Study Notes on Weathering and Sedimentary Rocks

Chapter 6: Weathering and Sedimentary Rocks

Overview of Weathering and Sedimentary Rock Formation

  • Parent Rock to Sedimentary Rock Transformation:

    • Weathering: physical/chemical breakdown of Earth’s materials at/near the surface

      • Physical/mechanical Weathering (leads to clastic)

      • Chemical Weathering (leads to non-clastic)

    • Erosion

    • Transport (w water/wind/ice)

      • As particles

      • In solution

    • Deposition

      • Types:

      • clastic sediments (physical)

      • non-clastic sediments (chemical)

    • Lithification

      • Compaction

      • Cementation

  • Mineralization Process - steps transforming parent rock to sedimentary rock.

  • Structural and chemical differences in rock can create spectacular formations.

  • Types of Weathering:

    • Mechanical Weathering

    • Chemical Weathering

      • Example location: Arches National Park, Utah.

Mechanical Weathering

  • Definition:

    • The breaking of rock materials by physical forces into smaller pieces, retaining the chemical composition of the parent material.

  • Processes Involved:

    • Frost wedging

    • Thermal expansion and contraction

    • Salt crystal growth - evaporation

    • Pressure release

    • Organic activity (e.g., roots, seeds)

Chemical Weathering

  • Definition:

    • rock materials are decomposed by chemical alteration of the parent material.

  • Importance:

    • Considered the most important weathering process due to the ubiquitous presence of water, even in arid climates.

  • Main Processes of Chemical Weathering:

    • Hydrolysis

    • Hydration

    • Oxidation

    • Solution/Leaching

Weathering, Sediment, and Sedimentary Rocks

  • Classification of Detrital Sedimentary Particles by Size:

    • Gravel: >2 mm in diameter (large)

    • Sand: 1/16 mm to 2 mm

    • Silt: 1/256 mm to 1/16 mm

    • Clay: <1/256 mm (small)

Sediment Transport and Deposition

  • Deposition Environments:

    • Sediment can be transported far from its source, depsoiting at:

    • Continental

    • Transitional

    • Marine

Lithification

  • Definition:

    • The process transforming sediment into sedimentary rock.

  • Key Processes of Lithification:

    • Compaction

    • Cementation

Types of Sedimentary Rocks

  • Clastic (Physical) Sedimentary Rocks:

    • classified by size and shape.

    • breccia vs. conglomerate - angular grains vs. round grains

  • Chemical (Non-clastic) Sedimentary Rocks:

    • precipitated by:

    • Chemical reactions

    • Metabolism of organisms

    • tyndall stone = limestone in manitoba

  • Sedimentary Structures:

    • Graded bedding (bigger rocks at bottom)

    • Ripple marks

    • Mudcracks:

  • Fossils:

    • Remains and traces of ancient life.

  • Principle of Uniformitarianism:

  • "The present is the key to the past."