During Spring 2007 the Geochemistry of Natural waters class conducted 4 projects. The abstracts, papers and posters are given below;

1: Analysis of white mica from the highly-weathered, Morton Gneiss near Redwood Falls, MN. William Mitchell, Zack McGuire, Michael Barrett and Jack Gibbons and Bereket Haileab,

ABSTRACT
An ancient saprolite was developed on the Precambrian Morton Gneiss in the Minnesota
River valley of southwestern Minnesota. This saprolite, containing the clay minerals
kaolinite and sericite, X-ray diffractometry (XRD), scanning electron microscopy (SEM),
electron dispersion spectroscopy (EDS), wavelength dispersion spectroscopy (WDS),
electron microprobe, and Fourier-transform infrared spectroscopy (FTIR). SEM analysis
indicates sericite within the saprolite is highly K-depleted, with a calculated range of 0.04
- 0.11 % K by weight compared to the accepted range of ~ 8-11 % by weight. We
propose that the K-depletion of sericite resulted from an addi

Paper:

Poster

2: Oxygen isotope analysis of sericite from a saprolite near Redwood Falls, Minnesota, Jake Gold, Hannah Kinzie, Ellen Root, Ellen Valkevich and Bereket Haileab, Carleton College Department of Geology, Northfield, Minnesota

Abstract
Stable oxygen and hydrogen isotope ratios can be used to infer paleoclimatic and
paleotemperature conditions for periods throughout Earth’s history. Secondary
minerals formed in igneous and metamorphic rocks during periods of weathering
record isotope ratios of fluids at the time of weathering. Analyses of sericite grains
collected from weathered Morton Gneiss saprolite near Redwood Falls, Minnesota
yielded ?18O values of 40-50 o/oo, suggesting water-rock interaction with enriched
18O waters. Recorded values are higher than those expected from natural processes,
suggesting the need for further refinement of analysis methods in order to obtain
accurate oxygen isotope ratios for micaceous minerals.

Paper

Poster

3: Carbon and oxygen isotope analysis of modern freshwater mollusk shells: applications for climate reconstruction: Lauren C. Andrews, Sarah C. Bergman, Gloria Jimenez, Yuichiro Takeshita
Carl Andrew Ulberg and Bereket Haileab

ABSTRACT
Modern freshwater mollusk shells record climatic trends across the lifespans of individual
organisms. In this study, we analyze growth bands in the carbonate shells of Lampsilis sp.
and Potamilns alatus from the Cannon River in southeastern Minnesota for ? 18O and ? 13C
content. Growth band ?18O signatures in the Potamilns shell show persistent variation on a
seasonal timescale and a larger-magnitude variation over multiple years. ? 13C signatures
show less variation and offer no coherent paleoclimate information. We argue that changes
in growth band ? 18O in Potamilns alatus reflect variations in water temperature as well as
changes in Cannon River geochemistry, so that the mollusk may serve as a high-resolution
paleoclimate proxy.

4: The Role of Iron-oxidizing Bacteria in Aquifers of Southeastern Minnesota: An Analysis of Springs in the Cannon River Wilderness Park and Goliath’s Cave: Megan Rohrssen, Susan Schnur. and Chris Ward

ABSTRACT
Iron-oxidizing bacteria have long been associated with the formation of iron-oxide-coated
mats at springs in southeastern Minnesota. However, no study has yet attempted to characterize
the complex ecosystems involved in the production of these mats and the impacts of iron-oxidation
on stream chemistry. The presence of iron-oxide-bearing mats at springs and in cave systems
reflects groundwater redox processes that have yet to be fully documented. Iron-oxidizing bacteria
from two circumneutral groundwater systems in SE Minnesota were cultured in FeS-O gradient
tubes. Bacteria from different sites grew at different levels in the tubes, indicating differing
optimum iron and oxygen concentrations. A discussion of potential redox cycles and possible
future interdisciplinary research topics is presented.

Paper

Poster