quartzcemented

Quartzcemented refers to a sedimentary rock, typically sandstone, in which quartz acts as the primary cementing material binding the grains. The cement forms by precipitation of silica from pore waters, producing quartz overgrowths on individual grains and along grain contacts. This diagenetic cementation reduces intergranular porosity and permeability, with the degree of reduction dependent on fluid chemistry, burial history, and time.

Formation and sources: Silica-rich fluids originate from the dissolution of siliceous components such as biogenic silica from microorganisms or from feldspar dissolution, transported through the pore network. Under suitable temperature and pressure conditions during diagenesis, dissolved silica precipitates as microcrystalline quartz along grain boundaries and at contact points, creating a rigid cement that binds grains together. Quartz cementation is common in quartz arenites and other mature sandstones with high quartz content and limited feldspar.

Petrological effects: Quartz cementation can preserve or obliterate primary porosity. Early cementation often reduces porosity quickly, while later cementation can create distinct pore geometries that alter permeability pathways. In some settings, secondary porosity may be generated elsewhere by dissolution or fracturing, partially offsetting the loss of porosity due to cementation.

Implications: In petroleum geology, quartz cementation frequently lowers reservoir quality by reducing porosity and permeability, though it can also influence fracture networks and flow behavior. In groundwater and hydrogeology, quartz cementation controls storage and flow characteristics of sand-dominated aquifers. Petrographic analysis, including thin-section examination, identifies quartz-cemented textures and assesses the degree of cementation.

See also: Diagenesis, Quartz overgrowth, Sandstone cementation, Porosity.