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, acid-base balances, and elemental cycling in the ocean. Diagenetic transport-reaction conditions, sediment-water fluxes, and the eventual storage of material are determined by properties of local depositional environments, including: water column oxygenation, particle size distributions, bulk geotechnical properties—permeability, sedimentation rates, sedimentary transport dynamics, and benthic biological communities. Reactions associated with thermodynamically unstable biogenic and lithogenic 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, silicates). This article reviews early diagenetic processes, reaction dominance, and sediment-water material fluxes as a function of depositional environments. It builds on and extends the earlier contributions on early diagenesis and sediment-water exchange in the first and second editions of the Treatise. It places relatively major emphasis on deltaic and shallow water depositional systems and unsteady diagenesis, and it incorporates recent data obtained through technical advances, such as planar imaging sensors, eddy correlation flux methods, and stable isotopic compositions. It does this in part at the expense of more detailed coverage of deep-sea processes and organic geochemistry which are treated more thoroughly in other chapters.