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WHY ARE THERE SO MANY DIFFERENT TYPES OF SEDIMENTARY ROCK?

The type of sediment that is deposited is determined by a location’s position on the landscape. Consider a shoreline environment: dunes along the coast (or farther inland) and beach sands become sandstones or quartzites (metamorphosed sandstones); mud and silt are deposited farther out to sea and become mudstones, siltstones, and shales; calcite accumulates in shallow tropical waters, both precipitating from the water and from the deposition of sea creatures. Fewer sediments are deposited and preserved in the interior of continents, which is why most sedimentary rocks are from shores, deltas, or shallow marine environments.

For different types of sediment to overlie each other, the shoreline’s location must keep shifting. Many factors lead to never-ending movement in the position of the shoreline, including continuous variation in the strength of the sun’s radiation and consequent changes in the amount of the Earth’s water stored as ice. Over hundreds of thousands to millions of years, a single location will experience different sedimentary environments—a history preserved as consecutive layers of sedimentary rock.