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Formation of sedimentary rocks

Short answer

Sedimentary rocks form by weathering, erosion, transportation, and deposition of particles in layers, followed by compaction from overburden and cementation by minerals like silica or calcite. This lithification (diagenesis) turns loose sediments into solid rocks like sandstone and shale.

How is sedimentary rock formed?

Sedimentary rocks form at the Earth's surface by the accumulation and hardening of sediments, in these stages.

  1. Weathering (physical, chemical) breaks existing rocks into fragments and dissolved material.
  2. Erosion and transportation by water, wind, ice or gravity carry the particles away. Particles get rounded and sorted by size.
  3. Deposition occurs in lakes, rivers, seas and deserts when the energy of the transporting agent falls, forming horizontal layers (strata). Chemical and organic matter also precipitate or accumulate.
  4. Compaction: the weight of overlying sediments squeezes out water and reduces pore space.
  5. Cementation: minerals such as silica, calcite and iron oxide precipitate from water and bind the grains.
  6. Lithification: the loose sediments become solid rock (diagenesis).

Result: layered rocks such as sandstone, shale and limestone, with fossils and structures like ripple marks.

✓ Answer checked by Claude Opus 5.5 (high effort)

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