Understanding Weathering, Erosion, and Sedimentary Rock Formation

Posted on Mar 4, 2025 in Geology

Weathering, Erosion, and Sedimentary Rock Formation

Weathering is the process by which the Earth’s surface rocks are altered and fragmented by the action of water, air, and living things. There are two main types of weathering: physical and chemical.

Physical Weathering

Physical weathering is the fragmentation or disintegration of rocks by physical processes without changing their chemical composition.

Chemical Weathering

Chemical weathering involves the alteration of the minerals within rocks due to chemical reactions between the minerals and components of the atmosphere. In this process, the rocks change their chemical composition.

Erosion

Erosion is the wearing away of the Earth’s surface rocks and the removal of materials due to impact and friction during their transport by external geological agents.

Transportation

Transportation is the transfer of rocky material eroded from the Earth’s surface from areas of erosion to areas of deposition.

Deposition

Deposition is the process where transported material accumulates when the carrying capacity of geological agents decreases. Sedimentary rocks are formed from sediments carried by different agents and deposited in sedimentary basins.

Diagenesis

Diagenesis is the set of physical, chemical, or biological processes that convert sediment into sedimentary rocks. These processes include:

  • Compaction: Sediments are subjected to increasing pressure from overlying layers.
  • Cementation: The precipitation of minerals that occupy the voids and pores between detrital particles.

Sedimentary Rock Classification

Sedimentary rocks are often classified based on the size of the particles that form them:

  • Conglomerates: Composed of particles with diameters between 2 mm and 256 mm.
  • Sandstone: Composed of particles with diameters between 1/16 mm and 2 mm.
  • Claystone/Shale: Composed of particles with diameters between 1/256 mm and 1/16 mm.

Sedimentary rocks can also be formed through chemical processes, including:

  • Carbonates
  • Evaporites
  • Organogenic (biochemical)

External Geological Processes

The Earth’s surface relief changes over time due to geological processes driven by solar energy and gravity. External geological processes shape the relief through erosion, transport, and sedimentation, carried out by external geological agents. These agents include:

  1. Surface water (rivers, streams, etc.)
  2. Subsurface water (infiltration)
  3. Glacial ice
  4. Wind
  5. Wave action and sea currents