions and vegetation, as well as fire frequency. The observation of different charcoal morphotypes has been suggested to reflect fuel sources and burn conditions present at the time of fire. My project was to classify and count charcoal from Little Round Lake, located in a sand plain in northwestern Wisconsin, to see if that lake's charcoal and pollen records change consistently with our hypotheses of how lakes with different soil textures and degrees of protection from fire respond to late Holocene climatic changes. Our results, by the end of the program, were consistent with the hypothesis that a lake on very coarse soil surrounded by many lakes will respond less to cooler/wetter conditions of the last 700 years than sites on more mesic soils. In the Limnological Research Center, I learned many skills for lake sediment core descriptions and special studies. These skills include using a DMT CoreScan Colour scanner for image analysis; a Geotek XYZ multisection automated split core logger for high-resolution magnetic susceptibility, natural gamma radiation, and color spectrophotometry; an electronic sediment description form ("barrel sheet"); charcoal counting using the sieve method; the CO2 Coulometer for total inorganic carbon concentration; smear slide analysis; and sampling for pollen processing and 14C radiocarbon dating.
Julie Greene, Macalester College
Advisor: Calvin Alexander
Dye Tracing to Understand Karst Groundwater Flow Systems In Southeastern Minnesota
The purpose of my summer research was to to better define springsheds, flow paths, and flow rates of water through the karst terrain of southeastern Minnesota. Sinkholes, sinking streams, and springs are abundant in southeastern Minnesota, due to its limestone karst terrain. Dye tracing can help to define where groundwater and other inputs move in the subsurface. After a tracer dye is poured into a sinkhole or sinking stream, it flows through the karst conduit system and eventually re-emerges at a spring. By placing packets of dye-absorbing carbon along anticipated flow routes and potential re-emergence spring sites, the path of groundwater flow and re-emergence can be better defined. This is particularly important in southeastern Minnesota in terms of understanding where waste from farms or contaminant spills travel, and in order to identify and protect recharge areas of trout stream source springs.
Over the course of ten weeks, I assisted with locating and mapping new sinkholes, sinking streams and springs, conducted three sets of dye traces, and analyzed the results. Each trace provided useful information about where water flows once it sinks into the subsurface in the areas of study and helped to define which springshed each sink is a part of. However, given the number of sinkholes and sinking streams in southeastern Minnesota, continued dye tracing is necessary in order to further define springshed boundaries and water flow paths.
Angela Huston, University of California-Santa Cruz
Advisor: Katsumi Matsumoto
During my internship with the Biogeochemical Cycles Research Group I worked on development and calibration of the iron code in an ocean based global climate model. Iron is the limiting nutrient in roughly 40% of the world ocean, so it is now included in the Minnesota Earth System Model for Ocean Biogeochemisty (MESMO) as an improvement to the accuracy and reliability of past and future climate constructions. Ocean primary production sequesters atmospheric CO2 as organic carbon, therefore the extent of iron availability and thus the amount of export production may play a role in the transient atmospheric CO2 levels thought to drive paleoclimate change. In MESMO, the surface ocean can be limited by light, mixed layer depth, Phosphorus, Nitrogen, Carbon, Iron, and/or Silicon, where nutrient uptake is based on Michaelis-Menton Kinetics. I worked on the Fortran code that determines the regional distribution of nutrient co-limitation in the grid-based model, meanwhile adjusting various other parameters in experimental runs to ensure proper iron complexation, uptake, and depth distribution.
Erik Larson, Unity College
Advisor: Calvin Alexander
Advances in sinkhole mapping in Houston County, Minnesota, USA: An application of LiDAR data
I used LiDAR (Light Detection and Ranging) data to update the sinkhole map of Houston County, in southeastern MN. LiDAR data allows the user to create a highly accurate (<0.5m vertical error) digital elevation model (DEM) of the Earth's surface. Using ArcGIS 9.3 I took these DEM's and created shaded reliefs from multiple azimuths and several different interval contour lines. With these I then searched through Houston County looking for closed depressions on permissive to sinkhole forming bedrock. In several cases these targets were also areas absent of agriculture, or were in forests. With this new data set (n=347, the existing data set was n=64), I went out and field checked several of the potential sinkholes. What I found was that there are several other features on the land surface that look like sinkholes, such as slumps, cattle rubbing pits, foundations, and push up ponds. Based on field work I discovered several of these slump features and was able to find a new one which helped to confirm that they were not a different type of sinkhole. I discovered that if the slope of the land surface was steep and there are sinkhole looking features, they are in reality most likely slumps. With knowing what these features looked like I was then able to go back through the list of potential sinkholes and refine it so that there were 227 new sinkholes found using the LiDAR data. This increased the sinkhole database for Houston County by over 350% to a total of 291 sinkholes.
