What is the name of the process in which sedimentary layers are turned into rock?

Lithification is the process that turns loose sediment into solid sedimentary rock.

It mainly occurs through compaction and cementation. As additional sediment accumulates, its weight squeezes grains together and reduces pore space. Groundwater can then deposit minerals such as silica, calcite, or iron oxides between the grains, binding them into a coherent rock.

Lithification is not the same as sediment deposition. Deposition places particles in a new location, while lithification changes those particles into rock. The process may begin soon after burial but can continue for thousands to millions of years.

Sandstone, shale, and conglomerate are common lithified sedimentary rocks. Their original grains, sorting, layering, and cement can preserve information about ancient rivers, deserts, lakes, and seas.