Sedimentary Rock Formation: Types, Textures & Processes

Sedimentary Rocks: Formation & Characteristics

Sedimentary rocks are formed by the accumulation of sediments, subjected to physical and chemical processes (diagenesis), resulting in consolidated material.

Sedimentary Rock Texture Types

Clastic Texture

Clastic texture characterizes sediments formed by the mechanical accumulation of detrital particles. This texture is influenced by the size and shape of the original mineral and rock particles, or by the types of organisms whose skeletons or shells accumulate.

Non-Clastic Texture

Non-clastic textures are formed by chemical and organic substances.

Major Types of Sedimentary Rocks

Detrital Sedimentary Rocks

Detrital rocks are formed by the accumulation of debris from erosion and deposited by gravity. These are primarily classified by the size of their clasts, which distinguishes between conglomerate, sandstone, and clay rocks.

Organogenic Sedimentary Rocks

Organogenic rocks are formed from the remains of living organisms. Most abundant skeletons result from biomineralization processes. Some, however, are shaped by the evolution of organic parts (cellular material) and are properly called organic rocks (e.g., coal).

Precipitation (Chemical) Sedimentary Rocks

Precipitation rocks are formed by the deposition of dissolved substances, or newly formed by metabolic processes. In the latter case, they are called biochemical rocks.

Formation Processes of Sedimentary Rocks

Weathering of Source Rocks

Mechanical and chemical action on existing material (source rocks) can produce rubble.

Transport and Deposition

Detrital material is transported by rivers and deposited in seas.

Sedimentation

Deposited material settles in different marine environments according to its density.

Diagenesis: Sediment Compaction & Solidification

Diagenesis is the final stage of the sedimentary cycle. At this stage, sediments are compacted and solidified, modified by several processes:

• Compaction: Individual elements accumulate due to the pressure of superimposed sediments.
• Cementation: Occurs when cementing materials, such as precipitated salts, bind the particles.
• Recrystallization: Minerals undergo changes between solid and ionic liquid states.
• Selection and Regeneration: Some components are selected, while others regenerate and develop.