This is the first time that LiDAR data has been used in MN in attempt to map sinkholes. With the findings of this work, and the knowledge of what sinkholes look like on the LiDAD imagery other researchers will be able to supplement the existing sinkhole databases for southeastern MN.
Alissa Morson, Carleton College
Advisor: Josh Feinberg
Funded by the Howard Hughes Medical Institute Summer Undergraduate Science Fellowship Program at Carleton College
Distal ash deposits, or tephras, are frequently used to correlate between stratigraphic sections exposed within different sedimentary basins. Generally, tephra layers are characterized using geochemical and geochronologic techniques, and while these techniques have been broadly successful, they are both labor intensive and time consuming. This research project explores the use of magnetic properties as a supplementary technique for the correlation of ash deposits. Four ash layers were sampled from two different sedimentary outcrops within the Mono Lake Basin of California where two of the tephras are known to have originated from the same eruption. A magnetic "fingerprint" will be constructed for each ash layer using a suite of magnetic measurements (e.g., susceptibility/remanence as a function of temperature, hysteresis loops and FORC diagrams). Measurements will be made on both bulk ash samples and a separate of cleaned volcanic glass shards. These magnetic fingerprints will then be used to calculate correlation coefficients between the ashes using the approach of Borchardt et al., 1972. Magnetic tephra correlation, if successful, would represent a comparatively rapid and nondestructive manner for identifying ash layers.
Michael Mounier, Northwestern University
Advisor: Marc Hirschmann
As part of the University of Minnesota Geology REU, I worked with Professor Marc Hirschmann and one of his graduate students, Ben Stanley, on experimental petrology for ten weeks in the summer of 2009. Specifically, we investigated the early development of the Martian atmosphere. Greenhouse gases present in the early atmosphere were probably responsible for raising the surface temperature enough to make the existence of liquid water possible. Such gases can come from a variety of sources, but the vast majority of the early Martian atmosphere is thought to have been degassed from the initial magma ocean and subsequently by volcanoes during the first 500 million years of the planet's existence. By experimentally simulating melt conditions in the upper mantle and crust, we can measure the amount of a greenhouse gas which would have been dissolved in a Martian basaltic melt and then degassed from the recently erupted basalt as it cooled.
The basalt used in these experiments is of the Humphrey composition, based on a sample taken from an actual Martian rock by one of the rovers. This analogue is mixed with silver oxalate, which disassociates upon heating and pressurizing to form carbon dioxide and silver metal. Carbon dioxide is the most commonly invoked greenhouse gas in models of the early Martian atmosphere, although there are other candidates for the main gas responsible for the warm climate. The mixed powder is placed in a cylindrical graphite shell which provides a reducing environment for melting to take place. The Martian mantle is known to be much more reduced than Earth's mantle, so almost all of its carbon will be present as graphite, not as carbonate like on Earth. The graphite is then packed into a platinum capsule with more graphite on top, and the whole apparatus is sealed. All of my experiments were conducted at a pressure of 2 GPa in a piston cylinder press. I varied the durations and temperatures of the experiments to refine the experimental procedure and to determine the relationship between CO2 solubility in the melt and temperature.
Experiments of a longer duration and using a graphite shell with a comparatively large hole were the most successful at obtaining mechanically continuous quenched melts. My early experiments, before a standard procedure was defined, had numerous issues with quench crystals nucleating around the silver deposits and with large graphite inclusions and cracks propagating throughout the glass. These made the samples mechanically weaker and thus difficult to polish to the extremely thin wafers necessary for analysis by Fourier Transform Infrared Spectrometry (FTIR), which allows us to find the weight percentage of CO2 left in the quenched melt after an experiment. However, the above refined techniques and ever more careful capsule preparation helped alleviate most of these problems.
We found that saturation of CO2 in Humphrey basalt in this cell assembly happens at about 0.98 weight percent, since the amount of dissolved CO2 in the quenched melt did not change significantly from this number whether the starting materials had 0, 3.0, or 5.0 weight percent added CO2 as long as temperature was held constant. Any extra CO2 in the starting material most likely diffused into the graphite shell, which is impervious to our current analysis methods.
CO2 solubility in the melt created under reducing conditions increased nearly linearly with increasing temperature, as predicted by theory. This is the opposite of a melt created under oxidizing conditions, where solubility decreases linearly with increasing temperature because the CO2 only has to equilibrate with the basalt melt itself and not also with the graphite as it does when melting takes place under reducing conditions.
