Detrital vs. Chemical Sedimentary Rocks

Detrital Sedimentary Rocks

• Detrital sedimentary rocks are made of fragments of pre-existing rocks that have been transported away from their source and deposited in a new location.
• As the rock fragments travel farther from their mountain source, the composition of the detrital sedimentary rock changes, with smaller grains and more rounded shapes indicating greater distance from the source.

Textures of Detrital Sedimentary Rocks

• The texture of a detrital sedimentary rock is determined by the size and shape of the rock fragments, as well as the amount of cement between them.

Depositional Features

• A depositional feature in a sedimentary rock is a characteristic that forms during or shortly after deposition, such as cross-bedding or graded bedding.

Importance of Sedimentary Rocks

• Geologists study the features preserved in sedimentary rocks to gain insights into the geological history of an area, including the environments and processes that operated in the past.

Detrital Sedimentary Rock Formation

• As a river exits the mountains, the large grains like cobbles and pebbles are deposited, while the smaller grains continue to be transported.
• Conglomerate and breccia sedimentary rocks are defined by their coarse-grained texture, with conglomerate having rounded grains and breccia having angular grains.

Chemical Sedimentary Rocks

• Organic chemical rocks like limestone form through the accumulation of calcium carbonate from organic sources, such as shell fragments or coral reefs.
• Inorganic chemical rocks form through chemical precipitation, such as when minerals precipitate out of solution in a hypersaline lake.
• Micritic limestone formed from inorganic processes is characterized by a fine-grained, microcrystalline texture.

Lithification Process

• Detrital or clastic sedimentary rocks form through the lithification process, which involves compaction, cementation, and other processes.
• The key process involved in creating both detrital and chemical sedimentary rocks is lithification, which transforms sediment into sedimentary rock.
• Compaction plays a crucial role in the formation of sedimentary rocks, as it squeezes out pore space and helps to bind the sediment grains together.
• As burial continues in the lithification process, the sediment becomes increasingly compacted and cemented, eventually forming a solid sedimentary rock.
• The common process involved in forming most sedimentary rocks is diagenesis, which includes all the changes that occur in sediment after deposition, from compaction to cementation.