What is dolomite telling us about ancient seawater chemistry

Modern environments that produce ordered dolomite on Earth today all share a key set of physical and chemical characteristics. At the same time, recent advances in our understanding of carbonate mineralisation indicate that specific chemical fluctuations are crucial in driving the precipitation of high-Mg carbonates. As a consequence, there is a unique opportunity to test key hypotheses related to the mechanisms of Mg-rich carbonate precipitation that reconcile available constraints on both the modern and ancient distributions of dolomite. This project will examine the mechanisms of high-Mg carbonate precipitation (including dolomite) by combining experimental geochemistry, the environmental geochemistry of modern hyper-saline systems, high-resolution microstructural investigations of modern and ancient dolomite-rich sediments, and numerical modeling.

This project provides an opportunity to combine field work in modern hyper-saline systems and/or well-preserved Precambrian dolomitic successions, experimental geochemistry, advanced geochemical and mineralogical analysis, and theoretical geochemistry. There is scope for these elements to be tailored somewhat to the student's interests. A key component will involve collecting (either through targeted field work or sample acquisition from collaborators) a wide range of early diagenetic and authigenic dolomitic samples that represent a broad spectrum of modern and paleo-environments. The student will also design and implement a targeted program of experimentation that deconstructs the key processes generating high-Mg carbonates and modifies their crystal chemistry and structure. In addition, the signatures of these mechanisms in synthetic, modern and ancient samples using a combination of EPMA, XRD, micro-Raman spectroscopy, solid state NMR, synchrotron-micro XRF and XANES, and high-resolution TEM. Finally, there is an opportunity to explore the biogeochemical significance to modern and ancient systems through geochemical modeling and dynamical simulations (box modeling).