Further research on the origins of the Martian greenhouse would study the solubilities of other potential greenhouse gases such as methane and sulfur dioxide in a similar way. Also, we currently lack a quantitative measure of the oxygen fugacity (redox state) of the quenched melt, but plans are in place to begin adding vanadium to the experiments in order to be able to better constrain exactly how oxidizing or reducing conditions are inside the capsule.
Will Nachlas, Virginia Tech
Advisors: Christian Teyssier and Donna Whitney
My research for the 2009 REU internship program was a continuation of a project begun at the U of M last summer and involves investigating the influence of fluids on the deformation of extensional detachment systems during metamorphic core complex exhumation, specifically the Kettle MCC in northeastern Washington and the Bitterroot MCC in western Montana. In order to do this, I prepared thin sections that were collected during 2008 field work for EMP analysis to evaluate compositional variation of white mica produced by fluid-rock interaction. These intra-grain chemical analyses and element maps provide insight into the composition and extent of the fluid reservoir and the rates and mechanisms of fluid flow in extensional shear zones. I was also provided ample time for literature reading to improve my understanding of past and current projects that relate to my research. In addition, I was a field assistant for 3 weeks of field work in WA and MT that involved detailed and precise sample collection and field interpretation. I plan to continue this project over the next school year at my home university and will present a poster with the results my research at GSA this fall. This study is in collaboration with a University of Lausanne PhD student who is measuring stable isotope variation and using numerical modeling to better understand fluid flow in extensional detachments.
Masaru Nobu, Carleton College
Advisor: Calvin Alexander
Microbial ecology of subsurface hypersaline anoxic groundwater in Soudan Mine
Description: 16s rRNA sequences of field samples reveal potential methanogenic archaea, anaerobic sulfide-oxidizing bacteria, and methanotrophic bacteria in the hypersaline groundwater. This ecosystem has no access to sun light and limited access to organic molecules from outer sources. On the other hand, methanogenic archaea can serve as the producer trophic level in this subsurface ecosystem by converting dissolved rock-derived COx into carbon compounds that other microbes can assimilate. Such an ecosystem that survives solely on rock-derived carbon and presence of water can serve as an analogue for extraterrestial life.
Michael Philben, Northwestern University
Advisor: Bill Seyfried
The formation of the Lucky Strike hydrothermal vent fluid was simulated using a hydrothermal gold bag experiment and computer modeling. For the experiment, an evolved seawater solution was mixed with a ground sample of Lucky Strike basalt and heated to 450°C at 500 bars. The fluid was sampled periodically and analyzed for pH, cations, anions, H2 and H2S. The experiment resulted in much higher iron and H2 concentrations than are found at the vent. This suggests that the vent fluid may conductively cool between its formation and its venting, allowing iron species to reequilibrate. As the Lucky Strike vent field is located around the perimeter of an impermeable lava lake, it is likely that the fluid is trapped under the lake and is allowed to cool before venting.
Nate Ryan, Carleton College
Advisosr: Christian Teyssier and Donna Whitney
DEFORMED KYANITE: ORIGIN AND SIGNIFICANCE IN THE RAFT RIVER CORE COMPLEX OF UTAH
RYAN, Nathaniel A.1, WHITNEY, Donna L.2, TEYSSIER, Christian2, GOTTARDI, RaphaëL.3, and SEATON, Nicholas3, (1) Department of Geology, Carleton College, One North College St, Northfield, MN 55057, email@example.com, (2) Geology & Geophysics, University of Minnesota, Minneapolis, MN 55455, (3) Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455
Deformed kyanite-quartz veins in the Miocene detachment fault zone of the Raft River metamorphic core complex, Utah, may provide information about P-T-fluid-deformation conditions prior to or during core complex development. In the field, boudinaged 2-50 cm thick kyanite-quartz veins are hosted in a distinctive muscovite-rich quartzite horizon and can be followed over 4 km along Clear Creek. Deformation of kyanite and quartz is also observed at the microstructural scale: although some kyanite appears undeformed, many crystals are kinked or folded. Samples of the vein consist of primarily quartz (~50%) and kyanite (~45%), but contain significant rutile (~2%) and trace tourmaline and zircon. Most quartz grains are <1mm but some are as large as 3-10mm; most kyanite grains are around 0.25 mm. Kyanite, quartz and rutile were confirmed with electron backscatter diffraction (EBSD) and zircon with EDS analyses.
