Sedimentary Diagenesis, Depositional Environments, and Benthic Fluxes

Sediment diagenesis is a critical component of the global sedimentary rock cycle. Sedimentary deposits behave as open systems, and sediment-water exchange has major influences on biogeochemical processes in the ocean and on elemental balances in seawater. Diagenetic transport-reaction conditions, sediment-water fluxes, and the eventual storage of material are determined by properties of the depositional environment, including water column oxygenation, particle size distributions, bulk geotechnical properties, sedimentation rates, sedimentary transport dynamics, and benthic biological communities. Reactions associated with thermodynamically unstable biogenic debris dominate early diagenetic processes. These include redox reactions coupled to organic matter decomposition and preservation, carbonate dissolution, opaline silica dissolution and alteration, and authigenic mineral formation (carbonates, sulfides, and silicates). This chapter reviews diagenetic processes and is patterned after the earlier contribution by Emerson and Hedges in the first edition of the Treatise, which stands on its own. It has been extended in some alternative directions, however, as it places greater emphasis on deltaic and shallow water depositional systems and unsteady diagenesis, and it incorporates more recent data obtained through technical advances, such as planar optodes and eddy correlation. It does this in part at the expense of more detailed coverage of deep-sea processes and organic geochemistry.