Formation and early diagenesis of microbialites in Storrs’ Lake, San Salvador, Bahamas: An alkaline earth metal isotope investigation
Funding: American Chemical Society Petroleum Research Fund “New Direction” (August 1, 2015 – August 31, 2017) and
The University of Texas at Arlington Research Enhancement Program (May 2014 – August 2015)
Students: Zijian (Tristan) Li (MS student), Emma Gaines (MS student)
Collaborators: Dr. David Wronkiewicz, Missouri University of Science and Technology (CO-PI)
Dr. Matt Fantle, Penn State University
This project involves fieldwork to collect samples from Storrs' Lake on the island of San Salvador and extensive lab and analytical work.
Outcomes: on-going
A stable Ca isotope investigation on modern microbially mediated travertine deposits at Honey Creek in the Arbuckle Mountains of southern Oklahoma
Funding: Geological Society of America Graduate Student Research Grant 2016 to Emmanuel Higa ($1875)
Students: Emmanuel High (MS student)
Collaborators: Dr. Matt Fantle, Penn State University
"Two distinct forms of travertine have been observed to precipitate from ambient-temperature, spring-fed water at Honey Creek in the Arbuckle Mountains of Southern Oklahoma: (1) laminated precipitates with a little algal growth on their surface and (2) encrustations with a distinct dendritic growth. Both travertines exhibit alternating seasonal layers of sparry and micritic calcite. Degassing of carbon dioxide is a large driver mediating their precipitation, however, dendritic growth forms clearly demonstrate close association with microbes on their surface and appear to dominate in slower moving portions of the stream. The goal of the proposed research is to investigate Ca isotope fractionation. Travertine precipitated in faster portions of the stream should display larger kinetically-driven isotopic signatures relative to microbially-mediated travertine formed in slower portions of the stream. Seasonal variation in Ca isotope fractionation should also be observed in our results." - from Emmanuel Higa's proposal
Outcomes: on-going
Stable strontium isotope ratios (88/86Sr) in abiotic and microbially mediated barite
Funding: NSF Earth Sciences (EAR) Geobiology & Low Temperature Geochemistry award #1053312 (March 1, 2011 - Feb. 28, 2015)
Ph.D. student I. Hasanthi Widanagamage (2011-2015)
REU student S. Lindsay Poluga (Summer 2012)
Collaborators: Dr. Howie Scher, University of South Carolina
Dr. Edwin Schauble, University of California – Los Angeles
Dr. John Senko, University of Akron
Dr. David Singer, Kent State University
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Results of novel stable Sr-isotope measurements from barite, a highly stable and widely-distributed mineral identify controlling parameters of stable Sr-isotopic fractionation in continental barite. Strontium concentrations and isotope ratios of barite from laboratory experiments along with samples collected in the field at an established field site in western Oklahoma and two additional sites in western Colorado and northern Utah are presented in current and forthcoming publications.
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Stable Sr-isotope fractionation for the experimental barite agrees in direction and order of magnitude with Density Functional Theory modeling. The isotope fractionation varied with distribution coefficient of Sr as a function of temperature and barite saturation state suggesting chemical kinetic effects control isotope fractionation rather than equilibrium temperature effects.
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We measured a large range of stable Sr-isotope ratios in continental waters and barite. Relationships between solution and barite chemistry in the natural systems are unclear suggesting that barite does not precipitate directly from solution in these environments, but heterogeously within diverse microenvironments created by microbial biomass or on sediment surfaces. Initial results of heterogeneous Sr incorporation in barite at the microscale is captured using synchrotron-based micro-XRF. Micro-XRD indicates celestine co-precipitation with barite at micron-scale.
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Additional stable isotope data (S and O isotope ratios) and radiogenic Sr-isotope ratios were completed and these new continental barite results are compared with marine pelagic barite, marine hydrothermal and diagenetic barite to identify mode of formation (publication in preparation) in collaboration with Drs. Adina Paytan (Univ. of California – Santa Cruz), Ulrich Wortmann (Univ. of Toronto), Howie Scher (Univ. of South Carolina) and Anton Eisenhauer (IFM-GEOMAR).