EBSD analysis of a bent kyanite crystal shows no internal grain boundaries with misorientations of >10°, but a consistent orientation shift along the 0.950 mm crystal producing a cumulative misorientation of 45° between the extremes of the crystal. EBSD analysis of a kinked kyanite displayed seven different orientation bands across the length of the 0.5 mm crystal. Misorentation between the bands ranges from 17° to 50° across the kink band boundaries. A pole figure from the kinked crystal displays a dense uniform point for the <010> pole, but the orientation of the <100>, and <001> axes are smeared, indicating rotation around the <010> pole. Rotation about <010> is consistent with the known easy glide system. Future work will involve determination of the quartz fabric with EBSD and stable oxygen isotope analysis of quartz, kyanite, muscovite, and rutile in the veins to determine the temperature at which these minerals equilibrated during deformation. Results will be compared for consistency with quartz-muscovite stable isotope thermometry from the rest of the section.
Rebecca Smith, University of California-Berkeley
Advisor: Josh Feinberg
Pyroxene and plagioclase crystals of mafic rocks commonly contain inclusions of magnetite and /or hematite, and recent work has shown that their silicate hosts may protect the magnetic particles from alteration during weathering and metamorphism, preserving their remanent magnetism. However, little is known about the environments in which these oxides are most likely to precipitate or the mechanisms by which this diffusion process takes place. The purpose of this study was to experimentally induce the exsolution of magnetite in pyroxene and plagioclase crystals by heating them to high temperatures under varying oxygen fugacities and heating times. Chemical compositions of the samples were measured prior to heating using electron microprobe analysis. Ambient magnetic field conditions were monitored during the cooling process so that the directional accuracy of the inclusions' remanence could be determined. Crystallographic relationships between the orientations of the exsolved magnetite and its host were studied in order to gain a better understanding of how the crystal structures of pyroxene and plagioclase might aid the diffusion process.
Benjamin Tutolo, Penn State University
Advisor: Martin Saar
My summer research was with Dr. Martin Saar, using temperature profiles across Minnesota to determine heat and groundwater flow properties. At first, the work was mostly reading and learning about the methods for using heat as a groundwater tracer and the relation between temperature profiles and geothermal energy. Eventually, I developed two different temperature probes for use in determining temperature profiles. One of the probes was created for determining flow properties using shallow, transient temperature profiles to determine hydraulic flux and hydraulic conductivity of lake sediments. It consists of four Resistance Temperature Devices (RTDs) attached to a piezometer and driven into shallow lake sediments. The other temperature probe which I created was a much larger undertaking and is an excellent tool for determining Minnesota's energy potential. The probe consists of an RTD at the end of an approximately 1180' cable. Temperature profiles obtained using this probe are particularly well suited for the determination of geothermal energy potential because it is able to reach considerably deeper than the extinction point for seasonal variations in temperature (~100 ft). The temperature gradient of the subsurface can then be more accurately extended to the depths necessary for energy to be generated from geothermal heat (which may be up to 5 km in Minnesota). I also used my knowledge for building probes to create a series of buried RTDs which monitored the groundwater flow surrounding a temporary drainage pond.
Results from my research have ranged. The lake sediment temperature probe yielded quality temperature profiles and I was able to use the data to estimate the hydraulic flux into and the hydraulic conductivity of Big Deep Lake in Hackensack, MN. This data has implications for lake and wetland management. Also, the probe will be able to be reused for other studies, which may have similar associated implications. The buried RTDs provided some very interesting data, although we believe there my have been some errors in our burial process. The system functions well, however, and will be reused in the future. Lastly, the results from the deep temperature probe have just started to come in. The development of the probe met with many roadblocks, but it is now a functioning temperature-depth probe and the first profiles have been recorded and analyzed. All of the work that I've done this summer has yielded results for me personally and will be able to be reused by others in the future.
Chelsea Willett, Yale University
Advisor: Larry Edwards
I spent the summer working in the Minnesota Isotope Lab under the direction of Dr. Larry Edwards. My work centered on a stalagmite from the Toca Da Boa Vista cave in northeastern Brazil. My goal was to determine the nature of a color change 107 mm from the top of the stalagmite. I employed three methods of analysis. First, I learned to drill for sub-samples, complete chemistry, and run U and Th fractions on the MC-ICP mass spectrometer. This dating indicated that the stalagmite grew during Heinrich Event 4 (~38-40 thousand years ago), a global climate event caused by ice-rafted debris in the North Atlantic. Second, I drill micro-samples and tested for heavy stable isotopes (C-13 and O-18), which are temperature and rainfall proxies. Finally, I took images on a microscope and counted growth bands in the sample. I concluded that the presence of a lengthy hiatus (300+ years) is unlikely, but that sudden climate change and some hiatus probably did occur where the calcite changes color. I learned an entire set of new skills and hope to return for more research next summer!