Sediment

Sediment is solid particulate material produced by weathering and erosion, transported by wind, water, ice, or gravity, and deposited when transport slows. It can consist of mineral grains, rock fragments, and organic matter. Sediments are commonly classified as clastic (detrital) sediments, chemical sediments formed from mineral precipitation, and biogenic or biochemical sediments derived from organisms.

Particle sizes range from gravel (>2 mm) to sand (2 mm to 0.062 mm), silt (0.062 to 0.004 mm), and clay (<0.004 mm). Transport processes include suspension, saltation, and traction, while deposition occurs in environments such as rivers, lakes, oceans, deserts, and glacial settings. Sedimentary structures such as bedding, cross-bedding, ripple marks, mud cracks, and graded beds record changes in energy, flow, and environment at the time of deposition.

When buried, sediments undergo diagenesis, including compaction and cementation, converting loose material into sedimentary rocks such as sandstone, shale, limestone, and coal. These rocks often preserve fossils and provide records of past environments, climates, and sea level. The porosity and permeability of sediments determine fluid storage and movement, influencing groundwater resources and hydrocarbon reservoirs.

Sedimentology, the study of sediments and their processes, informs interpretations of Earth's history and landscape evolution. Human actions—such as dam building, mining, erosion control, and coastal engineering—can alter sediment transport and deposition, affecting ecosystems and sediment budgets.