Final answer:
Sediments transform into sedimentary rocks mainly through compaction and cementation. Cementation is particularly effective in the lithification of sand- and gravel-sized sediments as it acts as a glue, solidifying the structure.
Step-by-step explanation:
The transformation of sediments into sedimentary rocks occurs primarily through two processes: compaction and cementation. Compaction is akin to pushing down on a full trash can to make more space; it reduces the porosity between grains by the weight of additional sediments deposited on top, bringing grains closer to each other. Cementation, on the other hand, involves the precipitation of minerals such as calcite, quartz, and pyrite in the pore spaces as water is expelled, effectively acting as a glue that binds the sediments into rock.
As for the more effective process in the lithification of sand- and gravel-sized sediments, cementation plays a crucial role. When considering larger grains like sand and gravel, the interlocking of particles through mineral precipitation is particularly important to form a solid and cohesive rock structure. Quartz is the most stable mineral and is often found in sand-sized grains due to its resistance to weathering, making it a common mineral in sandstone formations.