Biogeochemical signatures in Precambrian black shales: Window into the co-evolution of ocean chemistry and life on Earth

The degradation of sedimentary organic matter drives a suite of biologically-mediated redox reactions that in turn reflect the chemical composition of pore waters and bottom waters on local to global scales. By analyzing the chemical and isotopic composition of modern sediments and ancient black shales, biogeochemists can track the evolution of ocean/atmosphere redox conditions, the chemical composition of the oceans, and the evolutionary course of life throughout Earth history. Chapter 1 introduces the concepts of suboxic versus euxinic depositional environments and details the cycling of the transition metal molybdenum in each of these environments. A method for using Mo enrichments in ancient suboxic black shales as an environmental paleoproxy is proposed. Chapter 2 is a temporal survey of Mo enrichments in euxinic sediments and ancient black shales, throughout Earth's history. The purpose of this study is to test the hypothesis that widespread euxinic conditions during the Proterozoic would lead to Mo drawdown on a global scale, affecting the global nitrogen cycle. Chapter 3 is a biogeochemical description of the Mesoproterozoic Newland Formation, a non-euxinic black shale. Chapter 4 is a biogeochemical description of the Archean Jeerinah Formation, Earth's earliest known euxinic basin.