Question

How do sediments become sedimentary rock? What processes are involved?

Answer 1

Hint: Lithification is the process through which, by compaction or cementation, unconsolidated sediments are converted into coherent solid rock. This process has several stages, namely, burial, compaction, and cementation.

Complete answer: Sedimentary rocks are made of lithified sediment, which were once grains of rocks, minerals, or mineraloids deposited on the Earth’s surface. Sediments have to undergo burial, compaction and cementation in order to become sedimentary rocks.
When sediments start getting deposited in a particular area, this area is known as the sedimentary basin. As more and more layers of sediments are deposited on top of each other, it creates burial of the lower strata. This is usually accompanied by subsidence of the crust beneath into the mantle or by relative uplift of surrounding uplands. This can cause thousands of feet of burial of the sedimentary basin.
Now, the upper layers cause pressure for the lower sediments, such that it ‘squeezes’ into a smaller volume. This pressure is known as lithostatic pressure, which packs the grains of the sediments closer and reduces the porosity. This stage is known as compaction.
During both these processes, cementation occurs as well. It refers to formation of new minerals between the grains of the sediments, which help the sediments to bind together. Some common cementing minerals include quartz rims, hematite, calcite, etc.

Note: The flow of the formation of sedimentary rocks begins with denudation of the parent rock into sediments, and then lithification to give rise to sedimentary rocks. Try to remember the process of lithification in terms of the following flow chart: weathering >> erosion >> transport >> deposition >> burial >> compaction >> cementation >> sedimentary rock.