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2008 Annual Science Report

University of Wisconsin Reporting  |  JUL 2007 – JUN 2008

Production of Mixed Cation Carbonates in Abiologic and Biologic Systems

Project Summary

Carbonate minerals commonly occur in terrestrial environments and they are found in extraterrestrial materials, such as meteorites and interplanetary dust particles. On earth, carbonates hold one of the earliest records of seawater chemistry. Carbonate minerals that form in thermodynamic equilibrium (abiotic formation) are constrained in Ca-Mg-Fe composition by the solvi that limit solid-solution to the magnesite-siderite join, the dolomite-ankerite join, and the calcite end member. However, it is now known that microorganisms may produce Ca-Mg-Fe compositions that lie between these solvi, and are therefore out of thermodynamic equilibrium, and such compositions may represent a biosignature for microbially mediated formation. The goal of this project is to understand the mechanisms by which carbonate minerals of unusual chemistry form at relatively low temperature so that we may better understand the processes that may form these minerals in the early Earth, on Mars, and other planetary bodies of the Solar System.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

Year One accomplishments centered on completion of laboratory experiments to synthesize carbonate minerals of unusual “mixed cation” chemistry (Fe-Mg-Ca): These experiments may be broken down into three categories: 1) inorganic free-drift experiments, 2) inorganic chelation experiments, 3) microbial experiments. Inorganic free-drift experiments: twenty-five free-drift experiments have been completed to precipitate Fe-Mg-Ca carbonates of distinct composition (mol : Fe = 70 to 100; Mg = 0 to 40%: Ca = 0 to 30%) over a temperature range from 25° to 45°C. Sixteen additional experiments have been completed to precipitate Mg-Ca carbonates in the presence of inorganic ligands in addition to CO3. Inorganic chelation experiments: four chelation experiments have been completed to precipitate Mg-Ca carbonates in the presence of oxalic acid. Microbial experiments: multiple cultures have been grown using the proteolytic halophile Virgibacillus marismortui AJ009793 at 35°C under aerobic conditions to synthesize microbial dolomite for chemical and structural characterization.

These experiments have been targeted to reproduce the results of previous work to test proposed pathways for production of mixed cation carbonates. In addition, these experiments served to provide a foundation of laboratory experience and materials for characterization of redox sensitive materials such as Fe-bearing carbonate. The results will be used to develop a more sophisticated experimental approach to precipitate a chemically homogeneous solid from a solution held in a steady-state conditions (i.e., chemo-stat experiments). From these experiments, solids will be produced that will be chemically and structural characterized and analyzed for Ca, Mg, and Fe isotope compositions at the University of Wisconsin, as well as C and O isotope composition at the University of Georgia.