What process happened when mud or slit is buried and water and air are squeezed out producing such rocks as shale?

When mud or silt is buried under layers of sediment, the pressure from the overlying materials compresses it, squeezing out water and air. This process, known as compaction, leads to the consolidation of the sediment into a solid form. As the particles are compacted, they may also undergo cementation, where mineral-rich water fills the spaces between the particles, precipitating minerals that bind them together. The result is sedimentary rock, such as shale, formed from the lithification of fine-grained sediments.