Precambrian Molar-Tooth Structure: Unraveling the Diagenesis of Ancient Carbonates

Molar-tooth structure (MTS) is an enigmatic carbonate fabric that occurs mainly within Proterozoic carbonate host rocks. It is composed of two distinct features: cracks of various morphologies and crack-filling calcite microspar. Although the origins of MTS remain unknown, most previous investigation has focused on the formation of the cracks and mechanisms involved in the void space generation, with less emphasis on the intriguing carbonate fill. In this study I have investigated molar-tooth bearing carbonates from regions that span both paleogeography and geologic time. Analysis at the microscopic scale, including traditional petrography, cathodoluminescence petrography, scanning electron microscopy, and micrometer-scale geochemical analyses (Chapters 1 and 2) provides a fresh look at MTS that augments the more traditional sedimentological and stratigraphical observations in the field (Chapter 3). Combined, these works provide a solid base of evidence to guide studies into MTS and will aid in our understanding of the evolution of the Earth’s ancient oceans and processes of carbonate diagenesis through time. Specifically, this investigation demonstrates the complexity of carbonate precipitation and its earliest diagenesis, and therefore provides a key context for the evaluation and interpretation of isotopic and trace elements analyses that involve the evolution of carbonate phases through geologic time.