Geochemistry of Fine-Grained, Organic Carbon-Rich Facies

This chapter provides an overview of the fundamental concepts and tools that have been applied to study organic carbon-rich facies and the history of changes in marine redox conditions that they uniquely record. It first develops a conceptual model for the processes and feedbacks involved during the deposition of fine-grained organic carbon-rich black shales and illustrates how geochemical proxies are developed from detrital, biogenic, and authigenic fluxes and processes. The proxies reviewed include some recently introduced metal isotope proxies (isotope systematics of Mo, Fe, and Re-Os), in addition to elemental and compound concentration/accumulation proxies (trace metal, biomarker, CaCO₃, etc.) and stable isotopes (C and S) that have been in use for many years. A vast amount of recent work utilizing redox proxies has focused on Precambrian strata to reveal fundamental changes in the ocean-atmosphere system that influenced the evolution of life on the early Earth. Highlights from recent publications on Precambrian strata, along with selected studies of Phanerozoic and modern anoxic deposits (i.e., oceanic anoxic events and sapropels), are updated in this revision to provide a broad review of the concepts and methods used to study organic carbon-rich deposits.