Energy and transport
The size of rock fragments in sedimentary rocks indicates the amount of energy needed to deposit them. Rapidly flowing, turbulent streams have great energy and transport large rocks and pebbles, along with smaller-grained sediments. As the current slows and its energy decreases, particles begin to settle out of the water, with the larger pieces dropping out first. The finest clay and silt are deposited in the still waters of lagoons and river deltas.
This is a conglomerate – a rock containing fragments of previously formed rocks – from the Hermit-Supai formations in the Grand Canyon region.
Composed of grains coarser than those in shales, sandstones are created in environments such as beaches, rivers, and deserts, where waves, currents, or wind sift the sands, removing the finer particles.