Geologists use deposits such as rocks, dirt, and sand deposited from rain, waves, or wind erosion of beaches or cliffs as evidence of past environments; depositional environments.
Deposition is a legal proceeding in which attorneys ask witnesses questions under oath about issues relevant to a lawsuit.
Sedimentation
Sedimentation, the process by which solid material settles out of fluid such as water, is an integral component of Earth’s geological cycle and plays an essential part in shaping landscapes.
Size, shape and composition of sediment vary greatly due to geologic, geomorphic and organic influences; these variables impact how fast and where sediment moves through its journey.
As sediment is carried in flowing water, its size and density become increasingly distinguished as it travels downstream. This sorting can provide insight into the energy conditions in which the sediment was deposited.
When the energy of a transporting medium declines sufficiently, sediment deposits at an appropriate site. Such sites include river deltas, bar and island formations in channels, sandbars and even tea and coffee cups themselves – in the form of sediment sitting at the bottom! Sediment can also accumulate in pools formed by rain runoff in lakes as pools. It even finds its way into our tea and coffee mugs through tea leaves!
Lithification
Lithification is the geological process by which loose sediment becomes solid rock, an essential step for sedimentary rock formation. Lithification entails two stages: compaction and cementation.
Compression reduces sediment volumes by compressing layers together, forcing out any extra pore water that accumulates beneath and initiating the first stage of lithification.
Cementation fills pore space between sediment particles with mineral crystals to bind them together – this process represents the second stage in lithification.
Lithification encompasses more than just compaction and cementation – it also involves recrystallization and new mineral formation, both processes which reorganize minerals at an microscopic scale for increased stability and altered composition. These changes, known as diagenesis, occur at lower temperatures and pressures than what igneous and metamorphic rock undergoes; hence why fossils are often preserved better within sedimentary rocks.
Compaction
Weight and friction combine to form many distinct landforms. Gravity forms rockslides on mountains and hills; wind creates desert sand dunes; while ocean waves shape beaches and sand bars along coastlines.
Compression and shear forces compress and pack together soil particles, decreasing pore space while increasing bulk density. These forces may be applied through heavy machinery’s wheels, tracks or hooves or through animals grazing on them.
Compaction can dramatically change the physical and chemical properties of sediment layers, including their water infiltration/permeability properties and load bearing capacity in construction/natural stability applications. Geologically speaking, compaction has an influence over sedimentary rock formation over long time periods as well as helping capture organic materials for chemical transformation into fossil fuels over millions of years. To conduct density tests on the ground traditionally required laborious excavation followed by comparison using weight scales, but now nuclear density gages can be dropped directly into holes to measure density directly.
Cementation
Deposition is the geological process by which sediment, soil and rocks are added to a landform or mass through wind, ice or water transport, after their kinetic energy no longer suffices for keeping these materials moving.
Material then accumulates, creating layers of sediment. After being buried beneath, compaction and cementation occur to complete this cycle.
Compaction squeezes sediment together and transports eroded minerals to fill in between grain gaps, where ions chemically precipitate into mineral cements which then bond the sediment together into rock. Cementation reduces porosity in rocks by making them impermeable – common cementing minerals include calcite, silica and iron oxides.
Lithification, which includes both compaction and cementation processes, is more commonly known as diagenesis. Lithification provides insight into past environments and climate conditions on Earth.