1.1 SEDIMENTARYPROCESSES

Anotacoes

1.1 SEDIMENTARYPROCESSES The concept of interpreting rocks in terms of modern processes dates back to the 18th and 19th centuries (‘the present is the key to the past’). ‘Sedimentology’ has existed as a distinct branch of the geological sciences for only a few decades. It developed as the observational elements of physical stratigraphy became more quantitative and the layers of strata were considered in terms of the physical, chemical and biological processes that formed them. The nature of sedimentary material is very varied in origin, size, shape and composition. Particles such as grains and pebbles may be derived from the erosion of older rocks or directly ejected from volcanoes. Organ isms formaveryimportantsourceofmaterial,ranging from microbial filaments encrusted with calcium car bonatetowholeorbrokenshells,coralreefs,bonesand plant debris. Direct precipitation of minerals from solu tion in water also contributes to sediments in some situations. Formation of a body of sediment involves either the transport of particles to the site of deposition by grav ity, water, air, ice or mass flows or the chemical or biological growth of the material in place. Accumula tion of sediments...