Sedimentary Rock Formation and Diagenesis

• Sedimentary rocks' formation requires pre-existing rocks, sediment reserves, and fossilized living organisms.
• These elements accumulate on Earth's surface.
• Sediment is like a wet powder of small solid material pieces settled at the bottom of a liquid.
• Sedimentary rocks form from organic, mechanical, or chemical sediments.
• Lithification is the process where sediments harden into sedimentary rocks.
• Sand, silt, and organic material make up the components of lithified soil.
• Lithification needs less heat than igneous rock formation.
• Compaction and cementation also aid lithification.
• Diagenesis is the collective process of sediments becoming rock.

Diagenesis

• Diagenesis has four parts: compaction, cementation, recrystallization, and chemical changes.
• Compaction smashes sediments together and squeezes accumulated sediments.
• As more sediments deposit, overlying weight increases.
• During compaction, water within the sediments is squeezed out.
• Cementation happens after sediments compact.
• Water molecules are present between particles, since most sediments are in water.
• Dissolved minerals in surrounding water fall out and attach to sediment grains.
• Cementation binds particles together as glue.
• Ions of chlorine, magnesium, potassium, calcium, carbonate, sodium, and sulfate dissolve commonly in seawater.
• Silica and phosphorus in seawater contribute to sedimentary rock composition, but are only found in trace amounts.
• Ions in seawater crystallize into rock after evaporation.
• Biological precipitation of decayed shells of microorganisms forms carbonate sediments.
• Calcium-rich and bicarbonate-rich chemical sediments precipitate as calcium carbonate and carbonic acid through inorganic processes, but they are less common than biological precipitation.
• Plant and animal remains are common in sedimentary rocks due to their formation near Earth's surface.
• Sedimentary rocks are recognizable through layers or bedding planes formed by sediment settlement and sorting by wind or water.
• Sedimentary rocks are classified into Clastic and Non-Clastic.

Clastic Sedimentary Rocks

• Clastic sedimentary rocks are from sediments formed through physical weathering and erosion of pre-existing rocks.
• Clasts or detritus are the components of clastic sedimentary rocks, made of individual minerals or rock fragments.
• Clastic sedimentary rocks form when sediments transport, deposit, and lithify.
• Grains are minerals and fragments are pieces of rocks that compose clastic sedimentary rocks.
• Streams transport the largest proportion of sediments, modifying them as they travel downslope.
• Stream capacity is the amount of sediment streams can carry.
• Competence is the size of sediments streams can carry, which the stream speed affects.

Non-Clastic Sedimentary Rocks

• Non-clastic sedimentary rocks include biological and chemical sedimentary rocks.

Biological sedimentary rocks

• Biological sedimentary rocks form from lithified accumulation of dead organisms.
• They form when living organisms die, pile up, compress, and cement together.
• Examples are coal and limestone.

Chemical sedimentary rocks

• Chemical sedimentary rocks form from chemical precipitation.
• Rock salt is an example, formed when dissolved salts precipitate from a solution.
• Chemical sedimentary rocks form when temperatures or acidity levels change.
• They form when dissolved materials precipitate from solution.
• Examples are chert, dolomit and rock.