compaction

Deposition is the process by which sediment settles out of the water or wind carrying it. The process that presses sediments together is compaction.

Cementation is the process of precipitation of mineral matter (cements) in pores within sediments or rocks. Cements even form crusts on surfaces at sediment-water or sediment-air interfaces. Precipitation of cements can occur at any stage from deposition, through burial, to uplift and re-exposure.

Common cementing minerals are calcite (CaCO3), silica (SiO2), iron oxides and clay minerals.

Cementation, in geology, hardening and welding of clastic sediments (those formed from preexisting rock fragments) by the precipitation of mineral matter in the pore spaces. It is the last stage in the formation of a sedimentary rock.

The agents like mineral, water, and sediments are present for the sedimentation to occur. Explanation: Cementation is formed from pre existing rocks. This occurs due to precipitation of the mineral matter in that layer containing the pores.

The three, most common, chemical cements in sedimentary rocks such as sandstone are silica (quartz), calcium carbonate (calcite), and the iron oxides.

Dissolved minerals in the ground water precipitate (crystallize) from water in the pore spaces forming mineral crusts on the sedimentary grains, gradually cementing the sediments, thus forming a rock. Calcite (calcium carbonate), silica, and hematite (red iron oxide) are the most common cementing agents.

‘Diagenesis’ refers to the physical and chemical processes that affect sedimentary materials after deposition and before metamorphism and between deposition and weathering. The effects of diagenetic processes on rock properties such as porosity and the degree of lithification are progressive.

Common mineral cements include calcite, quartz, and silica phases like cristobalite, iron oxides, and clay minerals; other mineral cements also occur. Cementation is continuous in the groundwater zone, so much so that the term “zone of cementation” is sometimes used interchangeably.

The weight of the sediments squeezes the particles together. As more and more sediments are deposited the weight on the sediments below increases. Waterborne sediments become so tightly squeezed together that most of the water is pushed out. These minerals act as glue or cement to bind the sediments together.

Compaction and cementation lead to lithification of sedimentary rocks. Compaction is the squeezing of sediments by the weight of the rocks and sediments above them. Cementation is when cement from fluids bind sediments together.

Explanation: Lithification is the processes where rock particles are compacted and cemented together from pressure to form sedimentary rock.

Weathering describes how weather (such as rain and temperature) affects the rocks, while erosion is the physical deposition of sediment into a river. Weathering is when oxygen attacks the rock, while erosion is when water freezes in the cracks causing the rocks to break apart into smaller pieces.

Metamorphic rocks form when heat and pressure transform an existing rock into a new rock. Contact metamorphism occurs when hot magma transforms rock that it contacts. Regional metamorphism transforms large areas of existing rocks under the tremendous heat and pressure created by tectonic forces.

Like heat, pressure increases with depth. This pressure can actually squeeze the spaces out of the minerals within the rock. This makes the rocks denser. The heat and pressure together cause the rock to flow instead of break or fracture.

When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions. Temperature increases with depth in the Earth along the Geothermal Gradient. Thus higher temperature can occur by burial of rock.

Foliation occurs when minerals are flattened by heat and pressure. This results in a layered or banded texture.

Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.