Reports: UR854410-UR8: Stromatolites in Atypical Environments: From Mesoproterozoic to Modern
Julie K. Bartley, PhD, Gustavus Adolphus College
· Field work in the Death Valley region of eastern California and western Nevada
· Field work in the Bahamas
· Continued work on a stromatolite database and atlas
· Initial analyses of Death Valley region stromatolites
· Continued analysis of the relationship between microstructure, form, and geochemistry in diverse stromatolites
· Conference presentations by students
· One senior thesis
· Macrostructure, microstructure, and geochemistry are not closely correlated.
· The vast majority of stromatolites from all study areas are composed of precipitated carbonate textures.
· Trace element geochemistry, though not a good predictor of microtexture, shows traceable fingerprints that define contemporaneous laminae across stromatolite horizons.
Two field excursions, the first to the Death Valley region in January 2017 and the second to the Bahamas in June 2017, completed our suite of stromatolite samples and observations. Stromatolites from the western US included Proterozoic forms from the Noonday, Johnnie, Crystal Springs, and Beck Springs formations, and Pliocene spring-related forms from the Furnace Creek Formation. Fieldwork was conducted by Lindsey Reiners, a student who worked on this project for all three years, Sarah Bruihler, a new junior, and Charlotte Cowdery, a new sophomore. During the summer, Sarah Bruihler was invited to observe modern stromatolites in the Bahamas by the director of the Darby Island Research Station, Pamela Reid. She and I spent a week on Darby Island, examining modern forms in situ and planning a collaboration with Pamela that will involve borrowing previously-collected stromatolites for inclusion in our dataset.
Reiners completed a senior thesis in May 2017, titled Relationships Among Morphology, Texture, and Chemistry in Stromatolites of the Green River Formation (Eocene, Wyoming, USA). In her thesis work, she demonstrated that macroscopic morphology does not correlate with microscopic texture, confirming preliminary results from year 2 of this project. In addition, she undertook a lamina-by-lamina elemental analysis of several stromatolites, which also suggested no correlation between stromatolite microstructure and chemistry. However, a potential relationship between individual laminae and chemical composition was observed, suggesting that individual a laminae can be identified across stromatolites in the same horizon and geochemical trends can be traced through time within individual stromatolites.
During the summer, Sarah Bruihler and rising senior Caitlin Clause began morphological and petrographic analysis of the stromatolites collected in January and refined, expanded, and developed the stromatolites database begun in earlier years of the project, continuing the collaboration with students of Dr. Tom Hickson of the University of St. Thomas, also a PRF awardee, to share information, develop a common descriptive vocabulary for stromatolites, and share research results across projects. This collaboration resulted in PIs Bartley and Hickson convening a session at the Geological Society of America Annual Meeting, titled Microbialite textures and chemical signatures in continental settings: forging the link between the modern and ancient. The session is sponsored by the Geomicrobiology Division of the Geological Society and will occur in October 2017. Bartley and Hickson are contributing two co-authored talks in this session and Sarah Bruihler will present a poster.
Impact on students
The students who have worked on this project have been able to synthesize a great deal of information about stromatolites in a way that has not been done before. The overall finding that macroscopic morphology, microscopic texture, and trace element chemistry are not well correlated with each other is new, but not unexpected when interpreted against the backdrop of published work on stromatolites. Students Lindsey Reiners and Tanner Eischen (supported in years 1 and 2 of the project) presented their findings at the Geological Society of America meeting in 2016. Sarah Bruihler will represent this project at the 2017 GSA Annual Meeting in Seattle.
Three students (Reiners, Bruihler, and Cowdery) participated in fieldwork during year 3 of this project. Bruihler was additionally able to conduct fieldwork in the Bahamas. These experiences had significant impact on these students educational trajectories and have positioned them well for future undergraduate, graduate, and professional work.
Impact on faculty
The work of this project has invigorated Julie Bartleys research agenda and has opened up a host of new collaboration opportunities. Ongoing collaboration with Tom Hickson (University of St. Thomas) has been strengthened, and we foresee numerous additional opportunities to work together. A new collaboration, established with Pamela Reid (University of Miami and director of the Darby Island Research Station) will enhance comparisons between modern and ancient microbialites. We expect to have at least three publications arise from this work, and expect that this work will catalyze a future grant proposal, to be written in 2018 or 2019. Bartleys 2-year service as Dean of Sciences and Education at Gustavus will be completed in spring 2018, and she will return full-time to the faculty and to her research agenda.