Relationships between depositional environments, burial history and rock properties. Some principal aspects of diagenetic process in sedimentary basins

Sedimentology, sequence stratigraphy and facies analysis have for many years been disciplines rather separate from diagenesis which is concerned with processes occurring after deposition. Prediction of rock properties as a function of burial depth in sedimentary basins requires that these disciplines become more integrated. Compaction of sedimentary rocks is driven towards increased density (lower porosity) and higher rock velocity as functions of burial depth (effective stress) and temperature. Both the mechanical and chemical compaction of sedimentary rocks are functions of the primary textural and mineralogical composition of the sediments at the time of deposition and after shallow burial diagenesis. This is controlled by the provenance, transport and depositional environment. Many published sedimentological studies, however, contain little information about the mineralogical and textural composition of the sedimentary sequences. Near the surface, sediments are in an open geochemical system due to groundwater flow, diffusion and evaporation. Here their composition may be changed by mineral dissolution and transport of the dissolved components. At greater depth, below the reach of significant meteoric water flow, the porewater has an exceedingly low mobility and capacity to transport solids in solution. The porewater will gradually approach equilibrium with the minerals present, reducing the concentration gradients in the porewater and the potential for both advective and diffusive transport of solids in solution. Significant increased porosity (secondary porosity) is dependent on the dissolution and removal of solids in solution which may occur during freshwater flushing at shallow depth dissolving feldspar and precipitating kaolinite. Below the reach of freshwater the porewater flow is limited and represents a geochemically nearly closed system. The porewater will in most marine sediments be in equilibrium with calcite, even if it occurs in small amounts. Prediction of rock properties such as porosity and seismic velocity at a certain depth in a sedimentary basin must be based on the burial history (effective stress and temperature), but the primary mineralogical and textural composition of the sediments is equally important. Studies of depositional environments and provenance should therefore be integrated with diagenesis and be a part of basin analysis which is used for basin modelling. (C) 2013 Elsevier B.V. All rights reserved.