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Publications:
Singer, D. M., E. M. Griffith, J. M. Senko, K. Fitzgibbon, and I. H. Widanagamage (2016) Celestine in a sulphidic spring barite deposit – a potential biomarker?. Chemical Geology. Vol. 440, 15-25. pdf
Widanagamage*, I. H., E. M. Griffith, D. M. Singer, H. D. Scher, J. M Senko, and W. P. Buckley, Jr. (2015) Controls on stable Sr isotopic fractionation in continental barite. Chemical Geology. Vol. 411, 215-227. pdf
Widanagamage*, I. H., E. A. Schauble, H. D. Scher, and E. M. Griffith (2014) Stable Sr isotope fractionation in synthetic barite. Geochimica et Cosmochimica Acta. Vol. 147, 58-74. pdf
Scher, H. D., E. M. Griffith, and W. P. Buckley, Jr. (2014) Accuracy and precision of MC-ICPMS 88Sr/86Sr and 87Sr/86Sr measurements are compromised by high barium concentrations. Geochemistry, Geophysics, Geosystems., Vol. 15 (2), 499-508, doi:10.1002/2013GC005134. pdf
Calcium isotopes in marine pelagic barite
Collaborators: Dr. Adina Paytan, University of California – Santa Cruz
Dr. Tom Bullen, USGS – Menlo Park
Dr. Anton Eisenhauer, IFM-GEOMAR
Dr. Matt Fantle, Penn State University
Dr. Ellen Thomas, Yale University, Wesleyan University
Dr. Edwin Schauble, University of California – Los Angeles
Dr. Ken Caldeira, Stanford University
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Carbonate deposition and dissolution significantly affect oceanic alkalinity, atmospheric pCO2 and, ultimately, Earth's climate. Despite over a century’s worth of research, we are just beginning to understand the complexity of the carbonate system and reveal the feedbacks between the processes that control it. The biological precipitation of calcium carbonate (CaCO3) largely controls the Ca isotope ratio in seawater due to discrimination against heavy isotopes. Reconstructing the seawater Ca isotope ratio over time can help quantify the fluctuations in the amount of CaCO3 deposited in the oceans at any given time (assuming some knowledge of the isotopic composition of the sources and sinks). I developed a novel method to extract Ca isotope data from marine barite, a minor component of marine sediments, to reconstruct variations in seawater Ca isotopes.
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Our record over the past 28 million years reveals previously unrecognized features in seawater Ca isotope ratios which, based on our model, correspond to changes in seawater Ca concentration. The most pronounced change occurs at 15 million years ago and corresponds to a major climatic transition and global change in the carbon cycle revealed in marine oxygen and carbon isotopes, suggesting coupling between climate, weathering and seawater chemistry.
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I am looking at the implications of these results using higher resolution records over time intervals of extreme climate change (Eocene-Oliogocene and Paleocene-Eocene boundaries). Our record over the Eocene-Oligocene Transition reveals that the isotopic composition of dissolved Ca in the oceans was stable throughout this period of global cooling, whereas at other times of global cooling (e.g., the middle Miocene, ~ 13-15 millions of years ago), the Ca isotopic chemistry of the ocean change considerably. The response of ocean chemistry to climate change thus depends upon the composition of seawater and the rate of change. In addition, calcite precipitated by marine micro-organisms records not only changes in the seawater isotope ratio of calcium, but also changes in temperature and/or the assemblages of such organisms, which are sensitive to climate change.
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Publications:
Griffith, E. M., M. S. Fantle, A. Eisenhauer, A. Paytan, and T. D. Bullen (2015) Effects of ocean acidification on the marine calcium isotope record at the Paleocene-Eocene Boundary, Earth and Planetary Science Letters, Vol. 419, 81-92. pdf
Griffith, E. M. and A. Paytan (2012) Barite in the ocean – occurrence, geochemistry, and paleoceanographic applications. Sedimentology, Vol. 59, 1817-1835.
Griffith, E. M., A. Paytan, A. Eisenhauer, T. D. Bullen and E. Thomas (2011) Seawater calcium isotope ratios across the Eocene-Oligocene Transition. Geology, Vol. 39, 683-686, doi:10.1130/G31872.1
Griffith, E. M., A. Paytan, K. Caldeira, T. D. Bullen and E. Thomas (2008) A dynamic marine calcium cycle during the past 28 million years. Science, Vol. 322, 1671-1674.
Griffith, E. M., E. A. Schauble, T. D. Bullen and A. Paytan (2008) Characterization of calcium isotopes in natural and synthetic barite. Geochimica et Cosmochimica Acta, Vol. 72, 5641-5658.