Mississippi State University
Kirkland, Brenda L.
Thirumalai, Rooban Venkatesh K G
Date of Degree
Dissertation - Open Access
College of Arts and Sciences
Department of Geosciences
The objective of this study is to better understand the relationship between organic compounds and carbonate mineral growth in different natural environments by imaging the interface between organic compounds and carbonate precipitates in ancient and modern rocks, and laboratory experiments. Three separate projects were designed to document the organic/carbonate mineral interface through imagery. 1) Images of the interfaces between organic components and initial mineral precipitates were investigated in a deteriorating microbial mat from Vermelha, Brazil that was taken from the site in 2006. As the mat deteriorated the amount of calcification increased. A section of the transitional section between living algae and calcitic precipitate was taken for analysis. Transmission Electron Microscopy (TEM) along with Energy-dispersive X-ray spectroscopy (X-EDS) showed carbonate minerals growing on cell walls and using dark, amorphous structures as nucleation points. X-EDS results showed that the dark amorphous structures have high concentrations of silica, magnesium, and oxygen, which appears to promote carbonate mineral precipitation. 2) Laboratory experiments were designed to precipitate calcite in solution with varying organic compounds and then use TEM analysis to image the precipitants, specifically the transitional area between the organic compounds and carbonate minerals. Calcite crystals appeared to nucleate off of the surfaces of palmitic and stearic acid. X-EDS analysis verified the elemental transition from organic matter to carbonate mineral growth. 3) Cold water, authigenic carbonate rocks collected by Dr. Adam Skarke, on July 6, 2016 during the National Oceanographic Laboratory System (UNOLS) research cruise to a methane seep off the eastern North America coast were imaged and analyzed. Scanning Electron Microscope (SEM), EDS and XRD analysis were used to better understand the sequence of events that led to formation of this unusual rock. The rock grew in situ trapping quartz and metallic minerals in aragonitic cement, and then was cut and pushed apart by veins filled with aragonitic cement in a pattern reminiscent of septarian nodules.
Testa, Maurice Philip, "Imaging Calcium Carbonate Crystallization in Association with Organic Compounds" (2017). Theses and Dissertations. 2577.